Cara Membuat Crontab


1. Crontab Restrictions
____________
You can execute crontab if your name appears in the file /usr/lib/cron/cron.allow. If that file does not exist, you can use
crontab if your name does not appear in the file /usr/lib/cron/cron.deny.
If only cron.deny exists and is empty, all users can use crontab. If neither file exists, only the root user can use crontab. The allow/deny files consist of one user name per line.


2. Crontab Commands
__________
export EDITOR=vi ;to specify a editor to open crontab file.

crontab -e     Edit your crontab file, or create one if it doesn’t already exist.
crontab -l      Display your crontab file.
crontab -r      Remove your crontab file.
crontab -v      Display the last time you edited your crontab file. (This option is only available on a few systems.)

3. Crontab file
___________
Crontab syntax :-
A crontab file has five fields for specifying day , date and time  followed by the command to be run at that interval.

*     *   *   *    *  command to be executed
–     –    –    –    –
|     |     |     |     |
|     |     |     |     +—– day of week (0 – 6) (Sunday=0)
|     |     |     +——- month (1 – 12)
|     |     +——— day of month (1 – 31)
|     +———– hour (0 – 23)
+————- min (0 – 59)

* in the value field above means all legal values as in braces for that column.
The value column can have a * or a list of elements separated by commas. An element is either a number in the ranges shown above or two numbers in the range separated by a hyphen (meaning an inclusive range).

Note: The specification of days can be made in two fields: month day and weekday. If both are specified in an entry, they are cumulative meaning both of the entries will get executed .

4. Crontab Example
_______

A line in crontab file like below  removes the tmp files from /home/someuser/tmp each day at 6:30 PM.

30     18     *     *     *         rm /home/someuser/tmp/*

Changing the parameter values as below will cause this command to run at different time schedule below :

min hour day/month month day/week Execution time
30 0 1 1,6,12 * — 00:30 Hrs  on 1st of Jan, June & Dec.

:

0 20 * 10 1-5 –8.00 PM every weekday (Mon-Fri) only in Oct.

:

0 0 1,10,15 * * — midnight on 1st ,10th & 15th of month

:

5,10 0 10 * 1 — At 12.05,12.10 every Monday & on 10th of every month
:

Note : If you inadvertently enter the crontab command with no argument(s), do not attempt to get out with Control-d. This removes all entries in your crontab file. Instead, exit with Control-c.

5. Crontab Environment
___________
cron invokes the command from the user’s HOME directory with the shell, (/usr/bin/sh).
cron supplies a default environment for every shell, defining:
HOME=user’s-home-directory
LOGNAME=user’s-login-id
PATH=/usr/bin:/usr/sbin:.
SHELL=/usr/bin/sh

Users who desire to have their .profile executed must explicitly do so in the crontab entry or in a script called by the entry.

6. Disable Email
____________

By default cron jobs sends a email to the user account executing the cronjob. If this is not needed put the following command At the end of the cron job line .

>/dev/null 2>&1


7. Generate log file
________________

To collect the cron execution execution log in a file :

30 18  *    *   *    rm /home/someuser/tmp/* > /home/someuser/cronlogs/clean_tmp_dir.log

4 thoughts on “Cara Membuat Crontab

  1. Para master web
    ditempat

    saya akbar
    nubie dlm hal Cpanel. ada masalah dengan cara setting CRONJOB di cpanel
    begini ceritanya :

    saya beli script dari gemp*r.com, situs saya udah jadi, udah bisa diakses, hanya saja saya sekarang ini ingin setting CRONJOB di Cpanel.

    dari tutorial yang banyak beredar di google, saat setting COMMAND di CRONJOB
    code nya sbb :

    /usr/bin/php -q /home/username/public_html/autoresponder/run.php

    Nah, yang membuat saya binggung adalah : ” username” itu harus diisi apa ya ??
    username untuk login ke Cpanel ?
    username email ?
    username database di Cpanel ?

    Saya udah coba setting dengan username saya untuk masuk ke Cpanel, menjadi :

    /usr/bin/php -q /home/montok2/public_html/autoresponder/run.php

    akan tetapi keesokan harinya saat saya buka email, ada email masuk dari Cron Daemon
    yang mengatakan ” /bin/sh: usr/bin/php: No such file or directory ”

    mohon bantuan para master, karena saya gak tau lagi harus bertanya kepada siapa

    terima kasih
    salam
    akbar

  2. username yang dimaksud adalah username di OS unix/linux server.
    yang paling penting sebenarnya lokasi run.php itu ada dimana?
    jadi command nya spt ini :

    /usr/bin/php -q $DIREKTORI_RUN.PHP/run.php

    tinggal dicari $DIREKTORI_RUN.PHP ada dimana? klo memang sewa webhosting, coba tanya aja ke customer service nya, mereka pasti bisa ngasih lokasinya.

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