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  1. #1
    Join Date
    Feb 2004
    Posts
    16

    How to configure crontab

    Appreciate if you can show me the correct way to configure a cron job in unix. FYI, I need to create a cron job to run a shell script daily and this script must be run by user 'abc'. How can I acheive that?

    FYI, I have tried to configure them but it doesn't work. Below is the steps I took:

    1. run commad 'crontab -e -u abc'. It gave me 'ed' editor and I totally not familar at all. How can I change to vi editor?

    2. Since I cannot write/append a cron job in the crontab file (due to the unfamilarity with ed editor), I cheatly copied 'root' crontab file in /var/spool/cron/crontab folder to a new 'abc' crontab file and removed the entire content and insert a new cron job. I restarted the server and it still didn't run the program. Am I doing the right way?

  2. #2
    Join Date
    May 2003
    Location
    France
    Posts
    112

    Re: How to configure crontab

    login as abc

    export EDITOR=vi
    crontab -e



    Originally posted by tanboonhoe
    Appreciate if you can show me the correct way to configure a cron job in unix. FYI, I need to create a cron job to run a shell script daily and this script must be run by user 'abc'. How can I acheive that?

    FYI, I have tried to configure them but it doesn't work. Below is the steps I took:

    1. run commad 'crontab -e -u abc'. It gave me 'ed' editor and I totally not familar at all. How can I change to vi editor?

    2. Since I cannot write/append a cron job in the crontab file (due to the unfamilarity with ed editor), I cheatly copied 'root' crontab file in /var/spool/cron/crontab folder to a new 'abc' crontab file and removed the entire content and insert a new cron job. I restarted the server and it still didn't run the program. Am I doing the right way?

  3. #3
    Join Date
    Jan 2004
    Location
    Bordeaux, France
    Posts
    320
    You can also do :

    Code:
    crontab -l > crontab.dat
    vi crontab.dat
    crontab crontab.dat
    same as 'crontab -e', but 3 commands instead of only one ....
    Jean-Pierre.

  4. #4
    Join Date
    Feb 2004
    Posts
    16
    Originally posted by aigles
    You can also do :

    Code:
    crontab -l > crontab.dat
    vi crontab.dat
    crontab crontab.dat
    same as 'crontab -e', but 3 commands instead of only one ....
    Thanks.. it helps a lot... Cheers

  5. #5
    Join Date
    Apr 2009
    Posts
    2

    Need help!!!!!!!!!!!!

    Hi,

    I am extremely new to Crontab stuffs. The problem i am facing is i need to run a shell script every 15 minutes by itself.

    I need to use crontab to accomplish the task. I tried to use the above steps but the message i am getting is " cannot create mycrontab".

    Consider me as a layman in this crontab technology and please let me know the steps i can follow to solve the problem.

    Thanks in advance.

  6. #6
    Join Date
    Jan 2007
    Location
    Jena, Germany
    Posts
    2,721
    "man crontab" didn't help you?
    Knut Stolze
    IBM DB2 Analytics Accelerator
    IBM Germany Research & Development

  7. #7
    Join Date
    Apr 2009
    Posts
    2

    Red face

    Quote Originally Posted by stolze
    "man crontab" didn't help you?
    After doing enough RnD on net i have sufficient idea about crontab. My basic problem is how to configure it.

    "man crontab" also gave me some idea. The problem is i am not able to open crontab file using crontab -l. I thought of creating a crontab file where i can write down the commands and access my shell script, but when i am trying, its giving cant create. When i am trying to open the crontab , its giving cant open your crontab.

    Now i am wondering what shd i do.

  8. #8
    Join Date
    Jun 2009
    Location
    South Africa
    Posts
    33
    Quote Originally Posted by pkumar5
    After doing enough RnD on net i have sufficient idea about crontab. My basic problem is how to configure it.

    "man crontab" also gave me some idea. The problem is i am not able to open crontab file using crontab -l.

    Now i am wondering what shd i do.
    If no valid crontab has been created for the user yet, "crontab -l" has nothing to display. You might have also created the file as root, with the group set as root as well. This means that accessing the file as user 'abc' will not work, as 'abc' might not have permissions to access the file.
    Crontab files usually exists with permissions as follow (linux example) :
    [root@srvtst ~]# ls -l /var/spool/cron
    total 8
    -rw------- 1 abc root 1960 Jun 10 2009 abc

    Note that the file here belongs to user abc, and group is set as root. File permission is set to 600 (chmod), which is user has rw, no-one else has access.

    Either fix the permissions, or possibly delete / rename the crontab file that you created. Log in as the abc user. Ensure you can access the crontab with "crontab -e" and add / edit the intended line(s).
    If there is no crontab file, the first -e invocation will create it if you add at least one character/line to the file.

    It's always a good idea to add a similar "comments" heading to the file, just for your own reference :
    Code:
    # Crontab layout :
    # The first five fields shall be integer patterns that specify the following:
    #  1. Minute [0,59]
    #  2. Hour [0,23]
    #  3. Day of the month [1,31]
    #  4. Month of the year [1,12]
    #  5. Day of the week ([0,6] with 0=Sunday)
    # Each  of  these  patterns  can be either an asterisk (meaning all valid
    # values), an element, or a list of elements separated by commas. An ele-
    # ment  shall  be  either  a  number or two numbers separated by a hyphen
    # (meaning an inclusive range).
    
    ################################################################################
    # Run doyourthang.sh script daily at 03:00 on weekdays to "do your thang"
    ################################################################################
    00 03 * * 1-5 /home/abc/scripts/doyourthang.sh > /dev/null 2>&1
    
    #######
    # Fin #
    #######
    Edit: Wanted to add the comment on the " > /dev/null 2>&1" at the end of the crontab line. We always cat unwanted output from crons to /dev/null, so no mails are generated from the crons - in most cases nobody will ever read this. Our scripts do error checking internally, and mails required output to the various admins or groups accordingly.
    Last edited by Lerac; 06-22-09 at 12:27.

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