2006隨手札記

Cron

#crontab [-u user] file
#crontab [-l | -r | -e]

restrict allow user
/etc/cron.allow (預設不存在, all user都允許, 除非黑名單deny, 才不允許使用)
/etc/cron.deny


1. user's crontab file

#crontab -e
a b c d e command-scripts

a: minute [0-59]
b: hour [0-23]
c: day of month [1-31]
d: month [1-12]
e: day of week [0-7, 0 or 7 = Sunday, 1=Monday]

2. system crontab file

#將需要執行的scripts放入目錄中, ex: cron.hourly/a.scripts. 每小時就會執行一次
/etc/cron.hourly/*
/etc/cron.daily/*
/etc/cron.weekly/*
/etc/cron/monthly/*

[root@server1 sysconfig]# cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly

假設Sever並不是每天都開機(或停電)情況, 沒有執行到crontab file
在一開機時就會去執行 anacron system, 將沒做完的scripts繼續做完

[root@server1 cron.daily]# cat /etc/anacrontab
# /etc/anacrontab: configuration file for anacron

# See anacron(8) and anacrontab(5) for details.

SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

1 65 cron.daily run-parts /etc/cron.daily
7 70 cron.weekly run-parts /etc/cron.weekly
30 75 cron.monthly run-parts /etc/cron.monthly

field 1: not been run in this many days
field 2: wait this number of minutes after reboot and then run it
field 3: job identifer(描述)
field 4: job to run