How to fix subprocess new post-installation script returned error exit status 127 in APT

The error output will often show which command wasn't found. Look for the command name mentioned in the dpkg error. For example:

update-desktop-database: not found

This tells you that update-desktop-database is the missing command.

First, try to reconfigure dpkg and complete any pending package configurations. This often resolves the issue:

sudo dpkg --configure -a

This command configures all unpacked packages. If the post-install script runs again and completes successfully, the problem is resolved.

If the previous step doesn't work, search for which package provides the missing command. Common mappings:

# Find which package provides a command
apt search <command-name>

# Examples:
apt search update-desktop-database  # Provides: desktop-file-utils
apt search gtk-update-icon-cache    # Provides: libgtk2.0-bin
apt search update-mime              # Provides: mime-support

Once you identify the package, install it:

sudo apt install <package-name>

After installing the missing dependency, fix any broken packages:

sudo apt --fix-broken install

This will attempt to complete the installation of any packages that had post-installation script failures.

Confirm that the package is now properly installed and functional:

apt list --installed | grep <package-name>

Also check that the post-installation script completed without errors by reviewing apt's status.

If the previous steps don't work, completely remove and reinstall the package. Use Synaptic Package Manager and select "Mark for Complete Removal" (or use the CLI):

# Remove the package completely
sudo apt remove --purge <package-name>

# Reinstall it
sudo apt install <package-name>

Since post-installation scripts only run once during installation, the script should execute cleanly the second time around.