lockf - lock files from within shell-scripts (used by sn news system)
lockf
lockf can be used to lock files from within shell-scripts.
Filedescriptor 3 is always locked, and the lock remains until the
process is killed. The process-id is written to standard output, as to
facilitate killing the process.
It is used by the sn news system.
sn(8)
lockf(8)