Awesome use of read-only variables in bash scripts


I was reading through Jim Perrin’s CentOS hardening article, and saw one super interesting use of read-only bourne shell variables. If you have users that are frequently logging in and staying idle for days and or weeks, you can add a readonly TMOUT variable to /etc/profile:

$ echo "readonly TMOUT=3600" >> /etc/profile /etc/profile.d

The TMOUT variable controls the amount of time a user can be idle before the system logs them out. Since the variables in /etc/profile will be applied to the environment before a users .bash* and .profile files, you can be sure that users can’t override (this doesn’t address users who use C shells, but that can be addresses similarly) the read-only TMOUT variable and stay idle for longer periods of time. This also works well for HISTFILE environment variable, which is mentioned in the article. Great article Jim!

This article was posted by Matty on 2009-07-18 10:16:00 -0400 EDT