How do I backup to a specific device at an specific moment?

Question

Here is what I want to do:
- Any night of any day in the week, connect my external HDD to my Arch computer, and go to sleep.
- At the next morning there is a backup done on that HDD.
I understand the basics on some tools which can help me do that (crond, dd, udisks), but I utterly uncapable to make it work all together, so let me ask some questions to start looking myself:
- Is it possible to use some kind of "device ID" to take a signal from udev and pipe it anywhere else?
- Which daemon could be watching in order to take that signal and execute the backup script?
Thanks for patience =P
Last edited by JMO (2011-03-26 14:56:52)

Answer 1

Since it's happening so infrequently (once every 24 hours), why not just set up a simple script to run every night at a time you're usually asleep?
Here are some tools you'll probably find helpful:
1) Cron: runs a specific task at set times.  Arch Wiki: Cron
(If midnight works for you, you can simply place your script in /etc/cron.daily/; it will then run each night when the clock strikes 12.)
2) rsync: copies files incrementally (i.e. only files that have changed will be copied) Arch Wiki: Rsync
In your script, you can pretty easily check to see if the drive is plugged in using its label; there's a nice set of symlinks in /dev/disk/by-label. This short script runs one or more commands if and only if a block device is attached with label yourDiskLabel.
#!/bin/bash
if [ -b /dev/disk/by-label/yourDiskLabel ]
then
#perform your backup command(s)
fi
(If, for some reason, you have multiple drives with the same label, you can use their UUID/universally unique identifier. There are a similar set of symlinks in /dev/disk/by-uuid.
just got this idea, using udev script to start a backup.
When you plug in the media it will record and it could wait a specific moment to start the backup procedure.
I would think this would just take up more resources than just checking for the drive's presence at a set time.