Linux uses the Crontab command to implement timed restart

Article Title: Linux uses the Crontab command to implement timed restart. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

Crontab is a program that conveniently executes a task in a scheduled (Cyclic) manner on unix/linux systems.
　
Use the cron service and use the service crond status to view the cron service status. If it is not started, the service crond start starts it,
　
The cron service is a regular execution service. You can use the crontab command to add or edit tasks that require scheduled execution:
　
Crontab-u // set a user's cron service. Generally, the root user needs this parameter when executing this command.
　
Crontab-l // list the details of a user's cron Service
　
Crontab-r // Delete the cron service of no user
　
Crontab-e // edit a user's cron Service
　
For example, to view your cron settings as root: crontab-u root-l
　
For another example, root wants to delete fred's cron settings: crontab-u fred-r
　
When editing the cron service, the edited content has some formats and conventions. Enter crontab-u root-e.
　
In vi editing mode, the edited content must conform to the following format: */1 ***** ls>/tmp/ls.txt
　
Edit the/etc/crontab file and add a line at the end: 30 5 * root init 6 so that the system is configured to automatically restart at every morning.
　
You need to set crond as a service automatically started after the system starts. You can add
　
Service crond start
　
If you need to load other services in the system, you can continue to add the startup commands for other services.
　
For example, service mysqld start
　
Basic usage:
　
1. crontab-l
　
List the current crontab task
　
2. crontab-d
　
Delete the current crontab task
　
3. crontab-e (crontab-r above solaris5.8)
　
Edit a crontab task and ctrl_D ends.
　
4. crontab filename
　
Use filename as the crontab task list file and load it
　
Crontab file format:
　
Rows in the crontab file are composed of six fields. Different fields are separated by spaces or the tab key. The first five fields specify the time when the command will be run.
　
Minutes (0-59)
　
Hour (0-23)
　
Date (1-31)
　
Month (1-12)
　
Day of the week (0-6, 0 indicates Sunday)
　
The 6th fields are strings to be executed at the appropriate time
　
Example:
　
# MIN HOUR DAY MONTH DAYOFWEEK COMMAND
　
#06:10 every morning
　
10 6 **** date
　
# Every two hours
　
0 */2 *** date (solaris 5.8 does not seem to support this method)
　
# Every two hours from PM to am, am
　
0 23-7/2, 8 **** date
　
# Am on the 4th day of each month and from Monday to Wednesday of each week
　
0 11 4 * mon-wed date
　
# A.m. of July
　
0 4 1 jan * date
　
Note: When Using crontab, the environment variables that can be accessed in the running script may not be consistent with those in the current test environment, it is safer to set the environment variable (export) in the running script program)
　
(1ndcreate a file named crond.txt as follows and restart it at 05:36 every morning.
　
36 5 * reboot
　
(2) upload to the/opt directory
　
(3) run the command
　
Crontab/opt/crond.txt
　
Crontab-l
　
Make the configuration file take effect: If the configuration file takes effect, you have to restart cron. Remember that since the cron configuration file under each user is modified. Restart the cron server.
　
In Fedora and Redhat, we should use;
　
[Root @ localhost ~] #/Etc/init. d/crond restart
　
If you want crond to run at startup, you should change its running level;
　
[Root @ localhost ~] # Chkconfig -- levels 35 crond on
　
Service crond status: Check the cron service status. If it is not started, service crond start starts it. The cron service is a scheduled service. You can use the crontab command to add or edit tasks that require scheduled execution.

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