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Top Forums UNIX for Dummies Questions & Answers nohup has a terrible bad performance compared with interactive command, why? Post 302289552 by viniciov on Friday 20th of February 2009 12:19:35 AM
Old 02-20-2009
Question 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
 

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NICE(1) 						      General Commands Manual							   NICE(1)

NAME
nice, nohup - run a command at low priority (sh only) SYNOPSIS
nice [ -number ] command [ arguments ] nohup command [ arguments ] DESCRIPTION
Nice executes command with low scheduling priority. If the number argument is present, the priority is incremented (higher numbers mean lower priorities) by that amount up to a limit of 20. The default number is 10. The super-user may run commands with priority higher than normal by using a negative priority, e.g. `--10'. Nohup executes command immune to hangup and terminate signals from the controlling terminal. The priority is incremented by 5. Nohup should be invoked from the shell with `&' in order to prevent it from responding to interrupts by or stealing the input from the next per- son who logs in on the same terminal. FILES
nohup.out standard output and standard error file under nohup SEE ALSO
csh(1), setpriority(2), renice(8) DIAGNOSTICS
Nice returns the exit status of the subject command. BUGS
Nice and nohup are particular to sh(1). If you use csh(1), then commands executed with ``&'' are automatically immune to hangup signals while in the background. There is a builtin command nohup which provides immunity from terminate, but it does not redirect output to nohup.out. Nice is built into csh(1) with a slightly different syntax than described here. The form ``nice +10'' nices to positive nice, and ``nice -10'' can be used by the super-user to give a process more of the processor. 4th Berkeley Distribution May 8, 1986 NICE(1)
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