Moved from ZBXNEXT-6688 (25):
vfs.file.get[] and vfs.file.owner[] refuse to monitor files with unknown user or group.
zabbix_get shows an error like "ZBX_NOTSUPPORTED: Cannot obtain user name.".

On Unix it can happen when an administrator deletes a user but forgets to reassign files to other user.

Expected:

I think it can be improved by showing numerical user/group IDs instead of reporting an error, like 'ls' utility does:

# echo > abc.txt
# chown 12345:54321 abc.txt
# ls -l abc.txt 
-rw-r--r-- 1 12345 54321 0 okt 27 00:25 abc.txt