Hey all, I'm trying to use snapback2 to do automatic backups of a machine I've got running with about 1.1TB (~1.2 million files) of data on it onto another machine. I got it set up, and it works if I call snapback2 from the command line, however I'm trying to get it to run automatically as a cron job, which doesn't work. The crontab entry is "30 22 * * * snapback2 -d", which is exactly the same as when I call it manually (snapback2 -d) [-d is debug mode].

I checked some logs, and the call to rsync (which snapback2 makes) is exactly the same in both cases. So why does the cron job fail? I know cron runs once every minute, though I'm not familiar with the lower level workings. The only thing I can think of is that since the rsync call takes longer than a minute, something is cutting it off, hence the failures. Is this reasonable? I can restructure how the backup occurs (i.e. ~10 smaller backups of individual folders instead of one gigantic recursive backup), however it takes something like 2 days for the initial backup to be created (transferring over the net), so I don't want to wait around for that to happen if it wouldn't likely fix the problem.

I can post logs and more info if you think my idea isn't correct, just let me know.

Try specifying the full path to snapback2. cron works in a limited environment, it might not be able to access the command without the full path.

Well it makes the call to snapback2, snapback2 just fails when it calls rsync. I'll try it with the full path though...yeah, still fails.

Does cron perhaps not play well with ssh keys? I'm using them for the remote login (the machine I'm backing up is off site)

what are the error messages?
You also need to provide the whole path to all the commands in the script.

The snapback2 log message is

Also FYI, that rsync call is made at the end of a long list of other calls, so I know snapback2 isn't just straight up failing.

Edit:
I just checked the /var/mail log, and here's the mail I got for the last time I ran it: http://pastebin.com/m20c06a10

It now looks to me like it's something with SSH. Though I have keys generated as both my user and as root, both on the remote machine. And it still works if I just manually call snapback2...so what is cron doing that's breaking ssh?

I figured it out. cron wasn't picking up an environment variable that SSH needed, so SSH authentication was failing. I set up a script to export that variable and then call snapback2, and cron now calls that script instead of just calling snapback2.