Dynamic login messages with update-motd

Some time ago I was setting up my Debian server and I wanted to have a customized message on each login. In this post I will briefly introduce an easy way on how to create dynamic login messages which display a random session quote and some important system performance counters and information. This introduction is targeted for Debian and Ubuntu, because we will use the update-motd framework. Here is the example we will create in this post:

  _____ .__         .__     .__ 
_/ ____\|__|  ______|  |__  |__|
\   __\ |  | /  ___/|  |  \ |  |
 |  |   |  | \___ \ |   Y  \|  |
 |__|   |__|/____  >|___|  /|__|
                 \/      \/     
 
Debian GNU/Linux 7.x
 
Session Quote:
 _______________________________
< Programmers do it bit by bit. >
 -------------------------------
   \
    \
        .--.
       |o_o |
       |:_/ |
      //   \ \
     (|     | )
    /'\_   _/`\
    \___)=(___/

 
System Information on Tue Jan 13 01:50:25 CET 2015
==================================================
CPU Usage         : 1%
Memory Usage      : 53.1%
Swap Usage        : 3.3%
System Uptime     : 25 days
IP Address        : 3.3.4.5
Total Disk Usage  : 6%
Open Sessions     : 1
Running Processes : 129
 
Last login: Tue Jan 13 01:13:49 2015 from my.provider.12345.com
$

Debian and Ubuntu offer the update-motd framework which is provided by the libpam module. Each time a user logs into the system, pam_motd executes the scripts in /etc/update-motd.d/ as root and writes the results to /var/run/motd, which is then displayed on the user’s terminal. This makes it very easy to write dynamic login messages, since all we have to do is provide executable scripts in /etc/update-motd.d/.

Removing redundant information

As per default, the content from /etc/motd is printed on login. Further, notifications such as new emails or information about the last session are printed, for example:

Welcome to Debian GNU/Linux 7.x
 
You have new mail.
Last login: Tue Jan 13 01:00:39 2015 from my.provider.12345.com
$

In order to get rid of these, we first have to remove all content from /etc/motd. Next, we have to comment out the following in /etc/pam.d/sshd:

# Print the status of the user's mailbox upon successful login.
#session    optional     pam_mail.so standard noenv # [1]

This will stop the mail notification from being printed. About the last session info: I personally like to have the information about when and where the last login session was, so I kept it. If you don’t want it, you just have to change the following in /etc/ssh/sshd_config:

PrintLastLog no

Header with random session quote

Now that we have removed the things we do not want, lets move forward to the things we want. We create the file /etc/update-motd.d/00-header. Make sure this file is executable as it will be used to print the header of our login session message. First, we add the static banner:

Next, we create a random session quote. The program fortune is ideal to print random quotes. Further, we can use cowsay to get the quote told by Tux himself. Simply append the following to the header script:

Retrieving and printing performance counters

In a next step, we want to print some system and performance counter information. The stats are all available and just have to be transformed into a format of our liking. Most of this can be done using awk and wc. We create /etc/update-motd.d/00-sysinfo and ensure that it is executable. Inside the script we retrieve and print some interesting performance counters:

That’s it! Now every time when you ssh to your server, you get an instant overview of interesting system counters (and a nice quote from Tux!).