TMUX/screen and root shells: a new trick I just learned (TMOUT)

I'm currently doing some server management. My current favorite tool is TMUX, which among many other things, allows you to save your session even if you are disconnected, split your screen into panes, etc etc. If it sounds great, that's because it is. Every sysadmin would benefit from using TMUX (or it's cousin, GNU screen).

There's a security flaw though. Let's say I log in as user "andrew" and attach to my previous TMUX session: tmux attach. Now I have to run a number of commands as root. Well, prefixing every command with sudo and manually typing in all the /sbin/ paths to each executable it a pain in the ass. I know this is a bad idea, but I'll often spawn a root shell. Let's say I spawn a root shell in a TMUX session, then go do something else, fully intending log out later, but I forget. My computer disconnects, and I forget there's a root shell sitting there.

If someone manages to compromise the machine, and gain access to my user account, getting a root shell is as easy as doing tmux attach. Oops.

Well, I just found out you can timeout a shell after X seconds of inactivity, which is perfect for this case. As root:

1 echo -e "\n# logout after 5 minutes of inactivity\nexport TMOUT=300\n" >> /root/.bash_profile

Now I can open root shells until my ass bleeds, and after 5 minutes of inactivity, it will log out back into my normal user account.

A good sysadmin won't make mistakes. A great sysadmin will make mistakes self-correct ;-].