This section describes what behaviors have changed in automated installations (Kickstart).

$ ksverdiff --from RHEL5 --to RHEL6

The following commands were removed in RHEL6:
langsupport mouse key

The following commands were deprecated in RHEL6:
monitor

The following commands were added in RHEL6:
sshpw group rescue updates fcoe
...

$ ksvalidator --version RHEL6 my-rhel5-ks.cfg

This section describes what behaviors have changed in the graphical installer, relating to networking.

Red Hat Enterprise Linux 6 introduces an updated and more flexible service for content delivery and subscription management. This section describes the changes to the content service.

Performing an upgrade from a dmraid set to an mdraid set is not supported. A warning will be displayed when an upgrade of this type is attempted. Upgrades from existing mdraid sets and creation of new mdraid sets are possible.

The new default superblock can cause problems when upgrading sets. This new superblock format (used on all devices except when creating a RAID1 /boot partition) is now at the beginning of the array, and any file system or LVM data is offset from the beginning of the partition. When the array is not running, LVM and file system mount commands might not detect the device as having a valid volume or file system data. This is intentional, and means that if you want to mount a single disk in a RAID1 array, you need to start the array having only that single disk in it, then mount the array. You cannot mount the bare disk directly. This change has been made as mounting a bare disk directly can silently corrupt the array if a resync is not forced.

On subsequent reboots, the RAID system can then consider the disk that was not included in the array as being incompatible, and will disconnect that device from the array. This is also normal. When you are ready to re-add the other disk back into the array, use the mdadm command to hot add the disk into the array, at which point a resync of the changed parts of the disk (if you have write intent bitmaps) or the whole disk (if you have no bitmap) will be performed, and the array will once again be synchronized. From this point, devices will not be disconnected from the array, as the array is considered to be properly assembled.

The new superblock supports the concept of named mdraid arrays. Dependency on the old method of array enumeration (for instance, /dev/md0 then /dev/md1, and so on.) for distinguishing between arrays has been dropped. You can now choose an arbitrary name for the array (such as home, data, or opt). Create the array with your chosen name using the --name=opt option. Whatever name is given to the array, that name will be created in /dev/md/ (unless a full path is given as a name, in which case that path will be created; or unless you specify a single number, such as 0, and mdadm will start the array using the old /dev/mdx scheme). The Anaconda installer does not currently allow for the selection of array names, and instead uses the simple number scheme as a way to emulate how arrays were created in the past.

The new mdraid arrays support the use of write intent bitmaps. These help the system identify problematic parts of an array, so that in the event of an unclean shutdown, only the problematic parts need to be resynchronized, and not the entire disk. This drastically reduces the time required to resynchronize. Newly created arrays will automatically have a write intent bitmap added when suitable. For instance, arrays used for swap and very small arrays (such as /boot arrays) do not benefit from having write intent bitmaps. It is possible to add a write intent bitmap to your previously existing arrays after the upgrade is complete using the mdadm --grow command on the device, however write intent bitmaps do incur a modest performance hit (about 3-5% at a bitmap chunk size of 65536, but can increase to 10% or more at small bitmap chunk sizes such as 8192). This means that if a write intent bitmap is added to an array, it is best to keep the chunk size reasonably large. The recommended size is 65536.

Moving to ext4 must be done with a freshly formatted ext4 file system. Migrating in place from ext3 to ext4 is not supported and will not produce many of the benefits ext4 offers, since the data currently residing on the partition will not make use of the extents features and other changes.

Red Hat recommends that customers who cannot migrate to a cleanly formatted ext4 file system remain on their existing ext3 file system.

Red Hat Enterprise Linux 6 provides full support for ext4 and it is the default file system for new installations. This section explains the major changes in behavior that this new file system introduces.

Xinetd is a daemon used to start network services on demand. The changes in xinetd are related to the allowed limit of open file descriptors:

In Red Hat Enterprise Linux 6, the custom runlevels 7, 8 and 9 are no longer supported and cannot be used.

In Red Hat Enterprise Linux 6, init from the sysvinit package has been replaced with Upstart, an event-based init system. This system handles the starting of tasks and services during boot, stopping them during shutdown and supervising them while the system is running. For more information on Upstart itself, refer to the init(8) man page.

Processes are known to Upstart as jobs and are defined by files in the /etc/init directory. Upstart is very well documented using man pages. Command overview is in init(8) and job syntax is described in init(5).

Upstart provides the following behavioral changes in Red Hat Enterprise Linux 6:

As in prior releases, ttyS1 is required in /etc/securetty if you wish to allow root logins on this getty.

Because of the move to Upstart, using /etc/shutdown.allow for defining who can shut the machine down is no longer supported.

In some releases of Red Hat Enterprise Linux 5, the sendmail Mail Transport Agent (MTA) accepted network connections from external hosts by default. In Red Hat Enterprise Linux 6, sendmail by default only accepts connections from the local system (localhost). To grant sendmail the ability to act as a server for remote hosts, perform one of the following steps:

To put either of these changes into effect, install the sendmail-cf package, then regenerate /etc/mail/sendmail.cf. This is done by running the following commands:

su -c 'yum install sendmail-cf'
su -c 'make -C /etc/mail'

Exim has been removed from Red Hat Enterprise Linux 6. Postfix is the default and recommended MTA.

The MySQL DBD driver has been dual-licensed and the related licensing issues have been resolved. The resulting apr-util-mysql package is now included in the Red Hat Enterprise Linux 6 software repositories.

If you are upgrading from an existing Red Hat Enterprise Linux 5 installation in which PostgreSQL 8.4 (postgresql84-* packages) was in use, the Red Hat Enterprise Linux 6 PostgreSQL packages will operate as a drop-in replacement.

However, if you are upgrading from a Red Hat Enterprise Linux 5 installation in which PostgreSQL 8.1 (postgresql-* packages) or earlier was in use, and you have existing database content that needs to be preserved, you will need to follow the dump and reload procedure here due to changes in the data format: http://www.postgresql.org/docs/8.4/interactive/install-upgrading.html. Ensure that you perform the dump step before upgrading to Red Hat Enterprise Linux 6.

Refer to the following URL for possible application compatibility issues associated with the transition from PostgreSQL 8.1 to 8.4: http://wiki.postgresql.org/wiki/WhatsNew84

In order to support Bluetooth devices, the Bluetooth background service was started by default in previous versions of Red Hat Enterprise Linux. In this release, the Bluetooth service is started on demand when needed and automatically stops 30 seconds after the use of the device has stopped. This reduces overall initial startup time and resource consumption.

Red Hat Enterprise Linux 6 includes the cronie package as a replacement for vixie-cron. The main difference between these packages is how the regular jobs (daily, weekly, monthly) are done. Cronie uses the /etc/anacrontab file, which by default looks like the following:

# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=45

# the jobs will be started during the following hours only
START_HOURS_RANGE=3-22

# period in days   delay in minutes   job-identifier   			command

1			5		cron.daily	nice run-parts	/etc/cron.daily
7			25		cron.weekly	nice run-parts	/etc/cron.weekly
@monthly		45		cron.monthly	nice run-parts	/etc/cron.monthly

These regular jobs will be executed once a day in the 03:00-22:00 time interval, including a random delay. For example, cron.daily will have a 5 minute forced delay plus a random delay of 0-45 minutes. You could also run jobs with no delays, between 4 and 5:

RANDOM_DELAY=0 # or do not use this option at all

START_HOURS_RANGE=4-5

# period in days   delay in minutes   job-identifier   			command
1			0		cron.daily	nice run-parts	/etc/cron.daily
7			0		cron.weekly	nice run-parts	/etc/cron.weekly
@monthly		0		cron.monthly	nice run-parts	/etc/cron.monthly

Features of cronie include:

For further details about cronie and cronie-anacron, see the Red Hat Enterprise Linux Deployment Guide.

ACPI CPU hotplug is available as a Technology Preview in Red Hat Enterprise Linux 6.5. This is a platform-specific feature; as such, details of its use are outside the scope of this document.

The CONFIG_ACPI_HOTPLUG_CPU configuration option must be enabled in order to use this feature.

Additionally, if the platform implements the optional ACPI _OST method, the following configuration options must also be enabled. There are no harmful effects associated with enabling these configuration for all platforms.

The configuration required for the OpenLDAP service has changed in Red Hat Enterprise Linux 6. In previous versions, slapd was configured using the /etc/openldap/slapd.conf file. The slapd configuration in Red Hat Enterprise Linux 6 is now stored in a special LDAP directory (/etc/openldap/slapd.d/) with a pre-defined schema and Directory Information Tree (DIT). Further details of this configuration schema can be found at openldap.org. The following section details an example on how to convert the old configuration file to work with the new directory:

This example assumes that the file to convert from the old slapd configuration is located at /etc/openldap/slapd.conf and the new directory for OpenLDAP configuration is located at /etc/openldap/slapd.d/.

ABRT 2 adds configurable events to the ABRT workflow. Events are triggered when problem data is recorded. They specify actions to perform on problem data and can be used to modify how data is analyzed or to specify a location to which data should be uploaded. You can also have events run only on problem data with certain characteristics.

Event configuration files are stored in the /etc/libreport/events.d directory. They contain the following:

For further details, see the man page:

$ man report_event.conf

The system-config-bind tool has been deprecated and removed without replacement. Editing the name server configuration manually using the named.conf file is recommended in Red Hat Enterprise Linux 6. Comprehensive BIND documentation is installed as part of the bind package in /usr/share/doc/bind-x.y.z. Also, sample configurations can be found in the /usr/share/doc/bind-x.y.z/sample directory. The system-config-bind tool from previous versions does, however, generate standard BIND configuration, so depending on your environment it is possible to migrate to the version of BIND found in Red Hat Enterprise Linux 6 by moving old configuration files to the correct location and performing sufficient testing.

The system-config-boot tool allowed graphical configuration of the GRUB bootloader. In Red Hat Enterprise Linux 6 it has been deprecated and removed without replacement. The default GRUB configuration is sufficient for many users, however if manual changes are required, the boot configuration can be accessed and changed in the grub.conf file, located in the /boot/grub directory. Red Hat Enterprise Linux 6 uses version 1 of GRUB, also known as GRUB legacy. Full documentation for configuring GRUB can be found at the GRUB homepage: http://www.gnu.org/software/grub/.

The system-config-cluster tool has been deprecated and removed without replacement. Using ricci and luci (from the Conga project) is recommended.

The system-config-display tool has been replaced by XRandr configuration tools as found in both supported desktops: GNOME and KDE. There is no explicit configuration file (xorg.conf) in the default X server installation as display management is now done dynamically using one of the following menu options:

GNOME: System → Preferences → Display (or the system-config-display command).

KDE: System Settings → Computer Administration → Display

The command line utility (xrandr) can be also used for display configuration. See the xrandr --help command or the manual page using the man xrandr command for further details.

The system-config-httpd tool has been deprecated and removed without replacement. Users must configure web servers manually. Configuration can be done in the /etc/httpd directory. The main configuration file is located at /etc/httpd/conf/httpd.conf. This file is well documented with detailed comments in the file for most server configurations; however if required, the complete Apache web server documentation is shipped in the httpd-manual package.

The system-config-lvm tool has been deprecated. Management of logical volumes can be performed using the gnome-disk-util or the lvm tools.

The system-config-netboot tool has been deprecated and removed without replacement. Using Red Hat Network Satellite is recommended.

The system-config-nfs tool has been deprecated and removed without replacement. Users must set up NFS server configuration manually.

The system-config-rootpassword tool has been replaced by the system-config-users tool - a powerful user management and configuration tool. The root password can be set in the system-config-users tool by unchecking the "Hide system users and groups" option in the Preferences dialog. The root user will now be shown in the main listing, and the password can be modified like any other user.

The system-config-samba tool has been deprecated and removed without replacement. Users must set up SMB server configuration manually.

The system-config-securitylevel tool has been removed. The system-config-firewall tool is recommended for firewall configuration.

The system-config-soundcard tool has been removed. Sound card detection and configuration is done automatically.

The system-config-switchmail tool has been deprecated and removed without replacement. Postfix is the preferred and default MTA (Mail Transfer Agent) in Red Hat Enterprise Linux 6. If you are using another MTA, it must be configured manually according to its specific configuration files and techniques.

The Preupgrade Assistant (preupg) checks for potential problems you might encounter with an upgrade from Red Hat Enterprise Linux 6 to Red Hat Enterprise Linux 7 before making any changes to your system. This helps you assess your chances of successfully upgrading to Red Hat Enterprise Linux 7 before the actual upgrade process begins.

The Preupgrade Assistant assesses the system for possible in-place upgrade limitations, such as package removals, incompatible obsoletes, name changes, deficiencies in some configuration file compatibilities, and so on. It then provides the following:

Your system remains unchanged except for the information and logs stored by the Preupgrade Assistant.

For detailed instructions on how to obtain and use the Preupgrade Assistant, see https://access.redhat.com/site/node/637583/.

The new Red Hat Upgrade Tool is used after the Preupgrade Assistant, and handles the three phases of the upgrade process:

Both network and disk based upgrades are supported. For detailed instructions on how to upgrade your Red Hat Enterprise Linux 6 system to Red Hat Enterprise Linux 7, see https://access.redhat.com/site/node/637583/.

Further to the points already listed, quoting the pattern argument to the regular expression matching conditional operator =~ can cause regexp matching to stop working. This occurs on all architectures. In versions of bash prior to 3.2, the effect of quoting the regular expression argument to the [[ command's =~ operator was not specified. The practical effect was that double-quoting the pattern argument required backslashes to quote special pattern characters, which interfered with the backslash processing performed by double-quoted word expansion and was inconsistent with how the == shell pattern matching operator treated quoted characters.

In bash version 3.2, the shell was changed to internally quote characters in single- and double-quoted string arguments to the =~ operator, which suppresses the special meaning of the characters that are important to regular expression processing (`.', `[', `\', `(', `), `*', `+', `?', `{', `|', `^', and `$') and forces them to be matched literally. This is consistent with how the == pattern matching operator treats quoted portions of its pattern argument.

Since the treatment of quoted string arguments was changed, several issues have arisen, chief among them the problem of white space in pattern arguments and the differing treatment of quoted strings between bash 3.1 and bash 3.2. Both problems can be solved by using a shell variable to hold the pattern. Since word splitting is not performed when expanding shell variables in all operands of the [[ command, this provides the ability to quote patterns as you wish when assigning the variable, then expand the values to a single string that can contain whitespace. The first problem is solved by using backslashes or any other quoting mechanism to escape the white space in the patterns.

Bash 4.0 introduces the concept of a compatibility level, controlled by several options to the shopt builtin. If the compat31 option is enabled, bash will revert to the 3.1 behavior with respect to quoting the right-hand side of the =~ operator.

The following list details new packages in Red Hat Enterprise Linux 6.

The following table lists updated packages in Red Hat Enterprise Linux 6 and a description of noteworthy changes.

The following table lists discontinued (removed) packages in Red Hat Enterprise Linux 6 and their replacements or alternatives.