Linux VPS uses crontab to implement timed restart tasks

Because Chiang just helped a netizen on his behalf to deal with the requirements of the VPS host scheduled restart function, such as he needs to restart the server every morning 5, we can set the timing reboot execution can be.

First, install crontab executable environment

The general vps/server is supported, but some may not support the need for us to give the installation.

A-centos system

#安装Crontab
Yum Install Vixie-cron Crontabs
#设置开机启动Crontab
Chkconfig Crond on
#启动Crontab
Service Crond Start
B-debian system

#安装Crontab
Apt-get Install cron
#重启Crontab
/etc/init.d/cron restart

PS: Generally our VPS are installed, at least the old Chiang Test several machines are installed, if not perform the following add command is not good to perform, then look at the corresponding installation environment above.

Second, add crontab execute command

Crontab-e
Crontab Reboot Server VPS

Here we need to use the vi edit, the input above the script on behalf of the 5 o'clock restart, the specific details of the crontab application online There are many tutorials, the back of the old Chiang if there is a need to use the distinction point out, if it is all the digestion of indigestion.

: Wq exit after the default is to start a timed start command, if not assured that you can pause before starting.

/etc/rc.d/init.d/crond stop
/etc/rc.d/init.d/crond start

Add:

Basic format:
* * * * command
Time-sharing and Lunar Week command

The 1th column represents minutes 1~59 per minute with * or */1
The 2nd column represents the hour 1~23 (0 for 0 points)
The 3rd column represents the date 1~31
The 4th column represents the month 1~12
The 5th list of the week 0~6 (0 for Sunday)
6th column the command to run

Some examples of crontab files:

* * * */usr/local/etc/rc.d/lighttpd restart
The above example represents 21:30 restart Apache per night.

4 1,10,22 * */USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example represents the 4:45 reboot of Apache for 1, 10, and 22nd per month.

1 * * 6,0/USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example shows the 1:10 reboot of Apache every Saturday and Sunday.

0,30 18-23 * * * */usr/local/etc/rc.d/lighttpd restart
The example above shows that Apache is restarted every 30 minutes from 18:00 to 23:00 every day.

0 * * 6/USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example indicates that 11:00 PM restarts Apache every Saturday.

* */1 * * * */usr/local/etc/rc.d/lighttpd restart
Restart Apache every hour

* 23-7/1 * * * */usr/local/etc/rc.d/lighttpd restart
From 11 o'clock to 7 in the morning, restart Apache every hour.

0 4 * mon-wed/usr/local/etc/rc.d/lighttpd restart
4th per month with 11 points per Monday to Wednesday restart Apache

0 4 1/USR/LOCAL/ETC/RC.D/LIGHTTPD * Restart
Restart Apache at 4 o ' January 1.

Name: crontab

Use Rights: All users

How to use:

crontab file [-u user]-replaces the current crontab with the specified files.

Crontab-[-u user]-replaces the current crontab with standard input.

crontab-1[user]-lists the user's current crontab.

crontab-e[user]-Edit user's current crontab.

crontab-d[user]-deletes the user's current crontab.

Crontab-c dir-Specifies the directory for crontab.

crontab file format: M H d M D cmd.

M: Minutes (0-59).

H: Hours (0-23).

D: Days (1-31).

M: Month (1-12).

D: Days of the week (0~6,0 for Sunday).

CMD to run the program, the program was sent to SH execution, this shell only user,home,shell these three environment variables

Description

Crontab is used to allow the user to execute a program at a fixed time or at a fixed interval, in other words, a user-like schedule. -u user refers to the setting specified

User's time table, the premise is that you have to have permission (for example, root) to specify other people's schedule. If you do not use-u user, it means that you set the

Set your own schedule.

Parameters:

CRONTAB-E: Execute the text editor to set the schedule, the default text editor is VI, if you want to use another text editor, please set the VISUAL environment variables

To specify the use of that text editor (for example, Setenv VISUAL Joe)

Crontab-r: Deletes the current schedule table

Crontab-l: List the current schedule

crontab file [-u user]-replaces the current crontab with the specified files.

The format of the schedule table is as follows:

F1 F2 F3 f4 f5 program

Where F1 is the minute, F2 represents the Hour, F3 represents the day of the month, the F4 represents the month, and the F5 represents the day of the one week. program says to hold

Line of the program.

When F1 is *, it means that the PROGRAM,F2 is executed every minute for *, and the rest of the program is executed every hour.

When F1 is a-b to be executed from the time of the first a minute to the B minute, the F2 is a-b to be performed from A to a B-hour, and the remainder of the analogy

When F1 is */n, it is executed once every n minutes, F2 is performed once per N-hour intervals for */n, and the rest

When F1 is a, B, C,... The first A, B, C,... Minutes to execute, F2 for a, B, C,... The first is a, B, c ... An hour to execute, and the rest of the analogy

The user can also store all the settings in the file file, using crontab file to set the schedule.

Example:

#每天早上7点执行一次/bin/ls:

0 7 * * */BIN/LS

In December, every day at 6 to 12, every 3 hours of the morning/usr/bin/backup are performed:

0 6-12/3 */usr/bin/backup

Send a letter to Alex@domain.name from Monday to Friday every 5:00:

0 * * 1-5 mail-s "HI" Alex@domain.name </tmp/maildata

Every month at midnight 0:20, 2:20, 4:20 .... Execute echo "haha"

0-23/2 * * * echo "haha"

Attention:

When the program is executed at the time you specify, the system will send you a letter showing the execution of the program, and if you do not wish to receive such a letter, please leave a blank space in each line

After adding >/dev/null 2>&1

Example 2:

#每天早上6点10分

6 * * * Date

#每两个小时

0 */2 * * * Date

#晚上11点到早上8点之间每两个小时, 8 in the morning.

0 23-7/2,8 * * * Date

#每个月的4号和每个礼拜的礼拜一到礼拜三的早上11点

0 4 * mon-wed date

#1月份日早上4点

0 4 1, * date

Example

$crontab-L lists the user's current crontab.

Friendly tips:

Make the configuration file effective: If you have the configuration file in effect, you will have to restart Cron, and remember to restart the cron server after each user has modified the cron profile.
In Fedora and redhat, we should use:
/etc/rc.d/crond restart
If you want Crond to run at boot time, you should change its run level:
Chkconfig–level Crond on
Service Crond Status View Cron service state, if not started service Crond start it, cron service is a timed service, can add or edit tasks that need to be performed by Crontab command

In this article, Chiang has shared how to use the timed command line crontab to set the vps/server to reboot periodically.