How to Set a Crontab to Execute Commands on a Seconds Time Interval on GNU / Linux and Freebsd

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Walking in Light with Christ - Faith, Computing, Diary Articles & tips and tricks on GNU/Linux, FreeBSD, Windows, mobile phone articles, religious related texts http://www.pc-freak.net/blog How to set a crontab to execute commands on a seconds time interval on GNU / Linux and FreeBSD

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Have you ever been in need to execute some commands scheduled via a crontab, every let's say 5 seconds?, naturally this is not possible with crontab, however adding a small shell script to loop and execute a command or commands every 5 seconds and setting it up to execute once in a minute through crontab makes this possible. Here is an example shell script that does execute commands every 5 seconds:

#!/bin/bash command1_to_exec='/bin/ls'; command2_to_exec='/bin/pwd'; for i in $(echo 1 2 3 4 5 6 7 8 9 10 11); do sleep 5; $command1_to_exec; $command2_to_exec; done

This script will issue a sleep every 5 seconds and execute the two commands defined as $command1_to_exec and $command2_to_exec

Copy paste the script to a file or fetch exec_every_5_secs_cmds.sh from here

The script can easily be modified to execute on any seconds interval delay, the record to put on cron to use with this script should look something like:

# echo '* * * * * /path/to/exec_every_5_secs_cmds.sh' | crontab -

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Where of course /path/to/exec_every_5_secs_cmds.sh needs to be modified to a proper script name and path location.

Another way to do the on a number of seconds program / command schedule without using cron at all is setting up an endless loop to run/refresh via /etc/inittab with a number of predefined commands inside. An example endless loop script to run via inittab would look something like:

while [ 1 ]; do /bin/ls sleep 5; done

To run the above sample never ending script using inittab, one needs to add to the end of inittab, some line like:

mine:234:respawn:/path/to/script_name.sh

A quick way to add the line from consone would be with echo:

echo 'mine:234:respawn:/path/to/script' >> /etc/inittab

Of course the proper paths, should be put in:

Then to load up the newly added inittab line, inittab needs to be reloaded with cmd:

# init q

I've also red, some other methods suggested to run programs on a periodic seconds basis using just cron, what I found in stackoverflow.com's as a thread proposed as a solution is:

* * * * * /foo/bar/your_script * * * * * sleep 15; /foo/bar/your_script * * * * * sleep 30; /foo/bar/your_script * * * * * sleep 45; /foo/bar/your_script

One guy, even suggested a shorted way with cron:

0/15 * * * * * /path/to/my/script

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