This text and script is borrowed from the "Unix Horror Stories" document.
It states as follows
"""""Management told us to email a security notice to every user on the our system (at that time, around 3000 users). A certain novice administrator on our system wanted to do it, so I instructed them to extract a list of users from /etc/passwd, write a simple shell loop to do the job, and throw it in the background.
Here's what they wrote (bourne shell)...
for USER in `cat user.list`;
do mail $USER <message.text &
done
Have you ever seen a load average of over 300 ??? """" END
My question is this- What is wrong with the script above? Why did it find a place in the Horror stories? It worked well when I tried it.
Maybe he intended to throw the whole script in the background and not just the Mail part. But even so it works just as well... So?
I think, it does well deserve to be placed Horror stories.
Consider the given server for with or without SMTP service role, this script tries to process 3000 mail commands in parallel to send the text to it's 3000 repective receipents.
Have you ever tried with valid 3000 e-mail IDs, you can feel the heat of CPU(sar 1 100)
P.S.: I did not tested it but theoritically affirmed.
Best Regards.
Thank you for the reply. But isn't that exactly what the real admin asked the novice admin to do.
Is there a better script or solution ?
Well, Let me try to make it sequential to reduce the CPU load, but it will take no. of users*SLP_INT(default=1) seconds to execute....
#Interval between concurrent mail commands excution in seconds, minimum 1 second.
SLP_INT=1
for USER in `cat user.list`;
do; mail $USER <message.text; [ -z "${SLP_INT}" ] && sleep 1 || sleep ${SLP_INT}" ;
done
Think how you would do the following task manually: send the same message to moe, larry, and curly. Now, do you really send 3 email messages? Or do you send a single email with 3 recipients?
:o Nice and simple explanation. I assumed that the script was looping. Thank you Thunderbolt and Perderabo.