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diff --git a/cron.html b/cron.html deleted file mode 100644 index d3c2c1d..0000000 --- a/cron.html +++ /dev/null @@ -1,174 +0,0 @@ -<!DOCTYPE html> -<html lang=en> - <head> - <title>Cronjobs – LandChad.net</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>Basic Cronjobs</h2> - - <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 user's crontab - </p> - - <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 Mondays. - </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> - The five elements before the command tell when the command is supposed to be run automatically. - <p> - So for our Monday at 3:30 AM job we would do the following: - <p> - <pre><code> .---------------- minute (0 - 59) - | .------------- hour (0 - 23) - | | .---------- day of month (1 - 31) - | | | .------- month (1 - 12) - | | | | .---- day of week (0 - 6) - | | | | | - * * * * * -30 3 * * 1 apt -y update && apt -y upgrade</code></pre> - - <h3>Some notes</h3> - <ul> - <li>On the day of the week option, Sunday is 0 and counting up from there, Saturday will be 6.</li> - <li><code>*</code> designates "everything". Our command above has a <code>*</code> in the day of month and month columns. This means it will run regardless of the day of the month or month.</li> - <li>The hour option uses 24 hour time. 3 = 3AM, while use 15 for 3PM.</li> - </ul> - - <h3>More examples</h3> - <p> - Let's 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>0 23 * * * backup</code></pre> - - <h3>Consecutive times</h3> - - <p> - Suppose we want a command to run every weekday. - We know we can put <code>1</code> (Monday), but we can also use <code>1-5</code> - to signify from day 1 (Monday) to day 5 (Friday). - </p> - - <pre><code>0 6 * * 1-5 echo "Wakey, wakey, wagie!" >> /home/wagie/alarm</code></pre> - - <p>The above <code>echo</code> command runs every Monday through Friday at 6:00AM.</p> - - <h3>Non-consecutive times</h3> - - <p> - We can also randomly specify non-consecutive arguments with a comma. - Suppose you have a script you want to run at the midday of the 1st, 15th, and 20th day of every month. - You can specify that by putting <code>1,15,20</code> for the day of the month argument: - </p> - - <pre><code>0 12 1,15,20 * * /usr/bin/pay_bills_script</code></pre> - - <h3>"Every X minutes/days/months"</h3> - - <p>We can also easily run a command every several minutes or months, without specifying the specific times:</p> - - <pre><code>*/15 * * * * updatedb</code></pre> - - <p>This cronjob will run the <code>updatedb</code> command every 15 minutes.</p> - - <h3>Beware of this Rookie Mistake Though...</h3> - - <p> - Suppose you want to run a script once every other month. - You might be <em>tempted</em> write this: - </p> - - <pre><code>* * * */2 *</code></pre> - - <p> - That might <em>feel right</em>, but this script <em>will be running once every minute during that every other month</em>. - You should specify the first two arguments, because with <code>*</code> it will be running every minute and hour! - </p> - - <pre><code>0 0 1 */2 *</code></pre> - - <p>This makes the command run <em>only</em> at 0:00 (12:00AM) on the first day of every two months, which is what we really want.</p> - - <p> - Consult the website <a href="https://crontab.guru">crontab.guru</a> for an intuitive and interactive tester of cronjobs. - </p> - - <h2>User vs. Root Cronjobs</h2> - - <p> - It is important to note that user accounts all have different cronjobs. - If you have a user account <code>chad</code> and edit his crontab with <code>crontab -e</code>, - the commands you add will be run as the <code>chad</code> user, not <code>root</code> or anyone else. - </p> - - <p> - Bear in mind that if you need root access to run a particular command, - you will usually want to add it as root. - </p> - - <h2>System-wide cron directories</h2> - - <p> - <code>crontab -e</code> is the typical interface for adding cronjobs, but it's important to at least know that system-wide jobs are often stored in the file directory. - Some programs which need cronjobs will automatically install them in the following way. - </p> - - <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: - </p> - <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. - </p> - - <h2>Contribution</h2> - - <ul> - <li>Mark McNally -- <a href="https://mark.mcnally.je">website</a>, <a href="https://www.youtube.com/channel/UCMiInY8BhSUtCarO6uu6i_g">Youtube</a></li> - <li>Edits and examples by Luke</li> - </ul> - - - - </main> - <footer><a href="https://landchad.net">LandChad.net</a></br>Because Everyone should be an Internet LandChad.</br><a href="index.html"><li><img src="pix/chad.gif" alt="chad"></li></a><a href="rss.xml"><li><img src="pix/rss.svg" alt="RSS"></li></a><a href="donate-bitcoin.html"><li><img src="pix/btc.svg" alt="BTC"></li></a><a href="donate-monero.html"><li><img src="pix/xmr.svg" alt="XMR"></li></a><a href="https://github.com/lukesmithxyz/landchad"><li><img src="pix/git.svg" alt="Github"></li></a></footer> -</body> -</html> |