UNIX for Dummies Questions & Answers

hi,

i am using Sun Solaris 8 (Sparc). Currently there is a SNMP agent running on port 161.

How should I change it to port 8001?

which file to modify and restart is necessary?

pls teach me the information.

thanks

You would modify /etc/services. And yes a restart would be needed almost certainly. I'm not familiar with the program that you're using, but I'm never seen a program yet that monitors /etc/services for changes and then dynamically switches ports.

Thanks for the answer, but it does not seem right.

I checked the /etc/services file and confirmed there is no entry for snmp or port 161.

I am pretty sure that my workstation already has a SNMP agent running on port 161. But I am jsut not able to find where the port number is specified and how to change it.

Please give your advice .

Thanks

/etc/services is not (generally) used to change ports. It is simply (most often) a mapping between port number and friendly names... so when you do 'netstat' for example, there will be a name for the port versus a number.

There are very few (if any) programs (that I know of) that open and read /etc/services to determine what port to bind to. To change a listening port it would be necessary to either have a configuration file entry (like HTTP/Apache httpd.conf) or a command line switch that tells the forked process to listen on a certain (bind and listen) port.

It is a (very common) misconception that changing an entry in /etc/services changes how a program binds to a port/socket. There is also the misconception that commenting out these entries blocks ports (wrong!). Commenting out the entries simply insures that the name will not come up when you do a netstat, etc.

from ... Solaris 8 System Administrator Collection >> Solstice Enterprise Agents 1.0 User Guide >> 3. SNMP-Based Master/Subagent

http://docs.sun.com/db/doc/806-2905/6jc3duo34?a=view

Code:

snmpdx [-h] [-p port_number] [-r filename]

[-a filename] [-c dirname] [-i filename] [-o filename] [-y]

[-m GROUP|SPLIT] [-d debug_level]

BTW: Found this info with these keywords on Google: "snmpd.conf" "Solaris 8"

Seems our lives as a moderators is going to the net and doing Google searches for posters

Well, I must say that that with the versions of unix that I am familiar with, /etc/services does indeed control which ports a program will use.

To verify that this is still true I signed in to a Solaris 8 and a HP-UX 11 system. I did a "telnet localhost" and verified that I got a telnet session. Then I changed /etc/services so that the telnet entry said 21/tcp rather than 23/tcp. Then I repeated the "telnet localhost" test. In both cases I was now talking to a ftp server.

Yes, the telnet program does offer the user a way to override the default port on the command line. But even there, an /etc/services search is performed if the port is non-numeric. That's why "telnet localhost 25" and "telnet localhost smtp" both work.

Doesn't your unix system behave the same way?

Perderabo,

You are right!!! telnet reads /etc/services and starts-up based on the /etc/services mapping ALSO I can stop telnet from starting up based on commenting out /etc/services (running linux).

I stand corrected about telnet.

It does NOT work for Apache web server, however.

I think telnet is an exception (and there must be a few others) .... because generally I can't control ports with /etc/services.