How to run scripts every 5 seconds?

I have a script that needs to be run every five seconds. I know that cron can do tasks by the minute, but is there a way to run something every second?

5

8 Answers

Cron only allows for a minimum of one minute. What you could do is write a shell script with an infinite loop that runs your task, and then sleeps for 5 seconds. That way your task would be run more or less every 5 seconds, depending on how long the task itself takes.

#!/bin/bash
while true; do # Do something sleep 5;
done

You can create a my-task.sh file with the contents above and run it with sh my-task.sh. Optionally you can configure it with supervisor as a service so that it would start when the system boots, etc.

It really does sound like you're doing something that you probably shouldn't be doing though. This feels wrong.

2

You could have a cron job kick-off a script every minute that starts 12 backgrounded processes thusly:

* * * * * ~/dostuff.sh

dostuff.sh:

(sleep 5 && /path/to/task) &
(sleep 10 && /path/to/task) &
(sleep 15 && /path/to/task) &
(sleep 20 && /path/to/task) &
(sleep 25 && /path/to/task) &
(sleep 30 && /path/to/task) &
(sleep 35 && /path/to/task) &
(sleep 40 && /path/to/task) &
(sleep 45 && /path/to/task) &
(sleep 50 && /path/to/task) &
(sleep 55 && /path/to/task) &
(sleep 60 && /path/to/task) &

---

My question, though, is What on EARTH could you be doing that needs to run every 5 seconds?

7

Just use a loop:

while true ; do ./your-script & sleep 5; done

This will start your-script as a background job, sleep for 5 seconds, then loop again. You can use Ctrl-C to abort it, or use any other condition instead of true, e.g. ! test -f /tmp/stop-my-script to only loop while the file /tmp/stop-my-script does not exist.

3

You could use the GNU package mcron, a "Vixie cron" alternative.

"Can easily allow for finer time-points to be specified, i.e. seconds. In principle this could be extended to microseconds, but this is not implemented."

5

You could use a SystemD timer unit, which will trigger a service - that you'd set up to do what you want - every 5 seconds.

Suppose your service unit is called mystuff.service and is installed in /etc/systemd/system (check out SystemD user services if you want to replace a user's crontab), then you can write a timer unit to run the service at boot time and then every 5 seconds, like this:

/etc/systemd/system/mystuff.timer

[Unit]
Description=my stuff's schedule
[Timer]
OnBootSec=5
OnUnitActiveSec=5
[Install]
WantedBy=timers.target

Then reload the systemd configuration, enable the timer unit and start it.

5

Minimum configuration in cron is minutes, you can't set it for 5 seconds. You could use Quartz which does allow seconds.

3

Use cacti to monitor router and switch,but Cron only allows for a minimum of one minute,so if one port/device down,there is no warning until two minutes past.

1

I've done this sort of thing very successfully (and the end result rans weeks at a time, till the machine is rebooted). As for what I was doing right now, updating information and putting it into cache - updating every 10 seconds.

#!/bin/sh
SLEEP=5
# do stuff
sleep $SLEEP
# do stuff
sleep $SLEEP
# do stuff
sleep $SLEEP
# do stuff
sleep $SLEEP
# echo and restart...
exec $0

The 'exec $0' restarts the script, but replacing the running script. It can be initially started with a crontab '@reboot' line.

1