How do you write a cron job which immediately run, then run on every hour divisible by 4? Say I started the script at 13:25, the job fires up right away, then the next run would be at 16:00, 20:00, 00:00 and so on.
For the first immediate run, just execute the command manually. Then set your cron up like this to have it execute continuously every 4th hour
0 */4 * * * yourCommand
This will run yourCommand every 4 hours (00:00, 04:00, 08:00......)
Related
I would like to run the cron job every 20 minutes between 9 AM and 11 PM and once an hour after 11 PM until 9 AM.
cron job settings
I created 2 cron jobs for the same script to achieve my goal. Did I do it correctly?
Thank you.
Not really. There are two issues:
you run the script also on 23:20 and 23:40
you run the script twice from 09:00 till 23:00 every hour.
The way to do it is:
*/20 9-22 * * * command
0 0-8,23 * * * command
You can validate this using crontab guru
I have a script that I would like to run 60 seconds after initial system reboot and then every 10 minutes after that. I currently need two cron job listings to achieve this:
*/10 * * * * php myscript.php
#reboot /bin/sleep 60; php myscript.php
The first listing will run my cron job immediately after system boot and so I need to have the second listing to account for the on start wait time.
Is there anyway to combine the above two cron listings into one?
I'd like a cron job to run a command at:
8am
10am
5pm
7pm
9pm
11pm
I've tried this, but when I check my logs, I see that the command is run too many times.
* 8,10,17,19,21,23 * * * COMMAND >> mylog.txt
Your command means "run on every minute of the given hours". If you want to run it just once, you need to set the minute field, e.g.:
0 8,10,17,19,21,23 * * * COMMAND >> mylog.txt
This way the command only runs at the start (minute 0) of each of the given hours
I want to set up a cron job which will execute a command every hour. However, I want that this command should be started at 10 A.M and should run every hour till 4 P.M. This job is to run daily between these times. The command is nothing but a call to a Perl script. Following crontab entry runs fine and invokes the script every hour
* */1 * * * cd path_to_file; perl file.pl > path_to_logs/log.txt
Is there a way to limit the timings of this cron job so that it runs only between 10 A.M and 4 P.M ?
man 5 crontab is your friend. (Your example does not do what you claim it does; /1 is the default skip and therefore redundant, and that spec therefore runs once per minute due to the leading * instead of 0.)
0 10-15 * * * your command here
(I used 15, because it occurs to me that "between 10 and 4" is an exclusive range so you don't want to run at 16:00.)
If you want the script to be run every hour you can do something like this:
[code]
00 10,11,12,13,14,15,16 * * * cd path_to_file; perl file.pl > path_to_logs/log.txt
[/code]
This means when the minutes hit 00 and the hour hits any of 10 11 12 13 14 15 16 the script will be run
In your Perl script (or in a wrapper for the Perl script), you can use localtime to check the hour and exit if it isn't between 10am and 4pm:
use strict;
use warnings;
my #lt=localtime;
my $hour=$lt[2];
unless($hour>=10 and $hour<=16)
{
print "Not between 10am and 4pm. Exiting.\n";
exit;
}
#put the rest of your code here.
I want to set a cron run after an other cron. For example: Cron A finishs at 01:00 PM, cron B will start at 01:01 PM. The problem is I don't know when cron A finishs.
I checked the crontab syntax. It doesn't provide any param for that purpose.
My actual situation is:
# This cron must run first.
? ? * * * /usr/local/bin/php -f /path/select_and_print_to_log_file.php
# two these crons runs at the same time.
0 13 * * * /usr/local/bin/php -f /path/update_user.php
0 13 * * * /usr/local/bin/php -f /path/update_image.php
# This cron runs right after two above cron completes.
? ? * * * /usr/local/bin/php -f /path/select_and_print_to_log_file.php
You can use the batch command inside the first cron to have the second thing being scheduled to run.
Your first job could produce a timestamp when finished.
Then you estimate - for example - that job A needs about 60 to 90 minutes. After 60 minutes, you start job B. Job b looks for the timestamp. If it is present, job B starts, else it waits for a minute and looks again.
After finishing, job B deletes the timestamp, or renames it, maybe from 'todo' to 'done'. You could insert the current date inside the file, to check, whether your estimation is still acceptable, or should be adjusted.
What I do in such cases (commonly a backup scenario where I don't want to thrash the disk by having concurrent backups) is to write a script that cron calls, and in the script have the actual tasks run serially.
Something like:
#!/bin/bash
/usr/local/bin/php -f /path/update_user.php
/usr/local/bin/someOtherTaskToRunSecond
YMMV.