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snap-pac/README.md
James Barnett 54eec76bc8 update link to stable release of grub-btrfs
2016-04-24 21:00:56 -05:00

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snap-pac

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.

The snapshots are set up to use snapper's number algorithm. That is, snapper will periodically clean up snapshots tagged with number after reaching a set threshold in the snapper configuration file.

Additionally the package provides a hook to regenerate your GRUB configuration file after every pacman transaction. This is useful when using grub-btrfs. If you don't use GRUB, or if you don't want your configuration file generated every transaction, then you should remove 99_grub-config.hook after installation.

Note: Snapshots are only taken of the subvolume corresponding with the root snapper config; other subvolumes are not included. You must modify the scripts to include other subvolumes. Additionally, you should create subvolumes of directories you do not want included in your snapshots (e.g. /var/cache/pacman/pkg).

Installation

Install the package from the AUR.

Optionally, install grub-btrfs to populate your GRUB menu with the ability to boot into snapshots.

After installation, the hooks are located at /usr/share/libalpm/hooks, and the scripts are located at /usr/share/libalpm/hooks.bin/snap-pac.

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.

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

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