systemd-gpt-auto-generator creates efi.automounts unit in BIOS based system

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 9

Issue

  • What is systemd-gpt-auto-generator?

  • A system in BIOS mode has a /boot/efi entry in /etc/fstab. Commenting out this entry and rebooting results in the /efi partition being automatically mounted.

    • The /boot/efi entry in /etc/fstab has been commented out:

      Raw
      # cat /etc/fstab | grep efi          
#UUID=7B77-95E7  /boot/efi  vfat   defaults,uid=0,gid=0,umask=077,shortname=winnt    0   2

    • The /efi partition is automatically mounted post-reboot:

      Raw
      # lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
nvme0n1     259:0    0   70G  0 disk
├─nvme0n1p1 259:9    0    1M  0 part
├─nvme0n1p2 259:10   0  200M  0 part /efi            <------- Automatically mounted
├─nvme0n1p3 259:11   0  500M  0 part /boot

Resolution

What is systemd-gpt-auto-generator?

  • The systemd-gpt-auto-generator is a systemd utility that automatically mounts partitions based on the GUID Partition Table (GPT) layout. It identifies partitions by their type GUIDs and assigns appropriate mount points, such as /boot/efi, for UEFI systems. However, in BIOS mode, the generator may still detect the GPT layout and mount partitions like /efi if no explicit entry exists in /etc/fstab

Given this behavior, there are two possible approaches to address the problem:

  • Prevent the systemd-gpt-auto-generator from automatically mounting the partition by adding the following argument to the kernel command line:

    Raw
    # grubby --update-kernel=ALL --args=systemd.gpt_auto=no

  • Since the system is operating in BIOS mode, the /boot/efi partition is unnecessary. You can destroy the partition and remove its entry from /etc/fstab to avoid any confusion.

These steps ensure that the /efi partition is no longer automatically mounted and the system operates without unnecessary partitions in BIOS mode.

Root Cause

The automatic mounting of /efi is triggered by the systemd-gpt-auto-generator. This generator creates entries in /run/systemd/generator.late because there is no /boot/efi partition specified in /etc/fstab. In BIOS mode:

  • The generator behavior is expected since it detects the presence of an EFI partition layout but lacks the /boot/efi entry in /etc/fstab.

  • On UEFI based systems, /boot/efi is used as the default mount point, while /efi is not utilized. The generator misinterprets the absence of /boot/efi as a reason to mount /efi instead.

Diagnostic Steps

  • Install a system in BIOS mode with "EFI ready" partitioning.

    Raw
    ignoredisk --only-use=vda
clearpart --all --initlabel
zerombr
part biosboot --fstype="biosboot" --size=1
part /boot --fstype=xfs --size=1024
part /boot/efi --fstype=efi --size=200
part pv.00 --size=1 --grow
volgroup vg0 pv.00
logvol /              --name=root --vgname=vg0 --size=10240 --fstype=xfs
logvol swap           --name=swap --vgname=vg0 --size=1024

  • Comment out the /boot/efi entry in /etc/fstab.

    Raw
    #UUID=7B77-95E7 /boot/efi   vfat    defaults,uid=0,gid=0,umask=077,shortname=winnt  0   2

  • Reboot the system and verify the behavior of the /efi partition.

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