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Full Discussion: which one is better Run by Cron or Shell
Top Forums Shell Programming and Scripting which one is better Run by Cron or Shell Post 302273208 by Panos1962 on Saturday 3rd of January 2009 04:50:54 AM
Old 01-03-2009
There is another solution to this problem, but you have to add some code to your `myscript.sh'. Put some kind of lock while your program is runing, e.g. if your program is a shell script, you can add the following lines:

Code:
...
lock=/export/home/.myscript.lock
trap "rmdir ${lock}; exit 2" 1 2 3 15
# Now lock. If lock fails, then propably the program is runing.
mkdir ${lock} || exit 0
...
Here comes the script code
...
# Now unlock, so another instance of this program can run in the future.
rmdir ${lock}

I prefer this kind of coding in such cases, because it's better to protect this kind of programs to run overlaping processes. So, either you prefer cron, or sleeping nohup shell scripts, the process is vulnerable to run in simultaneus instances; if you use some kind of locking this is impossible.
Bye...
 

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LEARN ABOUT REDHAT

cron

CRON(8) 						      System Manager's Manual							   CRON(8)

NAME

       cron - daemon to execute scheduled commands (Vixie Cron)

SYNOPSIS

       cron

DESCRIPTION

       Cron should be started from /etc/rc or /etc/rc.local.  It will return immediately, so you don't need to start it with '&'.

       Cron searches /var/spool/cron for crontab files which are named after accounts in /etc/passwd; crontabs found are loaded into memory.  Cron
       also searches for /etc/crontab and the files in the /etc/cron.d/ directory, which are in a different format (see  crontab(5)).	Cron  then
       wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute.  When execut-
       ing commands, any output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab,	if
       such exists).

       Additionally,  cron checks each minute to see if its spool directory's modtime (or the modtime on /etc/crontab) has changed, and if it has,
       cron will then examine the modtime on all crontabs and reload those which have changed.	Thus cron need not be restarted whenever a crontab
       file is modified.  Note that the Crontab(1) command updates the modtime of the spool directory whenever it changes a crontab.

SEE ALSO

       crontab(1), crontab(5)

AUTHOR

       Paul Vixie <paul@vix.com>

4th Berkeley Distribution					 20 December 1993							   CRON(8)
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