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How can I prevent users from changing their passwords? I still want to be able to change the passwords as root if necessary but keep the user from changing their password.

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This question may be useful – yentup Feb 6 '13 at 0:55
    
Chmod the passwd command so that only you can execute it – Mawg Feb 6 '13 at 1:24
    
Why would you want to lower user security? – mdpc Feb 6 '13 at 2:40
    
@mdpc I don't. I plan on changing the password periodically, but I need it to be changed by me because it is a shared account and I don't want someone to change the password without the other people who have access being notified. – Vreality Feb 10 '13 at 1:17
up vote 5 down vote accepted

Do chmod go-rx /usr/bin/passwd Normal users can then not run passwd. If you want some users to be able to, you can put them in a special group perhaps.

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Would this still work? cp /usr/bin/passwd . ; chmod +x ./passwd ; ./passwd – f.ardelian Jul 16 '13 at 16:00
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@f.ardelian The thing is, passwd has some special magic called "setuid" on it - that means that when someone runs the file, they're running it as its owner (namely, root.) This allows normal users to change the /etc/shadow file containing the passwords. If you were to copy the file to a user's home directory, it would no longer be setuid, and therefore no longer be automatically run with root priviledges. To learn more, look up information about "Unix permissions" and "setuid". – JamesTheAwesomeDude Dec 7 '13 at 22:03
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@JamesTheAwesomeDude Thanks, that was very informative! – f.ardelian Dec 8 '13 at 4:53

passwd -n 9999 user will prevent user from changing his password for almost 274 years.

If you want to have passwordless user, which is unable to change his password, open /etc/shadow as root, find the line which begins with the name of the user, and change the content between first and second colon to U6aMy0wojraho.
(source: https://help.ubuntu.com/community/PasswordlessGuestAccount)

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