Quote:
Originally Posted by hemi
actually i dont no what is CRON job , can u tell me how to use this
|
Crontab is like an alarm clock. It's a TASK SCHEDULER. It's just a text file you create on your webserver (if they allow crontab - if they don't then MOVE to a REAL ISP.). The crontab file looks like this (below)
0 * * * * /etc/reset.cgi
0 0 * * * /etc/resetlogs.cgi
So what does this mean? Very simple. In this example we have a crontab file that contains 2 commands. A crontab file can have any number of commands. You put one command per line so [ 0 * * * * * /etc/reset.cgi ] is COMMAND ONE and [ 0 0 * * * /etc/resetlogs.cgi ] is COMMAND TWO. I could have COMMAND THREE - COMMAND 2,000 if I wanted to but what is important is you only put ONE COMMAND PER LINE. Also EVEN MORE IMPORTANT after the LAST COMMAND you MUST HAVE A BLANK LINE or CRONTAB WILL NOT RUN.
Ok, so let's look at each command. Here is what we have - very simple just remember this is just like setting an alarm clock. Each line or COMMAND is SCHEDULED to run at a specific time. The first 5 fields deal with setting the time the command (second field) will run.
0 * * * * is the SCHEDULE for COMMAND ONE [ /etc/reset.cgi]
0 0 * * * is the SCHEDULE for COMMAND TWO [ /etc/resetlogs.cgi]
The way the schedule looks is very cryptic but its really very simple. There are FIVE fields to the SCHEDULE
MINUTE(0-59) HOUR(0-23) DAYOFMONTH(1-31) MONTHOFYEAR(1-12) DAYOFWEEK(0-6) Note 0 = Sun
Also note that the ASTERISK (*) is what's called a WILDCARD meaning it will match any value.
Now maybe its a little clearer: The first command of our example
0 * * * * /etc/reset.cgi
Means literally "execute the script located at /etc/reset.cgi whenever the clock is equal to 0 minutes on ANYDAY, ANY HOUR,ANY DAYOFMONTH,ANY DAYOFWEEK. So the script is set to run ONCE PER HOUR EXACTLY ON THE HOUR regardless of what day it is or what hour.
Now the SECOND COMMAND
0 0 * * * /etc/resetlogs.cgi
is a little more picky. This crontab runs again whenever the internal clock hits ZERO (0) Minutes, but instead of running once per minute it will only run once per day. WHY? Because we also set the HOUR to zero so BOTH the MINUTES and HOUR must be equal to zero before crontab will execute /etc/resetlogs.cgi. So this example runs once per DAY at MIDNIGHT server time.
Now, you can get even more picky, final example lets setup a crontab to run only on Tuesday at 2:21 PM.
MIN = 21
HOUR = 14 (ah ha! note we are in a computer - only understands military time)
DAYOFMONTH = * (who cares as long as its on a Tuesday)
MONTHOFYEAR = * (again we don't care)
DAYOFWEEK = 2 (sun=0, mon=1, tue=2)
So our crontab entry would be
21 14 * * 2 /path/to/whatever/script.cgi
UPLOADING AND EXECUTING CRONTAB(s)
It does not matter what you call your crontab file. You should name it something so you remember what the file is (eg: cronstats or croncgi) or whatever.
Upload as ASCII file (they are text files) all text files are ASCII
When you are done with all that telnet into your server and run the crontab file by going to the directory containing the crontab file (again - it makes no difference where you put the crontab file). I would suggest making a special hidden directory or using a directory inside your cgi-bin so nobody can see it. So to finish and execute your crontab file just telnet into your server and type:
cd /path/to/crontab/directory
crontab nameofcrontabfile
================================================== ===========
Examples:
*/15 * * * * cp -f /dev/null /var/log/cgi.log
Copies /dev/null to the /var/log/cgi.log file every 15 minutes. This empties the file but doesn't delete it.
0,15,30,45 * * * * /usr/bin/foo
Will run /usr/bin/foo every 15 minutes on every hour, day-of-month, month, and day-of-week. In other words, it will run every 15 minutes for as long as the machine it running.
10 3 * * * /usr/bin/foo
Will run /usr/bin/foo at 3:10am on every day.
10 * 1 * * /usr/bin/foo
Will run /usr/bin/foo at 12:10am on the first day of the month.
10 * * 1 * /usr/bin/foo
Will run /usr/bin/foo at 12:10am on the first month of the year.
10 14 * * 1 /usr/bin/foo
Will run /usr/bin/foo at 2:10pm on every Monday.
There are more options for these. See man man crontab -S 5.
You must use crontab to load cron jobs into cron. First create a text file that uses the above rule to describe the cron job that you want to load into cron. But before you load it, type crontab -l to list any jobs that are currently loaded in crontab.
If none are listed, then it is safe to load your job. Example. If you wanted to run /usr/local/bin/foo once a day at 3:10am, then create a text file
10 3 * * * /usr/bin/foo
Save it as foo.cron. Then type crontab foo.cron. Check to see if it was loaded by typing crontab -l. It should display something like this:
# DO NOT EDIT THIS FILE - edit the master and reinstall.
# (ipwatch.cron installed on Thu Nov 18 11:48:02 1999)
# (Cron version -- $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)
10 3 * * * /usr/bin/foo
If you want to edit the cron job, then edit foo.cron and then remove the existing cron job (crontab -r) and load it again (crontab foo.cron). You can have multiple jobs. Just put each different one on a separate line in foo.cron.
Linear Mode
