nohup has a terrible bad performance compared with interactive command, why?

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nohup has a terrible bad performance compared with interactive command, why?

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02-20-2009

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nohup has a terrible bad performance compared with interactive command, why?

I have a strange situation. I'm running a shell script containing several data uploads (using Oracle sqlloader utility). This script is being run on a Red Hat server.

I tried to run it in background:

$ nohup upload.sh &

This script uploads some thousands files. After several hours I checked what the nohup.out was showing and I was quite surprised to see it was very and extremely slow, because it just processed around less than a hundred files. Probably it would took more than 3 days to complete...

I ran the script interactively, I mean direct from command line showing output to screen. Surprise! the script ran several times better that when using nohup, finishing less than an hour.

I suspicted this was because the process using nohup has a slower priority than the one being run interactively. That was not true, both processes had the same priority.

Why this behaviour? I'm not a linux expert. Please help.

Thanks

viniciov

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LEARN ABOUT HPUX

nohup

nohup(1)						      General Commands Manual							  nohup(1)

NAME

       nohup - run a command immune to hangups

SYNOPSIS

       command [arguments]

DESCRIPTION

       executes command with hangups and quits ignored.  If output is not redirected by the user, both standard output and standard error are sent
       to If is not writable in the current directory, output is redirected to otherwise, fails. If a file is created, the file's permission  bits
       will be set to

       If output from is redirected to a terminal, or is not redirected at all, the output is sent to

EXTERNAL INFLUENCES

   Environment Variables
       determines the language in which messages are displayed.

       If is not specified in the environment or is set to the empty string, the value of is used as a default for each unspecified or empty vari-
       able.  If is not specified or is set to the empty string, a default of "C" (see lang(5)) is used instead of

       If any internationalization variable contains an invalid setting, behaves as if all internationalization variables are  set  to	"C".   See
       environ(5).

   International Code Set Support
       Single- and multi-byte character code sets are supported.

EXAMPLES

       It  is  frequently desirable to apply to pipelines or lists of commands.  This can be done only by placing pipelines and command lists in a
       single file, called a shell script.  To run the script using

       features apply to the entire contents of file.  If the shell script file is to be executed often, the need to type  can	be  eliminated	by
       setting execute permission on file.  The script can also be run in the background with interrupts ignored (see sh(1)):

       file  typically	contains  normal keyboard command sequences that one would want to continue running in case the terminal disconnects, such
       as:

WARNINGS

       Be careful to place punctuation properly.  For example, in the command form:

       applies only to command1.  To correct the problem, use the command form:

       Be careful of where standard error is redirected.  The following command may put error messages on tape, making it unreadable:

       whereas

       puts the error messages into file

EXIT STATUS

       The following exit values are returned:

	      The command specified by
			command was found but could not be invoked

	      An error occurred in the nohup utility or the specified
			command could not be found

	      Otherwise, the exit status of nohup will be that of the command specified.

SEE ALSO

       chmod(1), nice(1), sh(1), signal(5).

STANDARDS CONFORMANCE

																	  nohup(1)