Ansible: Just mount an existing filesystem

Posted by ads' corner on Monday, 2019-12-09
Posted in [Ansible][Linux]

There is no easy way to “just mount” an existing filesystem in Ansible, using the mount module. I just want to mount an already defined mount point, and don’t really care about all the configuration here.

But if I try this:

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- name: Mount /backup filesystem
  mount:
    path: "/backup"
    state: mounted

I end up with the following error message:

TASK [Mount /backup filesystem] ********************
fatal: [xxx.xxx.xxx.xxx]: FAILED! => {"changed": false, "msg": "state is mounted but all of the following are missing: src, fstype"}

Ansible requires to configure the mount point all the way. Also specified in the documentation:

  • fstype is required when state is present or mounted
  • state == mounted:┬áthe device will be actively mounted and appropriately configured in fstab. If the mount point is not present, the mount point will be created.

Not what I want here!

My fallback is the Linux mount command. Also using the -v (verbose) flag, so I can figure out if the filesystem was already mounted, or if the task changed this.

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- name: Mount backup device
  command:
    cmd: mount -v /backup
    warn: no
  register: mount_backup
  failed_when: mount_backup.rc != 0 and mount_backup.rc != 32
  changed_when: mount_backup.stdout.find('mounted on') != -1

mount will return 0 when the filesystem can be mounted, and 32 when it was already mounted.

Also STDOUT will include mounted on when the mount changes. (Note: you might want to ensure that your locale settings are English).

The warn=no is there so Ansible will not complain about using the mount command instead of the module.

Finally this allows one to only execute subsequent commands when the mount was successful:

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- block:
  - debug: msg="Mount successful"
  when: mount_backup.stdout.find('mounted on') != -1 or mount_backup.stderr.find('already mounted on') != -1

I’m using the output from STDOUT and STDERR here, because - according to the manpage - RC=32 can be anything. If the text includes mounted on or already mounted on, the mount point worked.


Categories: [Ansible] [Linux]