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| author | Mark McNally <mark@mcnally.je> | 2021-06-30 18:01:49 +0100 |
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| committer | Mark McNally <mark@mcnally.je> | 2021-06-30 18:01:49 +0100 |
| commit | 9af5424f70e3f84cd08bdc771304d1c200c38c6c (patch) | |
| tree | d7292a4948e66e24eb2c6901237d8673db3f8988 /cron.html | |
| parent | e67d34aeadf3983a9ef908b2875ee950650ae760 (diff) | |
Added a articel on how to use cron. Added links to this article on
current articels that mention cron
Diffstat (limited to 'cron.html')
| -rw-r--r-- | cron.html | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/cron.html b/cron.html new file mode 100644 index 0000000..cc0ac0d --- /dev/null +++ b/cron.html @@ -0,0 +1,197 @@ +<!DOCTYPE html> +<html lang=en> + <head> + <title>Cronjobs</title> + <meta charset="utf-8"/> + <link rel="shortcut icon" href="favicon.ico" type="image/x-icon" /> + <link rel='stylesheet' type='text/css' href='style.css'> + <meta name="viewport" content="width=device-width, initial-scale=1"> + <link rel='alternate' type='application/rss+xml' title='Land Chad RSS' href='/rss.xml'> + </head> +<body> + <header><h1>Using Cronjobs to run scheduled tasks</h1></header> + <nav></nav> + <main> + <p> + Cron is a service that lets you run scheduled tasks. These tasks are called <strong> cronjobs. </strong> If you have already followed the initial course you will have already used cron when you set up certbot. + </p> + <h2> What tasks would I want to schedule? </h2> + <p> + You can schedule anything! Some examples of what you might have done already include: + <ul> + <li> <code> updatedb </code> to update your <code> locate </code> database </li> + <li> <code> certbot </code> to update renewing of your https certs </li> + </ul> + Some tasks that you might <em>want</em> to schedule may include: + <ul> + <li> Package updates - if you really just want to leave your server alone you can automated updating packages on your server </li> + <li> Backups - you may want to backup certain files every day and some every week, this is possible with cron </li> + </ul> + <p> + And many more, anything you can do can be turned into a cronjob. + </p> + + <h2> How do I schedule things? </h2> + + <p> + You can schedule tasks in the following ways: + <ol> + <li> Your users crontab </li> + <li> System wide cron directories </li> + </ol> + + + + <h3> Your user crontab </h3> + + <p> + This the preferred method for personal tasks and scripts, it's also the easiest to get started with. Run the command <code> crontab -e </code> to access your users crontab + </p> + <aside> + <p> + These crontabs are located at <code> /var/spool/cron/crontabs/ </code> If you wanted to you can edit these files instead of running <code> crontab -e </code> + </p> + </aside> + + <p> + Once you have figured out the command you want to run you need to figure out how often you want to run it and when. I am going to schedule my system updates once a week on at 3:30 AM on a Monday. + </p> + <p> + We now have to convert this time (Every Monday at 3:30 AM) into a cron time. Cron uses a simple but effective way of scheduling when to run things. + </p> + <p> + Crontab expressions look like this <code> * * * * * command-to-run </code> + <pre> + .---------------- minute (0 - 59) + | .------------- hour (0 - 23) + | | .---------- day of month (1 - 31) + | | | .------- month (1 - 12 + | | | | .---- day of week (0 - 6) + | | | | | + * * * * * + </pre> + <br> + <aside> + <p> Run the command <code> cat /etc/crontab </code> to see something similar to the above </p> + </aside> + + <p> + So for our Monday at 3:30AM job we would do the following: + <pre> + <code> 30 3 * * 1 apt-get -y update && apt-get -y dist-upgrade </code> + </pre> + <br> + <aside class=callout> + <p> + For day of the week field (the last field), the week starts on a Sunday, so Monday is <code> 1 </code> + </p> + </aside> + <br> + <aside> + <p> + The website <a href="crontab.guru">https://crontab.guru</a> is insanely helpful for figuring out specific cron timings + </p> + </aside> + <p> + Lets add another Job, our backup job (for the purposes of this our backup command is just called <code> backup </code> We want to run <code> backup </code> Every evening at 11PM, once we work out the timings for this we can add the to the same file as the above by running <code> crontab -e </code> This would mean our full crontab would look like this: + <pre> + <code> 30 3 * * 1 apt-get -y update && apt-get -y dist-upgrade </code> + <code> 0 23 * * * backup </code> + </pre> + + <h3> System wide cron directories </h3> + + <p> + Run the command <code> ls /etc/cron* </code> you should see a list of directories and there contents. The directories should be something like the below + <ul> + <li> /etc/cron.d <em> This is a crontab like the ones that you create with </em> <code> crontab -e </code> </li> + <li> /etc/cron.hourly </li> + <li> /etc/cron.daily </li> + <li> /etc/cron.weekly </li> + <li> /etc/cron.monthly </li> + </ul> + + <p> + + The directories cron.{hourly,daily,weekly,monthly} are where you can put <strong> scripts </strong> to run at those times. You don't put normal cron entries here. I prefer to use these directories for system wide jobs that don't relate to an individual user. For example If we wanted to put our backup job in <code> /etc/cron.daily </code> we would do the following: + <ol> + <li> Create and edit the file <code> /etc/cron.daily/backup/ </code>: + <ul> + <li> <code> vim /etc/cron.daily/backup </code> </li> + </ul> + <li> Add the backup command in there, we can also add some logging because it's a full script. The full thing will look like this: </li> + <p> + <pre> + #!/bin/sh + + # the logger command generates system logs + logger "starting backup daily job" + + # backup is hypothetical backup command + backup + + logger "finished backing up" + </pre> + </p> + </li> + <li> Save that file </li> + <li> Make that executable: </li> + <ul> + <li> <code> chmod +x /etc/cron.daily/backup </code> </li> + </ul> + </ol> + + <p> + It's that easy, no messing around with cron timers! A downside of this is that you can't choose when these run, most of the time they will run at ~6:30am every hour,day,week,month. + </p> + + <p> + That's it! There is not much more to know about cron. Hopefully you now know the appropriate cron method and have the ability to correctly schedule your tasks. + </p> + + <h2> Contribution </h2> + + <p> + This article was written by Mark McNally + </p> + + <ul> + <li> + I am a (internet) LandChad, my website is <a href="https://mark.mcnally.je">here</a> + </li> + <li> + Contact me about this article or just because <a href="mailto:mark@mcnally.je">here</a> + </li> + <li> + I have a <a href="https://www.youtube.com/channel/UCMiInY8BhSUtCarO6uu6i_g">youtube channel</a> where I may post some LandChad related content as well as other content that you will hopefully find interesting + <li> If you feel like donating: </li> + <ul> + <li> XMR: <code> 42ueuWXJGP48xtahfnujWDMFHJVdMGeFj85jxuwPBygkVw1GEBbHfTsDFBByTSLXpDV4bKcNr7EPCfvSJpyYLY5HPvqUmRB </code> </li> + <li> BTC: <code> 36mXUtU6Kh9pmYvGYPLY7peHU4TR7FBATT </code> </li> + </ul> + </ul> + <p> + Yes I know I need to set up OpenAlias... + </p> + + + + + + + + + + + </main> + <footer><a href="https://landchad.net">LandChad.net</a></br>Because Everyone should be an Internet LandChad.</br><li><a href="index.html"><img src="pix/chad.gif" alt="chad"></a></li><li><a href="rss.xml"><img src="pix/rss.svg" alt="RSS"></a></li><li><a href="pix/btc.png"><img src="pix/btc.svg" alt="BTC"></a></li><li><a href="pix/xmr.png"><img src="pix/xmr.svg" alt="XMR"></a></li><li><a href="https://github.com/lukesmithxyz/landchad"><img src="pix/git.svg" alt="Github"></a></footer> +</body> +</html> + + + + + + + + |