Snapshot and rollback of a `pot`¶

In this section we explore all features related to snapshot and rollback.

Take a snapshot of your `pot`¶

Thanks to ZFS, taking a snapshot of a pot is easy and super fast. Currently, it is not allowed to take a snapshot of pot that is running.

The syntax of the snapshot command is the same for a thin or a thick jail (single or multi type pot). However, the operations performed and the meaning is slightly different.

The snapshot name is always a number, that is the UNIX epoch time when the snapshot is taken.

Unix time monotony

UNIX time is used to desume the chronological order of snapshots. Many operations, like rollback and snapshot rotations depends on this assumption.

Let's take a snapshot of a single type pot:

# pot stop casserole
# pot snap -p casserole
# pot info -v -p casserole
[..]
    datasets:
        casserole/m
    snapshot:
        zroot/pot/jails/casserole@1583601150
        zroot/pot/jails/casserole/m@1583601150

snap or snapshot?

The command snapshot can be also invoked using the abbreviated form snap. Those two forms are fully equivalent, snap is just an alias of snapshot

It's possible to notice, that two datasets are considered: the main dataset and the filesystem dataset.

Let's take a snapshot of a multi type pot:

# pot stop saucepan
# pot snap -p saucepan
# pot info -v -p saucepan
[..]
    datasets:
        saucepan/m => bases/12.1
        saucepan/m/usr/local => jails/saucepan/usr.local
        saucepan/m/opt/custom => jails/saucepan/custom
    snapshots:
        zroot/pot/jails/saucepan@1583601687
        zroot/pot/jails/saucepan/custom@1583601687
        zroot/pot/jails/saucepan/usr.local@1583601687

When a snapshot of a pot is taken, a snapshot of all datasets that belongs to the pot is taken. The base of a thin jail doesn't belong to the pot, so a snapshot of the base is not taken.

Rollback¶

If a snapshot of a pot is available, a rollback can be performed. Currently, it is not allowed to rollback a snapshot of a pot that is running.

The syntax of the rollback command is the same for a think or a thick jail (single or mutli type pot). However, like for snapshots, the operations performed are slightly different.

Just for fun (and to prove that snapshot/rollback are really useful), some damage can be done to a pot (those steps are optional):

# pot run casserole
root@casserole:~ # rm -rf /*
[..]
root@casserole:~ # exit
# pot stop mypot

Almost every file has been deleted and the pot cannot start anymore. But no panic, we have a snapshot:

# pot revert -p casserole
# pot run casserole
root@casserole:~ # exit

The revert command automatically selects the latest snapshot available.

revert or rollback?

The command revert can be also invoked using the alternative form rollback. Those two forms are fully equivalent, rollback is just an alias of revert

Remove old snapshots¶

Snapshots are great, they can be used for backup/rollback or to export pot. However, snapshots use disk spaces and too many snapshots can fill up disk space.

pot provides two mechanism to keep the number of snapshot under control: an option to rotate snapshots and a command to remove old snapshots.

Snapshots rotation¶

In general, it's always possible to take other snapshots, even if nothing is changed:

# pot stop casserole
# pot snap -p casserole
# pot info -v -p casserole
[..]
    datasets:
        casserole/m
    snapshot:
        zroot/pot/jails/casserole@1583601150
        zroot/pot/jails/casserole@1583617777
        zroot/pot/jails/casserole/m@1583601150
        zroot/pot/jails/casserole/m@1583617777

A way to keep the same number of snapshots, is to use the -r flag in the snapshot command:

# pot snap -p casserole -r
# pot info -v -p casserole
[..]
    datasets:
        casserole/m
    snapshot:
        zroot/pot/jails/casserole@1583617777
        zroot/pot/jails/casserole@1583617881
        zroot/pot/jails/casserole/m@1583617777
        zroot/pot/jails/casserole/m@1583617881

From the snapshot epoch, it's possible to notice that the oldest snapshot (1583601150) has been removed and a new one (1583617881) has taken its place.

Snapshot purge¶

The command purge-snapshots has been designed to remove old snapshots and keep only the last one:

# pot info -v -p casserole
[..]
    datasets:
        casserole/m
    snapshot:
        zroot/pot/jails/casserole@1583617777
        zroot/pot/jails/casserole@1583617881
        zroot/pot/jails/casserole/m@1583617777
        zroot/pot/jails/casserole/m@1583617881
# pot purge-snapshots -p casserole
# pot info -v -p casserole
[..]
    datasets:
        casserole/m
    snapshot:
        zroot/pot/jails/casserole@1583617881
        zroot/pot/jails/casserole/m@1583617881

An additional flag, -a, allows to remove all snapshots, the last one included:

# pot purge-snapshots -p casserole -a
# pot info -v -p casserole
[..]
    datasets:
        casserole/m
    snapshot:
        no snapshots

Snapshot and rollback of a `fscomp`¶

fscomp is a ZFS dataset, managed by the pot framework and explained in the section about volumes.

All the commands that manipulate pot snapshots, have been extended to manipulate fscomp snapshots as well:

# pot create-fscomp -f lid
# pot info -v -f lid 
not yet implemented
# pot snapshot -f lid # take a snapshot
# pot rollback -f lid # revert to the last snapshot
# pot purge-snapshots -a -f lid # delete all snapshot

A snapshot of a fscomp can be taken even if a pot is using it. The responsibility of the consistency of the data contained in the fscomp is upon the user.

Last update: 2020-03-07

Snapshot and rollback of a pot¶

Take a snapshot of your pot¶