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crontab.md

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Crontab

On Linux

crond - daemon to execute scheduled commands

On BSD

A time-based job scheduler in Unix-like computer operating systems.

References

Related Command

  • crontab : maintain crontab files for individual users

Assume

  • on Linux ( CentOS 7 )

Notice

Usage

List current crontab

crontab -l

Edit crontab

crontab -e

Config

User

Content sample

# Setup Environment Variables
## Timezone
TZ=Asia/Shanghai
HOME=/path/to/home/
SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MAILTO=root

# Schedules
* * * * * ./script_to_execute.sh
15 * * * * ./script_with_output.sh &>> output.log

Source file paths

$ tree /var/spool/cron
/var/spool/cron
├── root
├── sysmon
└── icehe

System

Files & Direcotries

  • /etc/crontab ( file )
  • /etc/cron.d/*
  • /etc/cron.daily/*
  • /etc/cron.hourly/*
  • /etc/cron.monthly/*
  • /etc/cron.weekly/*

/etc/crontab ( just a template )

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# 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

# run ntp
0 * * * * root /bin/sleep $(($RANDOM\%120+10)) && /usr/sbin/ntpdate example.com.cn > /dev/null
0 3,7,10,13,16,19,23 * * *              root /var/cfengine/bin/cfexecd
# run sce_agent_update
0 * * * * root /bin/sleep $(($RANDOM\%120+10)) && /bin/sh /var/sce/sce_agent_update.sh >> /var/log/sce/sce_agent.lo
g 2>&1
#run sce_sync
*/10 * * * * root /bin/sleep $(($RANDOM\%120+10)) && /bin/sh /var/sce/sce_agent/jobs/sce_sync.sh >> /var/log/sce/sc
e_agent.log 2>&1
30 */1 * * * root /var/cfengine/inputs/files/script/cfengine_health_check.sh

Timing

crontab guru : https://crontab.guru/#0_*_*_*_*

  • The quick and simple editor for cron schedule expressions

Debug

Log

Log files

  • /var/log/cron
  • /var/log/cron-[YYYYMMdd]
  • /var/log/cron-[YYYYMMdd].gz

/var/log/cron

  • Log content sample
Sep  7 15:19:14 box029 crontab[17831]: (root) BEGIN EDIT (icehe)
Sep  7 15:19:17 box029 crontab[17831]: (root) REPLACE (icehe)
Sep  7 15:19:17 box029 crontab[17831]: (root) END EDIT (icehe)
Sep  7 15:20:01 box029 CROND[17915]: (root) CMD (/usr/lib64/sa/sa1 1 1)
Sep  7 15:21:01 box029 CROND[18033]: (sysmon) CMD (cd /usr/local && ./send.sh >/dev/null 2>&1)
Sep  7 16:01:01 box029 CROND[23251]: (root) CMD (run-parts /etc/cron.hourly)
Sep  7 16:01:01 box029 run-parts(/etc/cron.hourly)[23251]: starting 0anacron
Sep  7 16:01:01 box029 run-parts(/etc/cron.hourly)[23268]: finished 0anacron
Sep  7 16:01:01 box029 run-parts(/etc/cron.hourly)[23251]: starting mcelog.cron
Sep  7 16:01:01 box029 run-parts(/etc/cron.hourly)[23274]: finished mcelog.cron

Log written by rsyslog.service

  • Start if it's off
# systemv
systemctl status rsyslog
systemctl start rsyslog

# service
service rsyslog status
service rsyslog start

crond

Jobs run by crond.service

# systemv
systemctl <status|start|stop|restart> crond

# service
service crond <status|start|stop|restart> crond

On macOS

1. Open the Crontab config file

crontab -e

2. Install / Edit a crontab

* * * * * /usr/local/bin/terminal-notifier -title "定时提醒" -message "测试每分钟弹浮窗" -ignoreDnD -group 1
0,30 * * * * /usr/local/bin/terminal-notifier -title "定时提醒" -message "该喝水了～" -ignoreDnD -group 1
10 */1 * * * /usr/local/bin/terminal-notifier -title "定时提醒" -message "该活动颈椎了～" -ignoreDnD -group 2 ​​​

Not Working?

allow-cron-full-disk-access-mac.jpg