Linux? You geeks use Linux?
If you work in science, and you work on big datasets (such as analyzing next generation sequencing data), chances are that you use Linux for some of your work. I frequent several of our lab’s Red Hat servers for data analysis and code development purposes. However, these aren’t just my servers to use. Other lab members and, depending on the server, IT staff use them too. I try to remember to check and see who is on and what they’re running before getting too involved with something that’s going to hog memory or processor time. But, of course, I don’t always remember.
I decided to automate this process to take the remembering part out. By adding in a shell script + some code in my profile file, my ssh login immediately displays relevant information without having to invoke it manually.
Shell Script
The code is based on the Bash shell, so it may our may not apply to your ssh login. I keep the shell script in my /home/user directory with the name “.greeting.sh”. Adding the leading period just makes it invisible to standard “ls” queries so it doesn’t add to the clutter in my home directory. The code for the “.greeting.sh” follows between the lines of # signs:
##################################################
#!/bin/bash
UNAME=`whoami`
TIME=`date`
HOST=`hostname`
UCNT=`users | wc -w`
ULST=`users`
PROC=`ps aux|awk ‘NR > 0 { s +=$3 }; END {printf(”%d\n”, s + 0.5);}’`
MPCT=`free | grep Mem | awk ‘{printf(”%d\n”, $3 / $2 * 100 + 0.5);}’`
MYSHELL=`echo $SHELL`
echo
echo “$TIME”
echo “Shell: $MYSHELL”
echo “Hello $UNAME! Welcome to $HOST!”
if [ $UCNT -ge 2 ]
then
echo “$UCNT users are currently logged into $HOST:”
echo “$ULST”
else
echo “No other users currently logged in.”
fi
echo “System Status:”
if [ $PROC -ge 80 ]
then
echo “High processor usage at ${PROC}%”
elif [ $PROC -ge 50 ]
then
echo “Medium processor usage at ${PROC}%”
else
echo “Low processor usage at ${PROC}%”
fi
if [ $MPCT -ge 80 ]
then
echo “High memory usage at ${MPCT}%”
elif [ $MPCT -ge 50 ]
then
echo “Medium memory usage at ${MPCT}%”
else
echo “Low memory usage at ${MPCT}%”
fi
echo
exit 0
##################################################
For example, the code above prints the following when logging in: The date, a greeting, the hostname, my current shell, whether other users are logged in (and the list of users if others are on), and information about current processor and memory usage. I customize this script depending on the primary use of the server. If you have a server that should always be running a certain program, add a line that looks for that program. If it were called “myprogram” you could add the following line to the program:
PROG=`ps aux | grep -v grep | grep myprogram | wc -l`
If the program is running, then it will return 1 (if only one instance is running), or 0 if it isn’t running. By adding in some language later testing if $PROG -ge 1, a message could print saying the program was running or not.
Take note! Don’t forget to alter the permissions on the script to allow execution, using something like “chmod +x .greeting.sh”. Also note that the variables are defined using backticks (same key as the ~ on standard US QWERTY keyboards), not single quotes.
Automatically running
The script isn’t much use if you have to run it manually (if I remembered to do that, why would I need a script?), so I like to set the script to run automatically immediately following an ssh login. As I said before, I use Bash on most of the Linux servers I use. For this shell, there is a file called “.bash_profile” in the home directory of each user. This profile file is executed on every ssh connection to set some common environment variables, like PATH. By adding in code to run the greeting script, the output from the script will be displayed immediately after login. Example code to add to the bottom of your profile file:
##################################################
if [ -e "/home/user/.greeting.sh" ]
then
/home/user/.greeting.sh
fi
##################################################
That’s all there is to it. A simple, but powerfull script to automatically give you information on server login. Feel free to your system and purpose.
