Comment 6 for bug 391761

For oneiric this will be fixed soon with an updated pam package. For existing Ubuntu releases, we have not committed to providing an update. A workaround for this is to add a line such as the following to /etc/security/limits.conf:

* hard nproc 4096

(you may wish to adjust the value of the limit according to the resources of your environment)

Or you can disable pam_limits entirely in /etc/pam.d if you aren't otherwise using it, which would cause the system to fall back to the kernel defaults.