Linux crontab 命令

最新推荐文章于 2025-02-10 08:50:02 发布

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最新推荐文章于 2025-02-10 08:50:02 发布

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分类专栏： OPS 文章标签： shell crontab

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本文深入解析了crontab的使用方法、时间间隔设置，并提供了实例演示，帮助用户掌握如何创建、编辑、删除crontab任务，以及如何通过SELinux进行权限控制。

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简介

crontab 可以在 [指定时间] [时间段的间隔] 执行系统命令或执行 shell 脚本。

用法

crontab [-u user] file

crontab [-u user] [-l | -r | -e] [-i] [-s]

描述

Crontab  is the program used to install, remove or list the tables used to drive the cron(8) daemon.  Each user can have their own crontab, and
though these are files in /var/spool/ , they are not intended to be edited directly. For SELinux in mls mode can be even more  crontabs  -  for
each range. For more see selinux(8).

The cron jobs could be allow or disallow for different users. For classical crontab there exists cron.allow and cron.deny files.  If cron.allow
file exists, then you must be listed therein in order to be allowed to use this command.  If  the  cron.allow  file  does  not  exist  but  the
cron.deny  file  does exist, then you must not be listed in the cron.deny file in order to use this command.  If neither of these files exists,
only the super user will be allowed to use this command.  The second option is using PAM authentication, where you set up users, which could or
couldn’t use crontab and also system cron jobs from /etc/cron.d/.

The temporary directory could be set in enviroment variables. If it’s not set by user than /tmp is used.

参数

-u     Append  the  name  of  the user whose crontab is to be tweaked.  If this option is not given, crontab examines "your" crontab, i.e., the
       crontab of the person executing the command.  Note that su(8) can confuse crontab and that if you are running inside of su(8) you should
       always  use  the  -u  option for safety’s sake.  The first form of this command is used to install a new crontab from some named file or
       standard input if the pseudo-filename "-" is given.

-l     The current crontab will be displayed on standard output.

-r     The current crontab will be removed.

-e     This option is used to edit the current crontab using the editor specified by the VISUAL or EDITOR  environment  variables.   After  you
       exit from the editor, the modified crontab will be installed automatically.

-i     This option modifies the -r option to prompt the user for a ’y/Y’ response before actually removing the crontab.

-s     It  will  append  the  current  SELinux security context string as an MLS_LEVEL setting to the crontab file before editing / replacement
       occurs - see the documentation of MLS_LEVEL in crontab(5).

时间和间隔设置的说明

# 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