The system is set up, clean common system junk or some script to automatically perform system tasks, generally we do understand on the line, do not change the configuration file is / etc / conrtab
SHELL: scheduled task is to run the interpreter, the default is bash
Environment variables to execute the command: PATH
MAILTO: Departure user who scheduled tasks
HOME: home directory is /
run-parts is a script in the / usr / bin / run-parts, the role is all the scripts / programs under implementation of a directory.
run-parts /etc/cron.hourly execute all scripts / programs under the directory /etc/cron.hourly/.
The following run-parts command is run
vim / etc / crontab difference timed run with crontab -e written?
vim / etc / crontab : system level is defined crontab, / etc / crontab owner and group are root
-e crontab : crontab is user-defined, all users can write
Both methods record position is not the same, an in / etc / further in / var / inside. Cron service calls are
If the system does not boot in the above said time how to do? Then this script does is not performed? Designers have long thought of this problem, so there is a cron service expansion, the purpose is to prevent non-computer 24 hours a missing guard task, anacrontab automatically after a specified time interval to miss: Extended File System is scheduled tasks mission
The format is like this:
period delay job-identifier command
period - frequency command (days)
delay - delay Time (minutes)
job-identifier - description of the task, anacron used in the message and timestamp as the name of the job file, can contain any non-blank characters (except slashes).
command - command to execute
The first line means: every boot after 65 minutes cron.daily check whether a file is executed, and if not executed today on the implementation of his
The second line means: every 7 days after the boot is 70 minutes to check cron.weekly file is executed, and if not executed within a week of his execution
The third line means almost
Here to talk about the cron control services, and at the same, this is /etc/cron.deny configuration files to control, which is written to prohibit the use cron user name, a line on the OK