motd is a crate for printing the current MOTD (message of the day)
on linux. Most of the logic lives in the motd crate, and the dump-motd
tool is a thin wrapper which provides a command line interface for the
crate.
If using the socall feature (which is on by default), you must
install libpam headers to build this crate. On debian based
systems you can do so with
sudo apt-get install libpam0g-dev
There are two modes of operation for the motd crate. By default, it
will load and call into the pam_motd.so file used by the pam stack,
but you can instead use a pure rust reimplementation of the logic found
in pam_motd.so if you want. The downside of the pure rust implementation
is that it no longer uses the same source-of-truth logic to resolve the
motd, though this is likely not a huge deal because pam_motd is fairly
stable. The pure rust implementation has the advantages that it uses zero
unsafe code, does not require a (sometimes slow) directory walk to
locate pam_motd.so the first time it is run, and requires many fewer
dependencies.
The feature for calling pam_motd.so directly is socall, and it is
enabled by default. To use the pure rust implementation, disable
default features. This will change the signature of a few functions.