[SOLVED] PBS on NFS: Unable to acquire lock "/etc/proxmox-backup/.datastore.lck" ...


Well-Known Member
Aug 17, 2016
I'm trying to set up a datastore on top of NFS. I ran into this issue:

Unable to acquire lock "/etc/proxmox-backup/.datastore.lck" - Interrupted system call (os error 4)

I did the following:
  1. created a new datastore on an nfs mounted path
  2. tried to create another datastore also on an nfs mounted path
  3. I got the above mentioned error
Reason for the error:

If the user "backup" on the remote system is not known, the owner/group is set to the default user/group (anonymous?). Thatswhy PBS can no longer write/access the Datastore after having created it. So the remote System must a) know the user/group and b) it has to be with the same uid/gid like it is on the PBS.

This is how I fixed it:
  1. I checked on the NFS-Server if uid=34 and username "backup" is not used so far in /etc/passwd
  2. I checked on the NFS-Server if gid=34 and groupname "backup" is not used so far in /etc/group
  3. I created a user "backup" with uid=34 on the NFS-Server
  4. I created a group "backup" with gid=34 on the NFS-Server
  5. chown-ed all shared NFS-Directories on the NFS-Server (chown -r backup:backup /path/to/exported_dir1 ...)
  6. I unmounted all NFS-Shares on the PBS
  7. I mounted again all NFS-Shares on the PBS
  8. I deleted the file /etc/proxmox.backup/.datastore.lck (Be sure no task is running on the PBS!)
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NFS does not support locking.
The file which is pbs not able to lock is not located on NFS but locally in PXCFS (Proxmox Cluster File System). I assume the error because some process crashed and did not release the lock of /etc/proxmox-backup/.datastore.lck or did just not delete the Lock-file. So the error is not: The system can not lock a file on NFS. This is not needed.
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