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Rino Bino
Asked: 2022-10-06 14:13:07 +0800 CST

Linux changes mount point permissions after reboot

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This is specifically on Ubuntu 20.04, but I believe the behavior is common:

Please take this fstab entry, creating a read-only mount:

/data/testDir/iso/ubuntu-20.04.4-live-server-amd64.iso /data/testDir/mnt iso9660 ro 0 0

Here is the related directory structure for that:

# ls -l /data/testDir/
drwxr-xr-x 2 root root   50 Apr  7 22:07 iso
drwxr-xr-x 1 root root 2048 Feb 23  2022 mnt

Everything mounts fine: mount /data/testDir/mnt works as expected.

However, upon a reboot, the permissions change on the mount point:

# ls -l /data/testDir/
drwxr-xr-x 2 root root   50 Apr  7 22:07 iso
dr-xr-xr-x 1 root root 2048 Feb 23  2022 mnt

This sort-of makes sense since it's a read-only mount, but it works either way, and this caused an unexpected failure in my CI/CD/Config mgmt system when the permissions changed to 0555 on that mnt directory after a reboot and that directory is managed. Ansible tried to change the permissions back to 0755 and failed since it's read-only.

Easy fix just setting 0555 from the start in config mgmt, but I have some questions about the behavior:

My questions:

  • What exact mechanism is doing this?
  • Is there a way to disable/control this behavior?
linux

0 Answers