由于服务器上没有安装Crontab，当尝试执行 Crontab -l命令时，报错。

# crontab -l

-bash: crontab: command not found

crontab命令 来自 cronie包。

使用下面的命令安装它。
这也将安装所需的依赖项

安装计划任务Crontab

# yum install cronie

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirror.web-ster.com
 * updates: mirror.stanford.edu
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package cronie.x86_64 0:1.4.4-12.el6 will be installed
--> Processing Dependency: dailyjobs for package: cronie-1.4.4-12.el6.x86_64
--> Running transaction check
---> Package cronie-anacron.x86_64 0:1.4.4-12.el6 will be installed
--> Processing Dependency: crontabs for package: cronie-anacron-1.4.4-12.el6.x86_64
--> Running transaction check
---> Package crontabs.noarch 0:1.10-33.el6 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package                        Arch      Version           Repository     Size
================================================================================
Installing:
 cronie                         x86_64    1.4.4-12.el6      base           73 k
Installing for dependencies:
 cronie-anacron                 x86_64    1.4.4-12.el6      base           30 k
 crontabs                       noarch    1.10-33.el6       base           10 k

Transaction Summary
==========================================================
Install       3 Package(s)

Total download size: 114 k
Installed size: 220 k
Is this ok [y/N]: y
Downloading Packages:
(1/3): cronie-1.4.4-12.el6.x86_64.rpm                         |  73 kB     00:00
(2/3): cronie-anacron-1.4.4-12.el6.x86_64.rpm                 |  30 kB     00:00
(3/3): crontabs-1.10-33.el6.noarch.rpm                        |  10 kB     00:00
--------------------------------------------------------------------------------
Total                                                336 kB/s | 114 kB     00:00
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : cronie-1.4.4-12.el6.x86_64                   1/3
  Installing : crontabs-1.10-33.el6.noarch                  2/3
  Installing : cronie-anacron-1.4.4-12.el6.x86_64                           3/3
  Verifying  : crontabs-1.10-33.el6.noarch                                  1/3
  Verifying  : cronie-anacron-1.4.4-12.el6.x86_64                           2/3
  Verifying  : cronie-1.4.4-12.el6.x86_64                                   3/3

Installed:
  cronie.x86_64 0:1.4.4-12.el6

Dependency Installed:
  cronie-anacron.x86_64 0:1.4.4-12.el6            crontabs.noarch 0:1.10-33.el6

Complete!

如何在Crontab中添加新作业

执行crontab -e ，根据要求添加cron。

文件系统中的cron保存在文件 /var/spool/cron/ -l中