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Cron daemon
menuconfig Applications->Cron daemon
Pinning no
Ecmd yes
Depends on ECMD, Clock

Cron daemon manage cron jobs. This rules define repeated or unique events that call certain commands.

Cron jobs are implemented in two flavors: a static list that is defined at compile time and not changeable at runtime, and a dynamic approach, which loads the joblist to the RAM at statup. Jobs can be added and removed at runtime.


Both approaches have in common that you need to define a function that is called from the con daemon at a appropriate time. The function signature, however, varies dependend on the choosen implementation.


The module needs the current time to function properly. So you have to select at least one time source. To enable crontabs in ethersex select

 │ │                Load a Default Configuration  --->
 │ │                ...
 │ │                Applications  --->
 │ │                  ...
 │ │                  [*] Cron daemon --->
 │ │                  [ ] Cron daemon (static jobs)

Static Cron Daemon

The function to be called from the daemon has to have the signature void func(void) and has to be defined in cron_static/cron_static.c.

Furthermore you have to insert a rule of the type cron_static_event_t to the structure array events. The meaning of the values are minute, hour, day, month, days of week, callback function and a flag if UTC or local time is used (in that order).

A value of -1 is a wildcard. The entries are checked every minute, so an entry with all wildcards will be executed every minute.

Values less than -1 mean "every x-th minute/hour/etc.". So in case of -4 in the minute field the job will be executed every 4th minute.

Dynamic Cron Daemon

View jobs via ecmd

Simply execute the ecmd command cron list in your browser for instance. All jobs will be displayed, two lines for each job. The first line contains the job attributes (position, repeats, ecmd/callback job, use UTC, etc.), the second line shows the timing data (MIN HOUR DAY MONTH DAYOFWEEK) and the ecmd command/address of the callback function to be executed.

Remove jobs via ecmd

cron rm N removes the Nth job (start counting at 0) from the cron list. Caution! cron rm without paramater removes ALL jobs without confirmation request!

Add jobs via ecmd


MIN HOUR DAY MONTH and DAYOFWEEK can be -1 (as wildcard).

ECMD: The ecmd command to be executed.

After creating the new job it's position in the list will be displayed.

Mark job as persistent via ecmd

cron persistent N 1 mark job N as persistent

cron persistent N 0 remove persistent flag

cron persistent N show current state

Write persistent jobs to VFS/EEPROM via ecmd

cron save all persistent jobs will be stored in VFS/EEPROM.

Mark job for UTC time via ecmd

cron utc N 1 mark job N for UTC time

cron utc N 0 remove UTC flag

cron utc N show current state

Mark job as anacron job via ecmd

This flag provides a kind of anacron functionality which is intended for jobs that set specific states. Take the circulation pump of a central heating as example. If the pump has to be switched on at 6.00 and switched off at 9.00 this could be realized by a simple cron job. But if the controller reboots at 7.00 (as the result of a blackout for instance) the pump will not be switched on till 6.00 of the following day. The same counts in case of a time skip by NTP updates.

To solve this problem all anacron jobs that falls in the skiped time range will be executed (in case of boot this means from 1.1.1970 till the current time), each job just one time and in correct order (latest execution time counts). To keep the runtime of the decision loop short, the starting point in the past is limited to <current time> - CRON_ANACRON_MAXAGE secs. Default is one day (86400 secs).

cron anacron N 1 mark job N as anacron job

cron anacron N 0 remove anacron flag

cron anacron N show current state

Define cronjob in source code: callback function

As you may have noticed this functionality is also be covered by the static cron daemon, wich even consumes less resources. But there are some advantages:

  • No need to add code to a foreign module (clarity of cron_static.c suffers with every additional module)
  • You can remove the cronjob at runtime
  • You can pass extra data to the callback funtion

The function to be called by the daemon has to have the signature void func(char* data) and should not be defined in cron/cron.c but in the particular module that uses the cron functionality.

  1. Include 'cron/cron.h' in your module
  2. Call the function cron_jobinsert_callback from your initialization function to insert cronjobs on startup of ethersex.
  3. The semantic of the function parameters is:
  • Minute, -1 as wildcard, -2 means every 2nd minute, etc.
  • Hour, -1 as wildcard, -2 means every 2nd hour, etc.
  • Day, -1 as wildcard, -2 means every 2nd day, etc.
  • Month, -1 as wildcard, -2 means every 2nd month, etc.
  • Day of week, 1 = Sunday, 2 = Monday, 4 = Tuesday, 8 = Wednesday, 16 = Thursday, 32 = Friday, 64 = Saturday or adding of multiple values
  • Number of repeats, INFINIT_RUNNING for never ending, 1=once, etc.
  • Position to add to the cron list (CRON_APPEND = add to end)
  • Callback function
  • Size of extra data
  • Pointer to extra data

Example taken from the test entry file:

void test(void* data) { /* do something */ }
// in init
cron_jobinsert_callback(-1, -2, -1, -1, -1, INFINIT_RUNNING, CRON_APPEND, test, 0, NULL);

Extra data is cool stuff. Stella PWM for instance uses it to store the chanel no and the target value. If the cronjob is executed, it's extra data is passed to the callback function and can be processed. Please keep in mind that the pointer to extra data has to be the result of a call to malloc, which allocates the memory on the heap. (Example: char* extra = malloc(2); for 2 bytes on the heap)

Don't care about freeing the allocated memory. The cron daemon will do this job.

Define cronjob in source code: ecmd command

The static cron daemon is limited to use callback functions. With the dynamic cron daemon you are even able to call ecmd commands (set output pins, control Stella PWM, reset ethersex, etc.)

Here an example of a function call to insert such a job:

cron_jobinsert_ecmd(-1, -2, -1, -1, 127, INFINIT_RUNNING, CRON_APPEND, "ECMD");