Comment 3 for bug 1827159

Was able to reproduce using the command in /etc/nagios-plugins/config/disk.cfg; I've added this as a test case in the report body.

Adding -X squashfs did nothing, but -X tmpfs worked:

# /usr/lib/nagios/plugins/check_disk -w 10 -c 10 -e -X squashfs
DISK CRITICAL - free space: /dev 0 MB (100% inode=99%); /dev/lxd 0 MB (100% inode=99%); [...]

# /usr/lib/nagios/plugins/check_disk -w 10 -c 10 -e -X tmpfs
DISK OK| /=111171MB;119160;119160;0;119170

monitoring-plugins-gu/plugins/check_disk.c includes some filtering code, which skips:
* Remote file systems (me_remote)
* Pseudo file systems (me_dummy)
* Excluded filesystems (fs_exclude_list)
* Excluded filesystem types (dp_exclude_list)

Looks like by default the fs_exclude_list has only one fs type added to it:

  np_add_name(&fs_exclude_list, "iso9660");

Maybe a possible patch might be to add tmpfs there too (see attached; untested)?