sh: /usr/bin/lockfile: No such file or directory

Q.

A.

[I]n El Capitan B4, Apple decided to stop shipping Procmail, and with it, lockfile. It wasn’t deprecated and then removed… it was unceremoniously sent to the bit bucket. So, as of B4, scheduling in El Capitan broke.

—Shirt Pocket Watch: Oh yeah? Well, lock *this*!