Linux Users

I'm having some problems trying to change the linux users' password and so the mail password....

Thanks,

What kind of problems? Are you the administrator, or just a user? Are the passwords too simple? You'd be surprised how UN-simple "too simple" is :⁾

Are you doing this as the user, as root or from PHP?

If you are doing this as PHP it is unlikly to work unless PHP is running as the user or as root.