Databases Reference
In-Depth Information
■
Don't schedule the jobs that you enter in
cron
to run all at the same time. rather, spread them out so as not to
bog down
cron
or the system at any particular point in time.
Tip
Scheduling a Job to Run Automatically
To schedule a job, you must add a line in your
cron
table, specifying the time you want the job to execute. There are
two methods for adding entries in your
cron
table:
cron
table file directly
•
Editing the
cron
table from a file
•
Loading the
These two techniques are described in the following sections.
Editing the cron Table Directly
You an edit your
cron
table directly with the
-e
(editor) option of the
crontab
command:
$ crontab -e
When issuing the previous command, you will be presented with a file to edit. This file is known as your
cron
table (
crontab
). To schedule a script named
backup.bsh
to run daily, at 11:05 pm, enter the following line into your
cron
table:
5 23 * * * /home/oracle/bin/backup.bsh
Here, the 5 specifies that the job will run at 5 minutes after the top of the hour. The 23 is military time, specifying
that the job should run in the 2300 hour window (in this example, 5 minutes after the hour). The three stars (
* * *
)
signify that the job should run every day of the month, every month of the year, and every day of the week.
Exit the
cron
table file. If your default editor is
vi
, then type
wq
to exit. When you exit
crontab
, your
cron
table is
saved for you. To view your
cron
entries, use the
-l
(list) option of the
crontab
command:
$ crontab -l
To remove your
cron
table completely, use the
r
option:
$ crontab -r
Before running the previous command, you should save your
cron
table in a text file, as shown:
$ crontab -l > saved.cron
In this way, you can refer to the saved file, in the event that you didn't mean to delete your
cron
table.
■
Tip
I once worked with a Dba who thought
crontab -r
meant “read the
cron
table.” Don't ever make that mistake.
