OK!!.I'm a true newbie when it comes to Linux, but I really want to learn as much as I can. I switch from Red Hat to Ubuntu and I was using the crontab command and something strange happen. Keep in mind I'm totally playing around with these commands and I dont fully understand what they are able to do. Any good website will help tpp. But can someone PLEASE TELL WHAT JUST HAPPENED BELOW?

/home/newbie crontab
10 3 17 6 0 ps -uax> cron_ps_output

then I tried
/home/newbie crontab -l
#DO NOT EDIT THIS FILE - edit the master and reinstall.
#(-installed on Sat Jun 18 11:58:19 2011)
#(Cron version - $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)

10 3 17 6 0 ps -uax> cron_ps_output
/home/newbie crontab -r
/home/newbie crontab -l

no crontab for newbie

look , you can get most important information of each tools by using a 'man crontab' or man [some-thing] .

remember each program get it's argument after it's name not before it.
you can redirect the standard output of your program to specific file by '>' command as you did with 'ps' command output.

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OK. I understand that part, but what does this part mean.

/home/newbie crontab -l
#DO NOT EDIT THIS FILE - edit the master and reinstall.
#(-installed on Sat Jun 18 11:58:19 2011)
#(Cron version - $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)


I'm wondering if I did something really wrong.

1.you should know what crontab really do !
2.which file you had tried to change ?
3.what is your directory content ?!
ans:
1. $man crontab
2. $crontab [option] file // what was that file ?
3. $ls -l // see if there is related file to crontab

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$ crontab -l
$ crontab -r
$ crontab -l

You showed what is in your crontab, then you deleted your crontab, then you showed it again. The lines beginning with '#' are comments at the top of your crontab telling you not to change the file because you might prevent something from running properly.

As stated before more information can be displayed by "man crontab" in a console.

Hope this helps you.

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You edit crontab files by running crontab -e to bring up the editor, not by editing them directly.

Good reference here: http://adminschoice.com/crontab-quick-reference

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You can take look at /var/spool/cron/crontab directory. Here is your cron locates.
Do not modify the file on /var/spool/cron/crontab. Use crontab -e to make change.

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Even if you've used 'crontab -e' to modify your crontab, you may still see those "Do not edit this file" lines. As long as you're cron jobs are working and you are using 'crontab -e' to modify your crontab, you are probably fine.

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Thank you everyone for all your help. I've learned a lot