Installation: "Unable to lock database" Error

When downloading and installing software from the repositories, a special database lock file will be created in order to ensure that the current installation process is the only one running at that time. Otherwise, attempting to install multiple files from multiple sources simultaneously may corrupt the downloaded files, cause file conflicts - or worse still - damage your system. Once the installation has been completed, the lock file will then be automatically deleted. This error may therefore occur due to two possible reasons:

Another installation is still taking place and has not yet finished, or
A previous installation attempt had not finished properly (e.g. due to being aborted early)

It is therefore wise to first check to ensure that another installation is not (or had not been) in process at the time of the error. When satisfied that this is not the case, then the database lock file can be manually deleted. To do so, open up the terminal and enter the following command:

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

Once done, you should now be able to successfully re-attempt your intended installation.

Installation: "corrupted database" / "PGP signature" Error

We all have our own unique signatures which are used to authenticate who we are and to prevent fraudulent or even malicious activities by others. This is also the case with software packages available from the software repositories. They all contain an encrypted codes (signature keys) unique to their developers to ensure that they are authentic and not malicious in nature.

During the installation process, once any software packages have been downloaded, your system will first check its database against their signatures to ensure that they are authentic prior to actually installing them. If a signature cannot be verified for any reason, then the installation process will be aborted. This problem will usually occur due to:

your system's signature key database being corrupted or out of date
one or more software packages not having been signed off properly when placed in a repository

Where a package has not been signed off properly, it will be the responsibility of the developer(s) to correct this. However, as this problem will be more than likely due to a problem with your system's signature key database, this can be solved in three easy steps. Once you have opened your terminal:

1. Refresh and update you system's signature key database by entering the command:

sudo pacman-key --refresh-keys

2. Reload the signatures contained in your system's signature key database by entering the command:

sudo pacman-key --populate

3. Clear out the software packages downloaded during the aborted installation, as it will be necessary to download them again for installation, this time having refreshed and re-loaded the signature keys. To do so, enter the command:

sudo pacman -Scc

During this process, you will be asked to confirm that you wish to:

remove all files from the cache, and
remove unused repositories

Enter y for 'yes' to confirm on both occasions. Once complete, you can then re-attempt your intended installation. Should there still be a problem with installing software packages, then please raise this issue on the Manjaro Forum for help and advice.