Backing up N900 to a Linux PC

= Backup requirements =

Connectivity
It is assumed that the backups will have to take place over ssh, as the USB mass storage mode on the phone does not provide access to the root file system. Therefore, the first prerequisite is a working TCP/IP network between the phone and the target machine.

Power
We do not want our backups to drain the phone's battery, so we should only consider running the backup if we are connected to external power.

Automation
Once set up, the backups should happen automatically without intervention from the user, BUT complain loudly if they fail. This implies a script that we can schedule from cron that should perform whatever combination of tests and operations we may need. It also implies key-based access to our backup host.

Snapshots
At any given time we want a decent ability to backtrack, which means storing regular snapshots using something like rdiff-backup or rsnapshot.

So, what we've got so far is that we want to run a script on the N900 that tests whether we have external power (or dies), then tries to get a wireless connection to the backup server (or dies), then performs an incremental backup of the entire phone.