How to find?

Using the find command:

Search and list all files from current directory and down for the string PQR:

find ./ -name "*" -exec grep -H PQR {} \;

find ./ -type f -print | xargs grep -H "PQR" /dev/null

find . -type f -exec grep "string or options" /dev/null {} \;

Normally using only:

$ find . -type f -exec grep "string/options" {} \;

What is Cron?

CRON - Scheduling a re-occurring task:

Run a script  hourly, daily, weekly or monthly

/etc/cron.hourly/

/etc/cron.daily/

/etc/cron.weekly/

/etc/cron.monthly/

These are preconfigured schedules. To assign a very specific schedule add a line to the /etc/crontab file. Cron entries may also be added to a crontab formatted file located in the directory /var/spool/cron/.

Crontab Syntax:

A crontab file has five fields for specifying day , date and time  followed by the command to be run at that interval.

*     *   *   *    *  command to be executed

-     -    -    -    -

|     |     |     |     |

|     |     |     |     +----- day of week (0 - 6) (Sunday=0)

|     |     |     +------- month (1 - 12)

|     |     +--------- day of month (1 - 31)

|     +----------- hour (0 - 23)

+------------- min (0 - 59)

Scheduling access and control:

/etc/cron.deny and /etc/cron.allow :to allow users to use this facility

The at facility may be controlled with the /etc/at.deny and /etc/at.allow files.

Reference:Man pages:

cron

crontab