- There should be pam_limits.conf module present in /etc/pam.d/system-auth. On older systems, this entry must also be in system-auth and password-auth files.
grep limit /etc/pam.d/system-auth
session required pam_limits.so
- Add maxlogins entry in /etc/security/limits.conf as follows:
username hard maxlogins 'number of max logins'
- Enable PAM in /etc/ssh/sshd_config file as follows:
UsePAM yes