Dear Maintainer,
the semantic of check_memory's -w and -c arguments changes between version 35.20210511 and 37.20211217~bpo11+1. In version 35 check_memory is a Perl script and the arguments are the low-water mark of *free* memory, after which an warning or critical result will be reported. In version 37 check_memory is an ELF and the arguments are the high-water mark of *used* memory after which a warning or critical result will be reported.
With https://salsa.debian.org/nagios-team/pkg-nagios-plugins-contrib/-/commit/44c2d266922615928745c2adf18a7f9635332e6b the version of check_memory written in C from madrisan's nagios-plugins-linux was added to the source package, with https://salsa.debian.org/nagios-team/pkg-nagios-plugins-contrib/-/commit/eadc78562fbc869b6602b1d4bec0dfd63f563e77 the Perl version of check_memory was retired.
Hence invoking, e.g.,
/usr/lib/nagios/plugins/check_memory -w 10% -c 5%
will yield different results depending on the installed version. This is clearly not desirable and would require that users need to adjust their monitoring setup to work around the behavior change. May I suggest that the semantic of the new check_memory is adjusted to the existing one in the next Debian release?