Vaidas Jablonskis bio photo

Vaidas Jablonskis

Twitter Google+ Github

HOWTO Log Bash History to Syslog

I will show you a very nice and non-intrusive way how to log bash history to a syslog. You may wonder what problem I was trying to solve? Right, the issue is that I want to log root users bash history from multiple servers to a central syslog box. I also want to preserve root users history on each server for convenience purposes.

But first let's talk about my failed attempts to do so.

Failed attempts

  • Hacking bash source code. Really? We are talking about a server farm, who would like to maintain custom built bash packages, make sure that security fixes and bugs are also pushed to your custom bash sources etc etc? - No one! Unless you have nothing else to do.
  • Using trap. If you google for a solution you will come across this blog post. It sounds like a feasible idea until you actually try it. Using bash built-in trap command which allows you to basically catch users input and then pipe it to a logger command.

There are few problems taking this approach, first user input does not get logged on logout, second, if you press enter multiple times the previous command gets logged multiple times, third, how do you log shell's PID?

  • Using script (typescript). Sounds like a good idea too, but first script logs input and output what happens in the terminal. What is wrong with that? Well try to tail the same file you're logging to - you'll see what I mean. :-)

Successful attempt

There is an updated trick below which logs to syslog as well as writes commands to .bash_history file so you do not lose your bash history.

PROMPT_COMMAND='history -a >(tee -a ~/.bash_history | logger -t "$USER[$$] $SSH_CONNECTION")'

Is that simple? - Yes, it is! You can put the command (not the whole line, but just the command) into /etc/sysconfig/bash-prompt-default and make it executable. This will log all users bash history system wide to a syslog. Or you can add it to ~/.bashrc file per user - it's up to you. Surely, it's possible to tell the logger to send messages to specific log facility and so on, but that's out of the scope of this blog post. The way I do, I put that into /root/.bashrc, configure rsyslog to log to central log server, which then writes messages to a separate file. Please don't say - "oh that's easy to bypass, this is another failed attempt". Yes it is easy to bypass, but that's not the thing I am trying to achieve. At the end of the day root can bypass pretty much everything. This is a solution if you want to have some kind of audit trail what happens on your systems when you have multiple sys admins.

Your input is always welcome in the comments section below.

PS: Thanks to Steve Harris for an awesome brainstorming session which helped me to come up with this idea.