mlock1
Usage
/usr/bin/mlock
Overview
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.
Releases
12 releases since Debian 2.2 (Potato); the text changed 10 times.