参考：

crontab命令详解

mail用法(使用mail查看定时任务执行情况)

centos系统禁止普通用户使用crontab命令

普通用户定义crontab定时任务：

比如oracle用户定义一个定时任务：每分钟打印当前目录[oracle@node2 ~]$ crontab -e*/1 * * * * /bin/ls -al > /tmp/ls.log

如何判断定时任务有没有执行？

首先crond服务要处于运行状态[oracle@node2 ~]$ service crond status

Redirecting to /bin/systemctl status crond.service

● crond.service - Command Scheduler

Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)

Active: active (running) since Sun 2018-07-15 08:27:38 EDT; 2min 43s ago

Main PID: 6189 (crond)

CGroup: /system.slice/crond.service

└─6189 /usr/sbin/crond -n

[oracle@node2 ~]$

1.在root用户下使用mail命令[root@node2 ~]# mail

Heirloom Mail version 12.5 7/5/10. Type ? for help.

"/var/spool/mail/root": 801 messages 9 new 94 unread

N795 (Cron Daemon) Sun Jul 15 08:25 35/932 "Cron /bin/ls"

N796 (Cron Daemon) Sun Jul 15 08:26 35/932 "Cron /bin/ls"

N797 (Cron Daemon) Sun Jul 15 08:27 35/932 "Cron /bin/ls"

N798 (Cron Daemon) Sun Jul 15 08:28 35/932 "Cron /bin/ls"

N799 (Cron Daemon) Sun Jul 15 08:29 35/932 "Cron /bin/ls"

N800 (Cron Daemon) Sun Jul 15 08:30 35/932 "Cron /bin/ls"

& file

"/var/spool/mail/root": 801 messages 9 new 94 unread

& h

>N793 (Cron Daemon) Sun Jul 15 08:23 35/932 "Cron /bin/ls"

N794 (Cron Daemon) Sun Jul 15 08:24 35/932 "Cron /bin/ls"

N795 (Cron Daemon) Sun Jul 15 08:25 35/932 "Cron /bin/ls"

N796 (Cron Daemon) Sun Jul 15 08:26 35/932 "Cron /bin/ls"

N797 (Cron Daemon) Sun Jul 15 08:27 35/932 "Cron /bin/ls"

N798 (Cron Daemon) Sun Jul 15 08:28 35/932 "Cron /bin/ls"

N799 (Cron Daemon) Sun Jul 15 08:29 35/932 "Cron /bin/ls"

N800 (Cron Daemon) Sun Jul 15 08:30 35/932 "Cron /bin/ls"

&800

Message 800:

From root@node2.matengbing.com  Sun Jul 15 08:30:01 2018

Return-Path:

X-Original-To: root

Delivered-To: root@node2.matengbing.com

From: "(Cron Daemon)"

To: root@node2.matengbing.com

Subject: Cron /bin/ls

Content-Type: text/plain; charset=UTF-8

Auto-Submitted: auto-generated

Precedence: bulk

X-Cron-Env:

X-Cron-Env:

X-Cron-Env:

X-Cron-Env:

X-Cron-Env:

X-Cron-Env:

X-Cron-Env:

X-Cron-Env:

Date: Sun, 15 Jul 2018 08:30:01 -0400 (EDT)

Status: R

\

anaconda-ks.cfg

Desktop

Documents

Downloads

initial-setup-ks.cfg

Music

Pictures

Public

Templates

Videos

在mial交互环境下，通过file命令显示当前邮件总数等信息

通过head查看最近的邮件

输入编号查看该邮件的详细信息

2.查看日志：tail -n 10 /var/log/cron[root@node2 ~]# tail -n 10 /var/log/cron

Jul 15 08:31:01 node2 CROND[6297]: (root) CMD (/bin/ls)

Jul 15 08:31:01 node2 CROND[6298]: (oracle) CMD (/bin/ls -al > /tmp/ls.log )

Jul 15 08:32:01 node2 CROND[6321]: (oracle) CMD (/bin/ls -al > /tmp/ls.log )

Jul 15 08:32:01 node2 CROND[6322]: (root) CMD (/bin/ls)

Jul 15 08:33:02 node2 CROND[6342]: (root) CMD (/bin/ls)

Jul 15 08:33:02 node2 CROND[6343]: (oracle) CMD (/bin/ls -al > /tmp/ls.log )

Jul 15 08:34:01 node2 CROND[6362]: (root) CMD (/bin/ls)

Jul 15 08:34:01 node2 CROND[6363]: (oracle) CMD (/bin/ls -al > /tmp/ls.log )

Jul 15 08:35:01 node2 CROND[6382]: (oracle) CMD (/bin/ls -al > /tmp/ls.log )

Jul 15 08:35:01 node2 CROND[6383]: (root) CMD (/bin/ls)

[root@node2 ~]#

日志文件中记录了所有用户的定时任务执行情况

3.在普通用户下使用mail查看(定时任务中要明确执行定时任务的用户，否则即使在oracle用户下定义的定时任务可能不能收到邮件)[oracle@node2 ~]$ crontab -l

*/1 * * * * oracle /bin/ls -al > /tmp/ls.log

[oracle@node2 ~]$

[oracle@node2 ~]$ mail

Heirloom Mail version 12.5 7/5/10. Type ? for help.

"/var/spool/mail/oracle": 6 messages 1 unread

1 (Cron Daemon) Mon Mar 5 14:10 52/2476 "Cron ls -al"

2 (Cron Daemon) Sun Jul 15 06:10 57/2777 "Cron /bin/ls -al"

3 (Cron Daemon) Sun Jul 15 06:11 57/2777 "Cron /bin/ls -al"

4 (Cron Daemon) Sun Jul 15 06:12 57/2778 "Cron /bin/ls -al"

5 (Cron Daemon) Sun Jul 15 06:13 57/2778 "Cron /bin/ls -al"

>U 6 (Cron Daemon) Sun Jul 15 08:38 26/929 "Cron oracle /bin/ls -al > /tmp/ls.log"

&

在普通用户下不能直接查看/var/log/cron文件[oracle@node2 ~]$ tail -n 10 /var/log/cron

tail: cannot open ‘/var/log/cron’ for reading: Permission denied

You have new mail in /var/spool/mail/oracle

[oracle@node2 ~]$

定时任务还有一种写在/etc/crontab文件中的方式，但是在centos7中写在该文件中执行会报错[oracle@node2 ~]$ cat /etc/crontab

SHELL=/bin/bash

PATH=/sbin:/bin:/usr/sbin:/usr/bin

MAILTO=root

# For details see man 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

[oracle@node2 ~]$