04 September 2013

509. Very briefly: Send remote commands via the dropbox folder

This is probably fairly obvious to most people.

I've got a reverse ssh tunnel set up so that I can access my work computer from home. However, for the past few days I've had the connection get stuffed up on a regular basis (it doesn't get dropped, but the connection gets refused), and it frustrates me a little bit.

While a proper ssh connection is unbeatable, I would at least be able to copy files back and forth via dropbox if I only had a way of sending commands to my work computer.

And an obvious way of doing that would be to use a cronjob and a tiny bit of bash scripting. So here we go:
While we don't have to (we could just have an empty script file instead) I like the idea of testing for the presence of a specific file in the Dropbox folder, and if it exists, execute it.

Let's call the file that tests for it runremote.sh, and put it in our home folder (~/). I personally suspect that making sure that execution output and error messages get properly logged is a good thing if you're going to fly blind like this, hence the 1> and 2>

if [ -e ~/Dropbox/runme.sh ]; then sh ~/Dropbox/runme.sh 1>> ~/Dropbox/runme.log 2>> ~/Dropbox/runme.error & fi

Then when you want something executed, put a file called runme.sh in ~/Dropbox:
pwd echo 'Is it working?' cp ~/testfile.text ~/Dropbox date
Note that any command in runme.sh is going to be run in the ~/ folder -- not in ~/Dropbox.

And set the runremote.sh file to be executed e.g. every five minutes through cron:

crontab -e
*/5 * * * * sh ~/runremote.sh

Again, you don't need to have it test for the presence of a file, but I just instinctively like the idea.

Anyway, any command you put in ~/Dropbox/runme.sh should be executed and logged within five minutes from being synced.

You CAN use sudo (echo mypassword| sudo -S ls /root )as well by providing your password in the script file, but this is obviously not terribly safe.

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