Question

How to back up all files inside directory (all tree folders and files) to archive and then send to ftp server? Can I do this using cronjobs? How should tar command look like to back up /home/user/ directory and all files and folders inside to /home/ with compression?

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cd /my/very/interesting/and/important/directory & tar -cjf . backup.tar.bz2 –exclude & backup.tar.bz2 & sftp backup.tar.bz2 me@myserver
as far as i understand is equal to:

1. cd /my/very/interesting/and/important/directory
2. tar -cjf . backup.tar.bz2 –exclude
3. backup.tar.bz2

4. sftp backup.tar.bz2 me@myserver

   • what parameter j means in 2nd command?
   • probably there should not be a & between tar -cjf . backup.tar.bz2 --exclude AND backup.tar.bz2. Because &merges commands. Right?
   • what about password param in 4th command?

Answer 1

A cron job issues a command. If you can do it from the command line, you can to it with cron.

There are at least three simple ways to accomplish what you want:

• Create a shell script and run that.
• Write an ant build script and run that.
• Simply stack all the needed commands after one another, separated by &&. However, I don’t recommend this, see below.

This is an example series of skeleton commands that might be useful. This is more intended as a sketch of the concept rather than a comprehensive, working script. For instance, I’m not sure how to use sftp without having to manually enter a password, so I left that out. Look up the documentation for the commands used and figure out yourself what to use and how in your specific case, maybe you’ll even learn something along the way. 😉

cd my-important-directory
tar -cpvf backup.tar -C .. --exclude backup.tar* my-important-directory
bzip2 backup.tar
sftp backup.tar.bz2 me@myserver

You could put the above commands in a shell script, or combine them into one command, like so:

cd my-important-directory && tar -cpvf backup.tar -C .. --exclude backup.tar* my-important-directory && bzip2 backup.tar && sftp backup.tar.bz2 me@myserver

This, however, is horribly ugly if you ask me. I’d go with the shell or ant script options to improve readability and avoid maintenance headaches. Those methods also make it easier to maintain in another way: you don’t have to update the crontab every time you need to make a change to the backup script, just edit the script and you’re good to go.

The && operator

Separating two commands with && tells bash to run the second command if and only if the first command exits with status 0, which is the standard exit code used when commands exit successfully. This may be compared to ;, which can be used to run multiple commands in succession regardless of success or failure. Using && means that the series of commands stops if something goes wrong along the way. For instance, if tar fails to create an archive, there’s no use in attempting to compress that archive afterwards.

What really happens behind the scenes is short-circuit logic. cmd1 && cmd2 is a logic statement that says “Return true if both cmd1 and cmd2 exit with exit code 0, otherwise return false” (though true and false are actually represented by numbers). If cmd1 doesn’t exit with exit code 0, then the logic statement is already false, and the statement returns false without running cmd2.