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Old 09-16-2009, 02:34 PM   #1
btncix
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what is the difference between at and sleep


I saw this come up in
this thread, but I thought I should start a separate thread for this question. Please let me know if I should have kept this in the original thread.

I was wondering what the difference is in using at or sleep. The case I'm thinking of comes from the thread linked above:

case 1:
somewhere in /etc/rc.d/rc.local
at -f /path/to/script now + 5 min

case 2:
somewhere in /etc/rc.d/rc.local
/path/to/your/script &
at the top of /path/to/your/script
sleep 300


Specifically, I was wondering in terms of process context switch - which I know little about. I assume there is an efficient context switch in case 1 such that /path/to/script won't be eating up cpu cycles the first 5 mintues of its calling. Is the behavior the same for case 2? I assume the sleep command does not eat up cpu cycles according to this thread, but I wasn't sure.

I would also appreciate any other difference that you see between the two cases. Thanks.
 
Old 09-16-2009, 02:41 PM   #2
repo
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Quote:
sleep 300
will wait 300 sec before it executes, rc.local script will also wait for 300 sec, untill the script is executed; before it can continue

Quote:
at -f /path/to/script now + 5 min
The script will be executed in 5 minutes, rc.local will continue to execute

Last edited by repo; 09-16-2009 at 03:06 PM.
 
Old 09-16-2009, 03:05 PM   #3
anomie
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Note also that at will run in a separate thread (from the script), and it will have its own environment. See the at(1) manpages for more info.
 
Old 09-16-2009, 06:35 PM   #4
kapilbajpai88
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Hi All,

Sorry to interrupt in between, but what would be the better idea of scheduling a job...'at' or 'sleep' , especially when the cpu resources are the major concern for the execution of the job?

Regards,
Kapil
 
Old 09-16-2009, 06:39 PM   #5
repo
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Quote:
Originally Posted by kapilbajpai88 View Post
Sorry to interrupt in between, but what would be the better idea of scheduling a job...'at' or 'sleep' , especially when the cpu resources are the major concern for the execution of the job?
Depends what you want to do
How about cron ?
 
Old 09-16-2009, 06:44 PM   #6
kapilbajpai88
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Hi Repo,

Thank you for the reply....
I have a script that needs to be run in 1 hr of interval for three times in the night time. Script adds 100 records to Oracle table after every 1 hr. I was thinking to set 'at' like that it executes after every 1 hr on its own, but I lost it to stop and it keeps on executing after every 1 hr throughout the night untill unless we manually stops that.

can 'wait' solve out problem ??

Cheers,
Kapil.
 
Old 09-16-2009, 06:48 PM   #7
repo
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You can setup a cronjob for this
Take a look at
http://unixgeeks.org/security/newbie/unix/cron-1.html
 
Old 09-16-2009, 06:50 PM   #8
chrism01
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Use cron for that: http://www.adminschoice.com/docs/cro...Crontab%20file
 
Old 09-16-2009, 07:01 PM   #9
kapilbajpai88
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Hi All,

I think CRON will be a better idea for my work...I will go through the links again in detail and will edit the script accordingly.

Thank You All,
Kapil.
 
Old 09-16-2009, 09:36 PM   #10
btncix
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I'm not clear on what repo posted:

Wouldn't the & allow the rest of rc.local to get executed without waiting for /path/to/your/script to finish executing?

Also, how does the sleep command work exactly. This thread seems to explain that the sleep command doesn't eat up cpu cycles, but that a context switch occurs with the process, and the operating system will awaken the process after 300 seconds. So during the 300 seconds, no cpu cycle is used for /path/to/your/script. Is my understanding of this correct?


case 2: note: you have TWO files here

somewhere in /etc/rc.d/rc.local
/path/to/your/script &

at the top of /path/to/your/script
sleep 300
 
  


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