Bash script is not working as cron job

Question

I have the following shell script

$cat capture.sh 
TIME=$(date +"%H-%M-%d-%m-%y") 
IP="203.208.198.29" 
PREFIX=$TIME$IP 
tshark  -f "udp" -i eth0 -w /root/captures/$PREFIX.cap& 
pid=$! 
sleep 2m 
kill $pid 

it runs fine when i execute it from shell.

but when i add it to the cron tab nothing happens.

my crontab entry : 1 */2 * 2 3,4,5 sh /root/capture.sh

tail /var/log/cron 

shows that the command has executed .

but nothing happens. i have set executable permission for "all" for capture.sh and write permission for "all" for /root/captures directory.

Thanks in advance

Answer 1

Your PATH variable probably isn't what you expect it to be inside cron.

Use full paths to each executable in your script.

Also, a better way of stopping your tshark would be using the built-in functionality:

   -a  <capture autostop condition>
       duration:value Stop writing to a capture file after value seconds
       have elapsed.

Also #2: add a shebang line (#!)

Answer 2

Cron will limit the path used by cron jobs. Try /usr/sbin/tshark instead of just tshark. You can check where tshark is via which tshark

Answer 3

Looking at your script I see you're attempting to capture traffic for two minutes and write a file. Did you really mean to have a cronjob that runs on every Wed/Thur/Friday in February, every other hour at 1 past the hour? I'm guessing you wanted it to run every 2 minutes...

From crontab(5) (which can be read with man 5 crontab)

   cron(8) examines cron entries once every minute.

   The time and date fields are:

          field          allowed values
          -----          --------------
          minute         0-59
          hour           0-23
          day of month   1-31
          month          1-12 (or names, see below)
          day of week    0-7 (0 or 7 is Sun, or use names)

   A field may be an asterisk (*), which always stands for "first-last".

Answer 4

It because tshark command was not found, you have two options to fix it.

1. define path in crontab

   PATH=$PATH:/path-to-tshark

   */2 * 2 3,4,5 sh /root/capture.sh

2. Use full path of tshark in your script.

   option #1 is the preferred way