Unlocking your Firefox profile on Linux

Symptoms

Firefox fails to launch on your Linux desktop or in Remote Access Portal (RAP), giving this error message:

Firefox is already running, but is not responding. To use Firefox, you must first close the existing Firefox process, restart your device, or use a different profile.

Cause

The browser is still running on another machine. Because we use networked home directories (shared between machines), you can only run each browser on one machine at a time.

Solution

Run ls -l ~/.mozilla/firefox/*.*/lock to check for lock files:

$ ls -l ~/.mozilla/firefox/*.*/lock
lrwxrwxrwx 1 miller miller 23 Dec  8  2023 /home/miller/.mozilla/firefox/gvmkq7dl.default-release/lock -> 129.67.187.187:+3243300

Look for the IP address between -> and :+ - in this case, 129.67.184.161.

To find out the hostname for that machine, run host <ip> - for example:

$ host 129.67.184.161
161.184.67.129.in-addr.arpa domain name pointer syndrome.maths.ox.ac.uk.

If you are still logged into that machine (whether locally or remotely), return to it and close the browser. That will unlock your profile for use on other machines.

If you aren't able to do that, you can use SSH to connect to the machine, check what you are running, and forcibly close the browser:

# Connect to the machine
ssh <youruser>@<hostname>

# Check what is running (optional)
ps xf

# Forcibly close the browser
killall firefox

To prevent it happening again, we recommend you close the browser window whenever you have finished using it, and especially before disconnecting from a remote session (e.g. RAP).

Multiple Profiles

In the rare case that you need to run the same browser on multiple machines at once, you can use a separate profile instead:

firefox -P

Note that you won't have access to your normal bookmarks, history, etc.

You are reminded to limit the number of machines you use at once, to ensure there is capacity for other users.