1. Like tron and not kron, or chron
cron
Like tron and not kron, or chron

2. And crontabs… Like the windows task scheduler
Unix’s have a traditional job scheduling daemon named cron
$crontab is the command used to display/edit a user’s crontab file

3. Each user has their own
One crontab per user stored in /var/spool/cron/crontabs
This directory is not typically open for user viewing
Users can edit their file with a $crontab –e command

4. File must use a special record layout
Format is generally ‘at this time on this date run this command’
MM HH DM MN WK Command
Minutes
Hour
DayofMonth
Month
DayofWeek

5. Here are some sample records
#comments in file begin with a ‘#’
# run five minutes after midnight, every day
5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
# run at 2:15pm on the first of every month -- output mailed to paul
* * $HOME/bin/monthly
# run at 10 pm on weekdays, annoy Joe 0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%

6. More examples #using a ‘-’ to mean all values in between
#adding a ‘/2’ means to skip values
/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday“
#using either ‘sun’ or 0 or 7 for Sunday
5 4 * * 0 echo "run at 5 after 4 every sunday"
5 4 * * sun echo "run at 5 after 4 every sunday"

7. Commands $crontab –e #edit user’s crontab file
$crontab –l #list user’s crontab file
If you’re logged in as root and would like to view or edit a user’s file,
#crontab –u <username> -l or -e