mlock −− lock a mailbox
/usr/bin/mlock
If libc−client.so is unable to create a mailbox lock file, it will call this program. This makes using the mailbox safe over i.e. NFS . There is no reason to call mlock yourself or through another program. It is setgid mail so there is no need to change the permissions of /var/mail to 1777.
No documentation other than this crappy man page,
mlock was written by Mark Crispin <mrc AT cac DOT washington DOT edu> This man page was written for Debian GNU/Linux by Jaldhar H. Vyas <jaldhar AT debian DOT org>