Welcome to TQ CMS knowledge base. Here you will find useful information for all sorts of things.

How to set-up a crontab file

In Linux, Cron is a daemon/service that executes shell commands periodically on a given schedule. Cron is driven by a crontab, a configuration file that holds details of what commands are to be run along with a timetable of when to run them.

Creating a crontab file

You can create a crontab file by entering the following terminal command:

crontab -e

Entering the above command will open a terminal editor with a new blank crontab file, or it will open an existing crontab if you already have one. You can now enter the commands to be executed, see syntax below, before saving the file and exiting the editor. As long as your entries were entered correctly your commands should now be executed at the times/dates you specified. You can see a list of active crontab entries by entering the following terminal command:

crontab -l

Crontab syntax

A crontab file has six fields for specifying minute, hour, day of month, month, day of week and the command to be run at that interval. See below:

*     *     *     *     *  command to be executed
-     -     -     -     -
|     |     |     |     |
|     |     |     |     +----- day of week (0 - 6) (Sunday=0)
|     |     |     +------- month (1 - 12)
|     |     +--------- day of month (1 - 31)
|     +----------- hour (0 - 23)
+------------- min (0 - 59)

Crontab examples

Writing a crontab file can be a somewhat confusing for first time users, therefore I have listed below some crontab examples:

* * * * *  #Runs every minute
30 * * * *  #Runs at 30 minutes past the hour
45 6 * * *  #Runs at 6:45 am every day
45 18 * * *  #Runs at 6:45 pm every day
00 1 * * 0  #Runs at 1:00 am every Sunday
00 1 * * 7  #Runs at 1:00 am every Sunday
00 1 * * Sun  #Runs at 1:00 am every Sunday
30 8 1 * *  #Runs at 8:30 am on the first day of every month
00 0-23/2 02 07 *  #Runs every other hour on the 2nd of July

As well as the above there are also special strings that can be used:

@reboot  #Runs at boot
@yearly  #Runs once a year [0 0 1 1 *]
@annually  #Runs once a year [0 0 1 1 *]
@monthly  #Runs once a month [0 0 1 * *]
@weekly  #Runs once a week [0 0 * * 0]
@daily  #Runs once a day [0 0 * * *]
@midnight  #Runs once a day [0 0 * * *]
@hourly  #Runs once an hour [0 * * * *]

Multiple commands

A double-ampersand “&&” can be used to run multiple commands consecutively. The following example would run command_01 and then command_02 once a day:

@daily  && 

Disabling email notifications

By default a cron job will send an email to the user account executing the cronjob. If this is not needed put the following command at the end of the cron job line:

>/dev/null 2>&1

Specifying a crontab file to use

As mentioned at the top of this post, you can create a new crontab file with the “crontab -e” command. However, you may already have a crontab file, if you do you can set it to be used with the following command:

crontab -u  

Therefore the following command…

crontab -u tux ~/crontab

…would set Tux’s crontab file to that of the file named “crontab” residing in Tux’s home directory.

Removing a crontab file

To remove your crontab file simply enter the following terminal command:

crontab -r

Further information

Refer to the man page for further information about crontab. Enter the terminal command:

man crontab


 

There is 56 guides in the database.

More news

Bootstrap
25 February, 2014

Bootstrap

I have implemented bootstrap into the project and changed all code in the administration to use this new framework and I really love the result that I see after a couple of hours of coding. To make things look so good has never been so easy as with
Guides
20 February, 2014

Guides

I have added some of my guides for different things when it comes to the different areas in the computer, I will continue to add guides and especially when it comes to things that I am using every now and then in my own work.
First phase completed
17 February, 2014

First phase completed

Then I had time to finish the dirty work with the page and now it only remains little touches here and there and I need to upload information about what I'm doing and my progress on the project as well.
Time for a change
16 February, 2014

Time for a change

Today I've decided to update my own personal website with the latest version of my project called TQ CMS and with a completely new design that is responsive. My goal with this project is to make it as easy as possible for the end user while

Spotlight

The next step

The next step

I have now resumed my programming after a couple of months of vacation which was very much needed. I got a call one day from a friend that needed a system which can handle peoples reports on various problems like kitchen problems, water problems etc and I decided to make a system for it. Little did I know that it would totally revolutionise my own project and that it would teach me much needed jquery skills to further enhance the CMS. I also