202 lines
8 KiB
Markdown
202 lines
8 KiB
Markdown
# snap-pac
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[](https://aur.archlinux.org/packages/snap-pac/)
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[](https://github.com/wesbarnett/snap-pac/blob/master/LICENSE)
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[](https://aur.archlinux.org/packages/snap-pac/)
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This makes Arch Linux's pacman use
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[snapper](https://wiki.archlinux.org/index.php/Snapper) to automatically take a
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pre and post snapshot before and after pacman transactions using pacman's hooks
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feature, similar to how YaST does with OpenSuse. This provides a simple way to
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undo changes to a system after a pacman transaction.
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## Installation
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Install [the package from the
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AUR](https://aur.archlinux.org/packages/snap-pac/).
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After installation, the hooks will be located in `/usr/share/libalpm/hooks`, and
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the script will be located in `/usr/share/libalpm/hooks.bin`.
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In an effort to bring about a higher standard in distributing packages in the
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AUR, starting with release 0.6 (version 0.6-2 in the AUR), I have signed the
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release with my PGP key. You must import my public key to verify the signature
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if you are using the PKGBUILD in the AUR. This can be done
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via:
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$ gpg --recv-keys A3B8C5C3
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The key's fingerprint is:
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8535CEF3F3C38EE69555BF67E4B5E45AA3B8C5C3
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You can manually verify the signature of the tarball with:
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$ gpg --verify v*pkgver*.tar.gz.sig
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## Configuration
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Configuration is done via the snapper configuration files, with extra variables
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specific to these pacman hooks. The defaults should be suitable for most users.
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The following are possible settings you can place in each snapper configuration
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file:
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* `PACMAN_PRE_POST` - perform pacman pre/post snapshots for this configuration.
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Default is `"no"` for all configurations, except for the `root` configuration
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which is `"yes"`.
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* `PACMAN_CLEANUP_ALGORITHM` - snapper algorithm used in cleaning up the pacman pre/post
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snapshots. Default is `"number"`.
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* `PACMAN_PRE_DESCRIPTION` - snapper description used for the pacman pre snapshot.
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Default is the pacman command that called the snapshot.
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* `PACMAN_POST_DESCRIPTION` - snapper description used for the pacman post snapshot.
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Default is the pacman command that called the snapshot.
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These settings only need to be added to the snapper configuration files if you
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want to change the default.
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## Usage
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### Taking snapshots
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**Use pacman—and AUR helpers—as normal and watch snapper do its thing.** No
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bash scripts for you to call. No bash aliases to setup.
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Because these are pacman hooks, it doesn't matter how you call pacman—whether
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directly, through an AUR helper, or using an alias—snapper will create the
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snapshots when pacman installs, upgrades, or removes a package. The
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pacman command used is logged in the snapper description for the
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snapshots.
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### Undoing a transaction
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To undo changes from a pacman transaction, use `snapper undochange`. See the
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snapper manpage and the following example.
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If you have severe breakage—like snapper is gone for some reason and you can't
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get it back—you'll have to resort to more extreme methods, such as taking a
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snapshot of the pre snapshot and making it the default subvolume or mounting it
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as `/`. Most likely you'll need to use a live USB to get into a chroot
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environment to do any of these things. Snapper has a `snapper rollback` feature,
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but your setup has to be properly configured to use it. The exact procedure
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depends on your specific setup. Be careful.
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## Example
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Installing the `nano` package as normal:
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# pacman -S nano
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resolving dependencies...
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looking for conflicting packages...
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Packages (1) nano-2.5.3-1
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Total Installed Size: 2.14 MiB
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:: Proceed with installation? [Y/n] Y
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(1/1) checking keys in keyring [######################################] 100%
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(1/1) checking package integrity [######################################] 100%
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(1/1) loading package files [######################################] 100%
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(1/1) checking for file conflicts [######################################] 100%
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(1/1) checking available disk space [######################################] 100%
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:: Running pre-transaction hooks...
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(1/1) snapper pre snapshot
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:: Processing package changes...
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(1/1) installing nano [######################################] 100%
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:: Running post-transaction hooks...
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(1/2) snapper post snapshot
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(2/2) generate GRUB configuration file
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And here are the snapshots:
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# snapper -c root list -t pre-post | tail -n 1
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1033 | 1034 | Fri 22 Apr 2016 01:54:13 PM CDT | Fri 22 Apr 2016 01:54:14 PM CDT | pacman -S nano |
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What changed?
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# snapper -c root status 1033..1034
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+..... /etc/nanorc
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c..... /etc/snapper/.snap-pac-pre
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+..... /usr/bin/nano
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+..... /usr/bin/rnano
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+..... /usr/share/doc/nano
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+..... /usr/share/doc/nano/faq.html
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+..... /usr/share/doc/nano/fr
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+..... /usr/share/doc/nano/fr/nano.1.html
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+..... /usr/share/doc/nano/fr/nanorc.5.html
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+..... /usr/share/doc/nano/fr/rnano.1.html
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I truncated the above output, but it continues. See the manpage for snapper to
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see what each symbol means. You can also do `snapper diff` in the same
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way—I'll spare you that one.
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To undo the upgrade:
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# snapper -c root undochange 1033..1034
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create:0 modify:3 delete:100
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And `nano` is now gone, along with all the files it changed:
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$ pacman -Qi nano
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error: package 'nano' was not found
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## Troubleshooting
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**ERROR: /etc/conf.d/snapper does not exist!**
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*snap-pac* reads in the snapper configurations from `/etc/conf.d/snapper`. It
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can't do that if the file doesn't exist. I'm not sure what you've done to not
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have it exist in the default location.
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**WARNING: No snapper configurations found, so not taking any snapshots!**
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No snapper configurations were found in `/etc/conf.d/snapper`. This means you
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haven't created any configurations yet using `snapper create-config`. See the
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snapper manpage on how to do this.
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**WARNING: No snapper configurations are set up for snapshots to be taken!**
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Although you seem to have created at least one configuration, none of them are
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set up for *snap-pac*'s pacman hooks. By default *snap-pac* will take snapshots
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for the `root` configuration and any other configuration which has
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`PACMAN_PRE_POST` set to `yes` in its configuration file. This message means you
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don't have a snapper configuration named `root` (or `PACMAN_PRE_POST` is set to
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`no` for it) and no other configuration is set up for snapshots. See the
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configuration section above.
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**WARNING: *prefile* does not exist, so no post snapshot will be taken. If you are initially installing snap-pac, this is normal.**
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*snap-pac* saves the pre snapshot's number in a temporary file. Somehow it go
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removed before the post snapshot could be taken. When you initially install
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*snap-pac* the post hook is run, but the pre hook never was, so this message
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will show up then as well.
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## License
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snap-pac
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Copyright (C) 2016 James W. Barnett
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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## See also
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* [ArchWiki Btrfs article](https://wiki.archlinux.org/index.php/Btrfs)
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* [ArchWiki Snapper article](https://wiki.archlinux.org/index.php/Snapper)
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* [Btrfs homepage](https://wiki.archlinux.org/index.php/Btrfs)
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* [snapper homepage](http://snapper.io/)
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* `man alpm-hooks`
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* `man btrfs`
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* `man snapper`
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