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crontab
SYNTAX
/usr/lib/crontab
FUNCTION
crontab holds the schedule of processes to
be spawned/executed by the clock daemon cron.
The file /usr/lib/crontab consists of
entries of six fields each. The fields
are separated by spaces or tabs. The first
five fields are integers, the last one is the
process name.
These fields and the ranges of their values are:
minute hour day month day_of_the_week process
0-59 0-23 1-31 1-12 0-6, Sunday=0 (name)
Let us look at some typical /usr/lib/crontab entries.
0,10,20,30,40,50 * * * * /usr/lib/atrun
20 1 * * * /usr/bin/calendar -
45 16 * * * 5 /usr/weekend/wish
0 9 10 8 * /urgent/vacation
0,10,20,30,40,50 * * * * /usr/lib/atrun
The entry 0,10,20,30,40,50 * * * * /usr/lib/atrun
says that every ten minutes the process
/usr/lib/atrun, should be run!
0,10,20,30,40,50 * * * * /usr/lib/atrun
20 1 * * * /usr/bin/calendar -
The entry 20 1 * * * /usr/bin/calendar - says that at 1:20 AM,
every day the process calendar is to be run!
0,10,20,30,40,50 * * * * /usr/lib/atrun
20 1 * * * /usr/bin/calendar -
45 16 * * * 5 /usr/weekend/wish
The entry 45 16 * * 5 /usr/weekend/wish says that every Friday at 4:45 PM
the program /usr/weekend/wish is to be run.
0,10,20,30,40,50 * * * * /usr/lib/atrun
20 1 * * * /usr/bin/calendar -
45 16 * * * 5 /usr/weekend/wish
0 9 10 8 * /urgent/vacation
The entry 0 9 10 8 * /urgent/vacation says that every year at 9:00 AM
on August 10 the program /urgent/vacation is to be run!
Now, that you have an idea of how to
construct a /usr/lib/crontab entry,
let's write an entry to activate the
program /chore/backup at 9:30 AM
every Friday! (Use space between entries)
That is correct!
You've got it on the 2nd try.
Good, you understand the concept.
There must be six fields separated by spaces!
Think about the ranges of field values!
I will help you this time.
FORGET1
30 9 * * 5 /chore/backup
Observe the result on the terminal!
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