Telnet connects OK but remote client screen is blank

[Robert Milne]

Hi all,

I am just setting up Telnet for remote login (yes, I know about SSH, but is on small trusted LAN and Telnet will suffice) I have the port listening (can scan it OK) but when I login from a remote client, it connects OK, but screen remains blank and I get no login prompt. I have configured Telnet I think OK in xinet.d/telnet before I did this I only got the connection refused message.

Does anyone know what the problem is ? I assume it's somehow not spawning a console process or some such thing maybe ?

Thanks for your help, any suggestions appreciated.

Regards,

Rob.

[Tony Contratto]

Hi Rob,

I have seen situations where name resolution can cause problems.

Do you have some type of name resolution (DNS, /etc/hosts) configured?

Can the server do a reverse name lookup on the client? You can check this with:
nslookup

If the server cannot do a reverse lookup on the client IP address, it may cause a significant delay between the initial telnet connection and getting the "login:" prompt on the screen.

--
Tony

[Robert Milne]

Hi Anthony,

Thanks for your reply.
Yes, I do have entries in /etc/hosts for these clients. I have tried a connection both from a Windows PC with MS telnet and from a HP-UX 11i box, both with the same result. No matter how long I wait no login prompt appears, nothing does. But HP-UX does say it has connected.

Also nsswitch.conf as settings for files only. If I ping using the client's host names that works OK, say they seem to be resolved to some degree. However if I do an nslookup from the Linux server to these clients, I do get an error saying "server can't find clientname: SERVFAIL" if use nslookup with client's host name. And if I do it by IP address of the client I get server can't find 240.2.20.172.in-addr.arpa: NXDOMAIN

Client's IP address is 172.20.2.240 and hosts address (Linux box) is 172.20.0.22 the HP-UX "client" box address is 172.20.0.1 on the same domain as the linux server. When I do an nslookup on it from Linux I get "server can't find 1.0.20.172.in-addr.arpa: NXDOMAIN".

The HP-UX box successfully does an nslookup on the Linux server. Also I can successfully telnet into the HP-UX box from the Linux machine, no problem.

A curious problem, but I am not sure of the answer here, this stuff gets a bit out of my knowledge league !

All the best.

Rob.

[Ionut Grigorescu_2]

Can you please check

#more /var/log/secure, after you try to establish a telnet connection? - try to type your username-enter-password-enter, even if you don't see the prompt (maybe sounds silly, but try it!)
What is the content of your /etc/xinetd.conf? /etc/xinetd.d/telnet?

Thank you,
ionut

[Robert Milne]

Hi Ionut,

/var/log/secure shows an entry from xinetd for each telnet login attempt and it looks OK as it shows the orginating IP address and a valid process ID with telnet written next to it.

No, putting the username password on a blank screen does nothing.

One thing I did try however is telnetting from the Linux server console itself, to it's own hostname. This should start another Telnet session on its self. Telnst itself starts OK, but as in the remote sessions the screen is blank !

I am somehow sure that this must eliminate all the network validation stuff, as I have tried it from root. It must be related to it not creating the logon console process correctly. But what I don't know is, what is the link between a telnet process starting and this in turn starting the console process which produces the logon ?

Curious...

Regards,

Rob.

[Jeff Coburn]

Possibly some strange ipchains rules are set? Try ipchains -F and then connect. If you do a ctrl-], do you get the telnet prompt? What does a "status" and "display" tell you?

What distro and telnet daemon are you using?

[Ionut Grigorescu_2]

Hi Rob,

I think you have to take a look at the manpage for telnetd (not telnet) it's explained there what does the telnet server when it receives a telnet request. I suspect a wrong setup of TERM, I'm still thinking about it...

Good luck!
ionut