[Bug 1547033] [NEW] please allow /etc/mtab to be a pre-existing link on readonly filesystems

[Oliver Grawert]

Public bug reported:

booting a snappy system which comes with a readonly file system that
carries /etc/mtab as pre-created link in the readonly area of the fs
(pointing to /proc/mounts), we always get an error message on boot when
systemd-tmpfiles tries to re-create the mtab link.

systemd-tmpfiles should instead check if /etc/mtab is already there, is
a link and points to the desired target. in this case it should just
skip the creation attempt gracefully without error.

Feb 17 18:56:51 localhost systemd[1]: Starting Create Volatile Files and Directories...
Feb 17 18:56:51 localhost systemd-tmpfiles[631]: [/usr/lib/tmpfiles.d/var.conf:14] Duplicate line for path "/var/log"
, ignoring.
Feb 17 18:56:51 localhost systemd-tmpfiles[631]: symlink(../proc/self/mounts, /etc/mtab) failed: Read-only file syste
m
Feb 17 18:56:51 localhost systemd[1]: systemd-tmpfiles-setup.service: Main process exited, code=exited, status=1/FAIL
URE

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1547033

Title:
  please allow /etc/mtab to be a pre-existing link on readonly
  filesystems

Status in systemd package in Ubuntu:
  New

Bug description:
  booting a snappy system which comes with a readonly file system that
  carries /etc/mtab as pre-created link in the readonly area of the fs
  (pointing to /proc/mounts), we always get an error message on boot
  when systemd-tmpfiles tries to re-create the mtab link.

  systemd-tmpfiles should instead check if /etc/mtab is already there,
  is a link and points to the desired target. in this case it should
  just skip the creation attempt gracefully without error.

  Feb 17 18:56:51 localhost systemd[1]: Starting Create Volatile Files and Directories...
  Feb 17 18:56:51 localhost systemd-tmpfiles[631]: [/usr/lib/tmpfiles.d/var.conf:14] Duplicate line for path "/var/log"
  , ignoring.
  Feb 17 18:56:51 localhost systemd-tmpfiles[631]: symlink(../proc/self/mounts, /etc/mtab) failed: Read-only file syste
  m
  Feb 17 18:56:51 localhost systemd[1]: systemd-tmpfiles-setup.service: Main process exited, code=exited, status=1/FAIL
  URE

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