linux中普通用户的定时任务详解

前言

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 <root@node2> /bin/ls"
n796 (cron daemon) sun jul 15 08:26 35/932 "cron <root@node2> /bin/ls"
n797 (cron daemon) sun jul 15 08:27 35/932 "cron <root@node2> /bin/ls"
n798 (cron daemon) sun jul 15 08:28 35/932 "cron <root@node2> /bin/ls"
n799 (cron daemon) sun jul 15 08:29 35/932 "cron <root@node2> /bin/ls"
n800 (cron daemon) sun jul 15 08:30 35/932 "cron <root@node2> /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 <root@node2> /bin/ls"
n794 (cron daemon) sun jul 15 08:24 35/932 "cron <root@node2> /bin/ls"
n795 (cron daemon) sun jul 15 08:25 35/932 "cron <root@node2> /bin/ls"
n796 (cron daemon) sun jul 15 08:26 35/932 "cron <root@node2> /bin/ls"
n797 (cron daemon) sun jul 15 08:27 35/932 "cron <root@node2> /bin/ls"
n798 (cron daemon) sun jul 15 08:28 35/932 "cron <root@node2> /bin/ls"
n799 (cron daemon) sun jul 15 08:29 35/932 "cron <root@node2> /bin/ls"
n800 (cron daemon) sun jul 15 08:30 35/932 "cron <root@node2> /bin/ls"
&800
message 800:
from [e-mail] sun jul 15 08:30:01 2018
return-path: <[e-mail]>
x-original-to: root
delivered-to: [e-mail]
from: "(cron daemon)" <[e-mail]>
to: [e-mail]
subject: cron <root@node2> /bin/ls
content-type: text/plain; charset=utf-8
auto-submitted: auto-generated
precedence: bulk
x-cron-env: <xdg_session_id=278>
x-cron-env: <xdg_runtime_dir=/run/user/0>
x-cron-env: <lang=en_us.utf-8>
x-cron-env: <shell=/bin/sh>
x-cron-env: <home=/root>
x-cron-env: <path=/usr/bin:/bin>
x-cron-env: <logname=root>
x-cron-env: <user=root>
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 <oracle@localhost> ls -al"
2 (cron daemon) sun jul 15 06:10 57/2777 "cron <oracle@node2> /bin/ls -al"
3 (cron daemon) sun jul 15 06:11 57/2777 "cron <oracle@node2> /bin/ls -al"
4 (cron daemon) sun jul 15 06:12 57/2778 "cron <oracle@node2> /bin/ls -al"
5 (cron daemon) sun jul 15 06:13 57/2778 "cron <oracle@node2> /bin/ls -al"
>u 6 (cron daemon) sun jul 15 08:38 26/929 "cron <oracle@node2> 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 ~]$

总结

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