You can set an account to lock after some minutes of idle time.

To achieve this, edit /etc/profile (as root), adding this line at the top:

trap "" 1 2 3 15
  • This avoids that the processing of this file cannot be interrupted.

At the bottom of the file, add:

# log out after 120 seconds
export TMOUT=120
readonly TMOUT

This setting will apply next login. This does not work on graphical applications (but it will close terminal emulators).