Creating shell script to mimic CRON job and execute an external file

Dickster2 · 10-19-2016, 06:19 PM

Quote:

Originally Posted by NotionCommotion

Hi,

vi /etc/init.d/15_second_cron

Code:

#!/bin/bash
# /etc/init.d/15_second_cron

### BEGIN INIT INFO
# Provides:          15_second_cron
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: PHP Loop
# Description:       Initiate a given PHP file which updates the database every 15 seconds
### END INIT INFO

while true
do
 /usr/bin/php /var/www/cron.php &
 sleep 15
done
exit 0

Code:

# Make script executable
chmod +x /etc/init.d/15_second_cron

/etc/init.d/15_second_cron start
chkconfig --levels 235 15_second_cron on

You originally stated: "Currently, I can have multiple instances all running at once and updating the database causing havoc." If that's true, then you really only want one updating job running at any given time. So, after your "sleep 15", you could test if your previous instance of /usr/bin/php is still running. Insert code such as the following after "sleep 15" and before "done". This may solve your problem.

Code:

  myjob=$(ps -ax | grep '[/]usr/bin/php')
  while [ -n "$myjob" ]; do
    sleep 5
    myjob=$(ps -ax | grep '[/]usr/bin/php')
  done

cesarbergara · 01-03-2017, 01:26 PM

Hi. Why you dont try to execute like this in crontab or init:

echo Hello
sleep 15
exec PATH/BASH_SCRIPT_NAME &

When your script finish wait 15 seconds, and then executed himself like a new job, and finishing current job.

Have a nice day.

Dickster2 · 01-03-2017, 04:08 PM

Read the Description in the script. I believe the user's problem is that s/he can't force the "currently executing job" to stop until it's really done. Databases are very tricky, and don't like being left half-updated.

cesarbergara · 01-26-2017, 03:06 PM

Hi. I said 'use sleep' to do your job, in the meantime up to find or solve script problem (excuse my english).
I don't know about database, but in my experience like user, when you access a data on the database, the system 'block' data when you access it and could need to change it. But if you only 'see' it, you can access, but can't change (copy, move o change files).

Have a nice day.

Dickster2 · 01-26-2017, 04:01 PM

cesarbergara, I've been dealing with database processing since 1972. I can tell you that database processing can take varying amounts of time, depending upon many factors, such as index updating. Having a fixed amount of time may lead to timing conflicts. Note that the bash script is always running, in a while-loop. It spawns a php job, which supposedly performed a database update, but another simultaneous job would cause a conflict. That's why I suggested adding another loop to test for completion of a prior job, before submitting another.