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Pacman hook that creates a btrfs snapshot with snapper prior to the operation as a system restore point
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README.md

snap-pac

AUR Version License AUR Votes

This makes Arch Linux's pacman use snapper to automatically take a pre and post snapshot before and after pacman transactions using pacman's hooks feature, similar to how YaST does with OpenSuse. This provides a simple way to undo changes to a system after a pacman transaction.

Installation

Install the package from the AUR.

After installation, the hooks will be located in /usr/share/libalpm/hooks, and the script will be located in /usr/share/libalpm/hooks.bin.

In an effort to bring about a higher standard in distributing packages in the AUR, starting with release 0.6 (version 0.6-2 in the AUR), I have signed the release with my PGP key. You must import my public key to verify the signature if you are using the PKGBUILD in the AUR. This can be done via:

$ gpg --recv-keys A3B8C5C3

The key's fingerprint is:

8535CEF3F3C38EE69555BF67E4B5E45AA3B8C5C3

You can manually verify the signature of the tarball with:

$ gpg --verify 0.6.tar.gz.sig

Configuration

Configuration is done via the snapper configuration files, with extra variables specific to these pacman hooks. The defaults should be suitable for most users. The following are possible settings you can place in each snapper configuration file:

  • PACMAN_PRE_POST - perform pacman pre/post snapshots for this configuration. Default is "no" for all configurations, except for the root configuration which is "yes".
  • PACMAN_CLEANUP_ALGORITHM - snapper algorithm used in cleaning up the pacman pre/post snapshots. Default is "number".
  • PACMAN_PRE_DESCRIPTION - snapper description used for the pacman pre snapshot. Default is the pacman command that called the snapshot.
  • PACMAN_POST_DESCRIPTION - snapper description used for the pacman post snapshot. Default is the pacman command that called the snapshot.

These settings only need to be added to the snapper configuration files if you want to change the default.

Usage

Taking snapshots

Use pacman—and AUR helpers—as normal and watch snapper do its thing. No bash scripts for you to call. No bash aliases to setup.

Because these are pacman hooks, it doesn't matter how you call pacman—whether directly, through an AUR helper, or using an alias—snapper will create the snapshots when pacman installs, upgrades, or removes a package. The pacman command used is logged in the snapper description for the snapshots.

Undoing a transaction

To undo changes from a pacman transaction, use snapper undochange. See the snapper manpage and the following example.

If you have severe breakage—like snapper is gone for some reason and you can't get it back—you'll have to resort to more extreme methods, such as taking a snapshot of the pre snapshot and making it the default subvolume or mounting it as /. Most likely you'll need to use a live USB to get into a chroot environment to do any of these things. Snapper has a snapper rollback feature, but your setup has to be properly configured to use it. The exact procedure depends on your specific setup. Be careful.

Example

Installing the nano package as normal:

# pacman -S nano
resolving dependencies...
looking for conflicting packages...

Packages (1) nano-2.5.3-1

Total Installed Size:  2.14 MiB

:: Proceed with installation? [Y/n] Y
(1/1) checking keys in keyring                               [######################################] 100%
(1/1) checking package integrity                             [######################################] 100%
(1/1) loading package files                                  [######################################] 100%
(1/1) checking for file conflicts                            [######################################] 100%
(1/1) checking available disk space                          [######################################] 100%
:: Running pre-transaction hooks...
(1/1) snapper pre snapshot
:: Processing package changes...
(1/1) installing nano                                        [######################################] 100%
:: Running post-transaction hooks...
(1/2) snapper post snapshot
(2/2) generate GRUB configuration file

And here are the snapshots:

# snapper -c root list -t pre-post | tail -n 1
1033  | 1034   | Fri 22 Apr 2016 01:54:13 PM CDT | Fri 22 Apr 2016 01:54:14 PM CDT | pacman -S nano      |

What changed?

# snapper -c root status 1033..1034
+..... /etc/nanorc
c..... /etc/snapper/.snap-pac-pre
+..... /usr/bin/nano
+..... /usr/bin/rnano
+..... /usr/share/doc/nano
+..... /usr/share/doc/nano/faq.html
+..... /usr/share/doc/nano/fr
+..... /usr/share/doc/nano/fr/nano.1.html
+..... /usr/share/doc/nano/fr/nanorc.5.html
+..... /usr/share/doc/nano/fr/rnano.1.html

I truncated the above output, but it continues. See the manpage for snapper to see what each symbol means. You can also do snapper diff in the same way—I'll spare you that one.

To undo the upgrade:

# snapper -c root undochange 1033..1034
create:0 modify:3 delete:100

And nano is now gone, along with all the files it changed:

$ pacman -Qi nano
error: package 'nano' was not found

Troubleshooting

ERROR: /etc/conf.d/snapper does not exist!

snap-pac reads in the snapper configurations from /etc/conf.d/snapper. It can't do that if the file doesn't exist. I'm not sure what you've done to not have it exist in the default location.

WARNING: No snapper configurations found, so not taking any snapshots!

No snapper configurations were found in /etc/conf.d/snapper. This means you haven't created any configurations yet using snapper create-config. See the snapper manpage on how to do this.

WARNING: No snapper configurations are set up for snapshots to be taken!

Although you seem to have created at least one configuration, none of them are set up for snap-pac's pacman hooks. By default snap-pac will take snapshots for the root configuration and any other configuration which has PACMAN_PRE_POST set to yes in its configuration file. This message means you don't have a snapper configuration named root (or PACMAN_PRE_POST is set to no for it) and no other configuration is set up for snapshots. See the configuration section above.

WARNING: prefile does not exist, so no post snapshot will be taken. If you are initially installing snap-pac, this is normal.

snap-pac saves the pre snapshot's number in a temporary file. Somehow it go removed before the post snapshot could be taken. When you initially install snap-pac the post hook is run, but the pre hook never was, so this message will show up then as well.

License

snap-pac

Copyright (C) 2016 James W. Barnett

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

See also