CentOS下使用yum命令安装计划任务程序crontab

概述

利用“任务计划”，可以将任何脚本、程序或文档安排在某个最方便的时间运行。通俗的讲就是定时执行某个脚本、程序。

常见用途

定时关机 
定时检查更新 
定时对系统配置、数据库、日志进行备份 
定时清理垃圾文件

检测是否已安装

# crontab
-bash: crontab: command not found

执行 crontab 命令如果报 command not found，就表明没有安装.

开始安装

# yum -y install vixie-cron
Loaded plugins: fastestmirror, refresh-packagekit, security
Existing lock /var/run/yum.pid: another copy is running as pid 25960.
Another app is currently holding the yum lock; waiting for it to exit...

可能是系统自动升级正在运行，yum在锁定状态中。 
可以通过强制关掉yum进程： 
#rm -f /var/run/yum.pid 
然后就可以使用yum了。

# yum -y install vixie-cron
Loaded plugins: fastestmirror, refresh-packagekit, security
Determining fastest mirrors
 * base: mirrors.btte.net
 * extras: mirrors.sina.cn
 * updates: mirrors.sina.cn
base                                                                                                                                                                    | 3.7 kB     00:00     
extras                                                                                                                                                                  | 3.4 kB     00:00     
extras/primary_db                                                                                                                                                       |  32 kB     00:00     
updates                                                                                                                                                                 | 3.4 kB     00:00     
updates/primary_db                                                                                                                                                      | 1.9 MB     00:07     
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package cronie.x86_64 0:1.4.4-15.el6 will be installed
--> Processing Dependency: dailyjobs for package: cronie-1.4.4-15.el6.x86_64
--> Processing Dependency: /usr/sbin/sendmail for package: cronie-1.4.4-15.el6.x86_64
--> Running transaction check
---> Package cronie-anacron.x86_64 0:1.4.4-15.el6 will be installed
--> Processing Dependency: crontabs for package: cronie-anacron-1.4.4-15.el6.x86_64
---> Package sendmail.x86_64 0:8.14.4-9.el6 will be installed
--> Processing Dependency: procmail for package: sendmail-8.14.4-9.el6.x86_64
--> Running transaction check
---> Package crontabs.noarch 0:1.10-33.el6 will be installed
---> Package procmail.x86_64 0:3.22-25.1.el6_5.1 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

===============================================================================================================================================================================================
 Package                                          Arch                                     Version                                                Repository                              Size
===============================================================================================================================================================================================
Installing:
 cronie                                           x86_64                                   1.4.4-15.el6                                           base                                    74 k
Installing for dependencies:
 cronie-anacron                                   x86_64                                   1.4.4-15.el6                                           base                                    31 k
 crontabs                                         noarch                                   1.10-33.el6                                            base                                    10 k
 procmail                                         x86_64                                   3.22-25.1.el6_5.1                                      base                                   162 k
 sendmail                                         x86_64                                   8.14.4-9.el6                                           base                                   716 k

Transaction Summary
===============================================================================================================================================================================================
Install       5 Package(s)

Total download size: 994 k
Installed size: 2.1 M
Downloading Packages:
(1/5): cronie-1.4.4-15.el6.x86_64.rpm                                                                                                                                   |  74 kB     00:00     
(2/5): cronie-anacron-1.4.4-15.el6.x86_64.rpm                                                                                                                           |  31 kB     00:00     
(3/5): crontabs-1.10-33.el6.noarch.rpm                                                                                                                                  |  10 kB     00:00     
(4/5): procmail-3.22-25.1.el6_5.1.x86_64.rpm                                                                                                                            | 162 kB     00:00     
(5/5): sendmail-8.14.4-9.el6.x86_64.rpm                                                                                                                                 | 716 kB     00:00     
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                                                          1.3 MB/s | 994 kB     00:00     
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : procmail-3.22-25.1.el6_5.1.x86_64                                                                                                                                           1/5 
  Installing : sendmail-8.14.4-9.el6.x86_64                                                                                                                                                2/5 
  Installing : cronie-1.4.4-15.el6.x86_64                                                                                                                                                  3/5 
  Installing : crontabs-1.10-33.el6.noarch                                                                                                                                                 4/5 
  Installing : cronie-anacron-1.4.4-15.el6.x86_64                                                                                                                                          5/5 
ERROR:dbus.proxies:Introspect error on :1.2513:/org/freedesktop/PackageKit: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
Unable to send message to PackageKit
  Verifying  : crontabs-1.10-33.el6.noarch                                                                                                                                                 1/5 
  Verifying  : cronie-anacron-1.4.4-15.el6.x86_64                                                                                                                                          2/5 
  Verifying  : sendmail-8.14.4-9.el6.x86_64                                                                                                                                                3/5 
  Verifying  : cronie-1.4.4-15.el6.x86_64                                                                                                                                                  4/5 
  Verifying  : procmail-3.22-25.1.el6_5.1.x86_64                                                                                                                                           5/5 

Installed:
  cronie.x86_64 0:1.4.4-15.el6                                                                                                                                                                 

Dependency Installed:
  cronie-anacron.x86_64 0:1.4.4-15.el6               crontabs.noarch 0:1.10-33.el6               procmail.x86_64 0:3.22-25.1.el6_5.1               sendmail.x86_64 0:8.14.4-9.el6              

Complete!

查看命令帮助

crontab 并不支持-h或–help之类的选项，不过还是可以通过它查看命令帮助

# crontab -h
crontab：无效选项 -- h
crontab: usage error: unrecognized option
usage:  crontab [-u user] file
    crontab [-u user] [ -e | -l | -r ]
        (default operation is replace, per 1003.2)
    -e  (edit user's crontab)
    -l  (list user's crontab)
    -r  (delete user's crontab)
    -i  (prompt before deleting user's crontab)
    -s  (selinux context)

也可以使用 info crontab 命令查看详细的帮助信息。

cron服务提供crontab命令来设定cron服务的，以下是这个命令的一些参数与说明:

　　crontab -u //设定某个用户的cron服务，一般root用户在执行这个命令的时候需要此参数

　　crontab -l //列出某个用户cron服务的详细内容

　　crontab -r //删除没个用户的cron服务

　　crontab -e //编辑某个用户的cron服务

　　比如说root查看自己的cron设置:crontab -u root -l

　　再例如，root想删除fred的cron设置:crontab -u fred -r

　　在编辑cron服务时，编辑的内容有一些格式和约定，输入:crontab -u root -e

　　进入vi编辑模式，编辑的内容一定要符合下面的格式:/1 * * * ls >> /tmp/ls.txt

服务状态控制
/sbin/service crond start //启动服务 
/sbin/service crond stop //关闭服务 
/sbin/service crond restart //重启服务 
/sbin/service crond reload //重新载入配置 
/sbin/service crond status //查看状态

或者使用

# service crond start 
# service crond stop 
# service crond restart 
# service crond reload 
# service crond status

开机启动
你也可以将这个服务在系统启动的时候自动启动: 
在/etc/rc.d/rc.local这个脚本的末尾加上:

/sbin/service crond start

现在Cron这个服务已经在进程里面了，我们就可以用这个服务了。

 

原文链接：https://blog.csdn.net/testcs_dn/article/details/48780971