Bug 135125 - telnet: 0: Name or service not known
telnet: 0: Name or service not known
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: glibc (Show other bugs)
i386 Linux
medium Severity medium
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Assigned To: Jakub Jelinek
Brian Brock
Depends On:
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Reported: 2004-10-08 16:34 EDT by Mike Batchelor
Modified: 2007-11-30 17:07 EST (History)
0 users

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Doc Type: Bug Fix
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Last Closed: 2005-05-18 09:59:56 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description Mike Batchelor 2004-10-08 16:34:36 EDT
Description of problem: "telnet 0 25" does not connect to
localhost:25. Instead it throws an error "0: Name or service no known".

Version-Release number of selected component (if applicable):

How reproducible: fails every time

Steps to Reproduce:
1. telnet 0 25
2. weep
3. weep some more
Actual results:
telnet: 0: Name or service not known

Expected results:
Connected to
Escape character is '^]'.
220 hostname ESMTP Sendmail 8.12.10/8.12.10; Fri, 8 Oct 2004 13:36:17

Additional info:
For the past - Oh, I don't know, two decades? - 0 resolves to, and so "telnet 0 25" would connect to the local machine's
smtp server, or "telnet 0 80" connects to the local HTTP server.  Not
so in RHEL3.  WTF?
Comment 1 Harald Hoyer 2004-10-11 04:31:27 EDT
please provide:
$ which telnet
and do you have ipv6 enabled?
Comment 2 Mike Batchelor 2004-10-11 12:42:25 EDT
ipv6 is not enabled.  Turns out the telnet in my path was
/usr/kerberos/bin/telnet, but /usr/bin/telnet returns the same error.
I believe this is not a bug in telnet after all, but glibc's
gethostbyname().  In fact, it looks like this was broken intentionally
in the glibc 2.3 series, for some reason.  gethostbyname() no longer
resolves undotted decimal addresses, or hexadecimal or octal
addresses.  It used to, but not anymore. "telnet 0 25" is one of the
Comment 4 Jakub Jelinek 2005-01-20 06:30:41 EST
Both gethostname ("0") and getaddrinfo ("0", NULL, NULL, &res);
return the same thing as they used to.
So the change is not in glibc.
Comment 5 Harald Hoyer 2005-01-20 06:36:31 EST
well, nothing change in the source code of telnet
Comment 6 Harald Hoyer 2005-01-20 07:41:59 EST
Retested. Works for me on a RHEL3-U3...
Comment 7 Harald Hoyer 2005-01-20 07:44:07 EST
doh... fell in the trap... tested with /usr/kerberos/bin/telnet (which works)
/usr/bin/telnet failed like described in the bug report.
Comment 8 Harald Hoyer 2005-01-20 07:57:49 EST
With a RHEL3-U4 glibc:

getaddrinfo("0", "25", 0xbfffe250, 0xbfffd9e4)   = -2
gai_strerror(-2)                                 = "Name or service not known"
Comment 9 Jakub Jelinek 2005-01-20 11:38:31 EST
Ok, this seems to be http://sources.redhat.com/bugzilla/show_bug.cgi?id=296
Comment 10 Jakub Jelinek 2005-02-15 01:49:36 EST
Should be fixed in glibc-2.3.2-95.32.
Comment 11 Tim Powers 2005-05-18 09:59:56 EDT
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.


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