edit crontab

basics/cron.md

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