Cron Jobs
Crons are a very use full tool for any webmaster that has a lot of repetitive tasks that they need accomplished often. Crons can be used to automate just about anything from backing up a MySQL database to running a script or program on the server.
Crons basically use the server to accomplish tasks set forth by the user. For instance creating a cron job to handle a backup of a MySQL database can be setup to run at 2:00AM every Monday night. This will run the cron job once a week on Monday night at 2:00AM, which with a server that would be 14:00 hours. A server uses Military style time or a 24 hour clock instead of a 12 hour clock. The only differences in a 24 hour clock and a 12 hour clock is when it's 1:00 it would be 13:00 and so on.
UNIX or the server uses a Cron Daemon to handle the Cron Jobs which are set in the Crontab. I know this sounds confusing and you're wondering why there are so many Crons. Here is a simpler way to look at it. Windows Scheduler is the Crontab, so it's what is used to house or hold the Cron Jobs. The Windows Scheduler is also the Cron Daemon or just plain Cron; it's what runs the “Cron Jobs”.
There are two different modes that can be used to create a cron job.
Standard – The standard option will probable be the most useful for many new users. This option offers a range of preset options to choose from, which makes creating a cron job much faster and easier. The standard section uses a 12 hour clock style, so it's easier for the user to decide which times to choose.
Advanced (UNIX Style) – The advanced mode provides the UNIX style of adding a cron job. Users that have utilized cron jobs before, this will probable be the best one for them to use.
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Standard
The standard version of creating a cron job is probable the easiest for most users. Once in this section a user has a vast selection of options to choose from and select. Don't get over whelmed as they are very easy to understand once a moment is taken to read over all of them.
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The first option a user will notice is a place for an email address. This will be where the results of the cron job are sent. So use the email address that is relevant for this sort of information.
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The next section is for creating a cron job and has all the options needed to continue. The first section has a command line. This will be for the command that will be executed once the cron job activates. This can be any UNIX command, just remember to double check to make sure the command is correct.
In this case let's just use the “rm” command, which is used to delete files. We'll use this to clean out the temporary folder once a week.
So our command will look like this: rm /home/username/tmp/*
Notice the asterisk at the end of the folder location. This is a wildcard, which is used for all files in that folder. So the command “rm” will delete all the files located in the “tmp” folder once a week.
Once the command that will be executed has been established and entered we now need to find out when to run the cron job and how often to run it. The next options are just for that, this can be a bit confusing. Before we continue the best way to decide which options to choose is to find out when the cron job will actually be executed. Does it need to be executed once a day, twice a day, once a week; month, year and so on.. Once that has been decided we can determine which one to actually use.
Let's say it needs to be run once a week and a certain time of day. We'll say every Monday at 2:00AM. Now that we have our time frame set we can move on to choose the options below.
The first window is for setting the minute(s). We don't run it executed on a minute time, so we'll leave this one on zero.
Moving to the right we have hour(s). Now we've decided to run this cron job at 2:00AM. So we'll scroll down until we find 2:00AM. Below this we have the day(s) that it should run. In this case we want it ran every 7 days, so we'll choose 7 from the list.
Now for the home stretch, we have the month(s) and weekday(s) to select from. Sense we've decided to run this cron job once a month, we'll use the default option for the month(s) section and that's set for “Every Month”. Then we have weekday(s). Sense we want it ran on Monday, we'll select Monday from the list.
Now that we have all of our options and commands set we can now save the cron job. Simple click on “Save Crontab” and that's it. cPanel will then automatically create the cron job. Now when a user visits this section their new crontab will be present.
Advanced (UNIX Style)
The advanced style of adding Cron Jobs is very simple to read and understand as well. The only difference in the Standard version and the Advanced version is they layout of options. They both create and do the exact same thing.
