Multiple telnet connections changing their passwd.

I just set up a Linux server for an intro linux course that allows 30 students to login via telnet. I received a complaint when all the students tried to change their password at the same time. I figured this is because the passwd file could not be updated by more than one person (at the same time). Is this true? or is there a way everyone could change their password at the same time?

Thanks..

passwd doesn't actually update shadow or passwd. It creates a copy of it called nshadow and npasswd with the changes then renames them to shadow/passwd. Anyway it will return 5 if it cannot get a lock on the passwd or shadow file. The actual error in your logs should be someting like "can't lock password file" or "cant lock tcfs key db".

I also suggest you use ssh instead of telnet so passwords are not sent in clear text.

I wanted to use ssh but the the instructor wants telnet. There are no security issues with this server because thats all it does... I reghost it every term. I didn't see the errors "can't lock password file" or "cant lock tcfs key db" in my log, the instructor just wanted to know if all the students can change the password at the same time instead of going user by user, one at a time.

Everyone cannot change their pass at the sametime since only 1 process can have a lock on the files. You don't need go 1 by 1 since the actual password change is very quick but yes I would see a problem with having 30 users all change their pass at once.