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Is it possible to disable direct login for normal users (like oracle) in Linux but allow scp and sftp for that use?

5

Methods such as creating the file /etc/nologin, setting account login shells to /bin/false or /sbin/nologin effectively disable user accounts from logging into an interactive shell, but do not protect the system.

If you want to specifically restrict a user to using scp or sftp only, install a restricted shell that is designed to do exactly that. The rssh package is a restricted shell designed to work with OpenSSH.

: rssh is a restricted shell for use with OpenSSH, allowing only scp
: and/or sftp. For example, if you have a server which you only want
: to allow users to copy files off of via scp, without providing shell
: access, you can use rssh to do that. It is a alternative to scponly.

You should seriously consider setting a chroot for the users logging in with the restricted rssh shell.

Read and understand the security implications of restricting users in such a way. Start with the man pages for rssh and rssh.conf. You should also understand what a chroot is and how it works.

1

You can Add this to sshd_config:

Match User oracle
        ForceCommand set - ""$SSH_ORIGINAL_COMMAND; [ "$1" = "scp" ] || exit 1; CMD=`IFS='\`&;<>'; set - ""$SSH_ORIGINAL_COMMAND; echo $1`; [ "$CMD" ] || exit 1; exec $CMD

Here, I'm matching the user 'oracle'. Instead you can use Match group scponly to match users within the 'scponly' group. If anyone tries to connect in a way that doesn't run scp, then it will silently exit with return code 1.

If the account uses key-based authentication, you can prepend the key in the user's .ssh/authorized_keys file with command="<above commands>".

While I've added some safety against manipulating the file to cause a rogue command to be executed (by truncating at any &``;<> characters), I can't be sure that this can't be worked around some way I haven't thought of.

This is all a bit long and messy to stick into an sshd_config file, and a typo could break stuff for other users. It might be better to create a script that does the checking for "scp", and then just call that script from the ForceCommand, thus making the mods in sshd_config much simpler. Check out https://serverfault.com/questions/749474/ssh-authorized-keys-command-option-multiple-commands for some examples of this.

0

The login shell can be changed from bash to /usr/sbin/nologin or /bin/false do prevent a normal login. The login shell can be changed with usermod:

usermod user_name -s /usr/sbin/nologin
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  • Some sftp clients aren't using proper sftp, but rather trying to log on and execute basic commands like cd, ls, ... . In that case use scp or another sftp client program. – jippie May 5 '12 at 6:35

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