Linux crontab

[root@localhost target]# crontab -help

crontab: invalid option -- 'h'

crontab: usage error: unrecognized option

Usage:

 crontab [options] file

 crontab [options]

 crontab -n [hostname]

Options:

 -u <user>  define user

 -e         edit user's crontab

 -l         list user's crontab

 -r         delete user's crontab

 -i         prompt before deleting

 -n <host>  set host in cluster to run users' crontabs

 -c         get host in cluster to run users' crontabs

 -s         selinux context

 -x <mask>  enable debugging

Default operation is replace, per 1003.2

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[root@localhost etc]# pwd

/etc

[root@localhost etc]# more 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

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[root@localhost cron]# cat /var/spool/cron/root 

30 4 * * * /home/ops_scripts/reboot_router.py