Shell Programming and Scripting

Hello again, I have a script on my media server that wakes up my backup server, performs an 'rsync' backup, then shuts the backup server down. Currently, I have it send the Wake on LAN packet, and sleep for 5 minutes, just to give the backup server time to boot (of course it doesn't take that long, but just in case...). It occurred to me today that that isn't always going to cut it, in the sense that after so many days, the filesystem gets run through fsck (which takes a bit of time on these monster drives).
So, the question... Is it possible to include in a script, maybe a ping mechanism that can be run, then based on the results, determine if the remote server is booted or not? I did some reading on 'ping' (remember, I did use FNG in the title ) and the man page made a mention of using ping's exit status to determine if a server was up or not, but I honestly am not clear on exactly how I would implement that (i.e. if I used:

if [ ping remotehost ]
then blahblah
else blahblahblah
fi

would that necessarily be looking for the exit code 0 (successful), or am I just way out there? The example above seems to be missing something, but... Thanks again, you guys/girls are a great help!

Code:

ping -c 1 SERVER > /dev/null 2>&1
if [ $? -ne 0 ]
then
  # bail out
fi
# do the job

I used the bellow to check the remote server is up and accepting remote login ( here i checked if telnet port is open or not.

Code:

MACHINE=8.8.3.200 # Change to what ever you need
exec 3>/dev/tcp/${MACHINE}/23
if [ $? -eq 0 ]
then
    echo "Server is up Telnet accepting connections"
else
    echo "Telnet connections not possible"
fi

Dr. House is at it again! Thanks for the example, once again. It appears I have more reading to do though, as there re some bits that I don't understand. The '2>&1'... that sends stderr to the same spot as stdout, right? In this case, /dev/null... But I am foggy about the '$?'. I havent used that one before...

---------- Post updated at 10:40 AM ---------- Previous update was at 10:38 AM ----------

Thank you very much for that example as well! It looks like I have two options, one to see if the machine is up, and one to check if the service itself is up. Thanks again!

... is merely a "geek's quicky", meant to keep the shell clean, but completely irrelevant to the task at hand (- see this page for details).



... is meant to inform you about success or failure of the preceeding command, i.e. your pinging of a server (- see this page for details).

Is it possible to incorporate this into a while loop, so that it would ping every 5 seconds or so, and if '$?' is -ne to 0, keep pinging until $?= 0 (then once it does equal 0, continue with the script)? I came up with one sample, but of course, it didn't do anything, but give me a nice error

Code:

#! /bin/bash

while [ true ]
do
  ping -c 1 $SERVER > /dev/null 2>&1
  if [ $? -eq 0 ]
  then
    echo "ping"
    exit
  else
    echo "pong"
    sleep 5
  fi
done

exit 0