psql restore procedures

See the [upstream manual](https://www.bacula.org/9.4.x-manuals/en/main/Restore_Command.html) more information about the [restore

command](https://www.bacula.org/9.4.x-manuals/en/main/Restore_Command.html).

## PostgreSQL restore procedures

This is an adaptation of the [official recovery procedure](https://www.postgresql.org/docs/9.3/continuous-archiving.html#BACKUP-PITR-RECOVERY). 

Here we'll assume the backup server has access to the server we'll

restore files into. If not, you can do the following, on the backup

server, assuming `$IP` is the IP of the client and `$HOSTKEY` is its

hostkey (the `cat /etc/ssh/ssh_host_rsa_key.pub` on the client,

below):

    ssh-agent bash

    ssh-add /etc/ssh/ssh_host_rsa_key

    mkdir -p ~/.ssh

    echo "$IP $HOSTKEY" >> ~/.ssh/known_hosts

    cat /etc/ssh/ssh_host_rsa_key.pub

And on the client, allow the server `$HOSTKEY` (the above `cat

/etc/ssh/ssh_host_rsa_key.pub` on the backup server):

    cat /etc/ssh/ssh_host_rsa_key.pub

    echo "$HOSTKEY" >> /etc/ssh/userkeys/root

Once the backup server has access to the client, we can transfer files

over:

    cd /srv/backups/pg

    rsync -aP $CLIENT $CLIENT:restore

Then, on the client, install the software, stop the server and move

the template cluster out of the way:

    apt install postgres rsync

    service postgresql stop

    mv /var/lib/postgresql/*/main{,.orig}

    su -c 'mkdir -m 0700 /var/lib/postgresql/*/main' postgres

We'll be restoring files in that directory.

Make sure you run the SAME MAJOR VERSION of PostgreSQL than the

backup! You cannot restore across versions. This might mean installing

from backports or an older version of Debian.

Then you need to find the right `BASE` file to restore from. Each

`BASE` file has a timestamp in its filename, so just sorting them by

name should be enough to find the latest one. Uncompress the `BASE`

file in place:

    cat ~/$CLIENT/main.BASE.bungei.torproject.org-20190805-145239-$CLIENT.torproject.org-main-9.6-backup.tar.gz | su -c 'tar -C /var/lib/postgresql/11/main -x -z -f -'

(Use `pv` instead of `cat` for a progress bar with large backups.)

Make sure the `pg_xlog` directory doesn't contain any files.

From here on, you could start the server and it will resume from that

`BASE` backup. Since those are ran less frequently, however, you will

probably also want to restore transaction logs to get the most recent

version of the database. 

If you are restoring to the latest point in time, you can dump the WAL

files in the `pg_xlog` directory:

    cd ~/$CLIENT &&& tar -f -c main.WAL.* | su -c 'tar -f - -x -C /var/lib/postgresql/11/main/pg_xlog/' postgres 

Then start the server and look at the logs to follow the recovery

process:

    service postgresql start

    tail -f /var/log/postgresql/*

References

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