Have cron parse SSH config file for server addresses and options

How does one configure cron to parse ~/.ssh/config to get the IP addresses and other options (such as IdentityFile) for SSH? Obviously adding source /home/user/.ssh/config does not help.

I do not want to add the options in the script run from cron as it calls over twenty servers which have varying options. I keep the ~/.ssh/config file updated when IP addresses or PEM keys change, and I do not want to duplicate that effort to another file to maintain.

Cron does not inherit the environment of the user configures it. Thus, for a given script:

$ cat .ssh/config
Host alpha
    Hostname 1.2.3.4
    User dotan
    IdentityFile ~/.ssh/Dotan.pem
    IdentitiesOnly yes

$ cat script.sh
#!/bin/bash
echo "Alpha"
ssh alpha dmesg

This works:

$ ./script.sh > output.log
$ cat output.log
Alpha
[73542728.181371] type=1400 audit(1397118713.764:13): apparmor="STATUS" operation="profile_replace" name="/usr/lib/connman/scripts/dhclient-script" pid=710 comm="apparmor_parser"

However, this cronjob does not work:

0 0 * * * /home/dotan/script.sh > /home/dotan/output.log

The output is:

Alpha

That proves that the script ran, but SSH failed to connect.

EDIT: I just discovered that ssh has the option -F /home/dotan/.ssh/config to specify a config file, but this did not resolve the issue.

dotancohen

Posted 2014-05-12T07:17:42.160

Reputation: 9 798

I do not see how this has anything to do with cron. Can you give some more explanation of what you are trying to achieve and what your .ssh/config might look like? – Cameron Kerr – 2014-05-12T08:02:32.553

I have edited the question with more information. – dotancohen – 2014-05-12T08:16:23.343

Does ssh -v not give any information? – user1686 – 2014-05-12T09:28:40.823

@grawity: Discovering that ssh -v did not give any information was key to finding the problem, see my comment to Cameron's answer below. Thank you! – dotancohen – 2014-05-12T11:25:30.157

The issue was that the script called another script which did not use the full path. What an easy thing to overlook! – dotancohen – 2014-05-12T10:40:36.720

It happens quite freqently. You may find it useful to set things like SHELL and PATH in your crontab. Remember, if called as sh, don't expect Bash-specific behaviour to work. Also, there is no need to put ".sh" on the end of a script (or any extension for an executable file; that gives you the freedom to reimplement in a different language if needed. – Cameron Kerr – 2014-05-12T10:53:42.187

Thanks. Actually the real scripts don't have the extension, but I like to normalize my SO posts to be more readable. My PS1 is a mess, too! – dotancohen – 2014-05-12T11:12:14.557

Have cron parse SSH config file for server addresses and options

Answers