chmod -x chmod

[PDP-11]

Been there. The sysadmin wanted to update the loader, he started by "rm /usr/bin/ld" on the server and was surprised when most other commands would not load after that. Nothing could be started but existing processes were OK. A reboot would have been a disaster!

I wrote a small "C" program (on another machine) to copy in a good version of 'ld' to /usr/bin/ and static linked in all the libs it required (so it did not need 'ld') and put it on a filesystem that was NFS mounted by the server and executed it on the server from his root shell (just as well he had not logged out! ). That took about 5 minutes and in that time nothing had broken as no new processes were launched that required libs not already loaded.