error: failed to synchronize all databases (unable to lock database) (SOLVED)

When trying to update Arch Linux or a distribution based on it (for example, Manjaro or BlackArch), an error “failed to synchronize all databases (unable to lock database)”" may occur.

For example, when entering the command

sudo pacman -Syu

It can be output:

:: Synchronizing package databases...
error: failed to synchronize all databases (unable to lock database)

This means that a file has been created that indicates that the package database is locked for processing, because another program is currently working with the package database.

If this is indeed the case (for example, you have already started pacman in another tab), then it is recommended that you wait for this command to complete so that there are no errors in the cache and database of installed packages later.

If you are sure that this message is displayed exclusively by mistake – for example, you updated packages via SSH using pacman, but the session was unexpectedly terminated and you reconnect to the remote computer, but this error appears when you try to use pacman, then in this case for fixing it is enough to delete the file /var/lib/pacman/db.lck file as follows:

sudo rm /var/lib/pacman/db.lck

After that, run pacman again – the problem should be completely resolved.

If you are unsure whether to delete the db.lck file, you can check its creation date as follows:

ls -l /var/lib/pacman/db.lck

The creation date can tell you why this file is present in the system.

If the problem is not solved, then the second reason may be the disk is full – there is no space left on it to write the lock file. In this case, clean the disk and retry the command to update the system.

You can start the cleanup by deleting the logs. For example, to remove web server logs:

rm /var/log/httpd/*

To delete temporary files:

rm -rf /tmp/*

To remove installation package files:

pacman -Scc