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basics/cron.md
114
basics/cron.md
@ -2,9 +2,11 @@
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title: "cron"
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tags: [ "Documentation", "Basics" ]
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---
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# Cron
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# Cronie
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The crontab program might have various names, like `cronie` or `crond`.
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The `cronie` program is also known as `crond`.
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## Install
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```bash
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sudo apt search -n ^cron
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@ -17,29 +19,33 @@ sudo systemctl list-unit-files | grep cron
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sudo systemctl enable --now $NAME
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```
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Make a file for your crontab, like this:
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## Usage
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Show your current crontab:
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```bash
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echo '39 */3 * * * /usr/bin/updatedb' > "$USER".cron
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crontab -l
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```
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You can put this in a file and edit it:
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```bash
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crontab -l > $filename
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echo '39 3 */3 * * /bin/tar czf /tmp/etc_backup.tgz /etc/' >> $filename
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```
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Then apply that crontab:
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```bash
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crontab "$USER".cron
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rm "$USER".cron
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crontab $filename
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rm $filename
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```
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The `cron` program will check your syntax before adding the tab.
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Your crontab file sits somewhere in `/var/spool/`.
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Probably in `/var/spool/cron`.
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Check how your tab currently looks:
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```bash
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crontab -l
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```
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## Syntax
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`* * * * *`
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@ -50,43 +56,61 @@ These five points refer to:
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So '3pm every Sunday' would be:
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> 0 15 * * 7
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`0 15 * * 7`
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Here 'Sunday' is indicated by "7", and '3pm' is 'the 15th hour'.
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The minute is '0' (i.e. '0 minutes past three pm').
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Doing the same thing, but only in February, would be:
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> 0 15 * 2 7
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`0 15 * 2 7`
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### Full Paths
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### Variables
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`cronie` doesn't know where you live, so to put something in your `$HOME` directory, you have to tell it:
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Executing something requires the full path to where it is, so you cannot simply use `apt update -y`, because cron does not know where `apt` is.
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Instead, find out where it is:
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```bash
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type -P apt
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echo "HOME=$HOME" > $filename
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crontab -l >> $filename
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crontab $filename
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```
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`/usr/bin/apt`
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`cronie` doesn't know where anything lives, including programs.
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You can give it your usual `$PATH` variable like this:
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Then put that into the crontab:
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```bash
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sudo crontab -e
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echo $PATH > $filename
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crontab -l >> $filename
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crontab $filename
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```
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> 40 */3 * * * /usr/bin/apt update -y
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Now instead of doing this
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This will run `apt update -y` as root every 3 hours, at 40 minutes past the hour, e.g. 00:40, 03:40, 06:40.
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`40 */3 * * * /usr/bin/du -sh $HOME/* | sort -h > $HOME/sum.txt`
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## Directories
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You can simply do this:
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`40 */3 * * * du -sh $HOME/* | sort -h > $HOME/sum.txt`
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## Run as Root
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You can execute a script as root by putting it into a directory, instead of in the tab.
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Look at the available cron directories:
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```bash
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ls /etc/cron.\*
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ls -d /etc/cron.*
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```
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Make a script which runs daily:
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```bash
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f=apt_update.sh
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echo '#!/bin/bash' > $f
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echo 'apt update --yes' >> $f
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chmod +x $f
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sudo mv $f /etc/cron.daily/
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```
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### Testing with runparts
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@ -97,47 +121,9 @@ Run-parts runs all executable scripts in a directory.
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run-parts /etc/cron.hourly
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```
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## Tips
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### Variables
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Add your `$HOME` to crontab to use scripts.
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First add `HOME=/home/$USER`, then you can use syntax like this:
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0 * * * * $HOME/.scripts/myScript.sh
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*Remember to test the script by executing that line first*:
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```bash
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$HOME/.scripts/myScript.sh
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```
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You can also add your regular path to your crontab as a variable (see example below).
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If you're using vim as the editor, just run this at the top of your crontab:
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```bash
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:r!echo PATH=$PATH
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```
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# Troubleshooting
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### `date` Commands
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Cron doesn't understand the `%` sign, so if you want to use `date +%R`, then it should be escaped with a backslash: `date +\%R`.
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### File Location
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The crontab files are in `/var/spool/cron/`, so you can backup or restore them.
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# Example
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```
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HOME=/home/user
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PATH=/usr/condabin:/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl:/home/user/.local/bin:/home/user/.scripts/:/home/user/.local/bin:/home/user/.scripts/
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1 0 1 * * /usr/bin/mkdir -p $HOME/arc/$(date +\%Y/\%m)
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18 0 1 */3 * $HOME/.scripts/mail-clean.sh
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* * * * * ping -c 1 home || mail-pull.sh
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50 18 * * * /usr/bin/timeout 30m /usr/bin/syncthing
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```
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