AUTOMATIC JOBS
As a system administrator some tasks are respective like backup, monitoring, log files.
To automate them with the help of
1)at 2)batch 3)crontab Crontab:to run some tasks automatically to set a crontab for an user #crontab -e -u
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- /bin/echo "hello" A crontab file contains instructions to the cron deamon of the general form "run this command at this time on this date" Cron examines entries once every minute
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field allowed values ----- -------------- minute 0-59 hour 0-23 day of month 1-31 month 1-12 (or names, see below) day of week 0-7 (0 or 7 is Sun, or use names)
A field may be an asterisk (*), which always stands for ‘‘first-last’’.
Ranges of numbers are allowed. Ranges are two numbers separated with a
hyphen. The specified range is inclusive. For example, 8-11 for an
‘‘hours’’ entry specifies execution at hours 8, 9, 10 and 11.
Lists are allowed. A list is a set of numbers (or ranges) separated by
commas. Examples: ‘‘1,2,5,9’’, ‘‘0-4,8-12’’.
EXAMPLE CRON FILE # use /bin/sh to run commands, no matter what /etc/passwd says SHELL=/bin/sh # mail any output to ‘paul’, no matter whose crontab this is MAILTO=paul # # 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 15 14 1 * * $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?% 23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday" 5 4 * * sun echo "run at 5 after 4 every sunday"
To set a crontab for an user #crontab -e -u ex:crontab -e -u alex
To remove a crontab for an user #crontab -r -u ex:crontab -r -u alex