well, dyndns.org and an update client are too cumbersome so i wrote a script to check to see if my dynamic ip from my isp has changed. if it has changed, i get an text message with the new ip so i can update my dns and continue to ssh to my box at home even if my ip changes. i have the script executed through cron every 5 minutes. is there a better or alternate way to write the script where it is executed every 5 minutes without using cron? i was thinking of using wait, pause, sleep, etc and chkconfig and something that'll verify the process doesn't die. or should i just go ahead and use cron to exectute the script? here's the script.

DATE=`date +%m-%d-%Y`
TIME=`date +%r`
HOST='somedomain.net'
LFILE='/var/log/dynip/dynip.log'
RCPT='5555555555@cellprovider.net'
REPLY=`/bin/ping -c 1 $HOST | grep 'packets transmitted' | awk '{print $1}'`
DYNIP=`lynx -dump http://whatismyip.org`
DNSIP=`dig +short somedomain.net`

if [ "$REPLY" == "1" ]; then #Continue if the internet is up
if [ $DYNIP != $DNSIP ]; then #Compare Public IP to DNS IP
echo "$DATE: Email sent at $TIME." >> $LFILE
mail -s $DYNIP $RCPT < . &> /dev/null #Email new Public IP to Recipient
else
exit 0 #Exit if Public IP has not changed
fi
fi

Repetitive tasks are what cron is for - I always use it unless I have a specific reason not to (rare) so I recommend you just schedule it that way.

Was there a specific problem you were having with dyndns? I use it for my home set up with no issues. It has the advantage that I don't need to check my email for an IP address to connect to, I can always just SSH to the domain name.

gotcha. well with the dyndns service, i have to use their domain, i.e. kicks-ass.org and cannot use the one i've already registered unless i pay them. also, i have to install a linux update client to update dyndns whenever my ip changes and i would still need to manually update my zone file with the new ip. i just thought i'd created a script to text me the new ip so i'd know immediately when the ip changed so i could update my zone file quicker. testing has come out fine and i added to the script so it will only run if my connection is up. that way if the internet is down, it won't get confused thinking my ip changed.

Ah - I see what you mean. I don't have the situation here where I need to update my DNS since I'm only authoritative for the stuff behind my firewall.

Just for reassurance: cron is suitable for such a task. Generally I would use cron for task which run with larger intervals than 2-3 minutes, which is true in your case. For shorter intervals sleep might be better.

I have some scripts running in 10 and 20 seconds intervals for which I use sleep. I never have seen any of my scripts dying for no reason, therefor I have not built in a check to see if the process is alive. Of course you have to take care that you don't create a situation in the script which let the script finalize after encountering an error.

jlinkels

i see. thanks. i was having a problem with the script erroring out with the first if statment when i simulated the internet being down. it was trying to compare "" with "1" and erroring out. so i added the quotes around $REPLY and which resolved the unary problem and if the internet is down, the if statement completes to the last fi and wala, it exits the nested if.