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Full Discussion: Setting up crontab, still cant get it to work
Operating Systems Linux Setting up crontab, still cant get it to work Post 302514083 by Corona688 on Thursday 14th of April 2011 06:50:44 PM
Old 04-14-2011
The crontab entry looks okay, but there's lots wrong with your script.

Technically the name doesn't matter but shell scripts are usually .sh, not .txt. It being named .txt makes me wonder if you set it executable -- if it's not, cron can't run it. chmod +x crontab.sh

The first line in any shell script should be a #! line telling it what shell to use, like this:

Code:
#!/bin/sh

Also, cron's path is pretty minimal, way more than a users', so might not know where to find tcpdump. You can [icode]. /etc/profile[icode] to read in a more usual profile before you try and run things.

You're missing a space between -w and the filename. You should also tell it exactly where to put them since cron may run things where you expect it to.

Having a script still running for hours on end may prevent root's crontab from running anything else during that time. If you put the command into the background, the shell will return immediately and cron won't have to wait for it. (If it hangs, cron will end up creating one more hanging tcpdump process per day, heh.)

So:
Code:
#!/bin/sh

. /etc/profile

# just to prove this script's running at all
touch /root/cronranme

#captures packets in 15min segments and stops after 36 segments
#cronjob is setup for starting at 800 and then would go until 1700
#
# Some shells don't have "disown", you can just lop that off if yours doesn't.
nohup tcpdump -s2000 -w '/root/flowroute-%H%M.pcap' -G900 -W36 & disown

Last edited by Corona688; 04-14-2011 at 07:57 PM..
This User Gave Thanks to Corona688 For This Post:
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LEARN ABOUT X11R4

setsid

SETSID(1)                                                          User Commands                                                         SETSID(1)

NAME

       setsid - run a program in a new session

SYNOPSIS

       setsid [options] program [arguments]

DESCRIPTION

       setsid  runs  a  program in a new session. The command calls fork(2) if already a process group leader. Otherwise, it executes a program in
       the current process.

OPTIONS

       -c, --ctty
              Set the controlling terminal to the current one.

       -w, --wait
              Wait for the execution of the program to end, and return the exit value of this program as the return value of setsid.

       -V, --version
              Display version information and exit.

       -h, --help
              Display help text and exit.

SEE ALSO

       setsid(2)

AUTHOR

       Rick Sladkey <jrs@world.std.com>

AVAILABILITY

       The setsid command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux                                                           July 2014                                                           SETSID(1)
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