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Article #1949Re: SUMMARY: cpu usage of unused but enabled serial port
From: Mike Dixon
Date: Tue, 17 Nov 1992 19:51
Date: Tue, 17 Nov 1992 19:51
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(this should probably be put in the FAQ)
why does an unused serial port consume cpu?
because you've got a (probably fairly long) unshielded serial cable
attached to it, with either nothing at the other end or a powered-off
device at the other end. EE's call this an antenna. it's probably
picking up most of the radio stations in your area, which the serial
chip is interpreting as a continuous stream of garbage bytes, which
it feeds to getty, which tries to interpret them as login attempts.
how do you avoid this problem?
- leave the device at the other end switched on (even when it's not
transmitting, it will assert a voltage that overrides the noise)
- unplug the cable from the next when you're not using it
- use 'kill -STOP' & 'kill -CONT' to stop & resume the getty process
as needed
- buy an adequately shielded serial cable
.mike.
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Path: arc1-ca.pugleaf.net!sparky!uunet!zaphod.mps.ohio-state.edu!uwm.edu!biosci!parc!mdixon From: mdixon@parc.xerox.com (Mike Dixon) Newsgroups: comp.sys.next.sysadmin Subject: Re: SUMMARY: cpu usage of unused but enabled serial port Message-ID: <mdixon.722029867@thelonius> Date: 17 Nov 92 19:51:07 GMT References: <1992Nov17.142613.27644@news.th-darmstadt.de> Sender: news@parc.xerox.com Organization: Xerox PARC Lines: 24