Cannot backup a server with Dropbox Backup extension

Symptoms

• Cannot backup a server with Dropbox Backup extension:

  CONFIG_TEXT:Failed to Execute: '/usr/local/psa/bin/pleskbackup' server --output-file='/tmp/dropboxxxaact.tar' 2>&1
  Output: Runtime error: Unknown error from pmmcli

• Running the failed command with debug enabled shows the following information:

  # /usr/local/psa/bin/pleskbackup server -vvvvv --output-file='/tmp/dropboxQAPN2v.tar' 2>&1 | grep err
  <errcode>13</errcode>
  <errmsg>Not enough free disk space to backup selected objects. At least 15326.4082643 Mbytes free disk space is required.</errmsg>
  Runtime error: Unknown error from pmmcli

Cause

Insufficient disk space for creating a backup. Bug created for the issue with vague initial error reporting: #PPPM-9509.

Resolution

To stop error from appearing, it is necessary to increase the available diskspace for /var/lib, the location the backups stored before they are uploaded to Dropbox.