Linux Recurring Task Scheduler

I. Recurring Task schedule Type:

1, one-time task Execution (At,batch)-not important:

A, at:

Interactive: Let the user enter multiple commands to execute at the at> prompt.

For example: #at 10:02, go to the AT command prompt, as follows:

#at > Ls/usr/local

#at > CAT/ETC/PASSWD

#提交任务: Ctrl+d

#查看任务计划列表: At-l

#删除一个尚未执行作业的方法: at-d job_num or ATRM job_num

Batch: Writes each command of a task to a file, called by at, format: at-f/path/to/at_job_file time

such as: #at-F at.txt 15:22, where the contents of At.txt are as follows:

Ls/usr/local

cat/etc/passwd

The execution result of a task plan: sent to the task submitter by means of a message. Messages can be viewed through the mail command.

B, Batch: Unlike at, you cannot specify a time, it automatically selects the system to execute when idle.

2. Periodic task Execution (crontab, Anacron)--Important:

A, System cron: usually defined in/etc/crontab. For example, periodically delete files under the TMP directory.

#cat/etc/crontab, each line defines a separate task, as follows:

Shell=/bin/bash

Path=/sbin:/bin:/usr/sbin:/usr/bin

Mailto=root

home=/

# for details see Mans 4 Crontabs

# Example of Job definition:

#.----------------Minute (0-59)

# | .-------------Hour (0-23)

# |  | .----------Day of Month (1-31)

# |  |  | .-------month (1-12) OR jan,feb,mar,apr ...

# |  |  |  | .----Day of Week (0-6) (sunday=0 or 7) or Sun,mon,tue,wed,thu,fri,sat

# |  |  |  | |

# * * * * * * user-name command to be executed

B, user cron: usually defined in/var/spool/cron/username.

To implement user cron using the crontab command:

-L: View your cron Task List

-E: Opens the user's own cron configuration through the editor defined in the editor variable.

For example: #crontab-E, the definition reads as follows:

*/5 * * * */bin/echo "Hello cron"

-r: Remove user's crontab

If you are an administrator:

-U UserName: Configures crontab tasks for other users.

such as: #crontab-e-U Hadoop configures its tasks for Hadoop users.

Note 1: The command to execute is defined in cron, and the absolute path of the command must be used if it does not apply to a path similar to/etc/crontab.

*/5 * * * */bin/echo "Hello cron" &>/dev/null

NOTE 2: If crontab edits the file, if there is a%, transfer \% or use single quotation marks, otherwise it cannot be executed.

0 */3 * * */bin/touch ~/testfile_ ' date +\%y-\%m-\%d '. txt

0 */3 * * */bin/touch ~/testfile_ ' date + ' \%y-\%m-\%d '. txt

Note 3: If you do not want to receive messages, you can either redirect by redirection or mailto= "" If you do not wish to suggest a redirect.

*/5 * * * */bin/echo "Hello cron" &>/dev/null

Example: 6 9 12 per day, check all the file systems that are currently closed on the system, and append the results to the/tmp/mounts.txt file.

0 6,9,12 * * */bin/mount >>/tmp/mounts.txt

Note 4: Smaller than each of the units must give specific values, this value has its own to set.

Example: Take the current system memory headroom every two hours per day and save it to the/stats/memory.txt file.

0 */2 * * */bin/grep "^memfree"/proc/meminfo >>/stats/memory.txt

Note 5: Tasks that implement a second level (because the minimum time for a task is minutes)

Example: echo "Hello cron" is executed every 10 seconds

* * * * * * for i in {0..4};d o/bin/echo "Hello cron"; Sleep 10; Done

C, Time notation:

A, each time bit should use a value within its available valid range.

B, the * On a time bit indicates the valid value of the corresponding bit.

C,-: continuous point in time, such as 30-35 7 * * * 7 points per day 30-35 minutes execution, executed every minute.

D,,: Discrete point-in-time values such as: 5,15,25,35 * * * * 5 15 25 35 minutes per hour.

E,/#: Executes once every # within the specified time frame. such as: 0/20 * * * Every 20 minutes, 3-55/3 * * * is performed every three minutes between 3-55 minutes.

D, Anacron: is a cron supplement, can effectively check cron in a task in the past a certain period of time has not been performed tasks,

Execute it as soon as possible after the boot time. The point in time for this execution is defined in/etc/anacrontab.

#cat/etc/anacrontab, the contents are as follows:

Shell=/bin/sh

Path=/sbin:/bin:/usr/sbin:/usr/bin

Mailto=root

# The maximal random delay added to the base delay of the jobs

Random_delay=45

# The jobs would be started during the following hours only

Start_hours_range=3-22

#period in days delay in minutes job-identifier command

15cron.dailyNice run-parts/etc/cron.daily, tasks that have not been performed within a certain period, 5 minutes after power-on

7cron.weeklyNice run-parts/etc/cron.weekly, a task that has not been performed in a certain period and is executed 25 minutes after booting

@monthlycron.monthlyNice run-parts/etc/cron.monthly, a task that has not been performed in a certain period and is executed 45 minutes after boot

II. Mail command: Lists the mailing list. Quit the message with quit.

1, through-s to specify the subject subject, and the contents of the file/path/to/somefile as the message content, sent to username.

#mail-S "Subject" UserName </path/to/somefile

2, through-s to specify the theme subject, sent to the user, and in the > input message content, through ctrl+d submit mail.

#mail-S "Subject" UserName

Linux Recurring Task Scheduler