Creating a Pacman Hook to Run a Script After Package Upgrades in Arch Linux

Desired outcome

Configure a Pacman hook that automatically executes a custom script after every package upgrade or install transaction, without needing to reload any daemon.

Prerequisites

• Root access (or ability to use sudo) to write to /etc/pacman.d/hooks/.
• Pacman version 5.0 or newer (the hook mechanism has been stable since that release).
• The script you want to run must already exist and be executable (e.g., /usr/local/bin/post‑upgrade.sh).
• Optional: enable Pacman logging by ensuring LogFile is set in /etc/pacman.conf if you want hook execution recorded in /var/log/pacman.log.

Procedure

1. Create the hook file

   As root, create a new file with a .hook extension in the hooks directory:

   sudo touch /etc/pacman.d/hooks/post-upgrade.hook
   sudo chmod 644 /etc/pacman.d/hooks/post-upgrade.hook
   sudo nano /etc/pacman.d/hooks/post-upgrade.hook

   Insert the following content, adjusting the Exec path to point to your script:

   [Trigger]
   Operation=Upgrade
   Operation=Install
   Type=Package
   Target=*
   
   [Action]
   When=PostTransaction
   Exec=/usr/local/bin/post-upgrade.sh
   

   Save and exit the editor.

2. Verify the hook is readable

   Pacman will ignore a hook if the file is not world‑readable or if the syntax is wrong. Ensure the file permissions are 644 (readable by all).

   ls -l /etc/pacman.d/hooks/post-upgrade.hook
   # Expected: -rw-r--r-- 1 root root ...

3. Test the hook with a safe transaction

   Run a non‑disruptive Pacman operation, for example reinstalling the Pacman package itself:

   sudo pacman -Syu --needed pacman

   After the command finishes, check that your script executed. If your script writes to a log file, inspect that log; otherwise, add a temporary logging line (e.g., logger 'Hook ran') to verify.

4. Check Pacman’s internal log (optional)

   If LogFile is enabled in /etc/pacman.conf, look for hook execution entries:

   grep "running hook" /var/log/pacman.log
   # You should see a line referencing post-upgrade.hook

Expected checks

• Pacman exits with status 0 (no abort).
• The package database remains consistent: sudo pacman -Qk reports no missing files.
• Your script’s intended side‑effect (e.g., updating a database, sending a notification) occurs after the transaction completes.

Recovery / rollback options

Creating the hook file modifies system state. To undo the change:

1. Remove or rename the hook file:

sudo mv /etc/pacman.d/hooks/post-upgrade.hook /etc/pacman.d/hooks/post-upgrade.hook.disabled
# or
sudo rm /etc/pacman.d/hooks/post-upgrade.hook

2. Run another Pacman transaction to confirm the hook no longer triggers (your script should not run).

Limitations and cautions

• Hooks run with the same privileges as Pacman (typically root). Only use scripts you trust and have audited.
• If the hook script returns a non‑zero exit status, Pacman treats it as an error and aborts the transaction. Ensure your script returns 0 on success.
• Avoid actions inside the hook that modify the Pacman database or interfere with the ongoing transaction (e.g., removing packages).
• Some graphical front‑ends may bypass Pacman directly; test with plain pacman commands to guarantee hook execution.
• If Pacman’s logging is disabled (UseSyslog off and no LogFile), you will not see automatic hook logs; rely on your script’s own output or manual checks.