Difference between revisions of "Setting Up a Cron Job"

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== Setting up a Cron Job ==
== Setting Cron to run on Mac Os==
* Cron needs full disk access in order to run on mac
* Go to System Settings > Privacy & Security > Full Disk Access:
* Click on the (+) icon to add an item to the list.
* Press command+shift+G, type /usr/sbin/cron and press enter:
* Select the cron executable and click Open


<pre>
==Vim Editor Commands==
Using cron
shift + :
* :i // insert text
* esc key // get out of insert mode
* :wq Write file to disk and quit the editor


Use the personal crontab to setup your jobs
== Setting up a Cron Job ==
 
type
 
crontab -e  ** use the -e switch, do not edit the file directly
 
Everthing is the same as below except the 6th space in the personal crontab is the field to execute as oposed to the user to run the job
 
example
 
* * * * * /backup/script.sh
 
as opposed to
 
* * * * * root /backup/script.sh
 
 
crontab -l - shows scheduled jobs
 
crontab -r  remove the current crontab file
 
 
In the /etc directory you will probably find some sub directories called
 
'cron.hourly', 'cron.daily', 'cron.weekly' and 'cron.monthly'. If you place
 
a script into one of those directories it will be run either hourly, daily,
 
weekly or monthly, depending on the name of the directory.
 
 
If you want more flexibility than this, you can edit a crontab (the name
 
for cron's config files). The main config file is normally /etc/crontab.
 
On a default RedHat install, the crontab will look something like this:


crontab -e  # use the -e switch, do not edit the file directly
crontab -l # shows scheduled jobs
crontab -r  # remove the current crontab file
   
   
root@pingu # cat /etc/crontab
== Crontab sections ==
 
SHELL=/bin/bash
 
PATH=/sbin:/bin:/usr/sbin:/usr/bin
 
MAILTO=root
 
HOME=/
 
 
# run-parts


01 * * * * root run-parts /etc/cron.hourly
{| class="wikitable" style="margin:auto"
|+ Parts of cron tab
|-
! Minute !! Hour !! Day (month) !! Month !! Day (week)
|-
|*||*||* ||*||*
|-
|0-59||0-23||1-31 ||1-12 or jan, feb,mar,..||0-6 or sun, mon, tue


02 4 * * * root run-parts /etc/cron.daily
|}


22 4 * * 0 root run-parts /etc/cron.weekly
{| class="wikitable" style="margin:auto"
|Every Minute||* * * * *||Ever 5 Minute||*/5 * * * *||Ever 30 Minutes||*/30 * * * *
|-
|Every Hour||0 * * * *||Every Hour and 30 min||30 * * * *||Ever 2 hours||0 */2 * * *


42 4 1 * * root run-parts /etc/cron.monthly
|}


   
   
The first part is almost self explanatory; it sets the variables for cron.
* minute of the hour the command will run on, and is between '0' and '59'
* hour the command will run on, and is specified in the 24 hour clock, values must be between 0 and 23 (0 is midnight)
* Day of Month, that you want the command run on, e.g. to run a command on the 19th of each month, the dom would be 19.
* month a specified command will run on, it may be specified numerically (0-12), or as the name of the month (e.g. May)
* the Day of Week that you want a command to be run on, it can also be numeric (0-7) or as the name of the day (e.g. sun).
* user who runs the command.
* command that you want run. This field may contain multiple words or spaces.


SHELL is the 'shell' cron runs under. If unspecified, it will default to
* 12 10-16/2 * * /scripts/backup.sh


the entry in the /etc/passwd file.
<p class="subhead">When using the names of weekdays or months, it isn't case sensitive, but only the first three letters should be used, e.g. Mon, sun or Mar, jul.</p>
<p class="subhead">Comments are allowed in crontabs, but they must be preceded with a '#', and must be on a line by them self. </p>


----


PATH contains the directories which will be in the search path for cron
e.g if you've got a program 'foo' in the directory /usr/cog/bin, it might
be worth adding /usr/cog/bin to the path, as it will stop you having to use
the full path to 'foo' every time you want to call it.
MAILTO is who gets mailed the output of each command. If a command cron is
running has output (e.g. status reports, or errors), cron will email the output
to whoever is specified in this variable. If no one if specified, then the
output will be mailed to the owner of the process that produced the output.
HOME is the home directory that is used for cron. If unspecified, it will
default to the entry in the /etc/passwd file.
Now for the more complicated second part of a crontab file.
An entry in cron is made up of a series of fields, much like the /etc/passwd
file is, but in the crontab they are separated by a space. There are normally
seven fields in one entry. The fields are:
minute hour dom month dow user cmd
minuteThis controls what minute of the hour the command will run on,
and is between '0' and '59'
hourThis controls what hour the command will run on, and is specified in
        the 24 hour clock, values must be between 0 and 23 (0 is midnight)
domThis is the Day of Month, that you want the command run on, e.g. to
run a command on the 19th of each month, the dom would be 19.
monthThis is the month a specified command will run on, it may be specified
numerically (0-12), or as the name of the month (e.g. May)
dowThis is the Day of Week that you want a command to be run on, it can
also be numeric (0-7) or as the name of the day (e.g. sun).
userThis is the user who runs the command.
cmdThis is the command that you want run. This field may contain
multiple words or spaces.
Fields
.---------------- minute (0 - 59)
|  .------------- hour (0 - 23)
|  |  .---------- day of month (1 - 31)
|  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
|  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7)  OR sun,mon,tue,wed,thu,fri,sat
|  |  |  |  |
*  *  *  *  * 
If you don't wish to specify a value for a field, just place a * in the
field.
e.g.
01 * * * * root echo "This command is run at one min past every hour"
17 8 * * * root echo "This command is run daily at 8:17 am"
17 20 * * * root echo "This command is run daily at 8:17 pm"
00 4 * * 0 root echo "This command is run at 4 am every Sunday"
* 4 * * Sun root echo "So is this"
42 4 1 * * root echo "This command is run 4:42 am every 1st of the month"
01 * 19 07 * root echo "This command is run hourly on the 19th of July"
Notes:
Under dow 0 and 7 are both Sunday.
If both the dom and dow are specified, the command will be executed when
either of the events happen.
e.g.
* 12 16 * Mon root cmd
Will run cmd at midday every Monday and every 16th, and will produce the
same result as both of these entries put together would:
* 12 16 * * root cmd
* 12 * * Mon root cmd
Vixie Cron also accepts lists in the fields. Lists can be in the form, 1,2,3
(meaning 1 and 2 and 3) or 1-3 (also meaning 1 and 2 and 3).
e.g.
59 11 * * 1,2,3,4,5 root backup.sh
Will run backup.sh at 11:59 Monday, Tuesday, Wednesday, Thursday and Friday,
as will:
59 11 * * 1-5 root backup.sh
Cron also supports 'step' values.
A value of */2 in the dom field would mean the command runs every two days
and likewise, */5 in the hours field would mean the command runs every
5 hours.
e.g.
* 12 10-16/2 * * root backup.sh
is the same as:
* 12 10,12,14,16 * * root backup.sh
*/15 9-17 * * * root connection.test
Will run connection.test every 15 mins between the hours or 9am and 5pm
Lists can also be combined with each other, or with steps:
* 12 1-15,17,20-25 * * root cmd
Will run cmd every midday between the 1st and the 15th as well as the 20th
and 25th (inclusive) and also on the 17th of every month.
* 12 10-16/2 * * root backup.sh
is the same as:
* 12 10,12,14,16 * * root backup.sh
When using the names of weekdays or months, it isn't case sensitive, but only
the first three letters should be used, e.g. Mon, sun or Mar, jul.
Comments are allowed in crontabs, but they must be preceded with a '#', and
must be on a line by them self.
</pre>
----
==[[#Setting up a Cron Job|Back To Top]]-[[Main_Page| Home]] - [[Ubuntu_Tips|Category]]==
==[[#Setting up a Cron Job|Back To Top]]-[[Main_Page| Home]] - [[Ubuntu_Tips|Category]]==

Latest revision as of 15:03, 17 June 2024

Setting Cron to run on Mac Os

  • Cron needs full disk access in order to run on mac
  • Go to System Settings > Privacy & Security > Full Disk Access:
  • Click on the (+) icon to add an item to the list.
  • Press command+shift+G, type /usr/sbin/cron and press enter:
  • Select the cron executable and click Open

Vim Editor Commands

shift + :
  • :i // insert text
  • esc key // get out of insert mode
  • :wq Write file to disk and quit the editor

Setting up a Cron Job

crontab -e  # use the -e switch, do not edit the file directly 
crontab -l # shows scheduled jobs
crontab -r  # remove the current crontab file

Crontab sections

Parts of cron tab
Minute Hour Day (month) Month Day (week)
* * * * *
0-59 0-23 1-31 1-12 or jan, feb,mar,.. 0-6 or sun, mon, tue
Every Minute * * * * * Ever 5 Minute */5 * * * * Ever 30 Minutes */30 * * * *
Every Hour 0 * * * * Every Hour and 30 min 30 * * * * Ever 2 hours 0 */2 * * *


  • minute of the hour the command will run on, and is between '0' and '59'
  • hour the command will run on, and is specified in the 24 hour clock, values must be between 0 and 23 (0 is midnight)
  • Day of Month, that you want the command run on, e.g. to run a command on the 19th of each month, the dom would be 19.
  • month a specified command will run on, it may be specified numerically (0-12), or as the name of the month (e.g. May)
  • the Day of Week that you want a command to be run on, it can also be numeric (0-7) or as the name of the day (e.g. sun).
  • user who runs the command.
  • command that you want run. This field may contain multiple words or spaces.
* 12 10-16/2 * * /scripts/backup.sh

When using the names of weekdays or months, it isn't case sensitive, but only the first three letters should be used, e.g. Mon, sun or Mar, jul.

Comments are allowed in crontabs, but they must be preceded with a '#', and must be on a line by them self.

Back To Top- Home - Category

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