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Command line unlock ttys and users- user login

unlock

(This primarily references SCO Unix though part of it applies to any Unix/Linux OS).

SCO Unix can lock ttys administratively or for failed logins. This prevents any further logins on that tty. An administrator might do that to lock out a particular modem line, or to lock out a specific terminal at certain times of day.

Tty's can also be locked for too many unsuccessful logins. Typically this is set for a high number: it might require 99 failed logins before the lock is applied (the number of failed or unsuccesful logins can be set using Scoadmin). The purpose of this is security: failed logins might indicate a brute force password guessing attack. More often, it simply means a stuck keyboard, either because it is defective or because someone accidentally left a book on the keyboard.

Once locked, no one can login on that tty until the administrator removes the lock. The root user can login at the console even if it is locked if /etc/default/login contains (for example) "OVERRIDE=tty01". The unlocking can be done with "scoadmin" (scoadmin->System->Terminal Manager) , but it can also be done from the command line using ttyunlock (http://aplawrence.com/Detective/ttylocked.html)

A specific user can also be locked out - that applies to any tty and is a different message. Unlock with "passwd -u username". If that doesn't work, try

usermod -x "{administrativeLockApplied 0}" -x "{unsuccessfulLoginAttempts
0}" username
 

It's easy to see if tty's or users are locked by looking for the strings "u_lock" in the sub-files of /tcb/files/auth and the string "t_lock" in /etc/auth/system/ttys.

Other ways to restrict or prevent logins: (these apply to any Unix/Linux OS. not just SCO)
How do I restrict logins?.
How can I prevent root logins over telnet?
How can I restrict who can login with ssh?

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