cronjob run every 5 seconds

sag2662 · 04-04-2023, 02:31 AM

Hi all,

I wanted to run script for every 5 seconds, It seems with cronjob we cannot execute it. so i wrote a script with while loop

Code:

#!/bin/bash

while true; do
  date >> /tmp/save_date
  sleep 5;
done

but my question here is how wanted to schedule the cron so that it executes the above script. please suggest. can i still schedule cron to run for 1 minute

Guttorm · 04-04-2023, 02:38 AM

Hi

You can put @reboot in crontab so the script starts at reboot. Sometimes it's too early - maybe network and other services are not up yet? If so, wait a little before it starts.

Code:

@reboot sleep 60 && scriptname

Another way is to use supervisor instead of cron. It's made for running scripts like this, and will restart it if it crashes.

sag2662 · 04-04-2023, 02:45 AM

Quote:

Originally Posted by Guttorm

Hi

You can put @reboot in crontab so the script starts at reboot. Sometimes it's too early - maybe network and other services are not up yet? If so, wait a little before it starts.

Code:

@reboot sleep 60 && scriptname

Another way is to use supervisor instead of cron. It's made for running scripts like this, and will restart it if it crashes.

Now the server cannot be rebooted, its up now. so how to handle

Guttorm · 04-04-2023, 02:47 AM

If you just want to start it, and make it continue when you log out, you can start it like this:

Code:

nohup scriptname &

It will run unitil crash or reboot.

sag2662 · 04-04-2023, 02:52 AM

Quote:

Originally Posted by Guttorm

If you just want to start it, and make it continue when you log out, you can start it like this:

Code:

nohup scriptname &

It will run unitil crash or reboot.

have error
nohup:ignoring input and appending output to 'nohup.out'

pan64 · 04-04-2023, 03:02 AM

cronjob can start a script in every minute, so you only need to write a script (loop) to execute something 12 times and put that script into crontab.

sag2662 · 04-04-2023, 03:10 AM

Quote:

Originally Posted by pan64

cronjob can start a script in every minute, so you only need to write a script (loop) to execute something 12 times and put that script into crontab.

so which means i can run use for loop ? and schedule cron to every 1 minute ?

Code:

for i in {1..12}; do date; done
or 

for (let i = 0; i < 12; i++)

michaelk · 04-04-2023, 06:00 AM

Either method works. linux isn't a real time operating system so there is no guarantee what second your script actually starts running. This means the time difference of the last "period" of the prior minute might not be exactly 5 seconds to the start of the 1st "period" of the next minute.

MadeInGermany · 04-04-2023, 07:06 AM

Code:

for ((i=0; i<12; i++))

0 .. 55 seconds, then cron starts it again.

chrism01 · 04-04-2023, 08:11 PM

The nohup ... & cmd is fine, you just need to tell it where to o/p like eg

Code:

nohup /path/to/script >/path/to/logdir/script.log 2>&1 &

For something you want to run that frequently, this (daemon) approach makes more sense for 2 reasons :

1. cron is only configurable to the minute
2. Each cron job invocation involves the creation of a whole new process env, which takes some time.

You also need to worry about whether runs will overlap each other, which may cause issues, depending on exactly what the process is doing.
Running in daemon mode means only one process will be running at a time, assuming your code in post #1 .

lvm_ · 04-05-2023, 01:04 AM

[ana]cron cannot do seconds but systemd timer can https://www.freedesktop.org/software...emd.timer.html

sag2662 · 04-05-2023, 02:02 AM

Thanks all

sag2662 · 04-11-2023, 02:57 AM

Quote:

Originally Posted by sag2662

Thanks all

Hi all the logs are getting created according to date but the output writing to log file is wrong. I wanted the logs to be written according to each date and end at the same date if next day then the logs should be written accordingly. But my output is weird. may i know whats the wrong with code or cron

Code:

-rw-r--r-- 1 root root 1736496 Apr  9 14:07 2023-04-08-spx.log
-rw-r--r-- 1 root root 1986480 Apr 10 19:37 2023-04-09-spx.log
-rw-r--r-- 1 root root 1452102 Apr 11 07:53 2023-04-10-spx.log
-rw-r--r-- 1 root root  359724 Apr 11 07:53 2023-04-11-spx.log

Code:

for ((i=0; i<12; i++))
do
command >> /tmp/log/$(date +'%Y-%m-%d')-spx.log
done

cronjob

Code:

* * * * * /home/script.sh

michaelk · 04-11-2023, 05:36 AM

Without knowing what command actually does it is not possible to know whats wrong. How long does it take to actually run the it once? If it takes more then a minute to run the command 12 times you will have multiple processes which continue into the next day. You are also missing the sleep 5 command in your loop.

pan64 · 04-11-2023, 05:38 AM

does this machine run continuously?