My query is about what the following command means in my linux system, I know it is a bash of CONTRAB but I can not understand why it uses five asterisks:
* * * * * curl http://mi-ws/obtenerMensaje
My query is about what the following command means in my linux system, I know it is a bash of CONTRAB but I can not understand why it uses five asterisks:
* * * * * curl http://mi-ws/obtenerMensaje
The tasks cron follow a certain syntax.
* * * * * /ejecutar_comando
De izquierda a derecha, los asteriscos representan:
1. Minutos: de 0 a 59
2. Horas: de 0 a 23
3. Día del mes: de 1 a 31
4. Mes: de 1 a 12
5. Día de la semana: de 0 a 6, siendo 0 el domingo
In the example * * * * * means:
1. Cada minuto
2. Cada hora
3. Cada día del mes
4. Cada mes
5. Cada día de la semana
Another example:
30 2 * * 1 /ejecutar_comando
1. En el minuto 30
2. De las 2 de la noche
3. De cada día del mes
4. De cada mes
5. Sólo si es viernes
man 5 crontab establishes that the value of the asterisk (*) is taken as the values from the first to the last accepted value of each "first-last" field. A "*" in the field of minutes, would be equivalent to "0-59", analogous to the other fields.
The values accepted by field are:
field allowed values
----- --------------
minute 0-59
hour 0-23
day of month 1-31
month 1-12 (or names, see below)
day of week 0-7 (0 or 7 is Sun, or use names)
Where, on the day of the week, 1 is Monday, 5 is Friday, 0 and 7 is Sunday.
I put it this way because there will be notations of the form:
*/2 */6 * * * etc
That will be equivalent to
0-59/2 0-23/6 1-31 1-12 0-6 etc
Regarding your question about the user who executes the task. Each user has their own crontab. If you make a sudo crontab -e , you will edit the crontab file of the root user, at the same time that if you do crontab -e from a user, you will edit that user's crontab file.