Copy an SSH public key to a remote machine

This: 

   1 cat ~/.ssh/id_rsa.pub | ssh remoteuser@remotehost 'mkdir .ssh ; shat >> .ssh/authorized_keys'

will copy a public key to a remote machine, but most likely you want to use ssh-copy-id included with recent versions of OpenSSH.

Protect sshd from kernel OOM events

The kernel out-of-memory killer kills processes when a system runs out of RAM. Killing SSH typically does not help fix anything, and makes remotely-accessible systems inaccessible. 

   1 for pid in $(pidof sshd) ; do
   2         echo "disabling oom on pid $pid"
   3   echo -17 | sudo tee /proc/$pid/oom_adj > /dev/null
   4 done

This is done by a few distributions, but when working on an arbitrary remote machine may be useful to run just in case.

CategoryCheatSheet