Detailed explanation of scheduled tasks for ordinary users in Linux
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Preface Ordinary users define crontab scheduled tasks: For example, an oracle user defines a scheduled task: print the current directory every minute [oracle@node2 ~]$ crontab -e */1 * * * * /bin/ls -al > /tmp/ls.log How to determine whether a scheduled task has been executed? First, the crond service must be running [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. Use the mail command as the root user [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 [email protected] Sun Jul 15 08:30:01 2018 Return-Path: <[email protected]> X-Original-To: root Delivered-To: [email protected] From: "(Cron Daemon)" <[email protected]> To: [email protected] 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 In the mial interactive environment, use the file command to display the total number of current emails and other information. Use head to view the most recent email and enter the number to view the detailed information of the email. 2. View the log: 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 ~]# The log file records the execution of scheduled tasks for all users 3. Use mail to view under ordinary user (In the scheduled task, the user who executes the scheduled task must be clearly defined, otherwise even if the scheduled task is defined under the oracle user, the email may not be received) [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" & The /var/log/cron file cannot be directly viewed by ordinary users [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 ~]$ There is another way to write scheduled tasks in the /etc/crontab file, but in centos7, writing and executing in this file will result in an error [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 ~]$ Summarize The above is the full content of this article. I hope that the content of this article will have certain reference learning value for your study or work. Thank you for your support of 123WORDPRESS.COM. You may also be interested in:
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