CAEN Knowledge Base
CAEN Knowledge Base

I tried starting Mozilla Firefox and I received a message that "Firefox is already running, but is not responding..." How do I fix this?

Many times when you start a software program, the program will create a "lock" file for that session in your profile. This is mostly done to prevent other instances of the software from running and making changes to your settings. If the program quits improperly, or if you log out of the computer without first exiting the program, this lock file can remain and prevent the program from running in the future.

If you receive this type of error message when attempting to open Firefox, it is most likely referring to a previous (locked) process or session. In Linux, you can type the following commands to remove the lock file from your ~/.mozilla configuration folder, but you may need to examine the folder to determine the exact location of the lock file:

rm -f ~/.mozilla/firefox/*.default/lock
rm -f ~/.mozilla/firefox/*.default/.parentlock

In Microsoft Windows, you will want to remove the lock file from your Firefox profile, which can be accessed in your Windows home directory via the N: network drive. This can typically be found at:


where 201# is the academic year.

Once the lock file is removed, you should then be able to start Firefox normally. If you were using a program other than Firefox and receive a similar error, check that program's configuration directory for a lock file.