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runaway processes using cpu time

Subject: Re: Defunct processes hogging CPU?
References: <u7kru9af1iosb0@corp.supernews.com> 
From: spcecdt@deeptht.armory.com (John DuBois)
Date: 26 Feb 2002 02:56:03 GMT

In article <u7kru9af1iosb0@corp.supernews.com>,
Scott <news@sccsx-ltd.co.uk> wrote:
>I've noticed on our OSR5.0.5 system, that defunct processes (or processes
>that have been grabbed by init, where users have not logged off properly),
>seem to be hogging the CPU.
>These processes always have a very high C value on the PS listing, are
>always at the top of top, and send the load average on w sky high.
>Also, if there's two or three of these, sar reports idle time or 0%, it's
>normally rarely below 85!
>As soon as I've killed them off, everything returns to normal.
>
>Why should SCO bother with these redundant processes?

These are not defunct processes.  Defunct processes (zombies) are dead by
definition, and cannot consume CPU time.  The usual cause of the problem you
are seeing is an application that ignores failure indication when reading from
the tty and so after the tty is closed goes into a read loop consuming as much
CPU time as it can.  You can try setting SECSTOPIO to 1 (5.0.4 and later
only!), so that the process will get an extra signal when it tries this.  If
that doesn't work, you can try setting a CPU time limit to minimize the CPU
thrashing that misbehaving processes cause (invoke the application through a
ksh script that first does 'ulimit -t nnn').

        John
-- 
John DuBois  spcecdt@armory.com  KC6QKZ/AE  http://www.armory.com/~spcecdt/
 

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