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telnetd error

Posted on 1998-05-12
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Last Modified: 2013-12-27
We have a Sun server with an Informix database loaded on it.  About 60 users from PC's and other Suns telnet to the server to gain access to the database off and on throughout the day.  Here lately, i guess more users are trying to telnet at the same time and we get an error message like this:

telnetd:  All network ports in use.
Connection closed by foreign hosts.

What can be done to increase the number of users that can log into the Sun system at one time?

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Question by:j_k
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wex earned 50 total points
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You're not going to like this answer, but that's a kernel feature which is controlled by a compile-time constant.  If you like, I can explain why it's done that way but the short answer is that system resources are not infinite.

One possible answer would be to put more memory into the Sun.  This won't increase the number of concurrent telnet sessions which it allows, but it should make users' operations go faster so they'll get done quicker and be off sooner.  Likewise, getting a faster disk for the database might help.

Finally, you might be able to "solve" the problem socially.  Let your users know that telnet sessions are a limited resource and ask them to close their telnet sessions instead of sitting idle.  You can sort of enforce this by putting an autologout timeout into peoples' .cshrcs or somesuch.  This will boot them off when they're idle for X minutes (20-60 usually).
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by:j_k
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Wex, i would like more information as to how to modify the kernel, to gain telnet access points.  Unless thier is reason for not doing this.  I remember in the past we had to make some kernel changes, and all went well.
This server currently has 128mb of memory, it seems sufficient.  Is there a method for determining how much is used?
Also,  Can you elaborate on how to set up an autologout feature?  I'm not sure i want to use it for telnet, but there may be some other area i might want to implement this.

j_k

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by:wex
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OK, if you have the ability to recompile the kernel it's pretty simple -- there are constants in various .h files and all you need to do is find the one which is controlling telnet connections and change it.  You might also need to increase the total number of possible open file descriptors for the kernel as a whole (since each telnet session consumes at least 3 fds).

As for determining how much memory is in use at any given time, it varies by OS and I don't have a Sun handy to test it out.  Try swap -s

As for the autologout, it's set on a per-user basis; you can't actually control whether it's used on telnet connections without some clever shell-script hacking.  In general, you can put a line in peoples' .cshrc files which says something like
     set autologout=20

which should log them out after 20 minutes of idleness.
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by:j_k
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wex,
I didn't see any reference to telnet setting's in the *.h files.  Where or what reference should i be looking for?

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by:braveheart
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One approach that might work is to provide a CGI web browser interface to the database. This might involve a lot of work and you might still get contention for system resources but at least it would get round the idle login problem because connections would only be maintained for the duration of each access.

Another alternative would be to see investigate whether Informix provide some TCP/IP access to the database which could be accessed from the client machines. Again, this could be quite a lot of work but might prove to be the best ultimate solution.
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Thanks for the ideas.  Not sure what i will do, but for now this is not a pressing problem anymore; yeah right!  Wait till someone complains again!!
Thanks for now?

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