Linux Crontab Format
crontab - maintains crontab files for individual users
crontab [-u user] file crontab [-u user] [-l | -r | -e] [-i] [-s] crontab -n [ hostname ] crontab -c
DESCRIPTION Crontab is the program used to install, remove or list the tables used to serve the cron(8) daemon. Each user can have their own crontab, and though these are files in /var/spool/, they are not intended to be edited directly.
Running cron jobs can be allowed or disallowed for different users. For this purpose, use the cron.allow and cron.deny files. If the cron.allow file exists, a user must be listed in it to be allowed to use cron If the cron.allow file does not exist but the cron.deny file does exist, then a user must not be listed in the cron.deny file in order to use cron. If neither of these files exists, only the super user is allowed to use cron. Another way to restrict access to cron is to use PAM authentication to set up users, which are allowed or disallowed to use crontab or modify system cron jobs in the /etc/cron.d/ directory.
The temporary directory can be set in an environment variable. If it is not set by the user, the /tmp directory is used.