check-running-kernel: Add support for ZSTD compression

[amotl]

Dear Bernd and Jan,

first things first: Thanks a stack for conceiving and maintaining this collection of fine monitoring plugins.

As this is our very first contribution to Debian, please bear with us ¹. We recently discovered the check_running_kernel program and are now running it on 40+ machines. This is not that much, but it was enough diversity to give us the opportunity to discover some minor shortcomings, mostly on machines running derivate, non-vanilla Debian distributions like Proxmox and Ubuntu.

• First, we found that a modern Debian bullseye-based PVE/Proxmox machine already used a Linux kernel with ZSTD compression which was not supported yet.
• Secondly, we discovered that on the same Proxmox machine, and on another vanilla Ubuntu 20.04 machine, both running 5.x Linux kernel versions, there was a suffix added to the on-disk kernel image, which we stripped off using sed in order to satisfy the comparison operation. You can find more details about this topic in the comment section below. I've diverted this topic to check-running-kernel: Compensate for CONFIG_VERSION_SIGNATURE suffix #92 in order to keep things separate.

We hope you like those improvements and ask you to let us know about any adjustments you would like to see.

With kind regards,
Andreas.

/cc @Tonkenfo

Footnotes

1. While we just also signed up to https://salsa.debian.org/, we discovered this repository also on GitHub and found that both of you might be exchanging patches between here and https://salsa.debian.org/nagios-team/pkg-nagios-plugins-contrib already. So, we are submitting this patch to this repository. If this is wrong, please advise different places where to submit this patch. ↩

[waja]

I can confirm this issue

[waja]

Hi,

while the change seems to be fine, the zstd binary is needed to work. Maybe you can also adjust the following in your changes?

        if ! which ${filter%% *} >/dev/null; then
                echo "UNKNOWN: filter command '$filter' missing, perhaps install xz-utils, lz4 or lzop?" >&2
                exit $UNKNOWN
        fi

Thanks, Jan.

[waja]

Superseeded by #94