Cron: Difference between revisions

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=~~Using~~ Cron=

=Cron=

==Deprecated==

It is recommended to use [[Systemd/Timers|systemd-timers]]. A few of many reasons:

* logs are logged to journalctl instead of relying on local mail

* different timers are independent of each other and do not share an environment

* better configurability like random offsets, run missed timers when machine was powered down and full systemd service option

==General==

Cron is a very useful tool to run stuff at predefined times. Users, if allowed, can setup their own cron job, while the system crontab can be easily setup from the <tt>configuration.nix</tt>

Cron is a very useful tool to run stuff at predefined times. Users, if allowed, can setup their own cron job, while the system crontab can be easily setup from the <code>configuration.nix</code>

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</syntaxHighlight>

The above example would run the command <tt>date >> /tmp/cron.log</tt> as <tt>root</tt> user every <tt>5 minutes</tt> (indicated by <tt>*/5*</tt>.

The above example would run the command <code>date >> /tmp/cron.log</code> as <code>root</code> user every <code>5 minutes</code> (indicated by <code>*/5*</code>. For more information regarding the cronjob entries, see the link below.

==Loading environment==

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"*/10 * * * * johndoe . /etc/profile; /run/~~current~~-~~system/sw~~/bin/~~r2e run~~"

"*/10 * * * * johndoe . /etc/profile; ${pkgs.rss2email}/bin/r2e run"

</syntaxHighlight>

The <code>. /etc/profile;</code> part first sources the profile file and hence loading the environment. After that, the actual command is being run in the proper environment. The above entry would run the rss2email program every <code>10 minutes</code> as user <code>johndoe</code>

==Send mail only when error==

In case you have set proper sendmail and defined a user where cron should send output to, you might want limit those emails only when cron encounters a problem. This can easily be achieved by storing the output of the command given into a variable and use the <code>||</code> control operator to echo this output only when there is a non-zero exit status of the command.

"0 * * * * johndoe out=$( ${pkgs.pass}/bin/pass git pull 2>&1 ) || echo $out"

</syntaxHighlight>

~~The <tt>. /etc~~/~~profile;<~~/~~tt> part first sources the profile file and hence loading the environment~~. ~~After that, the actual command is being run in the proper environment~~. ~~The above entry would run the rss2email program every 10 minutes as user <tt>johndoe<~~/~~tt>~~

=See also=

* [https://linux.die.net/man/5/crontab crontab(5): tables for driving cron]

[[Category:Configuration]]

@@ Line 1: / Line 1: @@
-=Using Cron=
+=Cron=
+==Deprecated==
+It is recommended to use [[Systemd/Timers|systemd-timers]]. A few of many reasons:
+* logs are logged to journalctl instead of relying on local mail
+* different timers are independent of each other and do not share an environment
+* better configurability like random offsets, run missed timers when machine was powered down and full systemd service option
 ==General==
-Cron is a very useful tool to run stuff at predefined times. Users, if allowed, can setup their own cron job, while the system crontab can be easily setup from the <tt>configuration.nix</tt>
+Cron is a very useful tool to run stuff at predefined times. Users, if allowed, can setup their own cron job, while the system crontab can be easily setup from the <code>configuration.nix</code>
 <syntaxHighlight lang="nix">
@@ Line 14: / Line 21: @@
 </syntaxHighlight>
-The above example would run the command <tt>date >> /tmp/cron.log</tt> as <tt>root</tt> user every <tt>5 minutes</tt> (indicated by <tt>*/5*</tt>.
+The above example would run the command <code>date >> /tmp/cron.log</code> as <code>root</code> user every <code>5 minutes</code> (indicated by <code>*/5*</code>. For more information regarding the cronjob entries, see the link below.
 ==Loading environment==
@@ Line 21: / Line 28: @@
 <syntaxHighlight lang="nix">
-       "*/10 * * * *   johndoe   . /etc/profile; /run/current-system/sw/bin/r2e run"
+       "*/10 * * * *   johndoe   . /etc/profile; ${pkgs.rss2email}/bin/r2e run"
+</syntaxHighlight>
+The <code>. /etc/profile;</code> part first sources the profile file and hence loading the environment. After that, the actual command is being run in the proper environment. The above entry would run the rss2email program every <code>10 minutes</code> as user <code>johndoe</code>
+==Send mail only when error==
+In case you have set proper sendmail and defined a user where cron should send output to, you might want limit those emails only when cron encounters a problem. This can easily be achieved by storing the output of the command given into a variable and use the <code>||</code> control operator to echo this output only when there is a non-zero exit status of the command.
+<syntaxHighlight lang="nix">
+      "0 * * * *      johndoe   out=$( ${pkgs.pass}/bin/pass git pull 2>&1 ) || echo $out"
 </syntaxHighlight>
-The <tt>. /etc/profile;</tt> part first sources the profile file and hence loading the environment. After that, the actual command is being run in the proper environment. The above entry would run the rss2email program every 10 minutes as user <tt>johndoe</tt>
+=See also=
+* [https://linux.die.net/man/5/crontab crontab(5): tables for driving cron]
 [[Category:Configuration]]