Using the Software Updater doesn't work. Nor does the command: sudo apt update. For the latter I got the following in the terminal:
To run a command as administrator (user "root"), use "sudo ".
See "man sudo_root" for details.
scott@scott-ThinkPad-E590:~$ sudo apt update
[sudo] password for scott:
Reading package lists... Done
E: Could not get lock /var/lib/apt/lists/lock. It is held by process 11616 (packagekitd)
N: Be aware that removing the lock file is not a solution and may break your system.
E: Unable to lock directory /var/lib/apt/lists/
scott@scott-ThinkPad-E590:~$
Being a complete beginner (abandoned Windows 10 in Oct.) I'm not sure if this is exactly what is happening to the person in the following thread or if my problem is different.
Btw, my problem is happening on TWO laptops with 18.1. I only this morning got my desktop to upgrade from 17.3 to 18.1 but have not had a chance to check whether the Software Updater is throwing out the same error message.
I posted yesterday (May 3) about this same issue and received a reply that Canonical (the company who administers Ubuntu) has been under cyberattack. Software Updater has only worked twice for me in the last three days, and both times very briefly.