CRON ERROR: failed to open PAM security session: Protocol not supported

Got an interesting report of an error on one of our servers. I was told crons for a user account on our server weren’t running. I tailed the cron log (/var/log/cron) and came to find these errors:

Oct 13 06:32:01 secure crond[4558]: CRON (clients) ERROR: failed to open PAM security session: Protocol not supported
Oct 13 06:32:01 secure crond[4558]: CRON (clients) ERROR: cannot set security context

I’ve never seen the error before. I dug around in various PAM and related security configs, but didn’t see any issues. I then wanted to run the cron manually via the user, and tried to sudo down into the user’s account.

[root@secure~]# sudo su - clients
Too many logins for 'clients'.
could not open session
[root@secure~]#

There is the problem! Cron can’t run because two techs were logged into the ‘clients’ user account and it was being limited. In this case I decided to bump the limit to 5 users. Here is what I did:

[root@secure~]# nano -w /etc/security/limits.conf

Now I added the following line:

clients	hard	maxlogins	5

The crons were now running, problem solved.