How to Fix 'Could not get lock /var/lib/dpkg/lock-frontend' in Linux Mint

In this tutorial you will learn how to troubleshoot and fix the error "Could not get lock /var/lib/dpkg/lock-frontend" caused when trying to install an software or an package on your system when using the terminal.

The error says

Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 54240 (synaptic)

So the error message is basically saying the process can't continue because this process is being held by process number 54240(synaptic)

How to fix this?

Fixing this issue is easy and it doesn't take time, so simply follow the methods I explained below

Method 1

Make sure Synaptic Package Manager is closed when trying to install something using terminal.  The error comes up when both synaptic and terminal are trying to execute the apt command, so the solution to this error is simply to close the synaptic manager before trying to install an software on terminal.

Method 2

If you still get the same error even after closing Synaptic Package Manager, this means the software is still running in background and a force close might be necessary.

We know that synaptic is the cause of this error because the error says it.However, to learn more about this process you can also use the ps command, type the command below in order to get more information about the process.

The command below will output what command was executed by the process that is not allowing you to install the software using terminal

ps -p 54240 -o command

As you see in the screenshot below, the command running was /usr/sbin/synaptic, which means Synaptic Package Manager

To kill the process using the command line type the command below

This command will send a SIGTERM signal to the process id and will wait for the process to shutdown itself

sudo kill  pid

#The command should look like this 

sudo kill 54240

If the first command above didn't work out, and the process is still running, you can force kill it by using the command below

This command will send a SIGKILL signal which will immediately shut down the process

sudo kill -9 pid 

#The command should look like this 

sudo kill -9 54240

Method 3

Force killing a process is the last option to do when the software is closed or doesn't respond or the process is still running in background. However , depending on the linux distro and the software you are trying to force kill sometimes can cause data loss and glitches so you may need to reboot your system and try again.

These methods apply to all Linux distros and not only Linux Mint 20.1, as long as the root cause is caused by the same issue.

Conclusion

By now you should know how to fix the error "Could not get lock /var/lib/dpkg/lock-frontend" in Linux mint Ulyssa 20.1.