#method 1
crontab -e
crontab -u root -e #不同用户自己的任务计划
crontab -l
#method 2
vim /etc/crontab
# 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
这个目录下面很多已经存在的系统级别的计划任务
ll /etc/cron*
/etc/cron.d
├── 0hourly
├── raid-check
└── sysstat
/etc/cron.daily
├── cups
├── logrotate
├── makewhatis.cron
├── mlocate.cron
└── tmpwatch
/etc/cron.deny [error opening dir]
/etc/cron.hourly
└── 0anacron
/etc/cron.monthly
/etc/crontab [error opening dir]
/etc/cron.weekly
