sftp authentication failure only as cronjob

[Damien Miller]

On Thu, 1 Nov 2012, Lars Schade wrote:

> Hi all,
> 
> I have a problem using sftp which I cannot get solved even after
> searching all over the web, so maybe one of you has a useful hint:
> 
> I want to run a simple script that puts a file on a server using sftp.
> Keys are setup correctly, everything works fine if I run the script from
> within a terminal. When I run the same script from the crontab (my
> personal crontab as user) the script runs fine on one installation
> (running OpenSSH_5.4 on an older fedora 13 machine) but fails on another
> machine (running OpenSSH_5.3 on a recent centos 6.3).
> 
> I assume that the failure is not caused by the older version of OpenSSH
> but rather due to some difference in setup but simply cannot get to the
> root of the problem. The ssh_config files are identical on both
> machines.
> 
> The debug trace (using -v) when run interactively on the centos system
> is a follows:

...

> debug1: Offering public key: /home/lars/.ssh/id_rsa
> debug1: Server accepts key: pkalg ssh-rsa blen 277
> debug1: PEM_read_PrivateKey failed

The only thing that appears different is that the private key is failing
to load. You aren't using ssh-agent are you? (it doesn't look like you are)

Is SELinux enabled? It might be preventing jobs launched by cron from
accessing your private keys. You could test this by trying to run something
like "md5sum /home/lars/.ssh/id_rsa" from cron and seeing if it succeeds
(or by finding errors in the logs)

-d