By default when you add new user to system (/etc/passwd file) it grant shell access. If you are creating new users for POP3 or SMTP (mail server) or FTP then you do not need to grant shell access to a user. Remember as soon as you add a user he/she can login via telnet or ssh. The best way to put Linux shell access restriction is to use special shell called nologin, which politely refuse a login. It displays a message that an account is not available and exits non-zero. It is intended as a replacement shell field for accounts that have been disabled or have other user level access such as ftp, pop3, smtp etc. This is a very common practice followed by ISP or web hosting service provider's web, mail and FTP server(s).
/sbin/nologin Example
(a) First make sure nologin exists in /etc/shells file (else service such as ftp may not allow login)
# less /etc/shells
If nologin shell does not exist in above shell list, just add /sbin/nologin shell to it:
# echo "/sbin/nologin" >> /etc/shells
If you are using Debian then use following path:
# echo "/usr/sbin/nologin" >> /etc/shells
(b) Block shell access for user vivek (vivek user account must exits):
# usermod -s /sbin/nologin vivek
Debain Linux user modify above command as follows:
# usermod -s /usr/sbin/nologin vivek
Now user vivek's new login shell is /sbin/nologin. Vivek allowed to use other services such as ftp, pop3 but not shell access via ssh or telnet.
New user accounts
Add a new user called tony with no shell access:
# useradd -s /sbin/nologin tony
Debain / Ubuntu Linux user modify above command as follows:
# useradd -s /usr/sbin/nologin tony
Please note that above method is very easy to use but if you have a large setup. you need to take help of PAM (and may be OpenLDAP / MySQL). I will cover such setup some time later :).
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{ 4 comments… read them below or add one }
this does not work for me on debian system. however, nologin exist but the command did not work :( (user CAN still login via ssh)
Mantizke, you control that in /etc/ssh/sshd_config:
AllowUsers user
in this case, only user may login and all other users are denied access.
I protest. This article is prejudiced against Tony.
I WANT MY BASH ACCESS!
(Really, thanks. I was looking for a way to make an ftp user with no shell access on a debian box. This was precisely what I needed.)
Man!You save my day! Thank you very-very much for this usefull post.
At least i learned new security measure how to separate UID’s on my test webserver.
God Bless You.