Managing file systems
Creating, modifying, and administering file systems in Red Hat Enterprise Linux 8
Abstract
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Chapter 1. Overview of available file systems
Choosing the file system that is appropriate for your application is an important decision due to the large number of options available and the trade-offs involved. This chapter describes some of the file systems that ship with Red Hat Enterprise Linux 8 and provides historical background and recommendations on the right file system to suit your application.
1.1. Types of file systems
Red Hat Enterprise Linux 8 supports a variety of file systems (FS). Different types of file systems solve different kinds of problems, and their usage is application specific. At the most general level, available file systems can be grouped into the following major types:
Table 1.1. Types of file systems and their use cases
| Type | File system | Attributes and use cases |
|---|---|---|
| Disk or local FS | XFS | XFS is the default file system in RHEL. Because it lays out files as extents, it is less vulnerable to fragmentation than ext4. Red Hat recommends deploying XFS as your local file system unless there are specific reasons to do otherwise: for example, compatibility or corner cases around performance. |
| ext4 | ext4 has the benefit of longevity in Linux. Therefore, it is supported by almost all Linux applications. In most cases, it rivals XFS on performance. ext4 is commonly used for home directories. | |
| Network or client-and-server FS | NFS | Use NFS to share files between multiple systems on the same network. |
| SMB | Use SMB for file sharing with Microsoft Windows systems. | |
| Shared storage or shared disk FS | GFS2 | GFS2 provides shared write access to members of a compute cluster. The emphasis is on stability and reliability, with the functional experience of a local file system as possible. SAS Grid, Tibco MQ, IBM Websphere MQ, and Red Hat Active MQ have been deployed successfully on GFS2. |
| Volume-managing FS | Stratis (Technology Preview) | Stratis is a volume manager built on a combination of XFS and LVM. The purpose of Stratis is to emulate capabilities offered by volume-managing file systems like Btrfs and ZFS. It is possible to build this stack manually, but Stratis reduces configuration complexity, implements best practices, and consolidates error information. |
1.2. Local file systems
Local file systems are file systems that run on a single, local server and are directly attached to storage.
For example, a local file system is the only choice for internal SATA or SAS disks, and is used when your server has internal hardware RAID controllers with local drives. Local file systems are also the most common file systems used on SAN attached storage when the device exported on the SAN is not shared.
All local file systems are POSIX-compliant and are fully compatible with all supported Red Hat Enterprise Linux releases. POSIX-compliant file systems provide support for a well-defined set of system calls, such as read(), write(), and seek().
From the application programmer’s point of view, there are relatively few differences between local file systems. The most notable differences from a user’s perspective are related to scalability and performance. When considering a file system choice, consider how large the file system needs to be, what unique features it should have, and how it performs under your workload.
Available local file systems
- XFS
- ext4
1.3. The XFS file system
XFS is a highly scalable, high-performance, robust, and mature 64-bit journaling file system that supports very large files and file systems on a single host. It is the default file system in Red Hat Enterprise Linux 8. XFS was originally developed in the early 1990s by SGI and has a long history of running on extremely large servers and storage arrays.
The features of XFS include:
- Reliability
- Metadata journaling, which ensures file system integrity after a system crash by keeping a record of file system operations that can be replayed when the system is restarted and the file system remounted
- Extensive run-time metadata consistency checking
- Scalable and fast repair utilities
- Quota journaling. This avoids the need for lengthy quota consistency checks after a crash.
- Scalability and performance
- Supported file system size up to 1024 TiB
- Ability to support a large number of concurrent operations
- B-tree indexing for scalability of free space management
- Sophisticated metadata read-ahead algorithms
- Optimizations for streaming video workloads
- Allocation schemes
- Extent-based allocation
- Stripe-aware allocation policies
- Delayed allocation
- Space pre-allocation
- Dynamically allocated inodes
- Other features
- Reflink-based file copies (new in Red Hat Enterprise Linux 8)
- Tightly integrated backup and restore utilities
- Online defragmentation
- Online file system growing
- Comprehensive diagnostics capabilities
-
Extended attributes (
xattr). This allows the system to associate several additional name/value pairs per file. - Project or directory quotas. This allows quota restrictions over a directory tree.
- Subsecond timestamps
Performance characteristics
XFS has a high performance on large systems with enterprise workloads. A large system is one with a relatively high number of CPUs, multiple HBAs, and connections to external disk arrays. XFS also performs well on smaller systems that have a multi-threaded, parallel I/O workload.
XFS has a relatively low performance for single threaded, metadata-intensive workloads: for example, a workload that creates or deletes large numbers of small files in a single thread.
1.4. The ext4 file system
The ext4 file system is the fourth generation of the ext file system family. It was the default file system in Red Hat Enterprise Linux 6.
The ext4 driver can read and write to ext2 and ext3 file systems, but the ext4 file system format is not compatible with ext2 and ext3 drivers.
ext4 adds several new and improved features, such as:
- Supported file system size up to 50 TiB
- Extent-based metadata
- Delayed allocation
- Journal checksumming
- Large storage support
The extent-based metadata and the delayed allocation features provide a more compact and efficient way to track utilized space in a file system. These features improve file system performance and reduce the space consumed by metadata. Delayed allocation allows the file system to postpone selection of the permanent location for newly written user data until the data is flushed to disk. This enables higher performance since it can allow for larger, more contiguous allocations, allowing the file system to make decisions with much better information.
File system repair time using the fsck utility in ext4 is much faster than in ext2 and ext3. Some file system repairs have demonstrated up to a six-fold increase in performance.
1.5. Choosing a local file system
To choose a file system that meets your application requirements, you need to understand the target system on which you are going to deploy the file system. You can use the following questions to inform your decision:
- Do you have a large server?
- Do you have large storage requirements or have a local, slow SATA drive?
- What kind of I/O workload do you expect your application to present?
- What are your throughput and latency requirements?
- How stable is your server and storage hardware?
- What is the typical size of your files and data set?
- If the system fails, how much downtime can you suffer?
If both your server and your storage device are large, XFS is the best choice. Even with smaller storage arrays, XFS performs very well when the average file sizes are large (for example, hundreds of megabytes in size).
If your existing workload has performed well with ext4, staying with ext4 should provide you and your applications with a very familiar environment.
The ext4 file system tends to perform better on systems that have limited I/O capability. It performs better on limited bandwidth (less than 200MB/s) and up to around 1000 IOPS capability. For anything with higher capability, XFS tends to be faster.
XFS consumes about twice the CPU-per-metadata operation compared to ext4, so if you have a CPU-bound workload with little concurrency, then ext4 will be faster. In general, ext4 is better if an application uses a single read/write thread and small files, while XFS shines when an application uses multiple read/write threads and bigger files.
You cannot shrink an XFS file system. If you need to be able to shrink the file system, consider using ext4, which supports offline shrinking.
In general, Red Hat recommends that you use XFS unless you have a specific use case for ext4. You should also measure the performance of your specific application on your target server and storage system to make sure that you choose the appropriate type of file system.
Table 1.2. Summary of local file system recommendations
| Scenario | Recommended file system |
|---|---|
| No special use case | XFS |
| Large server | XFS |
| Large storage devices | XFS |
| Large files | XFS |
| Multi-threaded I/O | XFS |
| Single-threaded I/O | ext4 |
| Limited I/O capability (under 1000 IOPS) | ext4 |
| Limited bandwidth (under 200MB/s) | ext4 |
| CPU-bound workload | ext4 |
| Support for offline shrinking | ext4 |
1.6. Network file systems
Network file systems, also referred to as client/server file systems, enable client systems to access files that are stored on a shared server. This makes it possible for multiple users on multiple systems to share files and storage resources.
Such file systems are built from one or more servers that export a set of file systems to one or more clients. The client nodes do not have access to the underlying block storage, but rather interact with the storage using a protocol that allows for better access control.
Available network file systems
- The most common client/server file system for Red Hat Enterprise Linux customers is the NFS file system. Red Hat Enterprise Linux provides both an NFS server component to export a local file system over the network and an NFS client to import these file systems.
- Red Hat Enterprise Linux also includes a CIFS client that supports the popular Microsoft SMB file servers for Windows interoperability. The userspace Samba server provides Windows clients with a Microsoft SMB service from a Red Hat Enterprise Linux server.
1.9. Volume-managing file systems
Volume-managing file systems integrate the entire storage stack for the purposes of simplicity and in-stack optimization.
Available volume-managing file systems
Red Hat Enterprise Linux 8 provides the Stratis volume manager as a Technology Preview. Stratis uses XFS for the file system layer and integrates it with LVM, Device Mapper, and other components.
Stratis was first released in Red Hat Enterprise Linux 8.0. It is conceived to fill the gap created when Red Hat deprecated Btrfs. Stratis 1.0 is an intuitive, command line-based volume manager that can perform significant storage management operations while hiding the complexity from the user:
- Volume management
- Pool creation
- Thin storage pools
- Snapshots
- Automated read cache
Stratis offers powerful features, but currently lacks certain capabilities of other offerings that it might be compared to, such as Btrfs or ZFS. Most notably, it does not support CRCs with self healing.
Chapter 4. Securing NFS
To minimize NFS security risks and protect data on the server, consider the following sections when exporting NFS file systems on a server or mounting them on a client.
4.1. NFS security with AUTH_SYS and export controls
NFS provides the following traditional options in order to control access to exported files:
- The server restricts which hosts are allowed to mount which file systems either by IP address or by host name.
-
The server enforces file system permissions for users on NFS clients in the same way it does for local users. Traditionally, NFS does this using the
AUTH_SYScall message (also calledAUTH_UNIX), which relies on the client to state the UID and GIDs of the user. Be aware that this means that a malicious or misconfigured client might easily get this wrong and allow a user access to files that it should not.
To limit the potential risks, administrators often limits the access to read-only or squash user permissions to a common user and group ID. Unfortunately, these solutions prevent the NFS share from being used in the way it was originally intended.
Additionally, if an attacker gains control of the DNS server used by the system exporting the NFS file system, they can point the system associated with a particular hostname or fully qualified domain name to an unauthorized machine. At this point, the unauthorized machine is the system permitted to mount the NFS share, because no username or password information is exchanged to provide additional security for the NFS mount.
Wildcards should be used sparingly when exporting directories through NFS, as it is possible for the scope of the wildcard to encompass more systems than intended.
Additional resources
For more information on securing NFS and rpcbind, see the iptables man page.
4.2. NFS security with AUTH_GSS
All version of NFS support RPCSEC_GSS and the Kerberos mechanism.
Unlike AUTH_SYS, with the RPCSEC_GSS Kerberos mechanism, the server does not depend on the client to correctly represent which user is accessing the file. Instead, cryptography is used to authenticate users to the server, which prevents a malicious client from impersonating a user without having that user’s Kerberos credentials. Using the RPCSEC_GSS Kerberos mechanism is the most straightforward way to secure mounts because after configuring Kerberos, no additional setup is needed.
4.2.1. Configuring Kerberos
Kerberos is a network authentication system that allows clients and servers to authenticate to each other by using symmetric encryption and a trusted third party, the KDC. Red Hat recommends using Identity Management (IdM) for setting up Kerberos.
Prerequisites
-
The Kerberos Key Distribution Centre (
KDC) is installed and configured.
Configuring an NFS Server and Client for IdM to Use RPCSEC_GSS
-
Create the
nfs/hostname.domain@REALMprincipal on the NFS server side. -
Create the
host/hostname.domain@REALMprincipal on both the server and the client side. - Add the corresponding keys to keytabs for the client and server.
-
Create the
On the server side, use the
sec=option to enable the wanted security flavors. To enable all security flavors as well as non-cryptographic mounts:/export *(sec=sys:krb5:krb5i:krb5p)
Valid security flavors to use with the
sec=option are:-
sys: no cryptographic protection, the default -
krb5: authentication only -
krb5i: integrity protection -
krb5p: privacy protection
-
On the client side, add
sec=krb5(orsec=krb5i, orsec=krb5p, depending on the setup) to the mount options:# mount -o sec=krb5 server:/export /mnt
Additional resources
- For more information, see the exports(5) and nfs(5) man pages.
-
For further information on the
RPCSEC_GSSframework, including howgssproxyandrpc.gssdinter-operate, see the GSSD flow description.
4.2.2. NFSv4 security options
NFSv4 includes ACL support based on the Microsoft Windows NT model, not the POSIX model, because of the Microsoft Windows NT model’s features and wide deployment.
Another important security feature of NFSv4 is the removal of the use of the MOUNT protocol for mounting file systems. The MOUNT protocol presented a security risk because of the way the protocol processed file handles.
4.3. File permissions on mounted NFS exports
Once the NFS file system is mounted as either read or read and write by a remote host, the only protection each shared file has is its permissions. If two users that share the same user ID value mount the same NFS file system on different client systems, they can modify each others' files. Additionally, anyone logged in as root on the client system can use the su - command to access any files with the NFS share.
By default, access control lists (ACLs) are supported by NFS under Red Hat Enterprise Linux. Red Hat recommends to keep this feature enabled.
By default, NFS uses root squashing when exporting a file system. This sets the user ID of anyone accessing the NFS share as the root user on their local machine to nobody. Root squashing is controlled by the default option root_squash; for more information about this option, see Section 3.6, “NFS server configuration”.
When exporting an NFS share as read-only, consider using the all_squash option. This option makes every user accessing the exported file system take the user ID of the nfsnobody user.
Chapter 6. Overview of persistent naming attributes
As a system administrator, you need to refer to storage volumes using persistent naming attributes to build storage setups that are reliable over multiple system boots.
6.1. Disadvantages of non-persistent naming attributes
Red Hat Enterprise Linux provides a number of ways to identify storage devices. It is important to use the correct option to identify each device when used in order to avoid inadvertently accessing the wrong device, particularly when installing to or reformatting drives.
Traditionally, non-persistent names in the form of /dev/sd(major number)(minor number) are used on Linux to refer to storage devices. The major and minor number range and associated sd names are allocated for each device when it is detected. This means that the association between the major and minor number range and associated sd names can change if the order of device detection changes.
Such a change in the ordering might occur in the following situations:
- The parallelization of the system boot process detects storage devices in a different order with each system boot.
-
A disk fails to power up or respond to the SCSI controller. This results in it not being detected by the normal device probe. The disk is not accessible to the system and subsequent devices will have their major and minor number range, including the associated
sdnames shifted down. For example, if a disk normally referred to assdbis not detected, a disk that is normally referred to assdcwould instead appear assdb. -
A SCSI controller (host bus adapter, or HBA) fails to initialize, causing all disks connected to that HBA to not be detected. Any disks connected to subsequently probed HBAs are assigned different major and minor number ranges, and different associated
sdnames. - The order of driver initialization changes if different types of HBAs are present in the system. This causes the disks connected to those HBAs to be detected in a different order. This might also occur if HBAs are moved to different PCI slots on the system.
-
Disks connected to the system with Fibre Channel, iSCSI, or FCoE adapters might be inaccessible at the time the storage devices are probed, due to a storage array or intervening switch being powered off, for example. This might occur when a system reboots after a power failure, if the storage array takes longer to come online than the system take to boot. Although some Fibre Channel drivers support a mechanism to specify a persistent SCSI target ID to WWPN mapping, this does not cause the major and minor number ranges, and the associated
sdnames to be reserved; it only provides consistent SCSI target ID numbers.
These reasons make it undesirable to use the major and minor number range or the associated sd names when referring to devices, such as in the /etc/fstab file. There is the possibility that the wrong device will be mounted and data corruption might result.
Occasionally, however, it is still necessary to refer to the sd names even when another mechanism is used, such as when errors are reported by a device. This is because the Linux kernel uses sd names (and also SCSI host/channel/target/LUN tuples) in kernel messages regarding the device.
6.2. File system and device identifiers
This sections explains the difference between persistent attributes identifying file systems and block devices.
File system identifiers
File system identifiers are tied to a particular file system created on a block device. The identifier is also stored as part of the file system. If you copy the file system to a different device, it still carries the same file system identifier. On the other hand, if you rewrite the device, such as by formatting it with the mkfs utility, the device loses the attribute.
File system identifiers include:
- Unique identifier (UUID)
- Label
Device identifiers
Device identifiers are tied to a block device: for example, a disk or a partition. If you rewrite the device, such as by formatting it with the mkfs utility, the device keeps the attribute, because it is not stored in the file system.
Device identifiers include:
- World Wide Identifier (WWID)
- Partition UUID
- Serial number
Recommendations
- Some file systems, such as logical volumes, span multiple devices. Red Hat recommends accessing these file systems using file system identifiers rather than device identifiers.
6.3. Device names managed by the udev mechanism in /dev/disk/
This section lists different kinds of persistent naming attributes that the udev service provides in the /dev/disk/ directory.
The udev mechanism is used for all types of devices in Linux, not just for storage devices. In the case of storage devices, Red Hat Enterprise Linux contains udev rules that create symbolic links in the /dev/disk/ directory. This enables you to refer to storage devices by:
- Their content
- A unique identifier
- Their serial number.
Although udev naming attributes are persistent, in that they do not change on their own across system reboots, some are also configurable.
6.3.1. File system identifiers
The UUID attribute in /dev/disk/by-uuid/
Entries in this directory provide a symbolic name that refers to the storage device by a unique identifier (UUID) in the content (that is, the data) stored on the device. For example:
/dev/disk/by-uuid/3e6be9de-8139-11d1-9106-a43f08d823a6
You can use the UUID to refer to the device in the /etc/fstab file using the following syntax:
UUID=3e6be9de-8139-11d1-9106-a43f08d823a6You can configure the UUID attribute when creating a file system, and you can also change it later on.
The Label attribute in /dev/disk/by-label/
Entries in this directory provide a symbolic name that refers to the storage device by a label in the content (that is, the data) stored on the device.
For example:
/dev/disk/by-label/Boot
You can use the label to refer to the device in the /etc/fstab file using the following syntax:
LABEL=BootYou can configure the Label attribute when creating a file system, and you can also change it later on.
6.3.2. Device identifiers
The WWID attribute in /dev/disk/by-id/
The World Wide Identifier (WWID) is a persistent, system-independent identifier that the SCSI Standard requires from all SCSI devices. The WWID identifier is guaranteed to be unique for every storage device, and independent of the path that is used to access the device. The identifier is a property of the device but is not stored in the content (that is, the data) on the devices.
This identifier can be obtained by issuing a SCSI Inquiry to retrieve the Device Identification Vital Product Data (page 0x83) or Unit Serial Number (page 0x80).
Red Hat Enterprise Linux automatically maintains the proper mapping from the WWID-based device name to a current /dev/sd name on that system. Applications can use the /dev/disk/by-id/ name to reference the data on the disk, even if the path to the device changes, and even when accessing the device from different systems.
Example 6.1. WWID mappings
| WWID symlink | Non-persistent device | Note |
|---|---|---|
|
|
|
A device with a page |
|
|
|
A device with a page |
|
|
| A disk partition |
In addition to these persistent names provided by the system, you can also use udev rules to implement persistent names of your own, mapped to the WWID of the storage.
The Partition UUID attribute in /dev/disk/by-partuuid
The Partition UUID (PARTUUID) attribute identifies partitions as defined by GPT partition table.
Example 6.2. Partition UUID mappings
| PARTUUID symlink | Non-persistent device |
|---|---|
|
|
|
|
|
|
|
|
|
The Path attribute in /dev/disk/by-path/
This attribute provides a symbolic name that refers to the storage device by the hardware path used to access the device.
The Path attribute is unreliable, and Red Hat does not recommend using it.
6.4. The World Wide Identifier with DM Multipath
This section describes the mapping between the World Wide Identifier (WWID) and non-persistent device names in a Device Mapper Multipath configuration.
If there are multiple paths from a system to a device, DM Multipath uses the WWID to detect this. DM Multipath then presents a single "pseudo-device" in the /dev/mapper/wwid directory, such as /dev/mapper/3600508b400105df70000e00000ac0000.
The command multipath -l shows the mapping to the non-persistent identifiers:
-
Host:Channel:Target:LUN -
/dev/sdname -
major:minornumber
Example 6.3. WWID mappings in a multipath configuration
An example output of the multipath -l command:
3600508b400105df70000e00000ac0000 dm-2 vendor,product [size=20G][features=1 queue_if_no_path][hwhandler=0][rw] \_ round-robin 0 [prio=0][active] \_ 5:0:1:1 sdc 8:32 [active][undef] \_ 6:0:1:1 sdg 8:96 [active][undef] \_ round-robin 0 [prio=0][enabled] \_ 5:0:0:1 sdb 8:16 [active][undef] \_ 6:0:0:1 sdf 8:80 [active][undef]
DM Multipath automatically maintains the proper mapping of each WWID-based device name to its corresponding /dev/sd name on the system. These names are persistent across path changes, and they are consistent when accessing the device from different systems.
When the user_friendly_names feature of DM Multipath is used, the WWID is mapped to a name of the form /dev/mapper/mpathN. By default, this mapping is maintained in the file /etc/multipath/bindings. These mpathN names are persistent as long as that file is maintained.
If you use user_friendly_names, then additional steps are required to obtain consistent names in a cluster.
6.5. Limitations of the udev device naming convention
The following are some limitations of the udev naming convention:
-
It is possible that the device might not be accessible at the time the query is performed because the
udevmechanism might rely on the ability to query the storage device when theudevrules are processed for audevevent. This is more likely to occur with Fibre Channel, iSCSI or FCoE storage devices when the device is not located in the server chassis. -
The kernel might send
udevevents at any time, causing the rules to be processed and possibly causing the/dev/disk/by-*/links to be removed if the device is not accessible. -
There might be a delay between when the
udevevent is generated and when it is processed, such as when a large number of devices are detected and the user-spaceudevdservice takes some amount of time to process the rules for each one. This might cause a delay between when the kernel detects the device and when the/dev/disk/by-*/names are available. -
External programs such as
blkidinvoked by the rules might open the device for a brief period of time, making the device inaccessible for other uses.
6.6. Listing persistent naming attributes
This procedure describes how to find out the persistent naming attributes of non-persistent storage devices.
Procedure
To list the UUID and Label attributes, use the
lsblkutility:$ lsblk --fs storage-deviceFor example:
Example 6.4. Viewing the UUID and Label of a file system
$ lsblk --fs /dev/sda1 NAME FSTYPE LABEL UUID MOUNTPOINT sda1 xfs Boot afa5d5e3-9050-48c3-acc1-bb30095f3dc4 /boot
To list the PARTUUID attribute, use the
lsblkutility with the--output +PARTUUIDoption:$ lsblk --output +PARTUUID
For example:
Example 6.5. Viewing the PARTUUID attribute of a partition
$ lsblk --output +PARTUUID /dev/sda1 NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT PARTUUID sda1 8:1 0 512M 0 part /boot 4cd1448a-01
To list the WWID attribute, examine the targets of symbolic links in the
/dev/disk/by-id/directory. For example:Example 6.6. Viewing the WWID of all storage devices on the system
$ file /dev/disk/by-id/* /dev/disk/by-id/ata-QEMU_HARDDISK_QM00001: symbolic link to ../../sda /dev/disk/by-id/ata-QEMU_HARDDISK_QM00001-part1: symbolic link to ../../sda1 /dev/disk/by-id/ata-QEMU_HARDDISK_QM00001-part2: symbolic link to ../../sda2 /dev/disk/by-id/dm-name-rhel_rhel8-root: symbolic link to ../../dm-0 /dev/disk/by-id/dm-name-rhel_rhel8-swap: symbolic link to ../../dm-1 /dev/disk/by-id/dm-uuid-LVM-QIWtEHtXGobe5bewlIUDivKOz5ofkgFhP0RMFsNyySVihqEl2cWWbR7MjXJolD6g: symbolic link to ../../dm-1 /dev/disk/by-id/dm-uuid-LVM-QIWtEHtXGobe5bewlIUDivKOz5ofkgFhXqH2M45hD2H9nAf2qfWSrlRLhzfMyOKd: symbolic link to ../../dm-0 /dev/disk/by-id/lvm-pv-uuid-atlr2Y-vuMo-ueoH-CpMG-4JuH-AhEF-wu4QQm: symbolic link to ../../sda2
6.7. Modifying persistent naming attributes
This procedure describes how to change the UUID or Label persistent naming attribute of a file system.
Changing udev attributes happens in the background and might take a long time. The udevadm settle command waits until the change is fully registered, which ensures that your next command will be able to utilize the new attribute correctly.
In the following commands:
-
Replace new-uuid with the UUID you want to set; for example,
1cdfbc07-1c90-4984-b5ec-f61943f5ea50. You can generate a UUID using theuuidgencommand. -
Replace new-label with a label; for example,
backup_data.
Prerequisites
- If you are modifying the attributes of an XFS file system, unmount it first.
Procedure
To change the UUID or Label attributes of an XFS file system, use the
xfs_adminutility:# xfs_admin -U new-uuid -L new-label storage-device # udevadm settle
To change the UUID or Label attributes of an ext4, ext3, or ext2 file system, use the
tune2fsutility:# tune2fs -U new-uuid -L new-label storage-device # udevadm settle
To change the UUID or Label attributes of a swap volume, use the
swaplabelutility:# swaplabel --uuid new-uuid --label new-label swap-device # udevadm settle
Chapter 7. Getting started with partitions
As a system administrator, you can use the following procedures to create, delete, and modify various types of disk partitions.
For an overview of the advantages and disadvantages to using partitions on block devices, see the following KBase article: https://access.redhat.com/solutions/163853.
7.1. Viewing the partition table
As a system administrator, you can display the partition table of a block device to see the partition layout and details about individual partitions.
7.1.1. Viewing the partition table with parted
This procedure describes how to view the partition table on a block device using the parted utility.
Procedure
Start the interactive
partedshell:# parted block-device-
Replace block-device with the path to the device you want to examine: for example,
/dev/sda.
-
Replace block-device with the path to the device you want to examine: for example,
View the partition table:
(parted) print
Optionally, use the following command to switch to another device you want to examine next:
(parted) select block-device
Additional resources
-
The
parted(8)man page.
7.1.2. Example output of parted print
This section provides an example output of the print command in the parted shell and describes fields in the output.
Example 7.1. Output of the print command
Model: ATA SAMSUNG MZNLN256 (scsi) Disk /dev/sda: 256GB Sector size (logical/physical): 512B/512B Partition Table: msdos Disk Flags: Number Start End Size Type File system Flags 1 1049kB 269MB 268MB primary xfs boot 2 269MB 34.6GB 34.4GB primary 3 34.6GB 45.4GB 10.7GB primary 4 45.4GB 256GB 211GB extended 5 45.4GB 256GB 211GB logical
Following is a description of the fields:
Model: ATA SAMSUNG MZNLN256 (scsi)- The disk type, manufacturer, model number, and interface.
Disk /dev/sda: 256GB- The file path to the block device and the storage capacity.
Partition Table: msdos- The disk label type.
Number-
The partition number. For example, the partition with minor number 1 corresponds to
/dev/sda1. StartandEnd- The location on the device where the partition starts and ends.
Type- Valid types are metadata, free, primary, extended, or logical.
File system-
The file system type. If the
File systemfield of a device shows no value, this means that its file system type is unknown. Thepartedutility cannot recognize the file system on encrypted devices. Flags-
Lists the flags set for the partition. Available flags are
boot,root,swap,hidden,raid,lvm, orlba.
7.2. Creating a partition table on a disk
As a system administrator, you can format a block device with different types of partition tables to enable using partitions on the device.
Formatting a block device with a partition table deletes all data stored on the device.
7.2.1. Considerations before modifying partitions on a disk
This section lists key points to consider before creating, removing, or resizing partitions.
This section does not cover the DASD partition table, which is specific to the IBM Z architecture. For information on DASD, see:
- Configuring a Linux instance on IBM Z
- The What you should know about DASD article at the IBM Knowledge Center
The maximum number of partitions
The number of partitions on a device is limited by the type of the partition table:
On a device formatted with the Master Boot Record (MBR) partition table, you can have either:
- Up to four primary partitions, or
- Up to three primary partitions, one extended partition, and multiple logical partitions within the extended.
-
On a device formatted with the GUID Partition Table (GPT), the maximum number of partitions is 128. While the GPT specification allows for more partitions by growing the area reserved for the partition table, common practice used by the
partedutility is to limit it to enough area for 128 partitions.
The maximum size of a partition
The size of a partition on a device is limited by the type of the partition table:
- On a device formatted with the Master Boot Record (MBR) partition table, the maximum size is 2TiB.
- On a device formatted with the GUID Partition Table (GPT), the maximum size is 8ZiB.
If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.
Size alignment
The parted utility enables you to specify partition size using multiple different suffixes:
- MiB, GiB, or TiB
Size expressed in powers of 2.
- The starting point of the partition is aligned to the exact sector specified by size.
- The ending point is aligned to the specified size minus 1 sector.
- MB, GB, or TB
Size expressed in powers of 10.
The starting and ending point is aligned within one half of the specified unit: for example, ±500KB when using the MB suffix.
7.2.2. Comparison of partition table types
This section compares the properties of different types of partition tables that you can create on a block device.
Table 7.1. Partition table types
| Partition table | Maximum number of partitions | Maximum partition size |
|---|---|---|
| Master Boot Record (MBR) | 4 primary, or 3 primary and 12 logical inside an extended partition | 2TiB |
| GUID Partition Table (GPT) | 128 | 8ZiB |
7.2.3. Creating a partition table on a disk with parted
This procedure describes how to format a block device with a partition table using the parted utility.
Procedure
Start the interactive
partedshell:# parted block-device-
Replace block-device with the path to the device where you want to create a partition table: for example,
/dev/sda.
-
Replace block-device with the path to the device where you want to create a partition table: for example,
Determine if there already is a partition table on the device:
(parted) print
If the device already contains partitions, they will be deleted in the next steps.
Create the new partition table:
(parted) mklabel table-typeReplace table-type with with the intended partition table type:
-
msdosfor MBR -
gptfor GPT
-
Example 7.2. Creating a GPT table
For example, to create a GPT table on the disk, use:
(parted) mklabel gpt
The changes start taking place as soon as you enter this command, so review it before executing it.
View the partition table to confirm that the partition table exists:
(parted) print
Exit the
partedshell:(parted) quit
Additional resources
-
The
parted(8)man page.
Next steps
- Create partitions on the device. See Section 7.3, “Creating a partition” for details.
7.3. Creating a partition
As a system administrator, you can create new partitions on a disk.
7.3.1. Considerations before modifying partitions on a disk
This section lists key points to consider before creating, removing, or resizing partitions.
This section does not cover the DASD partition table, which is specific to the IBM Z architecture. For information on DASD, see:
- Configuring a Linux instance on IBM Z
- The What you should know about DASD article at the IBM Knowledge Center
The maximum number of partitions
The number of partitions on a device is limited by the type of the partition table:
On a device formatted with the Master Boot Record (MBR) partition table, you can have either:
- Up to four primary partitions, or
- Up to three primary partitions, one extended partition, and multiple logical partitions within the extended.
-
On a device formatted with the GUID Partition Table (GPT), the maximum number of partitions is 128. While the GPT specification allows for more partitions by growing the area reserved for the partition table, common practice used by the
partedutility is to limit it to enough area for 128 partitions.
The maximum size of a partition
The size of a partition on a device is limited by the type of the partition table:
- On a device formatted with the Master Boot Record (MBR) partition table, the maximum size is 2TiB.
- On a device formatted with the GUID Partition Table (GPT), the maximum size is 8ZiB.
If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.
Size alignment
The parted utility enables you to specify partition size using multiple different suffixes:
- MiB, GiB, or TiB
Size expressed in powers of 2.
- The starting point of the partition is aligned to the exact sector specified by size.
- The ending point is aligned to the specified size minus 1 sector.
- MB, GB, or TB
Size expressed in powers of 10.
The starting and ending point is aligned within one half of the specified unit: for example, ±500KB when using the MB suffix.
7.3.2. Partition types
This section describes different attributes that specify the type of a partition.
Partition types or flags
The partition type, or flag, is used by a running system only rarely. However, the partition type matters to on-the-fly generators, such as systemd-gpt-auto-generator, which use the partition type to, for example, automatically identify and mount devices.
-
The
partedutility provides some control of partition types by mapping the partition type to flags. The parted utility can handle only certain partition types: for example LVM, swap, or RAID. -
The
fdiskutility supports the full range of partition types by specifying hexadecimal codes.
Partition file system type
The parted utility optionally accepts a file system type argument when creating a partition. The value is used to:
- Set the partition flags on MBR, or
-
Set the partition UUID type on GPT. For example, the
swap,fat, orhfsfile system types set different GUIDs. The default value is the Linux Data GUID.
The argument does not modify the file system on the partition in any way. It only differentiates between the supported flags or GUIDs.
The following file system types are supported:
-
xfs -
ext2 -
ext3 -
ext4 -
fat16 -
fat32 -
hfs -
hfs+ -
linux-swap -
ntfs -
reiserfs
7.3.3. Creating a partition with parted
This procedure describes how to create a new partition on a block device using the parted utility.
Prerequisites
- There is a partition table on the disk. For details on how to format the disk, see Section 7.2, “Creating a partition table on a disk”.
- If the partition you want to create is larger than 2TiB, the disk must be formatted with the GUID Partition Table (GPT).
Procedure
Start the interactive
partedshell:# parted block-device-
Replace block-device with the path to the device where you want to create a partition: for example,
/dev/sda.
-
Replace block-device with the path to the device where you want to create a partition: for example,
View the current partition table to determine if there is enough free space:
(parted) print
- If there is not enough free space, you can resize an existing partition. For more information, see Section 7.5, “Resizing a partition”.
From the partition table, determine:
- The start and end points of the new partition
- On MBR, what partition type it should be.
Create the new partition:
(parted) mkpart part-type name fs-type start end
-
Replace part-type with with
primary,logical, orextendedbased on what you decided from the partition table. This applies only to the MBR partition table. - Replace name with an arbitrary partition name. This is required for GPT partition tables.
-
Replace fs-type with any one of
xfs,ext2,ext3,ext4,fat16,fat32,hfs,hfs+,linux-swap,ntfs, orreiserfs. The fs-type parameter is optional. Note thatparteddoes not create the file system on the partition. -
Replace start and end with the sizes that determine the starting and ending points of the partition, counting from the beginning of the disk. You can use size suffixes, such as
512MiB,20GiB, or1.5TiB. The default size megabytes.
Example 7.3. Creating a small primary partition
For example, to create a primary partition from 1024MiB until 2048MiB on an MBR table, use:
(parted) mkpart primary 1024MiB 2048MiB
The changes start taking place as soon as you enter this command, so review it before executing it.
-
Replace part-type with with
View the partition table to confirm that the created partition is in the partition table with the correct partition type, file system type, and size:
(parted) print
Exit the
partedshell:(parted) quit
Use the following command to wait for the system to register the new device node:
# udevadm settle
Verify that the kernel recognizes the new partition:
# cat /proc/partitions
Additional resources
-
The
parted(8)man page.
7.3.4. Setting a partition type with fdisk
This procedure describes how to set a partition type, or flag, using the fdisk utility.
Prerequisites
- There is a partition on the disk.
Procedure
Start the interactive
fdiskshell:# fdisk block-device-
Replace block-device with the path to the device where you want to set a partition type: for example,
/dev/sda.
-
Replace block-device with the path to the device where you want to set a partition type: for example,
View the current partition table to determine the minor partition number:
Command (m for help): printYou can see the current partition type in the
Typecolumn and its corresponding type ID in theIdcolumn.Enter the partition type command and select a partition using its minor number:
Command (m for help): type Partition number (1,2,3 default 3): 2
Optionally, list the available hexadecimal codes:
Hex code (type L to list all codes): LSet the partition type:
Hex code (type L to list all codes): 8eWrite your changes and exit the
fdiskshell:Command (m for help): write The partition table has been altered. Syncing disks.Verify your changes:
# fdisk --list block-device
7.4. Removing a partition
As a system administrator, you can remove a disk partition that is no longer used to free up disk space.
Removing a partition deletes all data stored on the partition.
7.4.1. Considerations before modifying partitions on a disk
This section lists key points to consider before creating, removing, or resizing partitions.
This section does not cover the DASD partition table, which is specific to the IBM Z architecture. For information on DASD, see:
- Configuring a Linux instance on IBM Z
- The What you should know about DASD article at the IBM Knowledge Center
The maximum number of partitions
The number of partitions on a device is limited by the type of the partition table:
On a device formatted with the Master Boot Record (MBR) partition table, you can have either:
- Up to four primary partitions, or
- Up to three primary partitions, one extended partition, and multiple logical partitions within the extended.
-
On a device formatted with the GUID Partition Table (GPT), the maximum number of partitions is 128. While the GPT specification allows for more partitions by growing the area reserved for the partition table, common practice used by the
partedutility is to limit it to enough area for 128 partitions.
The maximum size of a partition
The size of a partition on a device is limited by the type of the partition table:
- On a device formatted with the Master Boot Record (MBR) partition table, the maximum size is 2TiB.
- On a device formatted with the GUID Partition Table (GPT), the maximum size is 8ZiB.
If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.
Size alignment
The parted utility enables you to specify partition size using multiple different suffixes:
- MiB, GiB, or TiB
Size expressed in powers of 2.
- The starting point of the partition is aligned to the exact sector specified by size.
- The ending point is aligned to the specified size minus 1 sector.
- MB, GB, or TB
Size expressed in powers of 10.
The starting and ending point is aligned within one half of the specified unit: for example, ±500KB when using the MB suffix.
7.4.2. Removing a partition with parted
This procedure describes how to remove a disk partition using the parted utility.
Procedure
Start the interactive
partedshell:# parted block-device-
Replace block-device with the path to the device where you want to remove a partition: for example,
/dev/sda.
-
Replace block-device with the path to the device where you want to remove a partition: for example,
View the current partition table to determine the minor number of the partition to remove:
(parted) print
Remove the partition:
(parted) rm minor-number-
Replace minor-number with the minor number of the partition you want to remove: for example,
3.
The changes start taking place as soon as you enter this command, so review it before executing it.
-
Replace minor-number with the minor number of the partition you want to remove: for example,
Confirm that the partition is removed from the partition table:
(parted) print
Exit the
partedshell:(parted) quit
Verify that the kernel knows the partition is removed:
# cat /proc/partitions
-
Remove the partition from the
/etc/fstabfile if it is present. Find the line that declares the removed partition, and remove it from the file. Regenerate mount units so that your system registers the new
/etc/fstabconfiguration:# systemctl daemon-reload
If you have deleted a swap partition or removed pieces of LVM, remove all references to the partition from the kernel command line in the
/etc/default/grubfile and regenerate GRUB configuration:On a BIOS-based system:
# grub2-mkconfig --output=/etc/grub2.cfg
On a UEFI-based system:
# grub2-mkconfig --output=/etc/grub2-efi.cfg
To register the changes in the early boot system, rebuild the
initramfsfile system:# dracut --force --verbose
Additional resources
-
The
parted(8)man page
7.5. Resizing a partition
As a system administrator, you can extend a partition to utilize unused disk space, or shrink a partition to use its capacity for different purposes.
7.5.1. Considerations before modifying partitions on a disk
This section lists key points to consider before creating, removing, or resizing partitions.
This section does not cover the DASD partition table, which is specific to the IBM Z architecture. For information on DASD, see:
- Configuring a Linux instance on IBM Z
- The What you should know about DASD article at the IBM Knowledge Center
The maximum number of partitions
The number of partitions on a device is limited by the type of the partition table:
On a device formatted with the Master Boot Record (MBR) partition table, you can have either:
- Up to four primary partitions, or
- Up to three primary partitions, one extended partition, and multiple logical partitions within the extended.
-
On a device formatted with the GUID Partition Table (GPT), the maximum number of partitions is 128. While the GPT specification allows for more partitions by growing the area reserved for the partition table, common practice used by the
partedutility is to limit it to enough area for 128 partitions.
The maximum size of a partition
The size of a partition on a device is limited by the type of the partition table:
- On a device formatted with the Master Boot Record (MBR) partition table, the maximum size is 2TiB.
- On a device formatted with the GUID Partition Table (GPT), the maximum size is 8ZiB.
If you want to create a partition larger than 2TiB, the disk must be formatted with GPT.
Size alignment
The parted utility enables you to specify partition size using multiple different suffixes:
- MiB, GiB, or TiB
Size expressed in powers of 2.
- The starting point of the partition is aligned to the exact sector specified by size.
- The ending point is aligned to the specified size minus 1 sector.
- MB, GB, or TB
Size expressed in powers of 10.
The starting and ending point is aligned within one half of the specified unit: for example, ±500KB when using the MB suffix.
7.5.2. Resizing a partition with parted
This procedure resizes a disk partition using the parted utility.
Prerequisites
If you want to shrink a partition, back up the data that are stored on it.
WarningShrinking a partition might result in data loss on the partition.
- If you want to resize a partition to be larger than 2TiB, the disk must be formatted with the GUID Partition Table (GPT). For details on how to format the disk, see Section 7.2, “Creating a partition table on a disk”.
Procedure
- If you want to shrink the partition, shrink the file system on it first so that it is not larger than the resized partition. Note that XFS does not support shrinking.
Start the interactive
partedshell:# parted block-device-
Replace block-device with the path to the device where you want to resize a partition: for example,
/dev/sda.
-
Replace block-device with the path to the device where you want to resize a partition: for example,
View the current partition table:
(parted) print
From the partition table, determine:
- The minor number of the partition
- The location of the existing partition and its new ending point after resizing
Resize the partition:
(parted) resizepart minor-number new-end
-
Replace minor-number with the minor number of the partition that you are resizing: for example,
3. -
Replace new-end with the size that determines the new ending point of the resized partition, counting from the beginning of the disk. You can use size suffixes, such as
512MiB,20GiB, or1.5TiB. The default size megabytes.
Example 7.4. Extending a partition
For example, to extend a partition located at the beginning of the disk to be 2GiB in size, use:
(parted) resizepart 1 2GiB
The changes start taking place as soon as you enter this command, so review it before executing it.
-
Replace minor-number with the minor number of the partition that you are resizing: for example,
View the partition table to confirm that the resized partition is in the partition table with the correct size:
(parted) print
Exit the
partedshell:(parted) quit
Verify that the kernel recognizes the new partition:
# cat /proc/partitions
- If you extended the partition, extend the file system on it as well. See (reference) for details.
Additional resources
-
The
parted(8)man page.
Chapter 8. Getting started with XFS
This is an overview of how to create and maintain XFS file systems.
8.1. The XFS file system
XFS is a highly scalable, high-performance, robust, and mature 64-bit journaling file system that supports very large files and file systems on a single host. It is the default file system in Red Hat Enterprise Linux 8. XFS was originally developed in the early 1990s by SGI and has a long history of running on extremely large servers and storage arrays.
The features of XFS include:
- Reliability
- Metadata journaling, which ensures file system integrity after a system crash by keeping a record of file system operations that can be replayed when the system is restarted and the file system remounted
- Extensive run-time metadata consistency checking
- Scalable and fast repair utilities
- Quota journaling. This avoids the need for lengthy quota consistency checks after a crash.
- Scalability and performance
- Supported file system size up to 1024 TiB
- Ability to support a large number of concurrent operations
- B-tree indexing for scalability of free space management
- Sophisticated metadata read-ahead algorithms
- Optimizations for streaming video workloads
- Allocation schemes
- Extent-based allocation
- Stripe-aware allocation policies
- Delayed allocation
- Space pre-allocation
- Dynamically allocated inodes
- Other features
- Reflink-based file copies (new in Red Hat Enterprise Linux 8)
- Tightly integrated backup and restore utilities
- Online defragmentation
- Online file system growing
- Comprehensive diagnostics capabilities
-
Extended attributes (
xattr). This allows the system to associate several additional name/value pairs per file. - Project or directory quotas. This allows quota restrictions over a directory tree.
- Subsecond timestamps
Performance characteristics
XFS has a high performance on large systems with enterprise workloads. A large system is one with a relatively high number of CPUs, multiple HBAs, and connections to external disk arrays. XFS also performs well on smaller systems that have a multi-threaded, parallel I/O workload.
XFS has a relatively low performance for single threaded, metadata-intensive workloads: for example, a workload that creates or deletes large numbers of small files in a single thread.
8.2. Creating an XFS file system
As a system administrator, you can create an XFS file system on a block device to enable it to store files and directories.
8.2.1. Creating an XFS file system with mkfs.xfs
This procedure describes how to create an XFS file system on a block device.
Procedure
To create the file system:
If the device is a regular partition, an LVM volume, an MD volume, a disk, or a similar device, use the following command:
# mkfs.xfs block-device-
Replace block-device with the path to the block device. For example,
/dev/sdb1,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a, or/dev/my-volgroup/my-lv. - In general, the default options are optimal for common use.
-
When using
mkfs.xfson a block device containing an existing file system, add the-foption to overwrite that file system.
-
Replace block-device with the path to the block device. For example,
To create the file system on a hardware RAID device, check if the system correctly detects the stripe geometry of the device:
If the stripe geometry information is correct, no additional options are needed. Create the file system:
# mkfs.xfs block-deviceIf the information is incorrect, specify stripe geometry manually with the
suandswparameters of the-doption. Thesuparameter specifies the RAID chunk size, and theswparameter specifies the number of data disks in the RAID device.For example:
# mkfs.xfs -d su=64k,sw=4 /dev/sda3
Use the following command to wait for the system to register the new device node:
# udevadm settle
Additional resources
-
The
mkfs.xfs(8)man page.
8.2.2. Additional resources
-
The
mkfs.xfs(8)man page.
8.3. Backing up an XFS file system
As a system administrator, you can use the xfsdump to back up an XFS file system into a file or on a tape. This provides a simple backup mechanism.
8.3.1. Features of XFS backup
This section describes key concepts and features of backing up an XFS file system with the xfsdump utility.
You can use the xfsdump utility to:
Perform backups to regular file images.
Only one backup can be written to a regular file.
Perform backups to tape drives.
The
xfsdumputility also enables you to write multiple backups to the same tape. A backup can span multiple tapes.To back up multiple file systems to a single tape device, simply write the backup to a tape that already contains an XFS backup. This appends the new backup to the previous one. By default,
xfsdumpnever overwrites existing backups.Create incremental backups.
The
xfsdumputility uses dump levels to determine a base backup to which other backups are relative. Numbers from 0 to 9 refer to increasing dump levels. An incremental backup only backs up files that have changed since the last dump of a lower level:- To perform a full backup, perform a level 0 dump on the file system.
- A level 1 dump is the first incremental backup after a full backup. The next incremental backup would be level 2, which only backs up files that have changed since the last level 1 dump; and so on, to a maximum of level 9.
- Exclude files from a backup using size, subtree, or inode flags to filter them.
Additional resources
-
The
xfsdump(8)man page.
8.3.2. Backing up an XFS file system with xfsdump
This procedure describes how to back up the content of an XFS file system into a file or a tape.
Prerequisites
- An XFS file system that you can back up.
- Another file system or a tape drive where you can store the backup.
Procedure
Use the following command to back up an XFS file system:
# xfsdump -l level [-L label] \ -f backup-destination path-to-xfs-filesystem
-
Replace level with the dump level of your backup. Use
0to perform a full backup or1to9to perform consequent incremental backups. -
Replace backup-destination with the path where you want to store your backup. The destination can be a regular file, a tape drive, or a remote tape device. For example,
/backup-files/Data.xfsdumpfor a file or/dev/st0for a tape drive. -
Replace path-to-xfs-filesystem with the mount point of the XFS file system you want to back up. For example,
/mnt/data/. The file system must be mounted. -
When backing up multiple file systems and saving them on a single tape device, add a session label to each backup using the
-L labeloption so that it is easier to identify them when restoring. Replace label with any name for your backup: for example,backup_data.
-
Replace level with the dump level of your backup. Use
Example 8.1. Backing up multiple XFS file systems
To back up the content of XFS file systems mounted on the
/boot/and/data/directories and save them as files in the/backup-files/directory:# xfsdump -l 0 -f /backup-files/boot.xfsdump /boot # xfsdump -l 0 -f /backup-files/data.xfsdump /data
To back up multiple file systems on a single tape device, add a session label to each backup using the
-L labeloption:# xfsdump -l 0 -L "backup_boot" -f /dev/st0 /boot # xfsdump -l 0 -L "backup_data" -f /dev/st0 /data
Additional resources
-
The
xfsdump(8)man page.
8.3.3. Additional resources
-
The
xfsdump(8)man page.
8.4. Restoring an XFS file system from backup
As a system administrator, you can use the xfsrestore utility to restore XFS backup created with the xfsdump utility and stored in a file or on a tape.
8.4.1. Features of restoring XFS from backup
This section describes key concepts and features of restoring an XFS file system from backup with the xfsrestore utility.
The xfsrestore utility restores file systems from backups produced by xfsdump. The xfsrestore utility has two modes:
- The simple mode enables users to restore an entire file system from a level 0 dump. This is the default mode.
- The cumulative mode enables file system restoration from an incremental backup: that is, level 1 to level 9.
A unique session ID or session label identifies each backup. Restoring a backup from a tape containing multiple backups requires its corresponding session ID or label.
To extract, add, or delete specific files from a backup, enter the xfsrestore interactive mode. The interactive mode provides a set of commands to manipulate the backup files.
Additional resources
-
The
xfsrestore(8)man page.
8.4.2. Restoring an XFS file system from backup with xfsrestore
This procedure describes how to restore the content of an XFS file system from a file or tape backup.
Prerequisites
- A file or tape backup of XFS file systems, as described in Section 8.3, “Backing up an XFS file system”.
- A storage device where you can restore the backup.
Procedure
The command to restore the backup varies depending on whether you are restoring from a full backup or an incremental one, or are restoring multiple backups from a single tape device:
# xfsrestore [-r] [-S session-id] [-L session-label] [-i] -f backup-location restoration-path-
Replace backup-location with the location of the backup. This can be a regular file, a tape drive, or a remote tape device. For example,
/backup-files/Data.xfsdumpfor a file or/dev/st0for a tape drive. -
Replace restoration-path with the path to the directory where you want to restore the file system. For example,
/mnt/data/. -
To restore a file system from an incremental (level 1 to level 9) backup, add the
-roption. To restore a backup from a tape device that contains multiple backups, specify the backup using the
-Sor-Loptions.The
-Soption lets you choose a backup by its session ID, while the-Loption lets you choose by the session label. To obtain the session ID and session labels, use thexfsrestore -Icommand.Replace session-id with the session ID of the backup. For example,
b74a3586-e52e-4a4a-8775-c3334fa8ea2c. Replace session-label with the session label of the backup. For example,my_backup_session_label.To use
xfsrestoreinteractively, use the-ioption.The interactive dialog begins after
xfsrestorefinishes reading the specified device. Available commands in the interactivexfsrestoreshell includecd,ls,add,delete, andextract; for a complete list of commands, use thehelpcommand.
-
Replace backup-location with the location of the backup. This can be a regular file, a tape drive, or a remote tape device. For example,
Example 8.2. Restoring Multiple XFS File Systems
To restore the XFS backup files and save their content into directories under
/mnt/:# xfsrestore -f /backup-files/boot.xfsdump /mnt/boot/ # xfsrestore -f /backup-files/data.xfsdump /mnt/data/
To restore from a tape device containing multiple backups, specify each backup by its session label or session ID:
# xfsrestore -L "backup_boot" -f /dev/st0 /mnt/boot/ # xfsrestore -S "45e9af35-efd2-4244-87bc-4762e476cbab" \ -f /dev/st0 /mnt/data/
Additional resources
-
The
xfsrestore(8)man page.
8.4.3. Informational messages when restoring an XFS backup from a tape
When restoring a backup from a tape with backups from multiple file systems, the xfsrestore utility might issue messages. The messages inform you whether a match of the requested backup has been found when xfsrestore examines each backup on the tape in sequential order. For example:
xfsrestore: preparing drive xfsrestore: examining media file 0 xfsrestore: inventory session uuid (8590224e-3c93-469c-a311-fc8f23029b2a) does not match the media header's session uuid (7eda9f86-f1e9-4dfd-b1d4-c50467912408) xfsrestore: examining media file 1 xfsrestore: inventory session uuid (8590224e-3c93-469c-a311-fc8f23029b2a) does not match the media header's session uuid (7eda9f86-f1e9-4dfd-b1d4-c50467912408) [...]
The informational messages keep appearing until the matching backup is found.
8.4.4. Additional resources
-
The
xfsrestore(8)man page.
8.5. Repairing an XFS file system
As a system administrator, you can repair a corrupted XFS file system.
8.5.1. Error-handling mechanisms in XFS
This section describes how XFS handles various kinds of errors in the file system.
Unclean unmounts
Journalling maintains a transactional record of metadata changes that happen on the file system.
In the event of a system crash, power failure, or other unclean unmount, XFS uses the journal (also called log) to recover the file system. The kernel performs journal recovery when mounting the XFS file system.
Corruption
In this context, corruption means errors on the file system caused by, for example:
- Hardware faults
- Bugs in storage firmware, device drivers, the software stack, or the file system itself
- Problems that cause parts of the file system to be overwritten by something outside of the file system
When XFS detects corruption in the file system or the file-system metadata, it shuts down the file system and reports the incident in the system log. Note that if the corruption occurred on the file system hosting the /var directory, these logs will not be available after a reboot.
Example 8.3. System log entry reporting an XFS corruption
# dmesg --notime | tail -15 XFS (loop0): Mounting V5 Filesystem XFS (loop0): Metadata CRC error detected at xfs_agi_read_verify+0xcb/0xf0 [xfs], xfs_agi block 0x2 XFS (loop0): Unmount and run xfs_repair XFS (loop0): First 128 bytes of corrupted metadata buffer: 00000000027b3b56: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000005f9abc7a: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000005b0aef35: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000000da9d2ded: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000001e265b07: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000006a40df69: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000000b272907: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000000e484aac5: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ XFS (loop0): metadata I/O error in "xfs_trans_read_buf_map" at daddr 0x2 len 1 error 74 XFS (loop0): xfs_imap_lookup: xfs_ialloc_read_agi() returned error -117, agno 0 XFS (loop0): Failed to read root inode 0x80, error 11
User-space utilities usually report the Input/output error message when trying to access a corrupted XFS file system. Mounting an XFS file system with a corrupted log results in the following error message:
mount: /mount-point: mount(2) system call failed: Structure needs cleaning.
You must manually use the xfs_repair utility to repair the corruption. Unlike other file system repair utilities, xfs_repair does not run at boot time, even when an XFS file system was not cleanly unmounted. In the event of an unclean unmount, XFS simply replays the log at mount time, ensuring a consistent file system; xfs_repair cannot repair an XFS file system with a dirty log without remounting it first.
Additional resources
-
The
xfs_repair(8)man page provides a detailed list of XFS corruption checks.
8.5.2. Repairing an XFS file system with xfs_repair
This procedure repairs a corrupted XFS file system using the xfs_repair utility.
Procedure
Clear the log by remounting the file system:
# mount file-system # umount file-system
Use the
xfs_repairutility to repair the unmounted file system:If the mount succeeded, no additional options are required:
# xfs_repair block-deviceIf the mount failed with the Structure needs cleaning error, the log is corrupted and cannot be replayed. Use the
-Loption (force log zeroing) to clear the log:WarningThis command causes all metadata updates in progress at the time of the crash to be lost, which might cause significant file system damage and data loss. This should be used only as a last resort.
# xfs_repair -L block-device
Mount the file system:
# mount file-system
Additional resources
-
The
xfs_repair(8)man page.
8.6. Increasing the size of an XFS file system
As a system administrator, you can increase the size of an XFS file system to utilize larger storage capacity.
It is not currently possible to decrease the size of XFS file systems.
8.6.1. Increasing the size of an XFS file system with xfs_growfs
This procedure describes how to grow an XFS file system using the xfs_growfs utility.
Prerequisites
- Ensure that the underlying block device is of an appropriate size to hold the resized file system later. Use the appropriate resizing methods for the affected block device.
- Mount the XFS file system.
Procedure
While the XFS file system is mounted, use the
xfs_growfsutility to increase its size:# xfs_growfs file-system -D new-size
- Replace file-system with the mount point of the XFS file system.
With the
-Doption, replace new-size with the desired new size of the file system specified in the number of file system blocks.To find out the block size in kB of a given XFS file system, use the
xfs_infoutility:# xfs_info block-device ... data = bsize=4096 ...-
Without the
-Doption,xfs_growfsgrows the file system to the maximum size supported by the underlying device.
Additional resources
-
The
xfs_growfs(8)man page.
Chapter 9. Mounting file systems
As a system administrator, you can mount file systems on your system to access data on them.
9.1. The Linux mount mechanism
This section explains basic concepts of mounting file systems on Linux.
On Linux, UNIX, and similar operating systems, file systems on different partitions and removable devices (CDs, DVDs, or USB flash drives for example) can be attached to a certain point (the mount point) in the directory tree, and then detached again. While a file system is mounted on a directory, the original content of the directory is not accessible.
Note that Linux does not prevent you from mounting a file system to a directory with a file system already attached to it.
When mounting, you can identify the device by:
-
a universally unique identifier (UUID): for example,
UUID=34795a28-ca6d-4fd8-a347-73671d0c19cb -
a volume label: for example,
LABEL=home -
a full path to a non-persistent block device: for example,
/dev/sda3
When you mount a file system using the mount command without all required information, that is without the device name, the target directory, or the file system type, the mount utility reads the content of the /etc/fstab file to check if the given file system is listed there. The /etc/fstab file contains a list of device names and the directories in which the selected file systems are set to be mounted as well as the file system type and mount options. Therefore, when mounting a file system that is specified in /etc/fstab, the following command syntax is sufficient:
Mounting by the mount point:
# mount directoryMounting by the block device:
# mount device
Additional resources
-
The
mount(8)man page. - For information on how to list persistent naming attributes such as the UUID, see Section 6.6, “Listing persistent naming attributes”.
9.2. Listing currently mounted file systems
This procedure describes how to list all currently mounted file systems on the command line.
Procedure
To list all mounted file systems, use the
findmntutility:$ findmnt
To limit the listed file systems only to a certain file system type, add the
--typesoption:$ findmnt --types fs-typeFor example:
Example 9.1. Listing only XFS file systems
$ findmnt --types xfs TARGET SOURCE FSTYPE OPTIONS / /dev/mapper/luks-5564ed00-6aac-4406-bfb4-c59bf5de48b5 xfs rw,relatime ├─/boot /dev/sda1 xfs rw,relatime └─/home /dev/mapper/luks-9d185660-7537-414d-b727-d92ea036051e xfs rw,relatime
Additional resources
-
The
findmnt(8)man page.
9.3. Mounting a file system with mount
This procedure describes how to mount a file system using the mount utility.
Prerequisites
Make sure that no file system is already mounted on your chosen mount point:
$ findmnt mount-point
Procedure
To attach a certain file system, use the
mountutility:# mount device mount-point
Example 9.2. Mounting an XFS file system
For example, to mount a local XFS file system identified by UUID:
# mount UUID=ea74bbec-536d-490c-b8d9-5b40bbd7545b /mnt/data
If
mountcannot recognize the file system type automatically, specify it using the--typesoption:# mount --types type device mount-point
Example 9.3. Mounting an NFS file system
For example, to mount a remote NFS file system:
# mount --types nfs4 host:/remote-export /mnt/nfs
Additional resources
-
The
mount(8)man page.
9.4. Moving a mount point
This procedure describes how to change the mount point of a mounted file system to a different directory.
Procedure
To change the directory in which a file system is mounted:
# mount --move old-directory new-directory
Example 9.4. Moving a home file system
For example, to move the file system mounted in the
/mnt/userdirs/directory to the/home/mount point:# mount --move /mnt/userdirs /home
Verify that the file system has been moved as expected:
$ findmnt $ ls old-directory $ ls new-directory
Additional resources
-
The
mount(8)man page.
9.5. Unmounting a file system with umount
This procedure describes how to unmount a file system using the umount utility.
Procedure
Try unmounting the file system using either of the following commands:
By mount point:
# umount mount-pointBy device:
# umount device
If the command fails with an error similar to the following, it means that the file system is in use because of a process is using resources on it:
umount: /run/media/user/FlashDrive: target is busy.If the file system is in use, use the
fuserutility to determine which processes are accessing it. For example:$ fuser --mount /run/media/user/FlashDrive /run/media/user/FlashDrive: 18351
Afterwards, terminate the processes using the file system and try unmounting it again.
9.6. Common mount options
This section lists some commonly used options of the mount utility.
You can use these options in the following syntax:
# mount --options option1,option2,option3 device mount-point
Table 9.1. Common mount options
| Option | Description |
|---|---|
|
| Enables asynchronous input and output operations on the file system. |
|
|
Enables the file system to be mounted automatically using the |
|
|
Provides an alias for the |
|
| Allows the execution of binary files on the particular file system. |
|
| Mounts an image as a loop device. |
|
|
Default behavior disables the automatic mount of the file system using the |
|
| Disallows the execution of binary files on the particular file system. |
|
| Disallows an ordinary user (that is, other than root) to mount and unmount the file system. |
|
| Remounts the file system in case it is already mounted. |
|
| Mounts the file system for reading only. |
|
| Mounts the file system for both reading and writing. |
|
| Allows an ordinary user (that is, other than root) to mount and unmount the file system. |
9.7. Sharing a mount on multiple mount points
As a system administrator, you can duplicate mount points to make the file systems accessible from multiple directories.
9.7.2. Creating a private mount point duplicate
This procedure duplicates a mount point as a private mount. File systems that you later mount under the duplicate or the original mount point are not reflected in the other.
Procedure
Create a virtual file system (VFS) node from the original mount point:
# mount --bind original-dir original-dir
Mark the original mount point as private:
# mount --make-private original-dirAlternatively, to change the mount type for the selected mount point and all mount points under it, use the
--make-rprivateoption instead of--make-private.Create the duplicate:
# mount --bind original-dir duplicate-dir
Example 9.5. Duplicating /media into /mnt as a private mount point
Create a VFS node from the
/mediadirectory:# mount --bind /media /media
Mark the
/mediadirectory as private:# mount --make-private /media
Create its duplicate in
/mnt:# mount --bind /media /mnt
It is now possible to verify that
/mediaand/mntshare content but none of the mounts within/mediaappear in/mnt. For example, if the CD-ROM drive contains non-empty media and the/media/cdrom/directory exists, use:# mount /dev/cdrom /media/cdrom # ls /media/cdrom EFI GPL isolinux LiveOS # ls /mnt/cdrom #
It is also possible to verify that file systems mounted in the
/mntdirectory are not reflected in/media. For instance, if a non-empty USB flash drive that uses the/dev/sdc1device is plugged in and the/mnt/flashdisk/directory is present, use:# mount /dev/sdc1 /mnt/flashdisk # ls /media/flashdisk # ls /mnt/flashdisk en-US publican.cfg
Additional resources
-
The
mount(8)man page.
9.7.4. Creating a slave mount point duplicate
This procedure duplicates a mount point as a slave mount. File systems that you later mount under the original mount point are reflected in the duplicate but not the other way around.
Procedure
Create a virtual file system (VFS) node from the original mount point:
# mount --bind original-dir original-dir
Mark the original mount point as shared:
# mount --make-shared original-dirAlternatively, to change the mount type for the selected mount point and all mount points under it, use the
--make-rsharedoption instead of--make-shared.Create the duplicate and mark it as slave:
# mount --bind original-dir duplicate-dir # mount --make-slave duplicate-dir
Example 9.7. Duplicating /media into /mnt as a slave mount point
This example shows how to get the content of the /media directory to appear in /mnt as well, but without any mounts in the /mnt directory to be reflected in /media.
Create a VFS node from the
/mediadirectory:# mount --bind /media /media
Mark the
/mediadirectory as shared:# mount --make-shared /media
Create its duplicate in
/mntand mark it as slave:# mount --bind /media /mnt # mount --make-slave /mnt
Verify that a mount within
/mediaalso appears in/mnt. For example, if the CD-ROM drive contains non-empty media and the/media/cdrom/directory exists, use:# mount /dev/cdrom /media/cdrom # ls /media/cdrom EFI GPL isolinux LiveOS # ls /mnt/cdrom EFI GPL isolinux LiveOS
Also verify that file systems mounted in the
/mntdirectory are not reflected in/media. For instance, if a non-empty USB flash drive that uses the/dev/sdc1device is plugged in and the/mnt/flashdisk/directory is present, use:# mount /dev/sdc1 /mnt/flashdisk # ls /media/flashdisk # ls /mnt/flashdisk en-US publican.cfg
Additional resources
-
The
mount(8)man page.
9.7.5. Preventing a mount point from being duplicated
This procedure marks a mount point as unbindable so that it is not possible to duplicate it in another mount point.
Procedure
To change the type of a mount point to an unbindable mount, use:
# mount --bind mount-point mount-point # mount --make-unbindable mount-point
Alternatively, to change the mount type for the selected mount point and all mount points under it, use the
--make-runbindableoption instead of--make-unbindable.Any subsequent attempt to make a duplicate of this mount fails with the following error:
# mount --bind mount-point duplicate-dir mount: wrong fs type, bad option, bad superblock on mount-point, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so
Example 9.8. Preventing /media from being duplicated
To prevent the
/mediadirectory from being shared, use:# mount --bind /media /media # mount --make-unbindable /media
Additional resources
-
The
mount(8)man page.
9.8. Persistently mounting file systems
As a system administrator, you can persistently mount file systems to configure non-removable storage.
9.8.1. The /etc/fstab file
This section describes the /etc/fstab configuration file, which controls persistent mount points of file systems. Using /etc/fstab is the recommended way to persistently mount file systems.
Each line in the /etc/fstab file defines a mount point of a file system. It includes six fields separated by white space:
-
The block device identified by a persistent attribute or a path it the
/devdirectory. - The directory where the device will be mounted.
- The file system on the device.
-
Mount options for the file system. The option
defaultsmeans that the partition is mounted at boot time with default options. This section also recognizessystemdmount unit options in thex-systemd.optionformat. -
Backup option for the
dumputility. -
Check order for the
fsckutility.
Example 9.9. The /boot file system in /etc/fstab
| Block device | Mount point | File system | Options | Backup | Check |
|---|---|---|---|---|---|
|
|
|
|
|
|
|
The systemd service automatically generates mount units from entries in /etc/fstab.
Additional resources
-
The
fstab(5)man page. -
The fstab section of the
systemd.mount(5)man page.
9.8.2. Adding a file system to /etc/fstab
This procedure describes how to configure persistent mount point for a file system in the /etc/fstab configuration file.
Procedure
Find out the UUID attribute of the file system:
$ lsblk --fs storage-deviceFor example:
Example 9.10. Viewing the UUID of a partition
$ lsblk --fs /dev/sda1 NAME FSTYPE LABEL UUID MOUNTPOINT sda1 xfs Boot ea74bbec-536d-490c-b8d9-5b40bbd7545b /boot
If the mount point directory does not exist, create it:
# mkdir --parents mount-pointAs root, edit the
/etc/fstabfile and add a line for the file system, identified by the UUID.For example:
Example 9.11. The /boot mount point in /etc/fstab
UUID=ea74bbec-536d-490c-b8d9-5b40bbd7545b /boot xfs defaults 0 0
Regenerate mount units so that your system registers the new configuration:
# systemctl daemon-reload
Try mounting the file system to verify that the configuration works:
# mount mount-point
Additional resources
- Other persistent attributes that you can use to identify the file system: Section 6.3, “Device names managed by the udev mechanism in /dev/disk/”
9.9. Mounting file systems on demand
As a system administrator, you can configure file systems, such as NFS, to mount automatically on demand.
9.9.1. The autofs service
This section explains the benefits and basic concepts of the autofs service, used to mount file systems on demand.
One drawback of permanent mounting using the /etc/fstab configuration is that, regardless of how infrequently a user accesses the mounted file system, the system must dedicate resources to keep the mounted file system in place. This might affect system performance when, for example, the system is maintaining NFS mounts to many systems at one time.
An alternative to /etc/fstab is to use the kernel-based autofs service. It consists of the following components:
- A kernel module that implements a file system, and
- A user-space service that performs all of the other functions.
The autofs service can mount and unmount file systems automatically (on-demand), therefore saving system resources. It can be used to mount file systems such as NFS, AFS, SMBFS, CIFS, and local file systems.
Additional resources
-
The
autofs(8)man page.
9.9.2. The autofs configuration files
This section describes the usage and syntax of configuration files used by the autofs service.
The master map file
The autofs service uses /etc/auto.master (master map) as its default primary configuration file. This can be changed to use another supported network source and name using the autofs configuration in the /etc/autofs.conf configuration file in conjunction with the Name Service Switch (NSS) mechanism.
All on-demand mount points must be configured in the master map. Mount point, host name, exported directory, and options can all be specified in a set of files (or other supported network sources) rather than configuring them manually for each host.
The master map file lists mount points controlled by autofs, and their corresponding configuration files or network sources known as automount maps. The format of the master map is as follows:
mount-point map-name options
The variables used in this format are:
- mount-point
-
The
autofsmount point; for example,/mnt/data/. - map-file
- The map source file, which contains a list of mount points and the file system location from which those mount points should be mounted.
- options
- If supplied, these apply to all entries in the given map, if they do not themselves have options specified.
Example 9.12. The /etc/auto.master file
The following is a sample line from /etc/auto.master file:
/mnt/data /etc/auto.data
Map files
Map files configure the properties of individual on-demand mount points.
The automounter creates the directories if they do not exist. If the directories exist before the automounter was started, the automounter will not remove them when it exits. If a timeout is specified, the directory is automatically unmounted if the directory is not accessed for the timeout period.
The general format of maps is similar to the master map. However, the options field appears between the mount point and the location instead of at the end of the entry as in the master map:
mount-point options location
The variables used in this format are:
- mount-point
-
This refers to the
autofsmount point. This can be a single directory name for an indirect mount or the full path of the mount point for direct mounts. Each direct and indirect map entry key (mount-point) can be followed by a space separated list of offset directories (subdirectory names each beginning with/) making them what is known as a multi-mount entry. - options
- When supplied, these are the mount options for the map entries that do not specify their own options. This field is optional.
- location
-
This refers to the file system location such as a local file system path (preceded with the Sun map format escape character
:for map names beginning with/), an NFS file system or other valid file system location.
Example 9.13. A map file
The following is a sample from a map file; for example, /etc/auto.misc:
payroll -fstype=nfs4 personnel:/dev/disk/by-uuid/52b94495-e106-4f29-b868-fe6f6c2789b1 sales -fstype=xfs :/dev/disk/by-uuid/5564ed00-6aac-4406-bfb4-c59bf5de48b5
The first column in the map file indicates the autofs mount point: sales and payroll from the server called personnel. The second column indicates the options for the autofs mount. The third column indicates the source of the mount.
Following the given configuration, the autofs mount points will be /home/payroll and /home/sales. The -fstype= option is often omitted and is generally not needed for correct operation.
Using the given configuration, if a process requires access to an autofs unmounted directory such as /home/payroll/2006/July.sxc, the autofs service automatically mounts the directory.
The amd map format
The autofs service recognizes map configuration in the amd format as well. This is useful if you want to reuse existing automounter configuration written for the am-utils service, which has been removed from Red Hat Enterprise Linux.
However, Red Hat recommends using the simpler autofs format described in the previous sections.
Additional resources
-
The
autofs(5),autofs.conf(5), andauto.master(5)man pages. -
For details on the
amdmap format, see the/usr/share/doc/autofs/README.amd-mapsfile, which is provided by theautofspackage.
9.9.3. Configuring autofs mount points
This procedure describes how to configure on-demand mount points using the autofs service.
Prerequisites
Install the
autofspackage:# yum install autofs
Start and enable the
autofsservice:# systemctl enable --now autofs
Procedure
-
Create a map file for the on-demand mount point, located at
/etc/auto.identifier. Replace identifier with a name that identifies the mount point. - In the map file, fill in the mount point, options, and location fields as described in Section 9.9.2, “The autofs configuration files”.
- Register the map file in the master map file, as described in Section 9.9.2, “The autofs configuration files”.
Try accessing content in the on-demand directory:
$ ls automounted-directory
9.9.4. Overriding or augmenting autofs site configuration files
It is sometimes useful to override site defaults for a specific mount point on a client system.
Example 9.14. Initial conditions
For example, consider the following conditions:
Automounter maps are stored in NIS and the
/etc/nsswitch.conffile has the following directive:automount: files nis
The
auto.masterfile contains:+auto.master
The NIS
auto.mastermap file contains:/home auto.home
The NIS
auto.homemap contains:beth fileserver.example.com:/export/home/beth joe fileserver.example.com:/export/home/joe * fileserver.example.com:/export/home/&
-
The file map
/etc/auto.homedoes not exist.
Procedure
Example 9.15. Mounting home directories from a different server
Given the preceding conditions, let’s assume that the client system needs to override the NIS map auto.home and mount home directories from a different server.
In this case, the client needs to use the following
/etc/auto.mastermap:/home /etc/auto.home +auto.master
The
/etc/auto.homemap contains the entry:* labserver.example.com:/export/home/&
Because the automounter only processes the first occurrence of a mount point, the /home directory contains the content of /etc/auto.home instead of the NIS auto.home map.
Example 9.16. Augmenting auto.home with only selected entries
Alternatively, to augment the site-wide auto.home map with just a few entries:
Create an
/etc/auto.homefile map, and in it put the new entries. At the end, include the NISauto.homemap. Then the/etc/auto.homefile map looks similar to:mydir someserver:/export/mydir +auto.home
With these NIS
auto.homemap conditions, listing the content of the/homedirectory outputs:$ ls /home beth joe mydir
This last example works as expected because autofs does not include the contents of a file map of the same name as the one it is reading. As such, autofs moves on to the next map source in the nsswitch configuration.
9.9.5. Using LDAP to store automounter maps
This procedure configures autofs to store automounter maps in LDAP configuration rather than in autofs map files.
Prerequisites
-
LDAP client libraries must be installed on all systems configured to retrieve automounter maps from LDAP. On Red Hat Enterprise Linux, the
openldappackage should be installed automatically as a dependency of theautofspackage.
Procedure
-
To configure LDAP access, modify the
/etc/openldap/ldap.conffile. Ensure that theBASE,URI, andschemaoptions are set appropriately for your site. The most recently established schema for storing automount maps in LDAP is described by the
rfc2307bisdraft. To use this schema, set it in the/etc/autofs.confconfiguration file by removing the comment characters from the schema definition. For example:Example 9.17. Setting autofs configuration
DEFAULT_MAP_OBJECT_CLASS="automountMap" DEFAULT_ENTRY_OBJECT_CLASS="automount" DEFAULT_MAP_ATTRIBUTE="automountMapName" DEFAULT_ENTRY_ATTRIBUTE="automountKey" DEFAULT_VALUE_ATTRIBUTE="automountInformation"
Ensure that all other schema entries are commented in the configuration. The
automountKeyattribute replaces thecnattribute in therfc2307bisschema. Following is an example of an LDAP Data Interchange Format (LDIF) configuration:Example 9.18. LDF Configuration
# extended LDIF # # LDAPv3 # base <> with scope subtree # filter: (&(objectclass=automountMap)(automountMapName=auto.master)) # requesting: ALL # # auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: top objectClass: automountMap automountMapName: auto.master # extended LDIF # # LDAPv3 # base <automountMapName=auto.master,dc=example,dc=com> with scope subtree # filter: (objectclass=automount) # requesting: ALL # # /home, auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: automount cn: /home automountKey: /home automountInformation: auto.home # extended LDIF # # LDAPv3 # base <> with scope subtree # filter: (&(objectclass=automountMap)(automountMapName=auto.home)) # requesting: ALL # # auto.home, example.com dn: automountMapName=auto.home,dc=example,dc=com objectClass: automountMap automountMapName: auto.home # extended LDIF # # LDAPv3 # base <automountMapName=auto.home,dc=example,dc=com> with scope subtree # filter: (objectclass=automount) # requesting: ALL # # foo, auto.home, example.com dn: automountKey=foo,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: foo automountInformation: filer.example.com:/export/foo # /, auto.home, example.com dn: automountKey=/,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: / automountInformation: filer.example.com:/export/&
Additional resources
-
The
rfc2307bisdraft: https://tools.ietf.org/html/draft-howard-rfc2307bis.
9.10. Setting read-only permissions for the root file system
Sometimes, you need to mount the root file system (/) with read-only permissions. Example use cases include enhancing security or ensuring data integrity after an unexpected system power-off.
9.10.1. Files and directories that always retain write permissions
For the system to function properly, some files and directories need to retain write permissions. When the root file system is mounted in read-only mode, these files are mounted in RAM using the tmpfs temporary file system.
The default set of such files and directories is read from the /etc/rwtab file, which contains:
dirs /var/cache/man dirs /var/gdm <content truncated> empty /tmp empty /var/cache/foomatic <content truncated> files /etc/adjtime files /etc/ntp.conf <content truncated>
Entries in the /etc/rwtab file follow this format:
copy-method path
In this syntax:
- Replace copy-method with one of the keywords specifying how the file or directory is copied to tmpfs.
- Replace path with the path to the file or directory.
The /etc/rwtab file recognizes the following ways in which a file or directory can be copied to tmpfs:
emptyAn empty path is copied to
tmpfs. For example:empty /tmp
dirsA directory tree is copied to
tmpfs, empty. For example:dirs /var/run
filesA file or a directory tree is copied to
tmpfsintact. For example:files /etc/resolv.conf
The same format applies when adding custom paths to /etc/rwtab.d/.
9.10.2. Configuring the root file system to mount with read-only permissions on boot
With this procedure, the root file system is mounted read-only on all following boots.
Procedure
In the
/etc/sysconfig/readonly-rootfile, set theREADONLYoption toyes:# Set to 'yes' to mount the file systems as read-only. READONLY=yes
Add the
rooption in the root entry (/) in the/etc/fstabfile:/dev/mapper/luks-c376919e... / xfs x-systemd.device-timeout=0,ro 1 1Add the
rooption to theGRUB_CMDLINE_LINUXdirective in the/etc/default/grubfile and ensure that the directive does not containrw:GRUB_CMDLINE_LINUX="rhgb quiet... ro"Recreate the GRUB2 configuration file:
# grub2-mkconfig -o /boot/grub2/grub.cfg
If you need to add files and directories to be mounted with write permissions in the
tmpfsfile system, create a text file in the/etc/rwtab.d/directory and put the configuration there.For example, to mount the
/etc/example/filefile with write permissions, add this line to the/etc/rwtab.d/examplefile:files /etc/example/file
ImportantChanges made to files and directories in
tmpfsdo not persist across boots.- Reboot the system to apply the changes.
Troubleshooting
If you mount the root file system with read-only permissions by mistake, you can remount it with read-and-write permissions again using the following command:
# mount -o remount,rw /
Chapter 10. Discarding unused blocks
You can perform or schedule discard operations on block devices that support them.
10.1. Block discard operations
Block discard operations discard blocks that are no longer in use by a mounted file system. They are useful on:
- Solid-state drives (SSDs)
- Thinly-provisioned storage
Requirements
The block device underlying the file system must support physical discard operations.
Physical discard operations are supported if the value in the /sys/block/device/queue/discard_max_bytes file is not zero.
10.2. Types of block discard operations
You can run discard operations using different methods:
- Batch discard
- Are run explicitly by the user. They discard all unused blocks in the selected file systems.
- Online discard
- Are specified at mount time. They run in real time without user intervention. Online discard operations discard only the blocks that are transitioning from used to free.
- Periodic discard
-
Are batch operations that are run regularly by a
systemdservice.
All types are supported by the XFS and ext4 file systems and by VDO.
Recommendations
Red Hat recommends that you use batch or periodic discard.
Use online discard only if:
- the system’s workload is such that batch discard is not feasible, or
- online discard operations are necessary to maintain performance.
10.3. Performing batch block discard
This procedure performs a batch block discard operation to discard unused blocks on a mounted file system.
Prerequisites
- The file system is mounted.
- The block device underlying the file system supports physical discard operations.
Procedure
Use the
fstrimutility:To perform discard only on a selected file system, use:
# fstrim mount-pointTo perform discard on all mounted file systems, use:
# fstrim --all
If you execute the fstrim command on:
- a device that does not support discard operations, or
- a logical device (LVM or MD) composed of multiple devices, where any one of the device does not support discard operations,
the following message displays:
# fstrim /mnt/non_discard fstrim: /mnt/non_discard: the discard operation is not supported
Additional resources
-
The
fstrim(8)man page
10.4. Enabling online block discard
This procedure enables online block discard operations that automatically discard unused blocks on all supported file systems.
Procedure
Enable online discard at mount time:
When mounting a file system manually, add the
-o discardmount option:# mount -o discard device mount-point
-
When mounting a file system persistently, add the
discardoption to the mount entry in the/etc/fstabfile.
Additional resources
-
The
mount(8)man page -
The
fstab(5)man page
10.5. Enabling periodic block discard
This procedure enables a systemd timer that regularly discards unused blocks on all supported file systems.
Procedure
Enable and start the
systemdtimer:# systemctl enable --now fstrim.timer
Chapter 11. Managing layered local storage with Stratis
You can easily set up and manage complex storage configurations integrated by the Stratis high-level system.
Stratis is available as a Technology Preview. For information on Red Hat scope of support for Technology Preview features, see the Technology Preview Features Support Scope document.
Customers deploying Stratis are encouraged to provide feedback to Red Hat.
11.1. Setting up Stratis file systems
As a system administrator, you can enable and set up the Stratis volume-managing file system on your system to easily manage layered storage.
11.1.1. The purpose and features of Stratis
Stratis is a local storage-management solution for Linux. It is focused on simplicity and ease of use, and gives you access to advanced storage features.
Stratis makes the following activities easier:
- Initial configuration of storage
- Making changes later
- Using advanced storage features
Stratis is a hybrid user-and-kernel local storage management system that supports advanced storage features. The central concept of Stratis is a storage pool. This pool is created from one or more local disks or partitions, and volumes are created from the pool.
The pool enables many useful features, such as:
- File system snapshots
- Thin provisioning
- Tiering
11.1.2. Components of a Stratis volume
Externally, Stratis presents the following volume components in the command-line interface and the API:
blockdev- Block devices, such as a disk or a disk partition.
poolComposed of one or more block devices.
A pool has a fixed total size, equal to the size of the block devices.
The pool contains most Stratis layers, such as the non-volatile data cache using the
dm-cachetarget.Stratis creates a
/stratis/my-pool/directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.
filesystemEach pool can contain one or more file systems, which store files.
File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.
The file systems are formatted with XFS.
ImportantStratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.
Stratis creates links to file systems at the
/stratis/my-pool/my-fspath.
Stratis uses many Device Mapper devices, which show up in dmsetup listings and the /proc/partitions file. Similarly, the lsblk command output reflects the internal workings and layers of Stratis.
11.1.3. Block devices usable with Stratis
This section lists storage devices that you can use for Stratis.
Supported devices
Stratis pools have been tested to work on these types of block devices:
- LUKS
- LVM logical volumes
- MDRAID
- DM Multipath
- iSCSI
- HDDs and SSDs
- NVMe devices
In the current version, Stratis does not handle failures in hard drives or other hardware. If you create a Stratis pool over multiple hardware devices, you increase the risk of data loss because multiple devices must be operational to access the data.
Unsupported devices
Because Stratis contains a thin-provisioning layer, Red Hat does not recommend placing a Stratis pool on block devices that are already thinly-provisioned.
Additional resources
-
For iSCSI and other block devices requiring network, see the
systemd.mount(5)man page for information on the_netdevmount option.
11.1.4. Installing Stratis
This procedure installs all packages necessary to use Stratis.
Procedure
Install packages that provide the Stratis service and command-line utilities:
# yum install stratisd stratis-cli
Make sure that the
stratisdservice is enabled:# systemctl enable --now stratisd
11.1.5. Creating a Stratis pool
This procedure creates a Stratis pool from one or more block devices.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - The block devices on which you are creating a Stratis pool are not in use and not mounted.
- The block devices on which you are creating a Stratis pool are at least 1 GiB in size each.
On the IBM Z architecture, the
/dev/dasd*block devices must to be partitioned. Use the partition in the Stratis pool.For information on partitioning DASD devices, see Configuring a Linux instance on IBM Z.
Procedure
If the selected block device contains file system, partition table, or RAID signatures, erase them:
# wipefs --all block-deviceReplace block-device with the path to a block device, such as
/dev/sdb.To create a Stratis pool on the block device, use:
# stratis pool create my-pool block-device
- Replace my-pool with an arbitrary name for the pool.
-
Replace block-device with the path to the empty or wiped block device, such as
/dev/sdb.
To create a pool from more than one block device, list them all on the command line:
# stratis pool create my-pool device-1 device-2 device-n
To verify, list all pools on your system:
# stratis pool list
Additional resources
-
The
stratis(8)man page
Next steps
- Create a Stratis file system on the pool. See Section 11.1.6, “Creating a Stratis file system”.
11.1.6. Creating a Stratis file system
This procedure creates a Stratis file system on an existing Stratis pool.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis pool. See Section 11.1.5, “Creating a Stratis pool”.
Procedure
To create a Stratis file system on a pool, use:
# stratis fs create my-pool my-fs
- Replace my-pool with the name of your existing Stratis pool.
- Replace my-fs with an arbitrary name for the file system.
To verify, list file systems within the pool:
# stratis fs list my-pool
Additional resources
-
The
stratis(8)man page
Next steps
- Mount the Stratis file system. See Section 11.1.7, “Mounting a Stratis file system”.
11.1.7. Mounting a Stratis file system
This procedure mounts an existing Stratis file system to access the content.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis file system. See Section 11.1.6, “Creating a Stratis file system”.
Procedure
To mount the file system, use the entries that Stratis maintains in the
/stratis/directory:# mount /stratis/my-pool/my-fs mount-point
The file system is now mounted on the mount-point directory and ready to use.
Additional resources
-
The
mount(8)man page
11.1.8. Persistently mounting a Stratis file system
This procedure persistently mounts a Stratis file system so that it is available automatically after booting the system.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis file system. See Section 11.1.6, “Creating a Stratis file system”.
Procedure
Determine the UUID attribute of the file system:
$ lsblk --output=UUID /stratis/my-pool/my-fs
For example:
Example 11.1. Viewing the UUID of Stratis file system
$ lsblk --output=UUID /stratis/my-pool/fs1 UUID a1f0b64a-4ebb-4d4e-9543-b1d79f600283
If the mount point directory does not exist, create it:
# mkdir --parents mount-pointAs root, edit the
/etc/fstabfile and add a line for the file system, identified by the UUID. Usexfsas the file system type and add thex-systemd.requires=stratisd.serviceoption.For example:
Example 11.2. The /fs1 mount point in /etc/fstab
UUID=a1f0b64a-4ebb-4d4e-9543-b1d79f600283 /fs1 xfs defaults,x-systemd.requires=stratisd.service 0 0
Regenerate mount units so that your system registers the new configuration:
# systemctl daemon-reload
Try mounting the file system to verify that the configuration works:
# mount mount-point
Additional resources
11.2. Extending a Stratis volume with additional block devices
You can attach additional block devices to a Stratis pool to provide more storage capacity for Stratis file systems.
11.2.1. Components of a Stratis volume
Externally, Stratis presents the following volume components in the command-line interface and the API:
blockdev- Block devices, such as a disk or a disk partition.
poolComposed of one or more block devices.
A pool has a fixed total size, equal to the size of the block devices.
The pool contains most Stratis layers, such as the non-volatile data cache using the
dm-cachetarget.Stratis creates a
/stratis/my-pool/directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.
filesystemEach pool can contain one or more file systems, which store files.
File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.
The file systems are formatted with XFS.
ImportantStratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.
Stratis creates links to file systems at the
/stratis/my-pool/my-fspath.
Stratis uses many Device Mapper devices, which show up in dmsetup listings and the /proc/partitions file. Similarly, the lsblk command output reflects the internal workings and layers of Stratis.
11.2.2. Adding block devices to a Stratis pool
This procedure adds one or more block devices to a Stratis pool to be usable by Stratis file systems.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - The block devices that you are adding to the Stratis pool are not in use and not mounted.
- The block devices that you are adding to the Stratis pool are at least 1 GiB in size each.
Procedure
To add one or more block devices to the pool, use:
# stratis pool add-data my-pool device-1 device-2 device-n
Additional resources
-
The
stratis(8)man page
11.3. Monitoring Stratis file systems
As a Stratis user, you can view information about Stratis volumes on your system to monitor their state and free space.
11.3.1. Stratis sizes reported by different utilities
This section explains the difference between Stratis sizes reported by standard utilities such as df and the stratis utility.
Standard Linux utilities such as df report the size of the XFS file system layer on Stratis, which is 1 TiB. This is not useful information, because the actual storage usage of Stratis is less due to thin provisioning, and also because Stratis automatically grows the file system when the XFS layer is close to full.
Regularly monitor the amount of data written to your Stratis file systems, which is reported as the Total Physical Used value. Make sure it does not exceed the Total Physical Size value.
Additional resources
-
The
stratis(8)man page
11.3.2. Displaying information about Stratis volumes
This procedure lists statistics about your Stratis volumes, such as the total, used, and free size or file systems and block devices belonging to a pool.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running.
Procedure
To display information about all block devices used for Stratis on your system:
# stratis blockdev Pool Name Device Node Physical Size State Tier my-pool /dev/sdb 9.10 TiB In-use Data
To display information about all Stratis pools on your system:
# stratis pool Name Total Physical Size Total Physical Used my-pool 9.10 TiB 598 MiB
To display information about all Stratis file systems on your system:
# stratis filesystem Pool Name Name Used Created Device my-pool my-fs 546 MiB Nov 08 2018 08:03 /stratis/my-pool/my-fs
Additional resources
-
The
stratis(8)man page
11.4. Using snapshots on Stratis file systems
You can use snapshots on Stratis file systems to capture file system state at arbitrary times and restore it in the future.
11.4.1. Characteristics of Stratis snapshots
This section describes the properties and limitations of file system snapshots on Stratis.
In Stratis, a snapshot is a regular Stratis file system created as a copy of another Stratis file system. The snapshot initially contains the same file content as the original file system, but can change as the snapshot is modified. Whatever changes you make to the snapshot will not be reflected in the original file system.
The current snapshot implementation in Stratis is characterized by the following:
- A snapshot of a file system is another file system.
- A snapshot and its origin are not linked in lifetime. A snapshotted file system can live longer than the file system it was created from.
- A file system does not have to be mounted to create a snapshot from it.
- Each snapshot uses around half a gigabyte of actual backing storage, which is needed for the XFS log.
11.4.2. Creating a Stratis snapshot
This procedure creates a Stratis file system as a snapshot of an existing Stratis file system.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis file system. See Section 11.1.6, “Creating a Stratis file system”.
Procedure
To create a Stratis snapshot, use:
# stratis fs snapshot my-pool my-fs my-fs-snapshot
Additional resources
-
The
stratis(8)man page
11.4.3. Accessing the content of a Stratis snapshot
This procedure mounts a snapshot of a Stratis file system to make it accessible for read and write operations.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis snapshot. See Section 11.4.2, “Creating a Stratis snapshot”.
Procedure
To access the snapshot, mount it as a regular file system from the
/stratis/my-pool/directory:# mount /stratis/my-pool/my-fs-snapshot mount-point
Additional resources
- Section 11.1.7, “Mounting a Stratis file system”
-
The
mount(8)man page
11.4.4. Reverting a Stratis file system to a previous snapshot
This procedure reverts the content of a Stratis file system to the state captured in a Stratis snapshot.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis snapshot. See Section 11.4.2, “Creating a Stratis snapshot”.
Procedure
Optionally, back up the current state of the file system to be able to access it later:
# stratis filesystem snapshot my-pool my-fs my-fs-backup
Unmount and remove the original file system:
# umount /stratis/my-pool/my-fs # stratis filesystem destroy my-pool my-fs
Create a copy of the snapshot under the name of the original file system:
# stratis filesystem snapshot my-pool my-fs-snapshot my-fs
Mount the snapshot, which is now accessible with the same name as the original file system:
# mount /stratis/my-pool/my-fs mount-point
The content of the file system named my-fs is now identical to the snapshot my-fs-snapshot.
Additional resources
-
The
stratis(8)man page
11.4.5. Removing a Stratis snapshot
This procedure removes a Stratis snapshot from a pool. Data on the snapshot are lost.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis snapshot. See Section 11.4.2, “Creating a Stratis snapshot”.
Procedure
Unmount the snapshot:
# umount /stratis/my-pool/my-fs-snapshot
Destroy the snapshot:
# stratis filesystem destroy my-pool my-fs-snapshot
Additional resources
-
The
stratis(8)man page
11.5. Removing Stratis file systems
You can remove an existing Stratis file system or a Stratis pool, destroying data on them.
11.5.1. Components of a Stratis volume
Externally, Stratis presents the following volume components in the command-line interface and the API:
blockdev- Block devices, such as a disk or a disk partition.
poolComposed of one or more block devices.
A pool has a fixed total size, equal to the size of the block devices.
The pool contains most Stratis layers, such as the non-volatile data cache using the
dm-cachetarget.Stratis creates a
/stratis/my-pool/directory for each pool. This directory contains links to devices that represent Stratis file systems in the pool.
filesystemEach pool can contain one or more file systems, which store files.
File systems are thinly provisioned and do not have a fixed total size. The actual size of a file system grows with the data stored on it. If the size of the data approaches the virtual size of the file system, Stratis grows the thin volume and the file system automatically.
The file systems are formatted with XFS.
ImportantStratis tracks information about file systems created using Stratis that XFS is not aware of, and changes made using XFS do not automatically create updates in Stratis. Users must not reformat or reconfigure XFS file systems that are managed by Stratis.
Stratis creates links to file systems at the
/stratis/my-pool/my-fspath.
Stratis uses many Device Mapper devices, which show up in dmsetup listings and the /proc/partitions file. Similarly, the lsblk command output reflects the internal workings and layers of Stratis.
11.5.2. Removing a Stratis file system
This procedure removes an existing Stratis file system. Data stored on it are lost.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis file system. See Section 11.1.6, “Creating a Stratis file system”.
Procedure
Unmount the file system:
# umount /stratis/my-pool/my-fs
Destroy the file system:
# stratis filesystem destroy my-pool my-fs
Verify that the file system no longer exists:
# stratis filesystem list my-pool
Additional resources
-
The
stratis(8)man page
11.5.3. Removing a Stratis pool
This procedure removes an existing Stratis pool. Data stored on it are lost.
Prerequisites
- Stratis is installed. See Section 11.1.4, “Installing Stratis”.
-
The
stratisdservice is running. - You have created a Stratis pool. See Section 11.1.5, “Creating a Stratis pool”.
Procedure
List file systems on the pool:
# stratis filesystem list my-poolUnmount all file systems on the pool:
# umount /stratis/my-pool/my-fs-1 \ /stratis/my-pool/my-fs-2 \ /stratis/my-pool/my-fs-n
Destroy the file systems:
# stratis filesystem destroy my-pool my-fs-1 my-fs-2
Destroy the pool:
# stratis pool destroy my-poolVerify that the pool no longer exists:
# stratis pool list
Additional resources
-
The
stratis(8)man page
Chapter 12. Getting started with an ext3 file system
As a system administrator, you can create, mount, resize, backup, and restore an ext3 file system. The ext3 file system is essentially an enhanced version of the ext2 file system.
12.1. Features of an ext3 file system
Following are the features of an ext3 file system:
Availability: After an unexpected power failure or system crash, file system check is not required due to the journaling provided. The default journal size takes about a second to recover, depending on the speed of the hardware
NoteThe only supported journaling mode in ext3 is
data=ordered(default). For more information, see Is the EXT journaling option "data=writeback" supported in RHEL? Knowledgebase article.- Data Integrity: The ext3 file system prevents loss of data integrity during an unexpected power failure or system crash.
- Speed: Despite writing some data more than once, ext3 has a higher throughput in most cases than ext2 because ext3’s journaling optimizes hard drive head motion.
- Easy Transition: It is easy to migrate from ext2 to ext3 and gain the benefits of a robust journaling file system without reformatting.
Additional resources
-
The
ext3man page.
12.2. Creating an ext3 file system
As a system administrator, you can create an ext3 file system on a block device using mkfs.ext3 command.
Prerequisites
A partition on your disk. For information on creating MBR or GPT partitions, see Section 7.2, “Creating a partition table on a disk”.
Alternatively, use an LVM or MD volume.
Procedure
To create an ext3 file system:
For a regular-partition device, an LVM volume, an MD volume, or a similar device, use the following command:
# mkfs.ext3 /dev/block_deviceReplace /dev/block_device with the path to a block device.
For example,
/dev/sdb1,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a, or/dev/my-volgroup/my-lv. In general, the default options are optimal for most usage scenarios.
NoteTo specify a UUID when creating a file system:
# mkfs.ext3 -U UUID /dev/block_device
Replace UUID with the UUID you want to set: for example,
7cd65de3-e0be-41d9-b66d-96d749c02da7.Replace /dev/block_device with the path to an ext3 file system to have the UUID added to it: for example,
/dev/sda8.To specify a label when creating a file system:
# mkfs.ext3 -L label-name /dev/block_device
To view the created ext3 file system:
# blkid
Additional resources
-
The
ext3man page. -
The
mkfs.ext3man page.
12.3. Mounting an ext3 file system
As a system administrator, you can mount an ext3 file system using the mount utility.
Prerequisites
- An ext3 file system. For information on creating an ext3 file system, see Section 12.2, “Creating an ext3 file system”.
Procedure
To create a mount point to mount the file system:
# mkdir /mount/pointReplace /mount/point with the directory name where mount point of the partition must be created.
To mount an ext3 file system:
To mount an ext3 file system with no extra options:
# mount /dev/block_device /mount/point- To mount the file system persistently, see Section 9.8, “Persistently mounting file systems”.
To view the mounted file system:
# df -h
Additional resources
-
The
mountman page. -
The
ext3man page. -
The
fstabman page. - Chapter 9, Mounting file systems
12.4. Resizing an ext3 file system
As a system administrator, you can resize an ext3 file system using the resize2fs utility. The resize2fs utility reads the size in units of file system block size, unless a suffix indicating a specific unit is used. The following suffixes indicate specific units:
-
s (sectors) -
512byte sectors -
K (kilobytes) -
1,024bytes -
M (megabytes) -
1,048,576bytes -
G (gigabytes) -
1,073,741,824bytes -
T (terabytes) -
1,099,511,627,776bytes
Prerequisites
- An ext3 file system. For information on creating an ext3 file system, see Section 12.2, “Creating an ext3 file system”.
- An underlying block device of an appropriate size to hold the file system after resizing.
Procedure
To resize an ext3 file system, take the following steps:
To shrink and grow the size of an unmounted ext3 file system:
# umount /dev/block_device # e2fsck -f /dev/block_device # resize2fs /dev/block_device size
Replace /dev/block_device with the path to the block device, for example
/dev/sdb1.Replace size with the required resize value using
s,K,M,G, andTsuffixes.An ext3 file system may be grown while mounted using the
resize2fscommand:# resize2fs /mount/device sizeNoteThe size parameter is optional (and often redundant) when expanding. The
resize2fsautomatically expands to fill the available space of the container, usually a logical volume or partition.
To view the resized file system:
# df -h
Additional resources
-
The
resize2fsman page. -
The
e2fsckman page. -
The
ext3man page.
Chapter 13. Getting started with an ext4 file system
As a system administrator, you can create, mount, resize, backup, and restore an ext4 file system. The ext4 file system is a scalable extension of the ext3 file system. With Red Hat Enterprise Linux 8, it can support a maximum individual file size of 16 terabytes, and file system to a maximum of 50 terabytes.
13.1. Features of an ext4 file system
Following are the features of an ext4 file system:
- Using extents: The ext4 file system uses extents, which improves performance when using large files and reduces metadata overhead for large files.
- Ext4 labels unallocated block groups and inode table sections accordingly, which allows the block groups and table sections to be skipped during a file system check. It leads to a quick file system check, which becomes more beneficial as the file system grows in size.
- Metadata checksum: By default, this feature is enabled in Red Hat Enterprise Linux 8.
Allocation features of an ext4 file system:
- Persistent pre-allocation
- Delayed allocation
- Multi-block allocation
- Stripe-aware allocation
-
Extended attributes (
xattr): This allows the system to associate several additional name and value pairs per file. Quota journaling: This avoids the need for lengthy quota consistency checks after a crash.
NoteThe only supported journaling mode in ext4 is
data=ordered(default). For more information, see Is the EXT journaling option "data=writeback" supported in RHEL? Knowledgebase article.- Subsecond timestamps — This gives timestamps to the subsecond.
Additional resources
-
The
ext4man page.
13.2. Creating an ext4 file system
As a system administrator, you can create an ext4 file system on a block device using mkfs.ext4 command.
Prerequisites
A partition on your disk. For information on creating MBR or GPT partitions, see Section 7.2, “Creating a partition table on a disk”.
Alternatively, use an LVM or MD volume.
Procedure
To create an ext4 file system:
For a regular-partition device, an LVM volume, an MD volume, or a similar device, use the following command:
# mkfs.ext4 /dev/block_deviceReplace /dev/block_device with the path to a block device.
For example,
/dev/sdb1,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a, or/dev/my-volgroup/my-lv. In general, the default options are optimal for most usage scenarios.For striped block devices (for example, RAID5 arrays), the stripe geometry can be specified at the time of file system creation. Using proper stripe geometry enhances the performance of an ext4 file system. For example, to create a file system with a 64k stride (that is, 16 x 4096) on a 4k-block file system, use the following command:
# mkfs.ext4 -E stride=16,stripe-width=64 /dev/block_deviceIn the given example:
- stride=value: Specifies the RAID chunk size
- stripe-width=value: Specifies the number of data disks in a RAID device, or the number of stripe units in the stripe.
NoteTo specify a UUID when creating a file system:
# mkfs.ext4 -U UUID /dev/block_device
Replace UUID with the UUID you want to set: for example,
7cd65de3-e0be-41d9-b66d-96d749c02da7.Replace /dev/block_device with the path to an ext4 file system to have the UUID added to it: for example,
/dev/sda8.To specify a label when creating a file system:
# mkfs.ext4 -L label-name /dev/block_device
To view the created ext4 file system:
# blkid
Additional resources
-
The
ext4man page. -
The
mkfs.ext4man page.
13.3. Mounting an ext4 file system
As a system administrator, you can mount an ext4 file system using the mount utility.
Prerequisites
- An ext4 file system. For information on creating an ext4 file system, see Section 13.2, “Creating an ext4 file system”.
Procedure
To create a mount point to mount the file system:
# mkdir /mount/pointReplace /mount/point with the directory name where mount point of the partition must be created.
To mount an ext4 file system:
To mount an ext4 file system with no extra options:
# mount /dev/block_device /mount/point- To mount the file system persistently, see Section 9.8, “Persistently mounting file systems”.
To view the mounted file system:
# df -h
Additional resources
-
The
mountman page. -
The
ext4man page. -
The
fstabman page. - Chapter 9, Mounting file systems
13.4. Resizing an ext4 file system
As a system administrator, you can resize an ext4 file system using the resize2fs utility. The resize2fs utility reads the size in units of file system block size, unless a suffix indicating a specific unit is used. The following suffixes indicate specific units:
-
s (sectors) -
512byte sectors -
K (kilobytes) -
1,024bytes -
M (megabytes) -
1,048,576bytes -
G (gigabytes) -
1,073,741,824bytes -
T (terabytes) -
1,099,511,627,776bytes
Prerequisites
- An ext4 file system. For information on creating an ext4 file system, see Section 13.2, “Creating an ext4 file system”.
- An underlying block device of an appropriate size to hold the file system after resizing.
Procedure
To resize an ext4 file system, take the following steps:
To shrink and grow the size of an unmounted ext4 file system:
# umount /dev/block_device # e2fsck -f /dev/block_device # resize2fs /dev/block_device size
Replace /dev/block_device with the path to the block device, for example
/dev/sdb1.Replace size with the required resize value using
s,K,M,G, andTsuffixes.An ext4 file system may be grown while mounted using the
resize2fscommand:# resize2fs /mount/device sizeNoteThe size parameter is optional (and often redundant) when expanding. The
resize2fsautomatically expands to fill the available space of the container, usually a logical volume or partition.
To view the resized file system:
# df -h
Additional resources
-
The
resize2fsman page. -
The
e2fsckman page. -
The
ext4man page.