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 root@node2.matengbing.com Sun Jul 15 08:30:01 2018 Return-Path: <root@node2.matengbing.com> X-Original-To: root Delivered-To: root@node2.matengbing.com From: "(Cron Daemon)" <root@node2.matengbing.com> To: root@node2.matengbing.com 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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