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Hi everyone. In our previous lecture, we

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have learned how we could schedule jobs

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or tasks to cronjob or addjob. And as we

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all know, that addjob is used for ad hoc

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task for one time use. And if you want

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to schedule jobs or specially repetitive

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job, you would use cronjob or crontab.

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Now, I want to cover some

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additional things about cronjob. By

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default, there are four different types

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of cronjob, that is set for you, that is

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like out of the box, that operating

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system the Linux operating system offers

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you, and those jobs are hourly job, daily

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jobs, weekly, and monthly. So anything,

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any task that you want to run hourly

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basis, or weekly, or monthly basis, you

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could do it two ways. One, you could do

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through the crontab minus e, and

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specify it over there. Or you could

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simply have the script added inside of

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the hourly, daily, weekly, monthly

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directories. Those directories are in /etc/cron.,

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hourly, dot daily, weekly

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or monthly. So you go into each of these

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directories, and you put in your script

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that will run every hour, or depending

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on how often do you want to run. And

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then you don't have to do anything about

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the crontab or anything. Then the cron

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dot daily or hourly depending on which

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one you pick will do the job. Now the

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timing of each are set in /etc/anacrontab

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When you do cat, you will see

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that anacrontab has the timing of

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when the daily, weekly, and monthly job

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will run, except the hourly one. The

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hourly one is defined, the what time it

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runs it is defined in /etc/cron.d/0hourly.

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That's the file that

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defines when the hourly runs. So let me

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get into my Linux machine, and we'll see

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how these jobs are set up in each

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directory. So I have my terminal open, I

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am logged in as a root. Now first thing

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I want you to do is go to cd /etc.

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In here, you will do ls minus l

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cron.*, and you run, when you

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enter you will see, it will grep, it will

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grep everything that starts with cron. So

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it's getting cron.deny, cron hourly,

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sorry, right here. The directory we have

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is cron.monthly, cron.hourly, but the

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right way to show you is I will do is ls

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minus l grep for cron. So this way, you

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will see the directories that I want to

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go work for. So you see right here the

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cron.daily, cron.hourly, monthly,

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and weekly. And this is the crontab,

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the actual tab where you go in and

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specify manually if you don't want to go

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into each daily, hourly, or weekly. So

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let's say if I go into cd cron.daily,

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and which directory I am in, I'm an /etc/cron.daily

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do ls minus l, you will

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see it has three different cron, or the

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tasks, or the scripts that run daily.

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And these are the actual scripts that

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were run daily. If you have a script

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that you want to run daily, once a day,

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then you, all you have to do is put your

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script, move it in this directory, which

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is cron.daily. If you want to run your

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script, hourly, then you go into one

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step back and you go into cron.hourly,

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and then you add that into this

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directory. Your script moved that script

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into this directory. Similarly, if you

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want it to add or run your script every

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month, then you could do cron.monthly.

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Go into this directory and do

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ls minus l. You'll see there is nothing

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right now in that directory. So all you

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have to do is move your script to this

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directory and by default, it will run

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every month. Now question is how or

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when does the monthly runs or when daily

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runs. So that is specified in when you

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do cat /etc/anacrontab and hit

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enter, and you will see the timings that

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are set right here. So 1 5 cron.daily,

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that's the daily time it will run.

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7 25, it's the weekly. See period in

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days, seven, seven day, delay in minutes,

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delays in delay in minute, and job-identifier,

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and command, this is a

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command it will run. So this is the

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timing that it is telling you. These are

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the timing that it will run your daily,

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weekly or monthly jobs. Now what about

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the hourly? The hourly is not specified

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here. To view the hourly scheduled time

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you have to do cat /etc/cron.d/0hourly,

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and you will see 0hourly is

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scheduled to run at 01, which is 12:01.

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At midnight, every night, it runs.

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Anything that is specified in the

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hourly, sorry, not midnight, that would

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be daily. It is scheduled to run every

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one minute after the hour. So it will

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run at 12:01, 1:01, 2:01, 3:01. So every, one past

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minute, every hour if you define your

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script into cron.hourly. So anyway,

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this is what I wanted to cover. If you

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wanted to go over the cron details and

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you don't want to specify cron dot,

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crontab minus e. You don't want to write

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down into this cron, then you don't have

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to, you could simply go into each

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individual directory and all you have to

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do is put your script in that directory

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and let these directories or let these

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jobs run as they are scheduled to run.

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