Linux Scheduled tasks at Crontab Anacron

At: For performing one-time tasks

at related configuration files/etc/at.allow/etc/at.deny

If a/etc/at.allow file exists, only the users included in the At.allow are allowed to use at;

If the/etc/at.allow file does not exist, the/etc/allow.deny file is checked, and users not included in the At.deny file are allowed to use the at;

If none of the two files exist, only root is allowed to use at;

By default, there is an empty/etc/at.deny that allows all users to use at.

ATQ= at–l Query Task queue

[Email protected] ~]# ATQ
9 2014-08-29 17:00 a root
8 2014-08-28 16:00 a root
[Email protected] ~]# at-l
9 2014-08-29 17:00 a root
8 2014-08-28 16:00 a root

ATRM= at–d Delete Task

[Email protected] ~]# ATRM 8
[Email protected] ~]# ATQ
9 2014-08-29 17:00 a root

At 18:00 tomorrow–f fileRead a task from a file

[Email protected] ~]# at 18:00 tomorrow-f ccdb_rsync.sh
Job at 2014-08-29 18:00
[Email protected] ~]# ATQ
9 2014-08-29 17:00 a root
Ten 2014-08-29 18:00 a root
2014-08-29 18:00 a root

At 4pm + 3 daysPerform a task at 4 o'clock in the afternoon in 3 days

[[email protected] ~]# at 4pm + 3 days
at> echo "Hello"
At> <EOT>
Job at 2014-08-31 16:00

At 10:10 Sep 1At 10:10 on September 1, the mission was executed.

[Email protected] ~]# at 10:10 Sep 1
at> echo "Hello"
At> <EOT>
Job at 2014-09-01 10:10

crontab:Used to perform recurring tasks

crontab related configuration files:/var/spool/cron/etc/cron.allow/etc/cron.deny

/var/spool/cron/: The directory used to save the user's tasks

If a/etc/cron.allow file exists, only users who exist in the Cron.allow file are allowed to use crontab;

If a/etc/cron.deny file is present, only users stored in the Cron.deny file are denied use of crontab;

If/etc/cron.allow/etc/cron.deny is not present, only root is allowed to use crontab.

crontab–l display Task List Crontab–e Editing Tasks

[Email protected] cron]# crontab-l
*/5 * * * * echo "Hello world!"

0 5 * * * Touch file_ ' date +\%f '. txt

Crontab the format of a task

[Email protected] ~]# Cat/etc/crontab
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

1th *: Sub (0-59)

2nd *: Hours (0-23)

3rd *: Day (1-31)

4th *: Month (1-12)

5th *: Week (0-6 or Sun,mon,tue,wed,thu,fri,sat)

command to be executed: represents executed commands

Cases:

1. Execute once every 5 minutes

*/5 * * * * echo "Hello World"

2.10 minutes per hour, 20-30 minutes to execute

10,20-30 * * * * echo "Hello World"

3. Perform a second-level task that executes every 10 seconds

* * * * * for i in {1..5}; Do/bin/echo "How is it?"; Sleep Done

4. If you execute a command that contains%, you need to escape

0 5 * * * Touch file_ ' date +\%f '. txt

Or

0 5 * * * Touch file_ ' date + '%F '. txt

Anacron

Anacron is also used to perform periodic tasks, with frequencies of hourly, daily, weekly, monthly correspondence to/etc/cron.hourly,/etc/cron.daily,/etc/cron.weekly,/etc/monthly;

The Anacron is primarily used for systems that are not 24-hour power-up and perform tasks by reading/etc/anacrontab files.

Linux Scheduled tasks at Crontab Anacron