[plug] Backups

[James Devenish]

In message <4105F77C.80305 at smlintl.com.au>
on Tue, Jul 27, 2004 at 02:34:36PM +0800, Marc Wiriadisastra wrote:
> If I wanted to do [backups] to a DVD drive at a pre-determined time
> obviously I would use a cron job with a DVD but would it be in a
> script or just entered into the crontab?

This really need only depend on your administrative tendencies and the
complexity of the task. Generally, it would be better to make a nice
script in a nice file of its own, and simply invoke that file from a
cron job (rather than entering everything on one line in the crontab).
This also means that you can edit, backup, and modify your script
independently of cron (i.e. you can test the backup or do an unscheduled
backup easily).

> Also, would I use dd or some other method for [backups]?

(I think this is somewhat of a frequently-asked question, so there will
be further information in the list archives and via Google.) This
question about dd can be considered in the general case (i.e. not linked
to DVDs), in which you'd have to ask yourself whether `dd` will produce
a self-consistent backup. If the disk partition is in use for writing
(e.g. databases, log files), then this is unlikely. But depending on the
filesystem and nature of your files, it *might* still be acceptable, for
*your* purposes, to use dd (even if a bit of `fsck`ing is necessary).
But if you need to be careful, you'll have to take down your daemons,
sync, take a filesystem snapshot, then do a backup using the snapshot.
This sort of thing is mentioned in the list archives. This is in a sense
a "grey area" and people do whatever is gives the best tradeoff between
practicality and recoverability. Something like `dump` is generally
better, because you can restore files on a arbitrary basis onto
arbitrary partitions (whereas `dd` limits you to restoring an entire
filesystem onto an identical partition). There are various suggestions
and examples in the list archives.

> it has to all be bash based

No worries -- this will not limit what you can achieve, except to say
that you won't be able use GUI apps. It's pretty rare for anyone to use
GUI apps within cron anyway. Note that there may be two "phases" for
your backup process: one to generate a backup stream or "image" for your
DVD, and another phase to burn the DVD. Both of these can be done
without GUIs.

> can't be GUI because [it's] a server and we don't have X on it.

Just as a point of clarification: you don't necessarily "have to have X
installed" on a server just to use X11 programmes. Since X11 is
inherently based on a client-server model, you can use your own
/workstation/ to interact with your server's X11 programmes -- you don't
need to have a display or keyboard attached to your server. You /will/,
however, need to install a set of X11 software libraries on your server.
But at least you don't have to install an "X11 server" on your server --
you just use your workstation as the X11 server.