CRON

Cron can be configured using crontab.
An explanation of the configuration is available in /etc/crontab file (see below).

# .---------------- 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

Prior to create the cron job, make sure your command/script is working:

# find /var -type f -name "*.log" >> /var/log/varfiles
# cat /var/log/varfiles

Create the cron job using crontab. Set it to run every monday at 1h20am:

# crontab -e
    [...]
    20 1 * * 1 find /var -type f -name "*.log" >> /var/log/varfiles
    [...]

List the cronjobs for user root:

# crontab -l


AT

at tool is a very useful tool to schedule an action at a later time without setting up a cron job.
This tool is not installed by default in CentOS 7 minimal installation.

Install at:

# yum install -y at

Add alice to the file /etc/at.deny to forbid her to use at tool:

# echo alice > /etc/at.deny

Add ben to the file /etc/at.allow to allow him to use at tool:

# echo ben > /etc/at.allow

Let’s check:

# su - alice
$ at
	You do not have permission to use at.
$ exit
# su - ben
$ at
	Garbled time