Linux – How to Display SSH Banner at Login for Password Authentication Only

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I have a warning message that is displayed to a user after they enter their username to log in to our Linux servers. I only want to display this message for password authentications, and not when keys are used. It should only show to a user who is logging into a host, and not when they are sshing from one host to another (our hosts all have keys set up so we can ssh from one to another without entering passwords).

Currently, I have a line for Banner in the /etc/ssh/sshd_config file which points to a text file containing the warning message. Banner doesn't appear to have any further config options, so I'm wondering if there is a way to do this with pam or some other mechanism? Thanks.

Best Answer

Yes, you can use the pam_echo plugin:

auth required pam_unix.so
auth optional pam_echo.so file=/etc/ssh/password_banner.txt

This should produce the pam_echo output after password login.

See http://www.linux-pam.org/Linux-PAM-html/sag-pam_echo.html for docs.

Edit: You'll also need to make sure you have UsePAM yes in your sshd_config. Replaced password with auth.

Related Solutions

Ssh – How to automate SSH login with password

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.

Disable SSH Password Login – How to Disable SSH Login with Password for Some Users

Try Match in sshd_config:

Match User user1,user2,user3,user4
    PasswordAuthentication no

Or by group:

Match Group users
    PasswordAuthentication no

Or, as mentioned in the comment, by negation:

Match User !root
    PasswordAuthentication no

Note that match is effective "until either another Match line or the end of the file." (the indentation isn't significant)

Best Answer

Related Solutions

Ssh – How to automate SSH login with password

Disable SSH Password Login – How to Disable SSH Login with Password for Some Users

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