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docs(script): Give a ZFS output example (#1)

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2023-03-07 01:35:26 +01:00
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@@ -32,10 +32,27 @@ Get started like so:
In `pacman` on every `PreTransaction`, meaning right before any actual operation on a package begins, we trigger a ZFS snapshot. By default we identify the active system dataset by doing `findmnt / --noheadings --output source`. If exactly one source returns that is the exact name of a ZFS dataset in an imported zpool we create a snapshot on it. If no source returns we silently exit. If more than one source returns we raise an error and halt the `pacman` transaction. In `pacman` on every `PreTransaction`, meaning right before any actual operation on a package begins, we trigger a ZFS snapshot. By default we identify the active system dataset by doing `findmnt / --noheadings --output source`. If exactly one source returns that is the exact name of a ZFS dataset in an imported zpool we create a snapshot on it. If no source returns we silently exit. If more than one source returns we raise an error and halt the `pacman` transaction.
We retain two different snapshot chains, one for `pacman` transactions that only affect what we are calling _trivial_ packages and a separate chain for _important_ packages. By default only the exact regular expression package name match `^(linux)$` is considered important. Whenever an important package is affected by a transaction a snapshot goes into the corresponding chain. In all other cases - when an important package is not affected - snapshots go into the trivial chain. We retain two different snapshot chains, one for `pacman` transactions that only affect what we are calling _trivial_ packages and a separate chain for _important_ packages. By default only the exact regular expression package name match `^(linux|systemd|zfs-(dkms|utils))$` is considered important. Whenever an important package is affected by a transaction a snapshot goes into the corresponding chain. In all other cases - when an important package is not affected - snapshots go into the trivial chain.
The _trivial_ snapshot chain by default keeps 15 snapshots, the _important_ chain keeps 5. The thought process here is that you will likely not futz around with a kernel every day whereas you may very well install arbitrary packages multiple times a day. Snapshots should keep you safe for a couple of days hence the defaults of 5 and 15 snapshots, respectively. The _trivial_ snapshot chain by default keeps 15 snapshots, the _important_ chain keeps 5. The thought process here is that you will likely not futz around with a kernel every day whereas you may very well install arbitrary packages multiple times a day. Snapshots should keep you safe for a couple of days hence the defaults of 5 and 15 snapshots, respectively.
Snapshots may look like so:
```
$ zfs list -o name -t all
NAME ┌─── Important because systemd
zpool | is on our list of
zpool/root | important packages
zpool/root/archlinux ▼▼▼
zpool/root/archlinux@pacman_2023-03-07-0113_op:upgr_sev:imp_pkgs:systemd:bind:enchant:grep
zpool/root/archlinux@pacman_2023-03-07-0113_op:upgr_sev:trv_pkgs:jdk17-temurin
zpool/root/archlinux@pacman_2023-03-07-0115_op:upgr_sev:trv_pkgs:proton-ge-custom-bin
▲▲▲▲ ▲▲▲
| |
Pacman operation that triggered this snapshot ───┘ |
|
Severity based on affected packages, here trivial ───────┘
```
You may optionally include more ZFS datasets in this snapshot mechanism. Have a look at `pacman-zfs-snapshot.conf`, its comments should be clear enough to get you going. You may optionally include more ZFS datasets in this snapshot mechanism. Have a look at `pacman-zfs-snapshot.conf`, its comments should be clear enough to get you going.
# Development # Development