My First Cron Job(s)

Learning from this great “Automated Tasks” page at CentOS.org

Normally, I prefer stuff like this in a well-written tutorial (see below awesomeness from DigitalOcean) but the above is … wow.

Tangent Sidebar: You know what’s kind of irritating? How I use DigitalOcean documentation all the time — not just because it’s higher in the Google results but it is so much better than the documentation of my actual host. Far more subjects, ridiculously specific, much better written, and far more accurate.

Two cases in point:

The latter is especially useful today because I keep getting emails from Let’s Encrypt reminding me to renew my shizzle.

But, as it turns out, none of those told me exactly what I needed but this did:

How to run PHP scripts from cron jobs

That’s my host. I’m very proud of them. And if their customer support is ever consistently good or consistently “not bad,” I’ll totally apologize. Interestingly, that tute gave me the final piece I needed but if I hadn’t read the other tutes first I’d still have no idea what to do because it only gave the final step, not the first several. That’s my host.

The first three (the good) tutorials taught me how to write a line in the crontab using the columns:

  • minute
  • hour
  • day
  • month
  • dayofweek
  • command

“How to Use Cron …” even gave me the “shortcut” of using @weekly instead of 00**0.

But Newbie: Intro to Cron which I think — sincerely and seriously — is a beautifully designed page, gave me the best tip in telling me to look for the following folders in my /etc directory:

  • cron.daily
  • cron.hourly
  • cron.monthly
  • cron.weekly

Dude. Just drop a script in one of those and viola!

And … and … earlier, one of those tutorials stated, “Cron is a daemon …” and I wondered, “What is a daemon?” That Newbie tute said,

Cron is a daemon, which means that it only needs to be started once, and will lay dormant until it is required. A Web server is a daemon, it stays dormant until it gets asked for a web page. The cron daemon, or crond, stays dormant until a time specified in one of the config files, or crontabs.

I wish cogNiTioN wrote every tutorial on all of the sites and I wish all of the sites were designed like that one.

Okay, so I write a line in my crontab telling it to change directories to where I keep a certain php file, then use php to run that file. Like so …

00 16 * * * user-name cd /my/directory/path; php -q myfile.php

It’s almost 3:30pm now so in a little over half an hour, I’ll check to see if it worked. I’d love that. I’m rather sick of trying to remember to do this particular task.

I had it change directories first because from what I understand, the relative paths in the file would get all confused and fail if the little crontab tried to run the commands from /etc.

If you’re still reading and you care, it’s a script that will go grab popularity scores from Spotify for a bunch of artists I’m tracking.

Another nifty thing I think is interesting is … I did a magical “save as” on the php file I’ve been using for this task and realized, wow, the crontab doesn’t need all of the html, css, jquery, etc. because that’s for me to see so I know the script worked. Not only do I know it worked but the crontab couldn’t care less so I stripped it all out of a new, dedicated file. I also rewrote (or, rather, wrote a new script based on) the script I’ve been using because part of the original added rows to a table that the crontab wouldn’t look at even if it existed. Because the crontab doesn’t have eyes. And doesn’t care.

Advertisements

About jotascript

Aiming to please. Seeking to impress.
This entry was posted in CentOS, Linux, Server Admin, Site Admin, Spotify and tagged . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s