240 lines
8.4 KiB
Groff
240 lines
8.4 KiB
Groff
'\" t
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.TH SNAP-PAC 8 2017-02-04 SNAP-PAC
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.SH NAME
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snap-pac \- Pacman hooks that use snapper to create pre/post btrfs snapshots
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like openSUSE's YaST
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.SH DESCRIPTION
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This is a set of \fIpacman\fR hooks and script that causes \fIsnapper\fR to
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automatically take a pre and post snapshot before and after pacman transactions,
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similar to how YaST does with OpenSuse. This provides a simple way to undo
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changes to a system after a pacman transaction.
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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 pacman
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command used is logged in the snapper description for the snapshots.
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Additionally the snapshot numbers are output to the screen and to the pacman log
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for each snapper configuration during the pacman transaction.
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To undo changes from a pacman transaction, use \fIsnapper undochange\fR. See
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\fBsnapper\fR(8) 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 \fI/\fR. 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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.SH 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 (see \fBsnapper-configs\fR(5)). The defaults
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of the following 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 (e.g., \fI/etc/snapper/configs/root\fR, etc.). Follow the pattern of other
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variables in the configuration file (VAR=setting).
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\fBPACMAN_PRE_POST=\fR\fB\fIyes\fR\fR\fB or \fR\fB\fIno\fR\fR
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.RS 4
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Perform pacman pre/post snapshots for this configuration.
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Default is "no", except for the root configuration which is "yes".
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.RE
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.BR PACMAN_CLEANUP_ALGORITHM
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.RS 4
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Snapper algorithm used in cleaning up the pacman pre/post snapshots. See \fBsnapper\fR(8) for list of valid options.
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Default is "number".
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.RE
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\fBPACMAN_PRE_DESCRIPTION=\fR\fB\fIstring\fR\fR
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.RS 4
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snapper description used for the pacman pre snapshot.
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Default is the parent program (usually pacman) that called the snapshot script.
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.RE
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\fBPACMAN_POST_DESCRIPTION=\fR\fB\fIstring\fR\fR
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.RS 4
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snapper description used for the pacman post snapshot.
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Default is the parent program (usually pacman) that called the snapshot script.
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.RE
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The following setting can be changed in the snapper configuration file
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\fI/etc/conf.d/snapper\fR:
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\fBPACMAN_ABORT_ON_FAIL=\fR\fB\fIyes\fR\fR\fB or \fR\fB\fIno\fR\fR
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.RS 4
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When set to "yes" this causes pacman to abort a transaction if the snap-pac pre
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hook fails. This prevents an upgrade/installation/removal from occurring if a
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pre snapshot cannot be performed.
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Default is "no".
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.RE
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.SH EXAMPLE
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Installing the nano package as normal:
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.EX
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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) Performing snapper pre snapshots for the following configurations...
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root: 1033
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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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(1/1) Performing snapper post snapshots for the following configurations...
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root: 1034
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.EE
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The snapper snapshot number is given for each snapper configuration that is
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used. Tip: this is also logged in pacman's log).
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And here are the snapshots:
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.EX
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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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.EE
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What changed?
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.EX
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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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.EE
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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 way—I'll
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spare you that one.
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To undo the upgrade:
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.EX
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# snapper -c root undochange 1033..1034
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create:0 modify:3 delete:100
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.EE
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And nano is now gone, along with all the files it changed:
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.EX
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$ pacman -Qi nano
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error: package 'nano' was not found
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.EE
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.SH TROUBLESHOOTING
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.SS ERROR: \fI/etc/conf.d/snapper\fR does not exist!
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snap-pac reads in the snapper configurations from \fI/etc/conf.d/snapper\fR. It can't
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do that if the file doesn't exist. I'm not sure what you've done to not have it
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exist in the default location.
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.SS WARNING: No snapper configurations found, so not taking any snapshots!
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No snapper configurations were found in \fI/etc/conf.d/snapper\fR. 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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.SS 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 snapper configuration, none of
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them are set up for snap-pac's pacman hooks. By default snap-pac will take
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snapshots 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 no
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for it) and no other configuration is set up for snapshots. See configuration.
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.SS 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 got
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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 will
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show up then as well and is safe to ignore in that circumstance.
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.SS WARNING: Didn't find pacman running.
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The script gets the description from the pacman command that was run. If you get
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this warning it looks like you may have run the script directly instead of
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letting it run through pacman's hooks.
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.SS ERROR: Unable to use snapper without dbus. Are you in a chroot environment?
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Snapper requires dbus. If you chroot into another environment, dbus will not be
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available, so snapper can't take snapshots. Although snapper can be set up to
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not need dbus, this is a simple way to check if one is in a chroot and avoid
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attempting snapshots in it.
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.SS After restoring snapshot from snap-pac, pacman database is locked
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The pre/post snaphots are taken while pacman is running, so this is expected.
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Follow the instructions pacman gives you (e.g., removing the lock file).
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.SS snap-pac is only taking snapshots of the root configuration
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That's the default behavior. See \fBCONFIGURATION\fR.
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.SH FAQ
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.SS Does snap-pac backup non-btrfs /boot partitions?
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Nope. But you can add hook that does it for you. It would be something like the
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following:
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.EX
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[Trigger]
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Operation = Upgrade
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Operation = Install
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Operation = Remove
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Type = Package
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Target = linux
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[Action]
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Description = Backing up /boot...
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When = PreTransaction
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Exec = /usr/bin/rsync -avzq --delete /boot /.bootbackup
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.EE
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.SH HOMEPAGE
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https://github.com/wesbarnett
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.SH AUTHORS
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Wes Barnett <wes@wbarnett.us>
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.SH SEE ALSO
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.BR alpm-hooks (5),
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.BR snapper (8),
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.BR snapper-configs (5),
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.BR pacman (8)
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