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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..
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LEARN ABOUT SUSE

crontab

CRONTAB(1)						      General Commands Manual							CRONTAB(1)

NAME

       crontab - maintain crontab files for individual users (ISC Cron V4.1)

SYNOPSIS

       crontab [-u user] file
       crontab [-u user] [-l | -r | -e]

DESCRIPTION

       Crontab	is  the  program  used	to install, deinstall or list the tables used to drive the cron(8) daemon in ISC Cron.	Each user can have
       their own crontab, and though these are files in /var, they are not intended to be edited directly.

       If the cron.allow file exists, then you must be listed therein in order to be allowed to use this command.  If the cron.allow file does not
       exist  but  the	cron.deny  file does exist, then you must not be listed in the cron.deny file in order to use this command.  If neither of
       these files exists, only the super user will be allowed to use this command.

       If the -u option is given, it specifies the name of the user whose crontab is to be tweaked.  If this option is not given, crontab examines
       "your"  crontab,  i.e.,	the  crontab of the person executing the command.  Note that su(8) can confuse crontab and that if you are running
       inside of su(8) you should always use the -u option for safety's sake.

       The first form of this command is used to install a new crontab from some named file or standard input  if  the	pseudo-filename  ``-''	is
       given.

       The -l option causes the current crontab to be displayed on standard output.

       The -r option causes the current crontab to be removed.

       The -e option is used to edit the current crontab using the editor specified by the VISUAL or EDITOR environment variables.  After you exit
       from the editor, the modified crontab will be installed automatically.

SEE ALSO

       crontab(5), cron(8)

FILES

       /etc/cron.allow
       /etc/cron.deny

STANDARDS

       The crontab command conforms to IEEE Std1003.2-1992 (``POSIX'').  This new command syntax differs from previous versions of Vixie Cron,	as
       well as from the classic SVR3 syntax.

DIAGNOSTICS

       A fairly informative usage message appears if you run it with a bad command line.

AUTHOR

       Paul Vixie <vixie@isc.org>

4th Berkeley Distribution					 29 December 1993							CRONTAB(1)
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