Create a Linux kiosk at your library
Start without a guest account
The first few steps of this process don’t actually require a guest user directory to exist, so do NOT create your guest user account yet. However, you do need to choose what your guest user account is going to be called. A reasonable account name for Don’s purposes is libraryguest. On my personal computer I call my guest account guestaccount, and I’ve used kioskguest on some installations. I avoid just the name “guest” because in modern computing the term “guest” gets used in a few other ways (such as a “guest operating system” in a virtual environment), and it’s just easier to find something unique in logs.
Choose a unique name for you guest account, but don’t create it yet. For this article, I’m using libraryguest.
Create the PostSession script
By default, GDM recognises several states: Init, PostLogin, PreSession, and PostSession. Each state has a directory located in /etc/gdm. When you place a shell script called Default in one of those directories, GDM runs the script when it reaches that state.
To trigger actions to clean up a user’s environment upon logout, create the file /etc/gdm/PostSession/Default. You can add whatever actions you want to run upon logout to the Default script. In the case of Don’s library, we wanted to clear everything from the guest’s home directory, including browser history, any LibreOffice files or GIMP files they may have created, and so on. It was important that we limited the very drastic action of removing all user data to just the guest user. We didn’t want the admin’s data to be erased upon logout, so whatever rule we added to /etc/gdm/PostSession/Default had to be limited to the guest user.
Here’s what we came up with:
#!/usr/bin/sh
echo "$USER logged out at `date`" >> /tmp/PostSession.log
if [ "X$USER" = "Xlibraryguest" ]; then
rm -rf "$HOME"
fi
exit 0
The first line is for logging purposes. The /tmp directory gets cleared out on most distributions automatically, so we weren’t worried about creating a file that’ll grow forever and eventually crash the computer. If your distribution of choice doesn’t clean out /tmp automatically, create a cron job to do that for you.
GDM knows what user triggered the logout process, so the if statement verifies that the user logging out is definitely the libraryguest user (that’s the literal name of the user we created for library patrons).Note that the whitespace around the square brackets is important, so be precise when typing!
As long as it is libraryguest, then the script removes the entire user directory ($HOME). That can be extremely dangerous if you make a mistake, so do thorough testing on a dummy system before implementing a script like this! If you get a condition wrong, you could erase your entire home directory upon logout.
In this example, I’ve successfully limited the rm command to a logout action performed by user libraryguest. The entire /home/libraryguest directory is erased, and the computer returns to the GDM login screen. When a new user logs in, a fresh directory is created for the user.
You can put any number of commands in your script, of course. You don’t have to erase an entire directory. If all you really want to do is clear browser history and any stray data, then you can do that instead. If you need to copy specific configuration files into the environment, you can do that during the PreSession state.
Just be sure to test thoroughly before committing your creation to your
