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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
2<html>
3<head>
4<title>OpenSSH FAQ</title>
5<link rev= "made" href= "mailto:www@openbsd.org">
6<meta name= "resource-type" content= "document">
7<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
8<meta name= "description" content= "the OpenSSH FAQ page">
9<meta name= "keywords" content= "OpenSSH,SSH,Secure Shell,faq">
10<meta name= "distribution" content= "global">
11<meta name= "copyright" content= "This document copyright 1999-2010 OpenBSD.">
12</head>
13
14<body bgcolor= "#ffffff" text= "#000000" link= "#23238E">
15<a href="http://www.openssh.com/index.html"><img alt="[OpenSSH]" height="30" width="141" src="images/smalltitle.gif" border="0"></a>
16<p>
17
18<h1>OpenSSH FAQ (Frequently asked questions)</h1>
19
20<hr>
21
22<blockquote>
23<h3><a href= "#1.0">1.0 - What Is OpenSSH and Where Can I Get It?</a></h3>
24<ul>
25<li><a href= "#1.1">1.1 - What is OpenSSH and where can I download it?</a>
26<li><a href= "#1.2">1.2 - Why should it be used?</a>
27<li><a href= "#1.3">1.3 - What Operating Systems are supported?</a>
28<li><a href= "#1.4">1.4 - What about copyright, usage and patents?</a>
29<li><a href= "#1.5">1.5 - Where should I ask for help?</a>
30<li><a href= "#1.6">1.6 - I have found a bug. Where do I report it?</a>
31</ul>
32
33<h3><a href= "#2.0">2.0 - General Questions</a></h3>
34<ul>
35<li><a href= "#2.1">2.1 - Why does ssh/scp make connections from low-numbered ports. My firewall blocks these.</a>
36<li><a href= "#2.2">2.2 - Why is the ssh client setuid root?</a>
37<li><a href= "#2.3">2.3 - Why does SSH 2.3 have problems interoperating with OpenSSH 2.1.1?</a>
38<li><a href= "#2.4">2.4 - Why does OpenSSH print: Dispatch protocol error: type 20</a>
39<li><a href= "#2.5">2.5 - Old versions of commercial SSH encrypt host keys with IDEA.</a>
40<li><a href= "#2.6">2.6 - What are these warning messages about key lengths?</a>
41<li><a href= "#2.7">2.7 - X11 and/or agent forwarding does not work.</a>
42<li><a href= "#2.8">2.8 - After upgrading OpenSSH I lost SSH2 support.</a>
43<li><a href= "#2.9">2.9 - sftp/scp fails at connection, but ssh is OK.</a>
44<li><a href= "#2.10">2.10 - Will you add [foo] to scp?</a>
45<li><a href= "#2.11">2.11 - How do I use port forwarding?</a>
46<li><a href= "#2.12">2.12 - My ssh connection freezes or drops out after N minutes of inactivity.</a>
47<li><a href= "#2.13">2.13 - How do I use scp to copy a file with a colon in it?</a>
48<li><a href= "#2.14">2.14 - Why does OpenSSH report its version to clients?</a>
49</ul>
50
51<h3><a href= "#3.0">3.0 - Portable OpenSSH Questions</a></h3>
52<ul>
53<li><a href= "#3.1">3.1 - Spurious PAM authentication messages in logfiles.</a>
54<li><a href= "#3.2">3.2 - Empty passwords not allowed with PAM authentication.</a>
55<li><a href= "#3.3">3.3 - ssh(1) takes a long time to connect or log in</a>
56<li><a href= "#3.4">3.4 - "Can't locate module net-pf-10" messages in log under Linux.</a>
57<li><a href= "#3.5">3.5 - Password authentication doesn't work (eg on Slackware 7.0 or Red Hat Linux 6.x)</a>
58<li><a href= "#3.6">3.6 - Configure or sshd(8) complain about lack of RSA support</a>
59<li><a href= "#3.7">3.7 - "scp: command not found" errors</a>
60<li><a href= "#3.8">3.8 - Unable to read passphrase</a>
61<li><a href= "#3.9">3.9 - 'configure' missing or make fails</a>
62<li><a href= "#3.10">3.10 - Hangs when exiting ssh</a>
63<li><a href= "#3.11">3.11 - Why does ssh hang on exit?</a>
64<li><a href= "#3.12">3.12 - I upgraded to OpenSSH 3.1 and X11 forwarding stopped working.</a>
65<li><a href= "#3.13">3.13 - I upgraded to OpenSSH 3.8 and some X11 programs stopped working.</a>
66<li><a href= "#3.14">3.14 - I copied my public key to authorized_keys but public-key authentication still doesn't work.</a>
67<li><a href= "#3.15">3.15 - OpenSSH versions and PAM behaviour.</a>
68<li><a href= "#3.16">3.16 - Why doesn't "w" or "who" on AIX 5.x show users logged in via ssh?</a>
69</ul>
70
71</blockquote>
72
73<hr>
74
75<h2><u><a name= "1.0">1.0 - What Is OpenSSH and Where Can I Get It?</a></u></h2>
76
77<h2><a name= "1.1">1.1 - What is OpenSSH and where can I download it?</a></h2>
78
79OpenSSH provides end-to-end encrypted replacement of applications such as
80telnet, rlogin, and ftp.
81Unlike these legacy applications, OpenSSH never passes anything
82(including username and password) over the wire in unencrypted form, and
83provides host authentication, to verify that you really are talking to
84the system that you think you are and that no one else can take over
85that session.
86
87<p>
88The OpenSSH suite includes the
89<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&amp;sektion=1">ssh(1)</a>
90program which replaces rlogin and telnet, and
91<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&amp;sektion=1">scp(1)</a>
92which replaces
93<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=rcp&amp;sektion=1">rcp(1)</a> and
94<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ftp&amp;sektion=1">ftp(1)</a>.
95OpenSSH has also added
96<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp&amp;sektion=1">sftp(1)</a> and
97<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp-server&amp;sektion=8">sftp-server(8)</a>
98which implement an easier solution for file-transfer. This is based upon the
99<a href="http://www.openssh.com/txt/draft-ietf-secsh-filexfer-02.txt">secsh-filexfer</a> IETF draft.
100
101
102<p><strong>OpenSSH consists of a number of programs.</strong>
103
104<ul>
105<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd&amp;sektion=8">sshd(8)</a> - Server program run on the server machine. This listens for connections from client machines, and whenever it receives a connection, it performs authentication and starts serving the client.
106Its behaviour is controlled by the config file <i><a
107href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd_config&amp;sektion=5">
108sshd_config(5)</a></i>.
109<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&amp;sektion=1">ssh(1)</a> - This is the client program used to log into another machine or to execute commands on the other machine. <i>slogin</i> is another name for this program.
110Its behaviour is controlled by the global config file <i><a
111href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh_config&amp;sektion=5">
112ssh_config(5)</a></i> and individual users' <i>$HOME/.ssh/config</i> files.
113<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&amp;sektion=1">scp(1)</a> - Securely copies files from one machine to another.
114<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keygen&amp;sektion=1">ssh-keygen(1)</a> - Used to create Pubkey Authentication (RSA or DSA) keys (host keys and user authentication keys).
115<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-agent&amp;sektion=1">ssh-agent(1)</a> - Authentication agent. This can be used to hold RSA keys for authentication.
116<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-add&amp;sektion=1">ssh-add(1)</a> - Used to register new keys with the agent.
117<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp-server&amp;sektion=8">sftp-server(8)</a> - SFTP server subsystem.
118<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp&amp;sektion=1">sftp(1)</a> - Secure file transfer program.
119<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keyscan&amp;sektion=1">ssh-keyscan(1)</a> - gather ssh public keys.
120<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keysign&amp;sektion=8">ssh-keysign(8)</a> - ssh helper program for hostbased authentication.
121</ul>
122
123<h3>Downloading</h3>
124
125<p>
126The most recent version of OpenSSH is included with the current
127distribution of <a href="http://www.openbsd.org/">OpenBSD</a>, and
128installed as part of a basic install.
129
130<p>
131Today, most other operating systems include some version of OpenSSH
132(often re-badged or privately labeled), so most users can immediately
133use it.
134However, sometimes the included versions are quite old, and missing
135features of the current release of OpenSSH, and you may wish to install
136the current version, or install it on one of the few OSs that lacked it,
137and where the OS publisher does not make a modern version available.
138You may also wish to use OpenSSH on your embedded application.
139
140<p>
141Non-OpenBSD users will want to download, compile and install the
142multi-platform <a href="http://www.openssh.com/portable.html">Portable</a> distribution from a
143<a href="http://www.openssh.com/portable.html#mirrors">mirror</a> near you.
144
145
146<h2><a name= "1.2">1.2 - Why should it be used?</a></h2>
147
148<p>
149OpenSSH is a suite of tools to help secure your network
150connections. Here is a list of features:
151
152
153<ul>
154 <li>Strong authentication. Closes several security holes (e.g., IP, routing, and DNS spoofing).
155 <li>Improved privacy. All communications are automatically and transparently encrypted.
156 <li>Secure X11 sessions. The program automatically sets DISPLAY on the server machine, and forwards any X11 connections over the secure channel.
157 <li>Arbitrary TCP/IP ports can be redirected through the encrypted channel in both directions (e.g., for e-cash transactions).
158 <li>No retraining needed for normal users.
159 <li>Never trusts the network. Minimal trust on the remote side of the connection. Minimal trust on domain name servers. Pure RSA authentication never trusts anything but the private key.
160 <li>Client RSA-authenticates the server machine in the beginning of every connection to prevent trojan horses (by routing or DNS spoofing) and man-in-the-middle attacks, and the server RSA-authenticates the client machine before accepting <i>.rhosts</i> or <i>/etc/hosts.equiv</i> authentication (to prevent DNS, routing, or IP-spoofing).
161 <li>Host authentication key distribution can be centrally by the administration, automatically when the first connection is made to a machine.
162 <li>Any user can create any number of user authentication RSA keys for his/her own use.
163 <li>The server program has its own server RSA key which is automatically regenerated every hour.
164 <li>An authentication agent, running in the user's laptop or local workstation, can be used to hold the user's RSA authentication keys.
165 <li>The software can be installed and used (with restricted functionality) even without root privileges.
166 <li>The client is customizable in system-wide and per-user configuration files.
167 <li>Optional compression of all data with gzip (including forwarded X11 and TCP/IP port data), which may result in significant speedups on slow connections.
168 <li>Complete replacement for rlogin, rsh, and rcp.
169</ul>
170
171<p>
172Currently, almost all communications in computer networks are done
173without encryption. As a consequence, anyone who has access to any
174machine connected to the network can listen in on any communication.
175This is being done by hackers, curious administrators, employers,
176criminals, industrial spies, and governments. Some networks leak off
177enough electromagnetic radiation that data may be captured even from a
178distance.
179
180
181<p>
182When you log in, your password goes in the network in plain
183text. Thus, any listener can then use your account to do any evil he
184likes. Many incidents have been encountered worldwide where crackers
185have started programs on workstations without the owner's knowledge
186just to listen to the network and collect passwords. Programs for
187doing this are available on the Internet, or can be built by a
188competent programmer in a few hours.
189
190
191<p>
192Businesses have trade secrets, patent applications in preparation,
193pricing information, subcontractor information, client data, personnel
194data, financial information, etc. Currently, anyone with access to
195the network (any machine on the network) can listen to anything that
196goes in the network, without any regard to normal access restrictions.
197
198
199<p>
200Many companies are not aware that information can so easily be
201recovered from the network. They trust that their data is safe
202since nobody is supposed to know that there is sensitive information
203in the network, or because so much other data is transferred in the
204network. This is not a safe policy.
205
206
207<h2><a name= "1.3">1.3 - What operating systems are supported?</a></h2>
208
209<p>
210Even though OpenSSH is developed on
211<a href="http://www.openbsd.org/">OpenBSD</a> a wide variety of
212ports to other operating systems exist. The portable version of OpenSSH
213is headed by <a href="mailto:djm@openbsd.org">Damien Miller</a>.
214For a quick overview of the portable version of OpenSSH see
215<a href="http://www.openssh.com/portable.html">OpenSSH Portable Release</a>.
216Currently, the supported operating systems are:
217
218
219<ul>
220 <li>OpenBSD
221 <li>NetBSD
222 <li>FreeBSD
223 <li>AIX
224 <li>HP-UX
225 <li>IRIX
226 <li>Linux
227 <li>NeXT
228 <li>SCO
229 <li>SNI/Reliant Unix
230 <li>Solaris
231 <li>Digital Unix/Tru64/OSF
232 <li>Mac OS X
233 <li>Cygwin
234</ul>
235
236<p>
237A list of vendors that include OpenSSH in their distributions
238is located in the <a href="http://www.openssh.com/users.html">OpenSSH Users page</a>.
239
240<h2><a name= "1.4">1.4 - What about copyrights, usage and patents?</a></h2>
241<p>
242The OpenSSH developers have tried very hard to keep OpenSSH free of any
243patent or copyright problems. To do this, some options had to be
244stripped from OpenSSH. Namely support for patented algorithms.
245
246<p>
247OpenSSH does not support any patented transport algorithms. In SSH1 mode,
248only 3DES and Blowfish are available options. In SSH2 mode, only 3DES,
249Blowfish, CAST128, Arcfour and AES can be selected.
250The patented IDEA algorithm is not supported.
251
252<p>
253OpenSSH provides support for both SSH1 and SSH2 protocols.
254
255<p>
256Since the RSA patent has expired, there are no restrictions on the use
257of RSA algorithm using software, including OpenBSD.
258
259<h2><a name= "1.5">1.5 - Where should I ask for help?</a></h2>
260<p>
261There are many places to turn to for help. In addition to the main
262<a href="http://www.openssh.com/index.html">OpenSSH website</a>,
263there are many mailing lists to try. Before trying any mailing lists,
264please search through all mailing list archives to see if your question
265has already been answered. The OpenSSH Mailing List has been archived and
266put in searchable form and can be found at
267<a href="http://marc.info/?l=openssh-unix-dev&amp;r=1&amp;w=2">marc.info</a>.
268
269<p>
270For more information on subscribing to OpenSSH related mailing lists,
271please see <a href="http://www.openssh.com/list.html">OpenSSH Mailing lists</a>.
272
273<h2><a name= "1.6">1.6 - I have found a bug. Where do I report it?</a></h2>
274<p>
275Information about submitting bug reports can be found at the OpenSSH
276<a href="http://www.openssh.com/report.html">Reporting bugs</a> page.
277<p>
278If you wish to report a security bug, please contact the private developers
279list &lt;<a href="mailto:openssh@openssh.com">openssh@openssh.com</a>&gt;.
280
281<h2><u><a name= "2.0">2.0 - General Questions</a></u></h2>
282
283<h2><a name= "2.1">2.1 - Why does ssh/scp make connections from low-numbered ports.</a></h2>
284<p>
285The OpenSSH client uses low numbered ports for rhosts and rhosts-rsa
286authentication because the server needs to trust the username provided by
287the client. To get around this, you can add the below example to your
288<i>ssh_config</i> or <i>~/.ssh/config</i> file.
289
290
291<blockquote>
292<table border=0 width="800">
293 <tr>
294 <td nowrap bgcolor="#EEEEEE">
295<b>UsePrivilegedPort no</b>
296 </td>
297 </tr>
298</table>
299</blockquote>
300
301<p>
302Or you can specify this option on the command line, using the <b>-o</b>
303option to
304<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&amp;sektion=1">ssh(1)</a> command.
305
306<blockquote>
307<table border=0 width="800">
308 <tr>
309 <td nowrap bgcolor="#EEEEEE">
310$ <b>ssh -o "UsePrivilegedPort no" host.com</b>
311 </td>
312 </tr>
313</table>
314</blockquote>
315
316<h2><a name= "2.2">2.2 - Why is the ssh client setuid root?</a></h2>
317
318<p>
319In conjunction with the previous question, (<a href="#2.1">2.1</a>)
320OpenSSH needs root authority to be able to bind to low-numbered ports to
321facilitate <i>rhosts authentication</i>.
322A privileged port is also required for rhosts-rsa authentication to older
323SSH releases.
324
325<p>
326Additionally, for both <i>rhosts-rsa authentication</i> (in protocol
327version 1) and <i>hostbased authentication</i> (in protocol version 2)
328the ssh client needs to access the <i>private host key</i> in order to
329authenticate the client machine to the server.
330OpenSSH versions prior to 3.3 required the <code>ssh</code> binary to be
331setuid root to enable this, and you may safely remove it if you don't
332want to use these authentication methods.
333
334<p>
335Starting in OpenSSH 3.3, <code>ssh</code> is not setuid by default. <a
336href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keysign">ssh-keysign</a>,
337is used for access to the private hosts keys, and ssh does not use privileged
338source ports by default. If you wish to use a privileged source port, you must
339manually set the setuid bit on <code>ssh</code>.
340
341<h2><a name= "2.3">2.3 - Why does SSH 2.3 have problems interoperating with OpenSSH 2.1.1?</a></h2>
342
343<p>
344SSH 2.3 and earlier versions contain a flaw in their HMAC implementation.
345Their code was not supplying the full data block output from the digest,
346and instead always provided 128 bits. For longer digests, this caused
347SSH 2.3 to not interoperate with OpenSSH.
348
349<p>
350OpenSSH 2.2.0 detects that SSH 2.3 has this flaw. Recent versions of SSH
351will have this bug fixed. Or you can add the following to
352SSH 2.3 <i>sshd2_config</i>.
353
354
355<blockquote>
356<table border=0 width="800">
357 <tr>
358 <td nowrap bgcolor="#EEEEEE">
359<b>Mac hmac-md5</b>
360 </td>
361 </tr>
362</table>
363</blockquote>
364
365<h2><a name= "2.4">2.4 - Why does OpenSSH print: Dispatch protocol error: type 20</a></h2>
366
367<p>
368Problems in interoperation have been seen because older versions of
369OpenSSH did not support session rekeying. However the commercial SSH 2.3
370tries to negotiate this feature, and you might experience connection
371freezes or see the error message &quot;<b>Dispatch protocol error:
372type 20 </b>&quot;.
373To solve this problem, either upgrade to a recent OpenSSH release or
374disable rekeying by adding the following to your commercial SSH 2.3's
375<i>ssh2_config</i> or <i>sshd2_config</i>.
376
377
378<blockquote>
379<table border=0 width="800">
380 <tr>
381 <td nowrap bgcolor="#EEEEEE">
382<b>RekeyIntervalSeconds 0</b>
383 </td>
384 </tr>
385</table>
386</blockquote>
387
388<h2><a name= "2.5">2.5 - Old versions of commercial SSH encrypt host keys with IDEA.</a></h2>
389
390<p>
391The old versions of SSH used a patented algorithm to encrypt their
392<i>/etc/ssh/ssh_host_key</i>. This problem will manifest as
393<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd&amp;sektion=8">sshd(8)</a>
394not being able to read its host key. To solve this, use the command below
395to convert your ssh_host_key to use 3DES.
396<b>NOTE:</b> Use the
397<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keygen&amp;sektion=1">ssh-keygen(1)</a>
398program from the Commercial SSH product, *NOT* OpenSSH for the example
399below.
400
401
402<blockquote>
403<table border=0 width="800">
404 <tr>
405 <td nowrap bgcolor="#EEEEEE">
406# <b>ssh-keygen -u -f /etc/ssh/ssh_host_key</b>
407 </td>
408 </tr>
409</table>
410</blockquote>
411
412<h2><a name= "2.6">2.6 - What are these warning messages about key lengths</a></h2>
413
414<p>
415Commercial SSH's
416<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keygen&amp;sektion=1">ssh-keygen(1)</a>
417program contained a bug which caused it to occasionally generate Pubkey
418Authentication (RSA or DSA) keys which had their Most Significant Bit
419(MSB) unset. Such keys were advertised as being full-length, but are
420actually, half the time, smaller than advertised.
421
422<p>
423OpenSSH will print warning messages when it encounters such keys. To rid
424yourself of these message, edit your <i>known_hosts</i> files and replace the
425incorrect key length (usually "1024") with the correct key length
426(usually "1023").
427
428<h2><a name= "2.7">2.7 - X11 and/or agent forwarding does not work.</a></h2>
429
430<p>
431Check your <i>ssh_config</i> and <i>sshd_config</i>. The default
432configuration files disable authentication agent and X11 forwarding. To
433enable it, put the line below in <i>sshd_config</i>:
434
435<blockquote>
436<table border=0 width="800">
437 <tr>
438 <td nowrap bgcolor="#EEEEEE">
439<b>X11Forwarding yes</b>
440 </td>
441 </tr>
442</table>
443</blockquote>
444
445<p>
446and put the following lines in <i>ssh_config</i>:
447
448<blockquote>
449<table border=0 width="800">
450 <tr>
451 <td nowrap bgcolor="#EEEEEE">
452<b>ForwardAgent yes</b><br>
453<b>ForwardX11 yes</b>
454 </td>
455 </tr>
456</table>
457</blockquote>
458
459<p>
460X11 forwarding requires a working <a
461href="http://www.openbsd.org/cgi-bin/man.cgi?query=xauth&amp;sektion=1"
462>xauth(1)</a> binary. On OpenBSD this is in the <i>xbase</i> file
463set but will probably be different on other platforms. For OpenSSH
464Portable, xauth must be either found at configure time or specified
465via <b>XAuthLocation</b> in sshd_config(5) and ssh_config(5).
466
467<p>
468Note on agent interoperability: There are two different and
469incompatible agent forwarding mechanisms within the SSH2 protocol.
470OpenSSH has always used an extension of the original SSH1 agent
471requests, however some commercial products use a different, non-free
472agent forwarding protocol. This means that agent forwarding cannot
473be used between OpenSSH and those products.
474
475<p>
476<b>NOTE:</b> For users of Linux Mandrake 7.2, Mandrake modifies the
477<i>XAUTHORITY</i> environment variable in <i>/etc/skel/.bashrc</i>,
478and thus any bash user's home directory. This variable is set by OpenSSH
479and for either of the above options to work, you need to comment out
480the line:
481
482
483<blockquote>
484<table border=0 width="800">
485 <tr>
486 <td nowrap bgcolor="#EEEEEE">
487<b># export XAUTHORITY=$HOME/.Xauthority</b>
488 </td>
489 </tr>
490</table>
491</blockquote>
492
493<h2><a name= "2.8">2.8 - After upgrading OpenSSH I lost SSH2 support.</a></h2>
494
495<p>
496Between versions changes can be made to <i>sshd_config</i> or
497<i>ssh_config</i>. You should always check on these changes when upgrading
498versions of OpenSSH. After OpenSSH Version 2.3.0 you need to add the
499following to your <i>sshd_config</i>:
500
501
502<blockquote>
503<table border=0 width="800">
504 <tr>
505 <td nowrap bgcolor="#EEEEEE">
506<b>HostKey /etc/ssh_host_dsa_key</b><br>
507<b>HostKey /etc/ssh_host_rsa_key</b>
508 </td>
509 </tr>
510</table>
511</blockquote>
512
513<h2><a name= "2.9">2.9 - sftp/scp fails at connection, but ssh is OK.</a></h2>
514
515<p>
516sftp and/or scp may fail at connection time if you have shell
517initialization (.profile, .bashrc, .cshrc, etc) which produces output
518for non-interactive sessions. This output confuses the sftp/scp client.
519You can verify if your shell is doing this by executing:
520
521<blockquote>
522<table border=0 width="800">
523 <tr>
524 <td nowrap bgcolor="#EEEEEE">
525<b>ssh yourhost /usr/bin/true</b>
526 </td>
527 </tr>
528</table>
529</blockquote>
530
531<p>
532If the above command produces any output, then you need to modify your
533shell initialization.
534
535<h2><a name= "2.10">2.10 - Will you add [foo] to scp?</a></h2>
536
537<p>
538Short Answer: no.
539
540<p>
541Long Answer: scp is not standardized. The closest thing it has to a
542specification is "what rcp does". Since the same command is used on both ends
543of the connection, adding features or options risks breaking interoperability with other
544implementations.
545
546<p>
547New features are more likely in sftp, since the protocol is standardized
548(well, a <a href="http://www.ietf.org/html.charters/OLD/secsh-charter.html">
549draft standard</a>), extensible, and the client and server are decoupled.
550
551<h2><a name= "2.11">2.11 - How do I use port forwarding?</a></h2>
552
553<p>
554If the remote server is running sshd(8), it may be possible to
555``tunnel'' certain services via ssh. This may be desirable, for
556example, to encrypt POP or SMTP connections, even though the software
557does not directly support encrypted communications. Tunnelling uses
558port forwarding to create a connection between the client and server.
559The client software must be able to specify a non-standard port to
560connect to for this to work.
561
562<p>
563The idea is that the user connects to the remote host using ssh,
564and specifies which port on the client's machine should be used to
565forward connections to the remote server. After that it is possible
566to start the service which is to be encrypted (e.g. fetchmail, irc)
567on the client machine, specifying the same local port passed to
568ssh, and the connection will be tunnelled through ssh. By default,
569the system running the forward will only accept connections from
570itself.
571
572<p>
573The options most relevant to tunnelling are the -L and -R options,
574which allow the user to forward connections, the -D option, which
575permits dynamic port forwarding, the -g option, which permits other
576hosts to use port forwards, and the -f option, which instructs ssh
577to put itself in the background after authentication. See the <a
578href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&amp;sektion=1"
579>ssh(1)</a> man page for further details.
580
581<p>
582This is an example of tunnelling an IRC session from client machine
583``127.0.0.1'' (localhost) to remote server ``server.example.com'':
584
585<blockquote>
586<table border=0 width="800">
587 <tr>
588 <td nowrap bgcolor="#EEEEEE">
589<b>ssh -f -L 1234:server.example.com:6667 server.example.com sleep 10<br>
590irc -c '#users' -p 1234 pinky 127.0.0.1</b>
591 </td>
592 </tr>
593</table>
594</blockquote>
595
596<p>
597This tunnels a connection to IRC server server.example.com, joining
598channel ``#users'', using the nickname ``pinky''. The local port used
599in this example is 1234. It does not matter which port is used, as
600long as it's greater than 1023 (remember, only root can open sockets on
601privileged ports) and doesn't conflict with any ports already in use.
602The connection is forwarded to port 6667 on the remote server, since
603that's the standard port for IRC services.
604
605<p>
606The remote command ``sleep 10'' was specified to allow an amount
607of time (10 seconds, in the example) to start the service which is to
608be tunnelled. If no connections are made within the time specified,
609ssh will exit. If more time is required, the sleep(1) value can be
610increased appropriately or, alternatively, the example above could
611be added as a function to the user's shell. See ksh(1) and csh(1)
612for more details about user-defined functions.
613
614<p>
615ssh also has an -N option, convenient for use with port forwarding:
616if -N is specified, it is not necessary to specify a remote command
617(``sleep 10'' in the example above). However, use of this option
618causes ssh to wait around for ever (as opposed to exiting after a
619remote command has completed), and the user must take care to manually
620kill(1) the process afterwards.
621
622<h2><a name= "2.12">2.12 - My ssh connection freezes or drops out after N minutes of inactivity.</a></h2>
623
624<p>
625This is usually the result of a packet filter or NAT device
626timing out your TCP connection due to inactivity. You can enable
627<b>ClientAliveInterval</b> in the server's <i><a
628href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd_config&amp;sektion=5">
629sshd_config</a></i>, or enable <b>ServerAliveInterval</b> in the
630client's <i><a
631href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh_config&amp;sektion=5">
632ssh_config</a></i> (the latter is available in OpenSSH 3.8 and newer).
633
634<p>
635Enabling either option and setting the interval for less than the time
636it takes to time out your session will ensure that the connection is
637kept "fresh" in the device's connection table.
638
639<h2><a name= "2.13">2.13 - How do I use scp to copy a file with a colon in it?</a></h2>
640
641<b><a
642href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&amp;sektion=1">
643scp</a></b> will interpret the component before the colon to be a remote
644server name and attempt to connect to it. To prevent this, refer to
645the file by a relative or absolute path, eg:
646
647<blockquote>
648<table border=0 width="800">
649 <tr>
650 <td nowrap bgcolor="#EEEEEE">
651$ scp ./source:file sshserver:
652 </td>
653 </tr>
654</table>
655</blockquote>
656
657<h2><a name= "2.14">2.14 - Why does OpenSSH report its version to clients?</a></h2>
658
659<p>
660OpenSSH, like most SSH implementations, reports its name and version to clients
661when they connect, e.g.
662</p>
663
664<blockquote>
665SSH-2.0-OpenSSH_3.9
666</blockquote>
667
668<p>
669This information is used by clients and servers to enable protocol
670compatibility tweaks to work around changed, buggy or missing features in
671the implementation they are talking to. This protocol feature checking is
672still required at present because versions with incompatibilities are still
673in wide use.
674</p>
675
676<h2><u><a name= "3.0">3.0 - Portable OpenSSH Questions</a></u></h2>
677
678<h2><a name= "3.1">3.1 - Spurious PAM authentication messages in logfiles.</a></h2>
679
680<p>
681The portable version of OpenSSH will generate spurious authentication
682failures at every login, similar to:
683
684
685<blockquote>
686<table border=0 width="800">
687 <tr>
688 <td nowrap bgcolor="#EEEEEE">
689&quot;<b>authentication failure; (uid=0) -&gt; root for sshd service</b>&quot;
690 </td>
691 </tr>
692</table>
693</blockquote>
694
695<p>
696These are generated because OpenSSH first tries to determine whether a
697user needs authentication to login (e.g. empty password). Unfortunately
698PAM likes to log all authentication events, this one included.
699
700<p>
701If it annoys you too much, set &quot;<b>PermitEmptyPasswords no</b>&quot;
702in <i>sshd_config</i>. This will quiet the error message at the expense
703of disabling logins to accounts with no password set.
704This is the default if you use the supplied <i>sshd_config</i> file.
705
706<h2><a name= "3.2">3.2 - Empty passwords not allowed with PAM authentication.</a></h2>
707
708<p>
709To enable empty passwords with a version of OpenSSH built with PAM you
710must add the flag nullok to the end of the password checking module
711in the <i>/etc/pam.d/sshd</i> file. For example:
712
713<blockquote>
714<table border=0 width="800">
715 <tr>
716 <td nowrap bgcolor="#EEEEEE">
717auth required/lib/security/pam_unix.so shadow nodelay nullok
718 </td>
719 </tr>
720</table>
721</blockquote>
722
723<p>
724This must be done in addition to setting &quot;<b>PermitEmptyPasswords
725yes</b>&quot; in the <i>sshd_config</i> file.
726
727<p>
728There is one caveat when using empty passwords with PAM authentication:
729PAM will allow any password when authenticating an account with an empty
730password. This breaks the check that
731<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd&amp;sektion=8">sshd(8)</a>
732uses to determine whether an account has no password set and grant
733users access to the account regardless of the policy specified by
734<b>PermitEmptyPasswords</b>. For this reason, it is recommended that you
735do not add the <b>nullok</b> directive to your PAM configuration file
736unless you specifically wish to allow empty passwords.
737
738
739<h2><a name= "3.3">3.3 - ssh(1) takes a long time to connect or log
740in</a></h2>
741
742<p>
743Large delays (more than 10 seconds) are typically caused by a problem with
744name resolution:
745<ul>
746<li>Some versions of glibc (notably glibc 2.1 shipped with Red Hat 6.1)
747can take a long time to resolve "IPv6 or IPv4" addresses from domain
748names. This can be worked around with by specifying <b>AddressFamily
749inet</b> option in <i>ssh_config</i>.</li>
750
751<li>There may be a DNS lookup problem, either at the client or server.
752You can use the <code>nslookup</code> command to check this on both client
753and server by looking up the other end's name and IP address. In
754addition, on the server look up the name returned by the client's
755IP-name lookup. You can disable most of the server-side lookups by
756setting <b>UseDNS no</b> in <i>sshd_config</i>.</li>
757</ul>
758
759<p>
760Delays less than 10 seconds can have other causes.
761
762<ul>
763
764<li>OpenSSH releases prior to 3.8 had an <i>moduli</i> file with
765moduli that were just smaller than what sshd would look for, and
766as a result, sshd would end up using moduli significantly larger
767than requested, which resulted in a speed penalty. Replacing the
768<i>moduli</i> file will resolve this (note that in most cases this
769file will not be replaced during an upgrade and must be replaced
770manually).</li>
771
772<li>OpenSSH releases prior to 3.8 had a flaw in <code>ssh</code> that
773would cause it to request moduli larger than intended (which when
774combined with the above resulted in significant slowdowns).
775Upgrading the client to 3.8 or higher will resolve this issue.</li>
776
777<li>If either the client or server lack a kernel-based random number
778device (eg Solaris &lt; 9, AIX &lt; 5.2, HP-UX &lt; 11.11) and no
779substitute is available (eg <a href=
780"ftp://ftp.ayamura.org/pub/prngd/">prngd</a>) it's possible that
781one of the programs called by <code>ssh-rand-helper</code> to
782generate entropy is hanging. This can be investigated by running
783it in debug mode:
784
785<blockquote>
786<table border=0 width="800">
787 <tr>
788 <td nowrap bgcolor="#EEEEEE">
789/usr/local/libexec/ssh-rand-helper -vvv
790 </td>
791 </tr>
792</table>
793</blockquote>
794
795Any significant delays should be investigated and rectified, or the
796corresponding commands should be removed from <i>ssh_prng_cmds</i>.
797</li>
798
799</ul>
800
801<h3>How slow is "slow"?</h3>
802Under normal conditions, the speed of SSH logins is dependant on
803CPU speed of client and server. For comparison the following are
804typical connect times for <code>time ssh localhost true</code>
805with a 1024-bit RSA key on otherwise unloaded hosts. OpenSSH and
806OpenSSL were compiled with gcc 3.3.x.
807
808<p>
809<table>
810<tr><th>CPU</th><th>Time (SSHv1)<a href="#3.3fn1">[1]</a></th>
811 <th>Time (SSHv2)</th></tr>
812<tr><td>170MHz SPARC/sun4m</td><td>0.74 sec</td><td>1.25 sec</td></tr>
813<tr><td>236MHz HPPA/8200<a href="#3.3fn2">[2]</a></td><td>0.44 sec</td>
814 <td>0.79 sec</td></tr>
815<tr><td>375MHz PowerPC/604e</td><td>0.38 sec</td><td>0.51 sec</td></tr>
816<tr><td>933MHz VIA Ezra</td><td>0.34 sec</td><td>0.44 sec</td></tr>
817<tr><td>2.1GHz Athlon XP 2600+</td><td>0.14 sec</td><td>0.22 sec</td></tr>
818</table>
819
820<br>
821
822<a name="3.3fn1">[1]</a> The SSHv1 protocol is faster but is
823cryptographically weaker than SSHv2.<br>
824
825<a name="3.3fn2">[2]</a> At the time of writing, gcc generates
826relatively slow code on HPPA for RSA and Diffie-Hellman operations
827(see <a href= "http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7625">gcc
828bug #7625</a> and <a
829href="http://marc.info/?l=openssh-unix-dev&amp;m=102646106016694">
830discussion on openssh-unix-dev</a>).
831
832<h2><a name= "3.4">3.4 - "Can't locate module net-pf-10" messages in log under Linux.</a></h2>
833
834<p>
835The Linux kernel is looking (via modprobe) for protocol family 10 (IPv6).
836Either load the appropriate kernel module, enter the correct alias in
837<i>/etc/modules.conf</i> or disable IPv6 in <i>/etc/modules.conf</i>.
838
839
840<p>
841For some silly reason <i>/etc/modules.conf</i> may also be named
842<i>/etc/conf.modules</i>.
843
844
845<h2><a name= "3.5">3.5 - Password authentication doesn't work (eg on Slackware 7.0 or Red Hat 6.x)</a></h2>
846
847<p>
848If the password is correct password the login is still denied, the
849usual cause is that the system is configured to use MD5-type passwords
850but the
851<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=crypt&amp;sektion=3"
852>crypt(3)</a> function used by sshd doesn't understand them.
853
854<p>
855Affected accounts will have password strings in <i>/etc/passwd</i>
856or <i>/etc/shadow</i> that start with <b>$1$</b>.
857If password authentication fails for new accounts or accounts with
858recently changed passwords, but works for old accounts, this is the
859likely culprit.
860
861<p>
862The underlying cause is that some versions of OpenSSL have a crypt(3)
863function that does not understand MD5 passwords, and the link order of
864sshd means that OpenSSL's crypt(3) is used instead of the system's.
865OpensSSH's configure attempts to correct for this but is not always
866successful.
867
868<p>
869There are several possible solutions:
870
871<ul>
872<li>
873<p>
874Enable sshd's built-in support for MD5 passwords at build time.
875
876<blockquote>
877<table border=0 width="800">
878 <tr>
879 <td nowrap bgcolor="#EEEEEE">
880./configure --with-md5-passwords [options]
881 </td>
882 </tr>
883</table>
884</blockquote>
885
886This is safe even if you have both types of encryption as sshd will
887select the correct algorithm for each account automatically.
888
889<li>
890<p>
891If your system has a separate libcrypt library (eg Slackware 7) then you
892can manually add -lcrypt to the LIBS list so it's used instead of
893OpenSSL's:
894
895<blockquote>
896<table border=0 width="800">
897 <tr>
898 <td nowrap bgcolor="#EEEEEE">
899LIBS=-lcrypt ./configure [options]
900 </td>
901 </tr>
902</table>
903</blockquote>
904
905<li>
906<p>
907If your platforms supports PAM, you may configure sshd to use it
908(see <a href= "#3.15" >section 3.15</a>). This will mean that sshd will
909not verify passwords itself but will defer to the configured PAM modules.
910</ul>
911
912<h2><a name= "3.6">3.6 - Configure or sshd(8) complain about lack of RSA or DSA support</a></h2>
913
914<p>
915Ensure that your OpenSSL libraries have been built to include RSA or DSA
916support either internally or through RSAref.
917
918
919<h2><a name= "3.7">3.7 - "scp: command not found" errors</a></h2>
920
921<p>
922<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&amp;sektion=1">scp(1)</a>
923must be in the default PATH on both the client and the server. You may
924need to use the <b>--with-default-path</b> option to specify a custom
925path to search on the server. This option replaces the default path,
926so you need to specify all the current directories on your path as well
927as where you have installed scp. For example:
928
929<blockquote>
930<table border=0 width="800">
931 <tr>
932 <td nowrap bgcolor="#EEEEEE">
933$ <b>./configure --with-default-path=/bin:/usr/bin:/usr/local/bin:/path/to/scp</b>
934 </td>
935 </tr>
936</table>
937</blockquote>
938
939<p>
940Note that configuration by the server's admin will take precedence over the
941setting of <b>--with-default-path</b>. This includes resetting PATH in
942<i>/etc/profile</i>, PATH in <i>/etc/environment</i> on AIX, or (for 3.7p1 and
943above) setting PATH or SUPATH in <i>/etc/default/login</i> on Solaris or
944Reliant Unix.
945
946<h2><a name= "3.8">3.8 - Unable to read passphrase</a></h2>
947
948<p>
949Some operating systems set <i>/dev/tty</i> with incorrect modes, causing
950the reading of passwords to fail with the following error:
951
952<blockquote>
953<table border=0 width="800">
954 <tr>
955 <td nowrap bgcolor="#EEEEEE">
956You have no controlling tty. Cannot read passphrase.
957 </td>
958 </tr>
959</table>
960</blockquote>
961
962<p>
963The solution to this is to reset the permissions on <i>/dev/tty</i>
964to mode 0666 and report the error as a bug to your OS vendor.
965
966
967<h2><a name= "3.9">3.9 - 'configure' missing or make fails</a></h2>
968
969<p>
970If there is no 'configure' file in the tar.gz file that you downloaded
971or make fails with "missing separator" errors, you have probably
972downloaded the OpenBSD distribution of OpenSSH and are attempting to
973compile it on another platform. Please refer to the information on the
974<a href="http://www.openssh.com/portable.html">portable version</a>.
975
976
977<h2><a name= "3.10">3.10 - Hangs when exiting ssh</a></h2>
978
979<p>
980OpenSSH may hang when exiting. This can occur when there is an active
981background process. This is known to occur on Linux and HP-UX.
982The problem can be verified by doing the following:
983
984<blockquote>
985<table border=0 width="800">
986 <tr>
987 <td nowrap bgcolor="#EEEEEE">
988$ <b>sleep 20 &amp; exit</b>
989 </td>
990 </tr>
991</table>
992</blockquote>
993
994Try to use this instead:
995<blockquote>
996<table border=0 width="800">
997 <tr>
998 <td nowrap bgcolor="#EEEEEE">
999$ <b>sleep 20 &lt; /dev/null &gt; /dev/null 2&gt;&amp;1 &amp;</b>
1000 </td>
1001 </tr>
1002</table>
1003</blockquote>
1004
1005<p>
1006A work around for bash users is to place <b>"shopt -s huponexit"</b>
1007in either /etc/bashrc or ~/.bashrc. Otherwise, consult your shell's
1008man page for an option to enable it to send a HUP signal to active
1009jobs when exiting. See <a
1010href="http://bugzilla.mindrot.org/show_bug.cgi?id=52">bug #52</a>
1011for other workarounds.
1012
1013<h2><a name= "3.11">3.11 - Why does ssh hang on exit?</a></h2>
1014
1015<p>
1016When executing
1017<blockquote>
1018<table border=0 width="800">
1019 <tr>
1020 <td nowrap bgcolor="#EEEEEE">
1021$ <b>ssh host command</b>
1022 </td>
1023 </tr>
1024</table>
1025</blockquote>
1026ssh <b>needs</b> to hang, because it needs to wait:
1027<ul>
1028<li>
1029until it can be sure that <code>command</code> does not need
1030more input.
1031<li>
1032until it can be sure that <code>command</code> does not produce
1033more output.
1034<li>
1035until <code>command</code> exits because sshd needs to tell
1036the exit status from <code>command</code> to ssh.
1037</ul>
1038<p>
1039
1040<h2><a name= "3.12">3.12 - I upgraded to OpenSSH 3.1 and X11
1041forwarding stopped working.</a></h2>
1042
1043Starting with OpenSSH 3.1, the sshd x11 forwarding server listens on
1044localhost by default; see the sshd <b>X11UseLocalhost</b> option to
1045revert to prior behaviour if your older X11 clients do not function
1046with this configuration.<p>
1047
1048In general, X11 clients using X11 R6 should work with the default
1049setting. Some vendors, including HP, ship X11 clients with R6
1050and R5 libs, so some clients will work, and others will not work.
1051This is true for HP-UX 11.X.<p>
1052
1053<h2><a name= "3.13">3.13 - I upgraded to OpenSSH 3.8 and some
1054X11 programs stopped working.</a></h2>
1055
1056<p>
1057As documented in the <a href="http://www.openssh.com/txt/release-3.8">3.8 release notes</a>,
1058<code>ssh</code> will now use untrusted X11 cookies by
1059default. The previous behaviour can be restored by setting
1060<b>ForwardX11Trusted yes</b> in <i>ssh_config</i>.
1061
1062<p>
1063Possible symptoms include:<br>
1064<code>BadWindow (invalid Window parameter)<br>
1065BadAccess (attempt to access private resource denied)<br>
1066X Error of failed request: BadAtom (invalid Atom parameter)<br>
1067Major opcode of failed request: 20 (X_GetProperty)<br></code>
1068
1069<h2><a name= "3.14">3.14 - I copied my public key to authorized_keys
1070but public-key authentication still doesn't work.</a></h2>
1071
1072<p>
1073Typically this is caused by the file permissions on $HOME, $HOME/.ssh or
1074$HOME/.ssh/authorized_keys being more permissive than sshd allows by default.
1075
1076<p>
1077In this case, it can be solved by executing the following on the server.
1078<blockquote>
1079<table border=0 width="800">
1080<tr>
1081 <td nowrap bgcolor="#EEEEEE">
1082$ <b>chmod go-w $HOME $HOME/.ssh</b><br>
1083$ <b>chmod 600 $HOME/.ssh/authorized_keys</b><br>
1084$ <b>chown `whoami` $HOME/.ssh/authorized_keys</b><br>
1085 </td>
1086</tr>
1087</table>
1088</blockquote>
1089
1090<p>
1091If this is not possible for some reason, an alternative is to set
1092<b>StrictModes no</b> in <i>sshd_config</i>, however this is not
1093recommended.
1094
1095<h2><a name= "3.15">3.15 - OpenSSH versions and PAM behaviour.</a></h2>
1096
1097Portable OpenSSH has a configure-time option to enable sshd's use of the
1098<a href="http://www.opengroup.org/onlinepubs/008329799/">PAM</a>
1099(Pluggable Authentication Modules) interface.
1100
1101<blockquote>
1102<table border=0 width="800">
1103 <tr>
1104 <td nowrap bgcolor="#EEEEEE">
1105./configure --with-pam [options]
1106 </td>
1107 </tr>
1108</table>
1109</blockquote>
1110
1111To use PAM at all, this option must be provided at build time.
1112The run-time behaviour when PAM is built in varies with the version of
1113Portable OpenSSH, and on later versions it must also be enabled by setting
1114<b>UsePAM</b> to <b>yes</b> in <i>sshd_config</i>.
1115
1116<p>
1117The behaviour of the relevant authentications options when PAM support is built
1118in is summarised by the following table.
1119
1120<p>
1121<table border="1">
1122 <tr> <th>Version</th> <th>UsePAM</th> <th>PasswordAuthentication</th> <th>ChallengeResponseAuthentication</th> </tr>
1123 <tr>
1124 <td>&lt;=3.6.1p2</td>
1125 <td>Not applicable</td>
1126 <td>Uses PAM</td>
1127 <td>Uses PAM if <b>PAMAuthenticationViaKbdInt</b> is enabled</td>
1128 </tr>
1129 <tr>
1130 <td>3.7p1 - 3.7.1p1</td>
1131 <td>Defaults to <b>yes</b></td>
1132 <td>Does not use PAM</td>
1133 <td>Uses PAM if <b>UsePAM</b> is enabled</td>
1134 </tr>
1135 <tr>
1136 <td>3.7.1p2 - 3.8.1p1</td>
1137 <td>Defaults to <b>no</b></td>
1138 <td>Does not use PAM <a href="#3.15fn1">[1]</a></td>
1139 <td>Uses PAM if <b>UsePAM</b> is enabled</td>
1140 </tr>
1141 <tr>
1142 <td>3.9p1</td>
1143 <td>Defaults to <b>no</b></td>
1144 <td>Uses PAM if <b>UsePAM</b> is enabled</td>
1145 <td>Uses PAM if <b>UsePAM</b> is enabled</td>
1146 </tr>
1147</table>
1148<p>
1149
1150<a name= "3.15fn1">[1]</a> Some vendors, notably Redhat/Fedora, have
1151backported the PasswordAuthentication from 3.9p1 to their 3.8x based
1152packages. If you're using a vendor-supplied package then consult their
1153documentation.
1154
1155<p>
1156OpenSSH Portable's PAM interface still has problems with a few modules,
1157however we hope that this number will reduce in the future. As at the
11583.9p1 release, the known problems are:
1159
1160<ul>
1161 <li>Modules relying on module-private data (eg pam_dhkeys, pam_krb5, AFS)
1162 may fail to correctly establish credentials (bug <a
1163 href="http://bugzilla.mindrot.org/show_bug.cgi?id=688">#688</a>) when
1164 authenticating via <b>ChallengeResponseAuthentication</b>.
1165 <b>PasswordAuthentication</b> with 3.9p1 and above should work.
1166</ul>
1167
1168You can also check <a
1169href="http://bugzilla.mindrot.org/buglist.cgi?product=Portable+OpenSSH&amp;bug_status=RESOLVED&amp;bug_status=NEW&amp;bug_status=ACCEPTED&amp;component=PAM+support"
1170>bugzilla for current PAM issues</a>.
1171
1172<h2><a name= "3.16">3.16 - Why doesn't "w" or "who" on AIX 5.x show users
1173logged in via ssh?</a></h2>
1174
1175Between AIX 4.3.3 and AIX 5.x, the format of the wtmp struct changed. This
1176means that sshd binaries built on AIX 4.x will not correctly write wtmp
1177entries when run on AIX 5.x. This can be fixed by simply recompiling
1178sshd on an AIX 5.x system and using that.
1179
1180<hr>
1181<a href="http://www.openssh.com/index.html"><img height=24 width=24 src="back.gif" border=0 alt=OpenSSH></a>
1182<a href="mailto:www@openbsd.org">www@openbsd.org</a>
1183<br>
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1185
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