Pacman/Pacnew and Pacsave

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Revision as of 15:09, 11 September 2012 by Chingzilla (Talk | contribs) (Changed find command for locating .pac* files. The existing would match many unrelated files (for ex: git's .pack object files). Also redirect sterr so Permission errors are not printed)

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Getting Started

During package upgrades or removal Pacman will inform you of files (usually configurations in /etc) that are being installed with a .pacnew extension or backed up with a .pacsave extension.

A .pacnew file may be created during a package upgrade (pacman -Syu, pacman -Su or pacman -U) to avoid overwriting a file which already exists and was previously modified by the user. When this happens a message like the following will appear in the output of pacman:

warning: /etc/pam.d/usermod installed as /etc/pam.d/usermod.pacnew

A .pacsave file may be created during a package removal (pacman -R), or by a package upgrade (the package must be removed first). When the pacman database has record that a certain file owned by the package should be backed up it will create a .pacsave file. When this happens pacman outputs a message like the following:

warning: /etc/pam.d/usermod saved as /etc/pam.d/usermod.pacsave

These files require manual intervention from the user and it is good practice to handle them right after every package upgrade or removal. If left unhandled, improper configurations can result in improper function of the software, or the software being unable to run altogether.

Package backup files

A package's PKGBUILD file specifies which files should be preserved or backed up when the package is upgraded or removed. For example, the PKGBUILD for pulseaudio contains the following line:

backup=('etc/pulse/client.conf' 'etc/pulse/daemon.conf' 'etc/pulse/')

Types Explained

The different types of *.pac* files.


For each backup file in a package being upgraded, pacman cross-compares three md5sums generated from the file's contents: one sum for the version originally installed by the package, one for the version currently in the filesystem, and one for the version in the new package. If the version of the file currently in the filesystem has been modified from the version originally installed by the package, pacman cannot know how to merge those changes with the new version of the file. Therefore, instead of overwriting the modified file when upgrading, pacman saves the new version with a .pacnew extension and leaves the modified version untouched.

Going into further detail, the 3-way MD5 sum comparison results in one of the following outcomes:

original = X, current = X, new = X 
All three versions of the file have identical contents, so overwriting is not a problem. Overwrite the current version with the new version and do not notify the user. (Although the file contents are the same, this overwrite will update the filesystem's information regarding the file's installed, modified, and accessed times, as well as ensure that any file permission changes are applied.)
original = X, current = X, new = Y 
The current version's contents are identical to the original's, but the new version is different. Since the user has not modified the current version and the new version may contain improvements or bugfixes, overwrite the current version with the new version and do not notify the user. This is the only auto-merging of new changes that pacman is capable of performing.
original = X, current = Y, new = X 
The original package and the new package both contain exactly the same version of the file, but the version currently in the filesystem has been modified. Leave the current version in place and discard the new version without notifying the user.
original = X, current = Y, new = Y 
The new version is identical to the current version. Overwrite the current version with the new version and do not notify the user. (Although the file contents are the same, this overwrite will update the filesystem's information regarding the file's installed, modified, and accessed times, as well as ensure that any file permission changes are applied.)
original = X, current = Y, new = Z 
All three versions are different, so leave the current version in place, install the new version with a .pacnew extension and warn the user about the new version. The user will be expected to manually merge any changes necessary from the new version into the current version.


If the user has modified one of the files specified in backup then that file will be renamed with a .pacsave extension and will remain in the filesystem after the rest of the package is removed.

Template:Box Note


When a file (usually a configuration found in /etc) is encountered during package installation or upgrade that does not belong to any installed package but is listed in backup for the package in the current operation, it will be saved with a .pacorig extension and replaced with the version of the file from the package. Usually this happens when a configuration file has been moved from one package to another. If such a file were not listed in backup, pacman would abort with a file conflict error.

Template:Box Note

Locating .pac* Files

Arch Linux does not provide official utilities for .pacnew files. You'll need to maintain these yourself; a few tools are presented in the next section. To do this manually, first you will need to locate them. When upgrading or removing a large number of packages, updated *.pac* files may be missed. To discover whether any *.pac* files have been installed:

To just search where most global configurations are stored:

$ find /etc -regextype posix-extended -regex ".+\.pac(new|save|orig)" 2> /dev/null

or the entire disk:

$ find / -regextype posix-extended -regex ".+\.pac(new|save|orig)" 2> /dev/null

Or use locate if you have installed it. First re-index the database:

# updatedb


$ locate -e --regex "\.pac(new|orig|save)$"

Or use pacman's log to find them:

$ egrep "pac(new|orig|save)" /var/log/pacman.log

Note that the log does not keep track of which files are currently in the filesystem nor of which files have already been removed.

Managing .pacnew Files

Once all existing .pacnew files have been located, the user may handle them manually using common merge tools such as vimdiff, ediff (part of emacs), meld (a Gnome GUI tool), sdiff (part of diffutils, or Kompare (a KDE GUI tool), then deleting the .pacnew files afterwards.

A few third-party utilities providing various levels of automation for these tasks are available from the community repository and the AUR.

  • pacmerge-gitAUR - CLI interactive merge program
  • Dotpac - Basic interactive script with ncurses-based text interface and helpful walkthrough. No merging or auto-merging features.
  • pacdiff - Very minimal and undocumented CLI script. Part of the pacman-contrib package in the community repo.
  • pacdiffviewer - Full-featured interactive CLI script with auto-merging capability. Part of the yaourtAUR package.
  • diffpacAUR - Standalone pacdiffviewer replacement
  • Yaourt - A package manager that supports the AUR repository. Use yaourt -C to compare, replace and merge configuration files..
  • etc-updateAUR - Arch port of Gentoo's etc-update utility, providing a simple CLI to view changes, interactively edit and merge changes, and automatically merge trivial changes (e.g. comments.) Unlike some others above, this uses your preferred text editor rather than forcing you to learn a new one.
  • pacnews-gitAUR is a simple script aimed at finding all .pacnew files, then editing with vimdiff. It differs from the below script using meld.

A quick roundup of vimdiff

Merge-arrows-2.pngThis article or section is a candidate for merging with Vim.Merge-arrows-2.png

Notes: There is no need to duplicate Vim command information here. (Discuss in Talk:Pacman/Pacnew and Pacsave#)
vimdiff is part of the vim package. The command will open colored windows each showing the content of the file with colored highlights of differences, line by line.
# vimdiff file file.pacnew

You are left with two modes: the insert one, which let you edit the file, and the screen mode, which let you move around windows and lines.

  • press i to enter insert mode. --INSERT-- will then appear on the bottom line.
  • press Esc to leave the insert mode.
  • press Ctrl+ww to move from one window to another one
  • press yy to copy a line
  • press p to paste a line
  • press ]c to jump to the next change
  • press [c to jump to the previous change
  • press do when cursor is on a highlighted difference and changes from other window will move into the current one (diff obtain).
  • press dp is same as do but will put the changes from current windows into the other one (diff put).
  • press :wq to exit and save current window
  • press :wqa to exit and save both windows
  • press :q! to exit without saving

Once your file has been correctly edited taking account changes in file.pacnew:

# mv file file.bck
# mv file.pacnew file

Check if your new file is correct, then remove your backup:

# rm file.bck

Using Meld to Update Differences

Using meld in a loop can be used to update configuration files. This script will loop through the files one by one then prompt to delete the .pacnew file.

# Merge new *.pacnew configuration files with their originals

pacnew=$(find /etc -type f -name "*.pacnew")

# Check if any .pacnew configurations are found
if [[ -z "$pacnew" ]]; then
  echo " No configurations to update"

for config in $pacnew; do
  # Diff original and new configuration to merge
  gksudo meld ${config%\.*} $config &
  # Remove .pacnew file?
  while true; do
    read -p " Delete \""$config"\"? (Y/n): " Yn
    case $Yn in
      [Yy]* ) sudo rm "$config" && \
              echo " Deleted \""$config"\"."
              break                         ;;
      [Nn]* ) break                         ;;
      *     ) echo " Answer (Y)es or (n)o." ;;

The above script uses GNOME's gksudo for graphical sudo permissions. Use kdesu for KDE.