check_disk: Selectively exclude squashfs, tracefs and tmpfs by default.

[mirespace]

Hi,

In Ubuntu we're taken up the issue of #1608 (false positive DISK CRITICAL error), as we're encountering some DISK UNKNOWN messages as a consequence (https://bugs.launchpad.net/ubuntu/+source/monitoring-plugins/+bug/1940916). This bug is a side-effect of bug 1827159, where the synthetic filesystems (tmp, squash, trace) were excluded by default to avoid false positives: if the user wants to explicitly check such filesystem (by including them in the command line) or check a mount point based on one of them, the result was DISK UNKNOWN (as it was excluded by default and exclusion takes precedence over inclusion).

To strike a balance between the two, we propose here a solution that works on Ubuntu (see test cases in the bug description) and that we are considering accepting. The approach here has been to exclude this type of filesystem only if it is neither included via path (option -p) nor via include (option -N).

To minimise any possible impact, these changes are placed after all the argument logic has been performed, not altering what the user has requested via the command line.

Thank you in advance for review and consider this, as I think it can help in cases that scripts are in place and flags cannot be wrapped.