Technical issues on Linux

[Jerry Feldman]

From: Robert Anderson <Robert.E.Anderson at unh.edu>
To: gaf at sauron.zk3.dec.com



Here's my 2 cents worth of information.


>I'm looking for hints on fixing any of three technical problems associated
>with managing high-volume Linux servers...
>
>1)  The TCP connect() system call apparently never times out in current
>  versions of Linux.  This caused mail server crashes here during the AOL
>  outage Tuesday (hundreds of sendmail processes building up, waiting
>  indefinitely for the AOL server to come back up).

I'm surprised this would be in ther kernel.  I would think the
timeouts are settable by the application.  Perhaps a newer version of
sendmail or another of the many mailers (smail or procmail come to
mind) might handle this better?  You might be correct though, this
should be a simple test file to write and see it it does actually
timeout.

>2)  Packet fragmentation problems lead to frequent complaints that the
>  web pages can't be viewed without glitches (this includes www.bcs.org).

Normally this isn't the station itself causing this type of problem.
In most cases is the physical level connections between the computer
and the rest of the net.  Try changing your cables, micro mau,
repeater connection, wall jack, ... etc.  If you have test equipment
you could shoot the line between you and the repeater?  10BaseT (RJ45)
jacks age badly.

>3)  I notice syslogd taking up an inordinate amount of processor time,
>  causing slowdowns in POP3 email access and logins (ftp, etc).  Sometimes
>  it takes upwards of a minute for an item to get logged, if a lot of
>  system activity is taking place, during which the syslogd process (on a
>  P-133, mind you) is racking up 80% or more of CPU usage.

I've been looking at this stuff recently.  First off POP is annoying
since it logs way too much.  You should be able to drop all the crap
that POP sends to syslog in the /etc/syslog.conf file.  Check the man
page for syslogd for some examples.  If you need more information
about that send me email and I'll give you the lines you need.  The
other thing that might help you is to proceed the log files with a '-'
(for instance this would make it look like -/var/log/messages).  This
inhibits the sync that is ussually done after EVERY messages logged.
Keep in mind you might loose some messages in a system crash after
doing this.

Good luck solving these.

- -------------------------------------------------------------
 Robert E. Anderson  		 	email: rea at unh.edu
 Systems Programmer			phone: (603) 862-3489
 UNH Research Computing Center		  fax: (603) 862-1915
- -------------------------------------------------------------


------- End of Forwarded Message