cron in Mac OS X

By: Strauss K Emailed: 1673 times Printed: 2153 times    

Latest comments
By: rohit kumar - how this program is work
By: Kirti - Hi..thx for the hadoop in
By: Spijker - I have altered the code a
By: ali mohammed - why we use the java in ne
By: ali mohammed - why we use the java in ne
By: mizhelle - when I exported the data
By: raul - no output as well, i'm ge
By: Rajesh - thanx very much...
By: Suindu De - Suppose we are executing

Daemon to execute scheduled commands (Vixie Cron).

Syntax
      cron [-s] [-o] [-x debugflag[,...]]

Options
     -o      Disable the special handling of situations when the GMT offset of
             the local timezone changes, to be compatible with the old (default)
             behavior.

     -s      Enable special handling of situations when the GMT offset of the
             local timezone changes, such as the switches between the standard
             time and daylight saving time.

             The jobs run during the GMT offset changes time as intuitively
             expected.  If a job falls into a time interval that disappears
             (for example, during the switch from standard time) to daylight
             saving time or is duplicated (for example, during the reverse
             switch), then it's handled in one of two ways:

             The first case is for the jobs that run every at hour of a time
             interval overlapping with the disappearing or duplicated inter-
             val.  In other words, if the job had run within one hour before
             the GMT offset change (and cron was not restarted nor the
             crontab changed after that) or would run after the change at
             the next hour.  They work as always, skip the skipped time or run
             in the added time as usual.

             The second case is for the jobs that run less frequently.  They
             are executed exactly once, they are not skipped nor executed
             twice (unless cron is restarted or the user's crontab is
             changed during such a time interval).  If an interval disappears
             due to the GMT offset change, such jobs are executed at the same
             absolute point of time as they would be in the old time zone.
             For example, if exactly one hour disappears, this point would be
             during the next hour at the first minute that is specified for
             them in crontab.

If both options -o and -s are specified, the option specified last wins.

Cron should be started from /etc/rc or /etc/rc.local. It will return immediately, so you don't need to start it with '&'.

Cron searches /var/cron/tabs for crontab files which are named after accounts in /etc/passwd; crontabs found are loaded into memory. Cron also searches for /etc/crontab which is in a different format . Cron then wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute. When executing commands, any output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab, if such exists).

Additionally, cron checks each minute to see if its spool directory's modtime (or the modtime on /etc/crontab) has changed, and if it has, cron will then examine the modtime on all crontabs and reload those which have changed. Thus cron need not be restarted whenever a crontab file is mod- ified. Note that the crontab command updates the modtime of the spool directory whenever it changes a crontab.


macos Home | All macos Tutorials | Latest macos Tutorials

Sponsored Links

If this tutorial doesn't answer your question, or you have a specific question, just ask an expert here. Post your question to get a direct answer.



Bookmark and Share

Comments(0)


Be the first one to add a comment

Your name (required):


Your email(required, will not be shown to the public):


Your sites URL (optional):


Your comments:



More Tutorials by Strauss K
cut in Mac OS X
curl in Mac OS X
crontab in Mac OS X
cron in Mac OS X
cp in Mac OS X
continue in Mac OS X
complete in Mac OS X
command in Mac OS X
comm in Mac OS X
cmp in Mac OS X
cksum in Mac OS X
chroot in Mac OS X
chown in Mac OS X
chmod in Mac OS X
chgrp in Mac OS X

More Tutorials in macos
Getting PHP running on Mac OS 10.1
Installing gedit for python programming in Mac OS X
What is Mac OS X?
History of Mac OS X
Major features of Mac OS X
Different Versions of Mac OS X
What is new in Mac OS X Snow Leopard
alias, unalias in Mac OS X
apropos in Mac OS X
awk in Mac OS X
basename in Mac OS X
bash in Mac OS X
bg in Mac OS X
bless in Mac OS X
break in Mac OS X

More Latest News
Most Viewed Articles (in macos )
cut in Mac OS X
History of Mac OS X
alias, unalias in Mac OS X
basename in Mac OS X
bash in Mac OS X
cal, ncal in Mac OS X
caller in Mac OS X
case in Mac OS X
cat in Mac OS X
chflags in Mac OS X
chgrp in Mac OS X
chmod in Mac OS X
comm in Mac OS X
command in Mac OS X
cron in Mac OS X
Most Emailed Articles (in macos)
cal, ncal in Mac OS X
cut in Mac OS X
bg in Mac OS X
builtin in Mac OS X
cd in Mac OS X
chflags in Mac OS X
chmod in Mac OS X
chroot in Mac OS X
cmp in Mac OS X
comm in Mac OS X
cp in Mac OS X
What is Mac OS X?
Major features of Mac OS X
Different Versions of Mac OS X
apropos in Mac OS X