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- Committer: Bazaar Package Importer
- Author(s): Colin Watson
- Date: 2008-09-30 23:09:58 UTC
- mfrom: (1.13.3 upstream) (29 hardy)
- mto: This revision was merged to the branch mainline in revision 43.
- Revision ID: james.westby@ubuntu.com-20080930230958-o6vsgn8c4mm959s0
Tags: 1:5.1p1-3
* Remove unnecessary ssh-vulnkey output in non-verbose mode when no
compromised or unknown keys were found (closes: #496495).
* Configure with --disable-strip; dh_strip will deal with stripping
binaries and will honour DEB_BUILD_OPTIONS (thanks, Bernhard R. Link;
closes: #498681).
* Fix handling of zero-length server banners (thanks, Tomas Mraz; closes:
#497026).
compromised or unknown keys were found (closes: #496495).
* Configure with --disable-strip; dh_strip will deal with stripping
binaries and will honour DEB_BUILD_OPTIONS (thanks, Bernhard R. Link;
closes: #498681).
* Fix handling of zero-length server banners (thanks, Tomas Mraz; closes:
#497026).
- files added:
- PROTOCOL
- debian/tests
- files removed:
- debian/moduli.5
- files modified:
- ChangeLog
added
removed
debian/faq.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>OpenSSH FAQ</title>
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<link rev= "made" href= "mailto:www@openbsd.org">
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<meta name= "resource-type" content= "document">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name= "description" content= "the OpenSSH FAQ page">
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<meta name= "keywords" content= "OpenSSH,SSH,Secure Shell,faq">
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<meta name= "distribution" content= "global">
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<meta name= "copyright" content= "This document copyright 1999-2005 OpenBSD.">
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</head>
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<body bgcolor= "#ffffff" text= "#000000" link= "#23238E">
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<a href="http://www.openssh.org/index.html"><img alt="[OpenSSH]" height="30" width="141" src="images/smalltitle.gif" border="0"></a>
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<p>
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<h1>OpenSSH FAQ (Frequently asked questions)</h1>
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<strong>Date: 2005/09/20</strong>
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<hr>
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<blockquote>
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<h3><a href= "#1.0">1.0 - What Is OpenSSH and Where Can I Get It?</a></h3>
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<ul>
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<li><a href= "#1.1">1.1 - What is OpenSSH and where can I download it?</a>
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<li><a href= "#1.2">1.2 - Why should it be used?</a>
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<li><a href= "#1.3">1.3 - What Operating Systems are supported?</a>
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<li><a href= "#1.4">1.4 - What about copyright, usage and patents?</a>
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<li><a href= "#1.5">1.5 - Where should I ask for help?</a>
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</ul>
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<h3><a href= "#2.0">2.0 - General Questions</a></h3>
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<ul>
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<li><a href= "#2.1">2.1 - Why does ssh/scp make connections from low-numbered ports. My firewall blocks these.</a>
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<li><a href= "#2.2">2.2 - Why is the ssh client setuid root?</a>
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<li><a href= "#2.3">2.3 - Why does SSH 2.3 have problems interoperating with OpenSSH 2.1.1?</a>
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<li><a href= "#2.4">2.4 - Why does OpenSSH print: Dispatch protocol error: type 20</a>
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<li><a href= "#2.5">2.5 - Old versions of commercial SSH encrypt host keys with IDEA.</a>
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<li><a href= "#2.6">2.6 - What are these warning messages about key lengths?</a>
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<li><a href= "#2.7">2.7 - X11 and/or agent forwarding does not work.</a>
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<li><a href= "#2.8">2.8 - After upgrading OpenSSH I lost SSH2 support.</a>
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<li><a href= "#2.9">2.9 - sftp/scp fails at connection, but ssh is OK.</a>
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<li><a href= "#2.10">2.10 - Will you add [foo] to scp?</a>
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<li><a href= "#2.11">2.11 - How do I use port forwarding?</a>
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<li><a href= "#2.12">2.12 - My ssh connection freezes or drops out after N minutes of inactivity.</a>
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<li><a href= "#2.13">2.13 - How do I use scp to copy a file with a colon in it?</a>
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<li><a href= "#2.14">2.14 - Why does OpenSSH report its version to clients?</a>
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</ul>
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<h3><a href= "#3.0">3.0 - Portable OpenSSH Questions</a></h3>
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<ul>
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<li><a href= "#3.1">3.1 - Spurious PAM authentication messages in logfiles.</a>
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<li><a href= "#3.2">3.2 - Empty passwords not allowed with PAM authentication.</a>
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<li><a href= "#3.3">3.3 - ssh(1) takes a long time to connect or log in</a>
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<li><a href= "#3.4">3.4 - "Can't locate module net-pf-10" messages in log under Linux.</a>
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<li><a href= "#3.5">3.5 - Password authentication doesn't work (eg on Slackware 7.0 or Red Hat Linux 6.x)</a>
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<li><a href= "#3.6">3.6 - Configure or sshd(8) complain about lack of RSA support</a>
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<li><a href= "#3.7">3.7 - "scp: command not found" errors</a>
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<li><a href= "#3.8">3.8 - Unable to read passphrase</a>
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<li><a href= "#3.9">3.9 - 'configure' missing or make fails</a>
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<li><a href= "#3.10">3.10 - Hangs when exiting ssh</a>
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<li><a href= "#3.11">3.11 - Why does ssh hang on exit?</a>
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<li><a href= "#3.12">3.12 - I upgraded to OpenSSH 3.1 and X11 forwarding stopped working.</a>
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<li><a href= "#3.13">3.13 - I upgraded to OpenSSH 3.8 and some X11 programs stopped working.</a>
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<li><a href= "#3.14">3.14 - I copied my public key to authorized_keys but public-key authentication still doesn't work.</a>
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<li><a href= "#3.15">3.15 - OpenSSH versions and PAM behaviour.</a>
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<li><a href= "#3.16">3.16 - Why doesn't "w" or "who" on AIX 5.x show users logged in via ssh?</a>
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</ul>
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</blockquote>
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<hr>
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<h2><u><a name= "1.0">1.0 - What Is OpenSSH and Where Can I Get It?</a></u></h2>
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<h2><a name= "1.1">1.1 - What is OpenSSH and where can I download it?</a></h2>
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<p>
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OpenSSH is a <b>FREE</b> version of the SSH suite of network connectivity
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tools that increasing numbers of people on the Internet are coming to
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rely on. Many users of telnet, rlogin, ftp, and other such programs might
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not realize that their password is transmitted across the Internet
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unencrypted, but it is. OpenSSH encrypts all traffic (including passwords)
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to effectively eliminate eavesdropping, connection hijacking,
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and other network-level attacks.
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<p>
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The OpenSSH suite includes the
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&sektion=1">ssh(1)</a>
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program which replaces rlogin and telnet, and
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&sektion=1">scp(1)</a>
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which replaces
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=rcp&sektion=1">rcp(1)</a> and
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ftp&sektion=1">ftp(1)</a>.
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OpenSSH has also added
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp&sektion=1">sftp(1)</a> and
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp-server&sektion=8">sftp-server(8)</a>
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which implement an easier solution for file-transfer. This is based upon the
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<a href="http://www.openssh.org/txt/draft-ietf-secsh-filexfer-02.txt">secsh-filexfer</a> IETF draft.
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<p><strong>OpenSSH consists of a number of programs.</strong>
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<ul>
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd&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.
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Its behaviour is controlled by the config file <i><a
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href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd_config&sektion=5">
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sshd_config(5)</a></i>.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&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.
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Its behaviour is controlled by the global config file <i><a
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href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh_config&sektion=5">
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ssh_config(5)</a></i> and individual users' <i>$HOME/.ssh/config</i> files.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&sektion=1">scp(1)</a> - Securely copies files from one machine to another.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keygen&sektion=1">ssh-keygen(1)</a> - Used to create Pubkey Authentication (RSA or DSA) keys (host keys and user authentication keys).
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-agent&sektion=1">ssh-agent(1)</a> - Authentication agent. This can be used to hold RSA keys for authentication.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-add&sektion=1">ssh-add(1)</a> - Used to register new keys with the agent.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp-server&sektion=8">sftp-server(8)</a> - SFTP server subsystem.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sftp&sektion=1">sftp(1)</a> - Secure file transfer program.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keyscan&sektion=1">ssh-keyscan(1)</a> - gather ssh public keys.
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<li><a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keysign&sektion=8">ssh-keysign(8)</a> - ssh helper program for hostbased authentication.
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</ul>
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<h3>Downloading</h3>
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<p>
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OpenSSH comes in two downloadable distributions: the native <a
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href="http://www.openssh.org/openbsd.html">OpenBSD</a> distribution and the multi-platform
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<a href="http://www.openssh.org/portable.html">Portable</a> distribution. If you want
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OpenSSH for a recent OpenBSD or integration into a product, you
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probably want the <a href="http://www.openssh.org/openbsd.html">OpenBSD</a> distribution.
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If you want OpenSSH for another platform, or an older OpenBSD, you
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probably want the <a href="http://www.openssh.org/portable.html">Portable</a> distribution.
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<p>
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When downloading, please use a <a href="http://www.openssh.org/portable.html#mirrors">mirror</a>
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near you.
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<h2><a name= "1.2">1.2 - Why should it be used?</a></h2>
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<p>
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OpenSSH is a suite of tools to help secure your network
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connections. Here is a list of features:
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<ul>
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<li>Strong authentication. Closes several security holes (e.g., IP, routing, and DNS spoofing).
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<li>Improved privacy. All communications are automatically and transparently encrypted.
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<li>Secure X11 sessions. The program automatically sets DISPLAY on the server machine, and forwards any X11 connections over the secure channel.
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<li>Arbitrary TCP/IP ports can be redirected through the encrypted channel in both directions (e.g., for e-cash transactions).
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<li>No retraining needed for normal users.
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<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.
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<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).
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<li>Host authentication key distribution can be centrally by the administration, automatically when the first connection is made to a machine.
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<li>Any user can create any number of user authentication RSA keys for his/her own use.
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<li>The server program has its own server RSA key which is automatically regenerated every hour.
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<li>An authentication agent, running in the user's laptop or local workstation, can be used to hold the user's RSA authentication keys.
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<li>The software can be installed and used (with restricted functionality) even without root privileges.
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<li>The client is customizable in system-wide and per-user configuration files.
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<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.
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<li>Complete replacement for rlogin, rsh, and rcp.
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</ul>
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<p>
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Currently, almost all communications in computer networks are done
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without encryption. As a consequence, anyone who has access to any
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machine connected to the network can listen in on any communication.
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This is being done by hackers, curious administrators, employers,
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criminals, industrial spies, and governments. Some networks leak off
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enough electromagnetic radiation that data may be captured even from a
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distance.
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<p>
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When you log in, your password goes in the network in plain
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text. Thus, any listener can then use your account to do any evil he
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likes. Many incidents have been encountered worldwide where crackers
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have started programs on workstations without the owner's knowledge
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just to listen to the network and collect passwords. Programs for
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doing this are available on the Internet, or can be built by a
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competent programmer in a few hours.
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<p>
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Businesses have trade secrets, patent applications in preparation,
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pricing information, subcontractor information, client data, personnel
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data, financial information, etc. Currently, anyone with access to
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the network (any machine on the network) can listen to anything that
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goes in the network, without any regard to normal access restrictions.
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<p>
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Many companies are not aware that information can so easily be
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recovered from the network. They trust that their data is safe
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since nobody is supposed to know that there is sensitive information
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in the network, or because so much other data is transferred in the
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network. This is not a safe policy.
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<h2><a name= "1.3">1.3 - What operating systems are supported?</a></h2>
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<p>
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Even though OpenSSH is developed on
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<a href="http://www.openbsd.org/">OpenBSD</a> a wide variety of
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ports to other operating systems exist. The portable version of OpenSSH
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is headed by <a href="mailto:djm@openbsd.org">Damien Miller</a>.
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For a quick overview of the portable version of OpenSSH see
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<a href="http://www.openssh.org/portable.html">OpenSSH Portable Release</a>.
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Currently, the supported operating systems are:
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<ul>
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<li>OpenBSD
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<li>NetBSD
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<li>FreeBSD
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<li>AIX
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<li>HP-UX
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<li>IRIX
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<li>Linux
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<li>NeXT
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<li>SCO
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<li>SNI/Reliant Unix
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<li>Solaris
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<li>Digital Unix/Tru64/OSF
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<li>Mac OS X
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<li>Cygwin
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</ul>
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<p>
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A list of vendors that include OpenSSH in their distributions
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is located in the <a href="http://www.openssh.org/users.html">OpenSSH Users page</a>.
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<h2><a name= "1.4">1.4 - What about copyrights, usage and patents?</a></h2>
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<p>
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The OpenSSH developers have tried very hard to keep OpenSSH free of any
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patent or copyright problems. To do this, some options had to be
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stripped from OpenSSH. Namely support for patented algorithms.
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<p>
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OpenSSH does not support any patented transport algorithms. In SSH1 mode,
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only 3DES and Blowfish are available options. In SSH2 mode, only 3DES,
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Blowfish, CAST128, Arcfour and AES can be selected.
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The patented IDEA algorithm is not supported.
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<p>
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OpenSSH provides support for both SSH1 and SSH2 protocols.
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<p>
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Since the RSA patent has expired, there are no restrictions on the use
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of RSA algorithm using software, including OpenBSD.
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<h2><a name= "1.5">1.5 - Where should I ask for help?</a></h2>
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<p>
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There are many places to turn to for help. In addition to the main
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<a href="http://www.openssh.org/index.html">OpenSSH website</a>,
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there are many mailing lists to try. Before trying any mailing lists,
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please search through all mailing list archives to see if your question
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has already been answered. The OpenSSH Mailing List has been archived and
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put in searchable form and can be found at
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<a href="http://marc.info/?l=openssh-unix-dev&r=1&w=2">marc.info</a>.
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<p>
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For more information on subscribing to OpenSSH related mailing lists,
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please see <a href="http://www.openssh.org/list.html">OpenSSH Mailing lists</a>.
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<p>
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Information about submitting bug reports can be found at the OpenSSH
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<a href="http://www.openssh.org/report.html">Reporting bugs</a> page.
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<h2><u><a name= "2.0">2.0 - General Questions</a></u></h2>
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<h2><a name= "2.1">2.1 - Why does ssh/scp make connections from low-numbered ports.</a></h2>
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<p>
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The OpenSSH client uses low numbered ports for rhosts and rhosts-rsa
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authentication because the server needs to trust the username provided by
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the client. To get around this, you can add the below example to your
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<i>ssh_config</i> or <i>~/.ssh/config</i> file.
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<blockquote>
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<table border=0 width="800">
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<tr>
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<td nowrap bgcolor="#EEEEEE">
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<b>UsePrivilegedPort no</b>
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</td>
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</tr>
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</table>
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</blockquote>
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<p>
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Or you can specify this option on the command line, using the <b>-o</b>
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option to
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&sektion=1">ssh(1)</a> command.
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<blockquote>
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<table border=0 width="800">
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<tr>
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<td nowrap bgcolor="#EEEEEE">
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$ <b>ssh -o "UsePrivilegedPort no" host.com</b>
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</td>
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</tr>
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</table>
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</blockquote>
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<h2><a name= "2.2">2.2 - Why is the ssh client setuid root?</a></h2>
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<p>
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In conjunction with the previous question, (<a href="#2.1">2.1</a>)
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OpenSSH needs root authority to be able to bind to low-numbered ports to
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facilitate <i>rhosts authentication</i>.
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A privileged port is also required for rhosts-rsa authentication to older
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SSH releases.
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<p>
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Additionally, for both <i>rhosts-rsa authentication</i> (in protocol
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version 1) and <i>hostbased authentication</i> (in protocol version 2)
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the ssh client needs to access the <i>private host key</i> in order to
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authenticate the client machine to the server.
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OpenSSH versions prior to 3.3 required the <code>ssh</code> binary to be
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setuid root to enable this, and you may safely remove it if you don't
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want to use these authentication methods.
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<p>
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Starting in OpenSSH 3.3, <code>ssh</code> is not setuid by default. <a
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href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keysign">ssh-keysign</a>,
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is used for access to the private hosts keys, and ssh does not use privileged
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source ports by default. If you wish to use a privileged source port, you must
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manually set the setuid bit on <code>ssh</code>.
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<h2><a name= "2.3">2.3 - Why does SSH 2.3 have problems interoperating with OpenSSH 2.1.1?</a></h2>
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<p>
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SSH 2.3 and earlier versions contain a flaw in their HMAC implementation.
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Their code was not supplying the full data block output from the digest,
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and instead always provided 128 bits. For longer digests, this caused
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SSH 2.3 to not interoperate with OpenSSH.
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<p>
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OpenSSH 2.2.0 detects that SSH 2.3 has this flaw. Recent versions of SSH
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will have this bug fixed. Or you can add the following to
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SSH 2.3 <i>sshd2_config</i>.
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<blockquote>
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<table border=0 width="800">
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<tr>
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<td nowrap bgcolor="#EEEEEE">
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<b>Mac hmac-md5</b>
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</td>
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</tr>
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</table>
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</blockquote>
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<h2><a name= "2.4">2.4 - Why does OpenSSH print: Dispatch protocol error: type 20</a></h2>
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<p>
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Problems in interoperation have been seen because older versions of
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OpenSSH did not support session rekeying. However the commercial SSH 2.3
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tries to negotiate this feature, and you might experience connection
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freezes or see the error message "<b>Dispatch protocol error:
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type 20 </b>".
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To solve this problem, either upgrade to a recent OpenSSH release or
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disable rekeying by adding the following to your commercial SSH 2.3's
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<i>ssh2_config</i> or <i>sshd2_config</i>.
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<blockquote>
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<table border=0 width="800">
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<tr>
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<td nowrap bgcolor="#EEEEEE">
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<b>RekeyIntervalSeconds 0</b>
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</td>
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</tr>
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</table>
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</blockquote>
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<h2><a name= "2.5">2.5 - Old versions of commercial SSH encrypt host keys with IDEA.</a></h2>
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<p>
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The old versions of SSH used a patented algorithm to encrypt their
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<i>/etc/ssh/ssh_host_key</i>. This problem will manifest as
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd&sektion=8">sshd(8)</a>
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not being able to read its host key. To solve this, use the command below
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to convert your ssh_host_key to use 3DES.
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<b>NOTE:</b> Use the
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keygen&sektion=1">ssh-keygen(1)</a>
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program from the Commercial SSH product, *NOT* OpenSSH for the example
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below.
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<blockquote>
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<table border=0 width="800">
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<tr>
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<td nowrap bgcolor="#EEEEEE">
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# <b>ssh-keygen -u -f /etc/ssh/ssh_host_key</b>
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</td>
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</tr>
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</table>
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</blockquote>
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<h2><a name= "2.6">2.6 - What are these warning messages about key lengths</a></h2>
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<p>
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Commercial SSH's
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<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh-keygen&sektion=1">ssh-keygen(1)</a>
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program contained a bug which caused it to occasionally generate Pubkey
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Authentication (RSA or DSA) keys which had their Most Significant Bit
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(MSB) unset. Such keys were advertised as being full-length, but are
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actually, half the time, smaller than advertised.
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<p>
413
OpenSSH will print warning messages when it encounters such keys. To rid
414
yourself of these message, edit your <i>known_hosts</i> files and replace the
415
incorrect key length (usually "1024") with the correct key length
416
(usually "1023").
417
418
<h2><a name= "2.7">2.7 - X11 and/or agent forwarding does not work.</a></h2>
419
420
<p>
421
Check your <i>ssh_config</i> and <i>sshd_config</i>. The default
422
configuration files disable authentication agent and X11 forwarding. To
423
enable it, put the line below in <i>sshd_config</i>:
424
425
<blockquote>
426
<table border=0 width="800">
427
<tr>
428
<td nowrap bgcolor="#EEEEEE">
429
<b>X11Forwarding yes</b>
430
</td>
431
</tr>
432
</table>
433
</blockquote>
434
435
<p>
436
and put the following lines in <i>ssh_config</i>:
437
438
<blockquote>
439
<table border=0 width="800">
440
<tr>
441
<td nowrap bgcolor="#EEEEEE">
442
<b>ForwardAgent yes</b><br>
443
<b>ForwardX11 yes</b>
444
</td>
445
</tr>
446
</table>
447
</blockquote>
448
449
<p>
450
X11 forwarding requires a working <a
451
href="http://www.openbsd.org/cgi-bin/man.cgi?query=xauth&sektion=1"
452
>xauth(1)</a> binary. On OpenBSD this is in the <i>xbase</i> file
453
set but will probably be different on other platforms. For OpenSSH
454
Portable, xauth must be either found at configure time or specified
455
via <b>XAuthLocation</b> in sshd_config(5) and ssh_config(5).
456
457
<p>
458
Note on agent interoperability: There are two different and
459
incompatible agent forwarding mechanisms within the SSH2 protocol.
460
OpenSSH has always used an extension of the original SSH1 agent
461
requests, however some commercial products use a different, non-free
462
agent forwarding protocol. This means that agent forwarding cannot
463
be used between OpenSSH and those products.
464
465
<p>
466
<b>NOTE:</b> For users of Linux Mandrake 7.2, Mandrake modifies the
467
<i>XAUTHORITY</i> environment variable in <i>/etc/skel/.bashrc</i>,
468
and thus any bash user's home directory. This variable is set by OpenSSH
469
and for either of the above options to work, you need to comment out
470
the line:
471
472
473
<blockquote>
474
<table border=0 width="800">
475
<tr>
476
<td nowrap bgcolor="#EEEEEE">
477
<b># export XAUTHORITY=$HOME/.Xauthority</b>
478
</td>
479
</tr>
480
</table>
481
</blockquote>
482
483
<h2><a name= "2.8">2.8 - After upgrading OpenSSH I lost SSH2 support.</a></h2>
484
485
<p>
486
Between versions changes can be made to <i>sshd_config</i> or
487
<i>ssh_config</i>. You should always check on these changes when upgrading
488
versions of OpenSSH. After OpenSSH Version 2.3.0 you need to add the
489
following to your <i>sshd_config</i>:
490
491
492
<blockquote>
493
<table border=0 width="800">
494
<tr>
495
<td nowrap bgcolor="#EEEEEE">
496
<b>HostKey /etc/ssh_host_dsa_key</b><br>
497
<b>HostKey /etc/ssh_host_rsa_key</b>
498
</td>
499
</tr>
500
</table>
501
</blockquote>
502
503
<h2><a name= "2.9">2.9 - sftp/scp fails at connection, but ssh is OK.</a></h2>
504
505
<p>
506
sftp and/or scp may fail at connection time if you have shell
507
initialization (.profile, .bashrc, .cshrc, etc) which produces output
508
for non-interactive sessions. This output confuses the sftp/scp client.
509
You can verify if your shell is doing this by executing:
510
511
<blockquote>
512
<table border=0 width="800">
513
<tr>
514
<td nowrap bgcolor="#EEEEEE">
515
<b>ssh yourhost /usr/bin/true</b>
516
</td>
517
</tr>
518
</table>
519
</blockquote>
520
521
<p>
522
If the above command produces any output, then you need to modify your
523
shell initialization.
524
525
<h2><a name= "2.10">2.10 - Will you add [foo] to scp?</a></h2>
526
527
<p>
528
Short Answer: no.
529
530
<p>
531
Long Answer: scp is not standardized. The closest thing it has to a
532
specification is "what rcp does". Since the same command is used on both ends
533
of the connection, adding features or options risks breaking interoperability with other
534
implementations.
535
536
<p>
537
New features are more likely in sftp, since the protocol is standardized
538
(well, a <a href="http://www.ietf.org/html.charters/secsh-charter.html">
539
draft standard</a>), extensible, and the client and server are decoupled.
540
541
<h2><a name= "2.11">2.11 - How do I use port forwarding?</a></h2>
542
543
<p>
544
If the remote server is running sshd(8), it may be possible to
545
``tunnel'' certain services via ssh. This may be desirable, for
546
example, to encrypt POP or SMTP connections, even though the software
547
does not directly support encrypted communications. Tunnelling uses
548
port forwarding to create a connection between the client and server.
549
The client software must be able to specify a non-standard port to
550
connect to for this to work.
551
552
<p>
553
The idea is that the user connects to the remote host using ssh,
554
and specifies which port on the client's machine should be used to
555
forward connections to the remote server. After that it is possible
556
to start the service which is to be encrypted (e.g. fetchmail, irc)
557
on the client machine, specifying the same local port passed to
558
ssh, and the connection will be tunnelled through ssh. By default,
559
the system running the forward will only accept connections from
560
itself.
561
562
<p>
563
The options most relevant to tunnelling are the -L and -R options,
564
which allow the user to forward connections, the -D option, which
565
permits dynamic port forwarding, the -g option, which permits other
566
hosts to use port forwards, and the -f option, which instructs ssh
567
to put itself in the background after authentication. See the <a
568
href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh&sektion=1"
569
>ssh(1)</a> man page for further details.
570
571
<p>
572
This is an example of tunnelling an IRC session from client machine
573
``127.0.0.1'' (localhost) to remote server ``server.example.com'':
574
575
<blockquote>
576
<table border=0 width="800">
577
<tr>
578
<td nowrap bgcolor="#EEEEEE">
579
<b>ssh -f -L 1234:server.example.com:6667 server.example.com sleep 10<br>
580
irc -c '#users' -p 1234 pinky 127.0.0.1</b>
581
</td>
582
</tr>
583
</table>
584
</blockquote>
585
586
<p>
587
This tunnels a connection to IRC server server.example.com, joining
588
channel ``#users'', using the nickname ``pinky''. The local port used
589
in this example is 1234. It does not matter which port is used, as
590
long as it's greater than 1023 (remember, only root can open sockets on
591
privileged ports) and doesn't conflict with any ports already in use.
592
The connection is forwarded to port 6667 on the remote server, since
593
that's the standard port for IRC services.
594
595
<p>
596
The remote command ``sleep 10'' was specified to allow an amount
597
of time (10 seconds, in the example) to start the service which is to
598
be tunnelled. If no connections are made within the time specified,
599
ssh will exit. If more time is required, the sleep(1) value can be
600
increased appropriately or, alternatively, the example above could
601
be added as a function to the user's shell. See ksh(1) and csh(1)
602
for more details about user-defined functions.
603
604
<p>
605
ssh also has an -N option, convenient for use with port forwarding:
606
if -N is specified, it is not necessary to specify a remote command
607
(``sleep 10'' in the example above). However, use of this option
608
causes ssh to wait around for ever (as opposed to exiting after a
609
remote command has completed), and the user must take care to manually
610
kill(1) the process afterwards.
611
612
<h2><a name= "2.12">2.12 - My ssh connection freezes or drops out after N minutes of inactivity.</a></h2>
613
614
<p>
615
This is usually the result of a packet filter or NAT device
616
timing out your TCP connection due to inactivity. You can enable
617
<b>ClientAliveInterval</b> in the server's <i><a
618
href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd_config&sektion=5">
619
sshd_config</a></i>, or enable <b>ServerAliveInterval</b> in the
620
client's <i><a
621
href="http://www.openbsd.org/cgi-bin/man.cgi?query=ssh_config&sektion=5">
622
ssh_config</a></i> (the latter is available in OpenSSH 3.8 and newer).
623
624
<p>
625
Enabling either option and setting the interval for less than the time
626
it takes to time out your session will ensure that the connection is
627
kept "fresh" in the device's connection table.
628
629
<h2><a name= "2.13">2.13 - How do I use scp to copy a file with a colon in it?</a></h2>
630
631
<b><a
632
href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&sektion=1">
633
scp</a></b> will interpret the component before the colon to be a remote
634
server name and attempt to connect to it. To prevent this, refer to
635
the file by a relative or absolute path, eg:
636
637
<blockquote>
638
<table border=0 width="800">
639
<tr>
640
<td nowrap bgcolor="#EEEEEE">
641
$ scp ./source:file sshserver:
642
</td>
643
</tr>
644
</table>
645
</blockquote>
646
647
<h2><a name= "2.14">2.14 - Why does OpenSSH report its version to clients?</a></h2>
648
649
<p>
650
OpenSSH, like most SSH implementations, reports its name and version to clients
651
when they connect, e.g.
652
</p>
653
654
<blockquote>
655
SSH-2.0-OpenSSH_3.9
656
</blockquote>
657
658
<p>
659
This information is used by clients and servers to enable protocol
660
compatibility tweaks to work around changed, buggy or missing features in
661
the implementation they are talking to. This protocol feature checking is
662
still required at present because the SSH protocol has not been yet published
663
as a RFC and more incompatible changes may be made before this happens.
664
</p>
665
666
<h2><u><a name= "3.0">3.0 - Portable OpenSSH Questions</a></u></h2>
667
668
<h2><a name= "3.1">3.1 - Spurious PAM authentication messages in logfiles.</a></h2>
669
670
<p>
671
The portable version of OpenSSH will generate spurious authentication
672
failures at every login, similar to:
673
674
675
<blockquote>
676
<table border=0 width="800">
677
<tr>
678
<td nowrap bgcolor="#EEEEEE">
679
"<b>authentication failure; (uid=0) -> root for sshd service</b>"
680
</td>
681
</tr>
682
</table>
683
</blockquote>
684
685
<p>
686
These are generated because OpenSSH first tries to determine whether a
687
user needs authentication to login (e.g. empty password). Unfortunately
688
PAM likes to log all authentication events, this one included.
689
690
<p>
691
If it annoys you too much, set "<b>PermitEmptyPasswords no</b>"
692
in <i>sshd_config</i>. This will quiet the error message at the expense
693
of disabling logins to accounts with no password set.
694
This is the default if you use the supplied <i>sshd_config</i> file.
695
696
<h2><a name= "3.2">3.2 - Empty passwords not allowed with PAM authentication.</a></h2>
697
698
<p>
699
To enable empty passwords with a version of OpenSSH built with PAM you
700
must add the flag nullok to the end of the password checking module
701
in the <i>/etc/pam.d/sshd</i> file. For example:
702
703
<blockquote>
704
<table border=0 width="800">
705
<tr>
706
<td nowrap bgcolor="#EEEEEE">
707
auth required/lib/security/pam_unix.so shadow nodelay nullok
708
</td>
709
</tr>
710
</table>
711
</blockquote>
712
713
<p>
714
This must be done in addition to setting "<b>PermitEmptyPasswords
715
yes</b>" in the <i>sshd_config</i> file.
716
717
<p>
718
There is one caveat when using empty passwords with PAM authentication:
719
PAM will allow any password when authenticating an account with an empty
720
password. This breaks the check that
721
<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=sshd&sektion=8">sshd(8)</a>
722
uses to determine whether an account has no password set and grant
723
users access to the account regardless of the policy specified by
724
<b>PermitEmptyPasswords</b>. For this reason, it is recommended that you
725
do not add the <b>nullok</b> directive to your PAM configuration file
726
unless you specifically wish to allow empty passwords.
727
728
729
<h2><a name= "3.3">3.3 - ssh(1) takes a long time to connect or log
730
in</a></h2>
731
732
<p>
733
Large delays (more that 10 seconds) are typically caused a problem with
734
name resolution:
735
<ul>
736
<li>Some versions of glibc (notably glibc 2.1 shipped with Red Hat 6.1)
737
can take a long time to resolve "IPv6 or IPv4" addresses from domain
738
names. This can be worked around with by specifying <b>AddressFamily
739
inet</b> option in <i>ssh_config</i>.</li>
740
741
<li>There may be a DNS lookup problem, either at the client or server.
742
You can use the <code>nslookup</code> command to check this on both client
743
and server by looking up the other end's name and IP address. In
744
addition, on the server look up the name returned by the client's
745
IP-name lookup. You can disable most of the server-side lookups by
746
setting <b>UseDNS no</b> in <i>sshd_config</i>.</li>
747
</ul>
748
749
<p>
750
Delays less than 10 seconds can have other causes.
751
752
<ul>
753
754
<li>OpenSSH releases prior to 3.8 had an <i>moduli</i> file with
755
moduli that were just smaller than what sshd would look for, and
756
as a result, sshd would end up using moduli significantly larger
757
than requested, which resulted in a speed penalty. Replacing the
758
<i>moduli</i> file will resolve this (note that in most cases this
759
file will not be replaced during an upgrade and must be replaced
760
manually).</li>
761
762
<li>OpenSSH releases prior to 3.8 had a flaw in <code>ssh</code> that
763
would cause it to request moduli larger than intended (which when
764
combined with the above resulted in significant slowdowns).
765
Upgrading the client to 3.8 or higher will resolve this issue.</li>
766
767
<li>If either the client or server lack a kernel-based random number
768
device (eg Solaris < 9, AIX < 5.2, HP-UX < 11.11) and no
769
substitute is available (eg <a href=
770
"ftp://ftp.ayamura.org/pub/prngd/">prngd</a>) it's possible that
771
one of the programs called by <code>ssh-rand-helper</code> to
772
generate entropy is hanging. This can be investigated by running
773
it in debug mode:
774
775
<blockquote>
776
<table border=0 width="800">
777
<tr>
778
<td nowrap bgcolor="#EEEEEE">
779
/usr/local/libexec/ssh-rand-helper -vvv
780
</td>
781
</tr>
782
</table>
783
</blockquote>
784
785
Any significant delays should be investigated and rectified, or the
786
corresponding commands should be removed from <i>ssh_prng_cmds</i>.
787
</li>
788
789
</ul>
790
791
<h3>How slow is "slow"?</h3>
792
Under normal conditions, the speed of SSH logins is dependant on
793
CPU speed of client and server. For comparison the following are
794
typical connect times for <code>time ssh localhost true</code>
795
with a 1024-bit RSA key on otherwise unloaded hosts. OpenSSH and
796
OpenSSL were compiled with gcc 3.3.x.
797
798
<p>
799
<table>
800
<tr><th>CPU</th><th>Time (SSHv1)<a href="#3.3fn1">[1]</a></th>
801
<th>Time (SSHv2)</th></tr>
802
<tr><td>170MHz SPARC/sun4m</td><td>0.74 sec</td><td>1.25 sec</td></tr>
803
<tr><td>236MHz HPPA/8200<a href="#3.3fn2">[2]</a></td><td>0.44 sec</td>
804
<td>0.79 sec</td></tr>
805
<tr><td>375MHz PowerPC/604e</td><td>0.38 sec</td><td>0.51 sec</td></tr>
806
<tr><td>933MHz VIA Ezra</td><td>0.34 sec</td><td>0.44 sec</td></tr>
807
<tr><td>2.1GHz Athlon XP 2600+</td><td>0.14 sec</td><td>0.22 sec</td></tr>
808
</table>
809
810
<br>
811
812
<a name="3.3fn1">[1]</a> The SSHv1 protocol is faster but is
813
cryptographically weaker than SSHv2.<br>
814
815
<a name="3.3fn2">[2]</a> At the time of writing, gcc generates
816
relatively slow code on HPPA for RSA and Diffie-Hellman operations
817
(see <a href= "http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7625">gcc
818
bug #7625</a> and <a
819
href="http://marc.info/?l=openssh-unix-dev&m=102646106016694">
820
discussion on openssh-unix-dev</a>).
821
822
<h2><a name= "3.4">3.4 - "Can't locate module net-pf-10" messages in log under Linux.</a></h2>
823
824
<p>
825
The Linux kernel is looking (via modprobe) for protocol family 10 (IPv6).
826
Either load the appropriate kernel module, enter the correct alias in
827
<i>/etc/modules.conf</i> or disable IPv6 in <i>/etc/modules.conf</i>.
828
829
830
<p>
831
For some silly reason <i>/etc/modules.conf</i> may also be named
832
<i>/etc/conf.modules</i>.
833
834
835
<h2><a name= "3.5">3.5 - Password authentication doesn't work (eg on Slackware 7.0 or Red Hat 6.x)</a></h2>
836
837
<p>
838
If the password is correct password the login is still denied, the
839
usual cause is that the system is configured to use MD5-type passwords
840
but the
841
<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=crypt&sektion=3"
842
>crypt(3)</a> function used by sshd doesn't understand them.
843
844
<p>
845
Affected accounts will have password strings in <i>/etc/passwd</i>
846
or <i>/etc/shadow</i> that start with <b>$1$</b>.
847
If password authentication fails for new accounts or accounts with
848
recently changed passwords, but works for old accounts, this is the
849
likely culprit.
850
851
<p>
852
The underlying cause is that some versions of OpenSSL have a crypt(3)
853
function that does not understand MD5 passwords, and the link order of
854
sshd means that OpenSSL's crypt(3) is used instead of the system's.
855
OpensSSH's configure attempts to correct for this but is not always
856
successful.
857
858
<p>
859
There are several possible solutions:
860
861
<ul>
862
<li>
863
<p>
864
Enable sshd's built-in support for MD5 passwords at build time.
865
866
<blockquote>
867
<table border=0 width="800">
868
<tr>
869
<td nowrap bgcolor="#EEEEEE">
870
./configure --with-md5-passwords [options]
871
</td>
872
</tr>
873
</table>
874
</blockquote>
875
876
This is safe even if you have both types of encryption as sshd will
877
select the correct algorithm for each account automatically.
878
879
<li>
880
<p>
881
If your system has a separate libcrypt library (eg Slackware 7) then you
882
can manually add -lcrypt to the LIBS list so it's used instead of
883
OpenSSL's:
884
885
<blockquote>
886
<table border=0 width="800">
887
<tr>
888
<td nowrap bgcolor="#EEEEEE">
889
LIBS=-lcrypt ./configure [options]
890
</td>
891
</tr>
892
</table>
893
</blockquote>
894
895
<li>
896
<p>
897
If your platforms supports PAM, you may configure sshd to use it
898
(see <a href= "#3.15" >section 3.15</a>). This will mean that sshd will
899
not verify passwords itself but will defer to the configured PAM modules.
900
</ul>
901
902
<h2><a name= "3.6">3.6 - Configure or sshd(8) complain about lack of RSA or DSA support</a></h2>
903
904
<p>
905
Ensure that your OpenSSL libraries have been built to include RSA or DSA
906
support either internally or through RSAref.
907
908
909
<h2><a name= "3.7">3.7 - "scp: command not found" errors</a></h2>
910
911
<p>
912
<a href="http://www.openbsd.org/cgi-bin/man.cgi?query=scp&sektion=1">scp(1)</a>
913
must be in the default PATH on both the client and the server. You may
914
need to use the <b>--with-default-path</b> option to specify a custom
915
path to search on the server. This option replaces the default path,
916
so you need to specify all the current directories on your path as well
917
as where you have installed scp. For example:
918
919
<blockquote>
920
<table border=0 width="800">
921
<tr>
922
<td nowrap bgcolor="#EEEEEE">
923
$ <b>./configure --with-default-path=/bin:/usr/bin:/usr/local/bin:/path/to/scp</b>
924
</td>
925
</tr>
926
</table>
927
</blockquote>
928
929
<p>
930
Note that configuration by the server's admin will take precedence over the
931
setting of <b>--with-default-path</b>. This includes resetting PATH in
932
<i>/etc/profile</i>, PATH in <i>/etc/environment</i> on AIX, or (for 3.7p1 and
933
above) setting PATH or SUPATH in <i>/etc/default/login</i> on Solaris or
934
Reliant Unix.
935
936
<h2><a name= "3.8">3.8 - Unable to read passphrase</a></h2>
937
938
<p>
939
Some operating systems set <i>/dev/tty</i> with incorrect modes, causing
940
the reading of passwords to fail with the following error:
941
942
<blockquote>
943
<table border=0 width="800">
944
<tr>
945
<td nowrap bgcolor="#EEEEEE">
946
You have no controlling tty. Cannot read passphrase.
947
</td>
948
</tr>
949
</table>
950
</blockquote>
951
952
<p>
953
The solution to this is to reset the permissions on <i>/dev/tty</i>
954
to mode 0666 and report the error as a bug to your OS vendor.
955
956
957
<h2><a name= "3.9">3.9 - 'configure' missing or make fails</a></h2>
958
959
<p>
960
If there is no 'configure' file in the tar.gz file that you downloaded
961
or make fails with "missing separator" errors, you have probably
962
downloaded the OpenBSD distribution of OpenSSH and are attempting to
963
compile it on another platform. Please refer to the information on the
964
<a href="http://www.openssh.org/portable.html">portable version</a>.
965
966
967
<h2><a name= "3.10">3.10 - Hangs when exiting ssh</a></h2>
968
969
<p>
970
OpenSSH may hang when exiting. This can occur when there is an active
971
background process. This is known to occur on Linux and HP-UX.
972
The problem can be verified by doing the following:
973
974
<blockquote>
975
<table border=0 width="800">
976
<tr>
977
<td nowrap bgcolor="#EEEEEE">
978
$ <b>sleep 20 & exit</b>
979
</td>
980
</tr>
981
</table>
982
</blockquote>
983
984
Try to use this instead:
985
<blockquote>
986
<table border=0 width="800">
987
<tr>
988
<td nowrap bgcolor="#EEEEEE">
989
$ <b>sleep 20 < /dev/null > /dev/null 2>&1 &</b>
990
</td>
991
</tr>
992
</table>
993
</blockquote>
994
995
<p>
996
A work around for bash users is to place <b>"shopt -s huponexit"</b>
997
in either /etc/bashrc or ~/.bashrc. Otherwise, consult your shell's
998
man page for an option to enable it to send a HUP signal to active
999
jobs when exiting. See <a
1000
href="http://bugzilla.mindrot.org/show_bug.cgi?id=52">bug #52</a>
1001
for other workarounds.
1002
1003
<h2><a name= "3.11">3.11 - Why does ssh hang on exit?</a></h2>
1004
1005
<p>
1006
When executing
1007
<blockquote>
1008
<table border=0 width="800">
1009
<tr>
1010
<td nowrap bgcolor="#EEEEEE">
1011
$ <b>ssh host command</b>
1012
</td>
1013
</tr>
1014
</table>
1015
</blockquote>
1016
ssh <b>needs</b> to hang, because it needs to wait:
1017
<ul>
1018
<li>
1019
until it can be sure that <code>command</code> does not need
1020
more input.
1021
<li>
1022
until it can be sure that <code>command</code> does not produce
1023
more output.
1024
<li>
1025
until <code>command</code> exits because sshd needs to tell
1026
the exit status from <code>command</code> to ssh.
1027
</ul>
1028
<p>
1029
1030
<h2><a name= "3.12">3.12 - I upgraded to OpenSSH 3.1 and X11
1031
forwarding stopped working.</a></h2>
1032
1033
Starting with OpenSSH 3.1, the sshd x11 forwarding server listens on
1034
localhost by default; see the sshd <b>X11UseLocalhost</b> option to
1035
revert to prior behaviour if your older X11 clients do not function
1036
with this configuration.<p>
1037
1038
In general, X11 clients using X11 R6 should work with the default
1039
setting. Some vendors, including HP, ship X11 clients with R6
1040
and R5 libs, so some clients will work, and others will not work.
1041
This is true for HP-UX 11.X.<p>
1042
1043
<h2><a name= "3.13">3.13 - I upgraded to OpenSSH 3.8 and some
1044
X11 programs stopped working.</a></h2>
1045
1046
<p>
1047
As documented in the <a href="http://www.openssh.org/txt/release-3.8">3.8 release notes</a>,
1048
<code>ssh</code> will now use untrusted X11 cookies by
1049
default. The previous behaviour can be restored by setting
1050
<b>ForwardX11Trusted yes</b> in <i>ssh_config</i>.
1051
1052
<p>
1053
Possible symptoms include:<br>
1054
<code>BadWindow (invalid Window parameter)<br>
1055
BadAccess (attempt to access private resource denied)<br>
1056
X Error of failed request: BadAtom (invalid Atom parameter)<br>
1057
Major opcode of failed request: 20 (X_GetProperty)<br></code>
1058
1059
<h2><a name= "3.14">3.14 - I copied my public key to authorized_keys
1060
but public-key authentication still doesn't work.</a></h2>
1061
1062
<p>
1063
Typically this is caused by the file permissions on $HOME, $HOME/.ssh or
1064
$HOME/.ssh/authorized_keys being more permissive than sshd allows by default.
1065
1066
<p>
1067
In this case, it can be solved by executing the following on the server.
1068
<blockquote>
1069
<table border=0 width="800">
1070
<tr>
1071
<td nowrap bgcolor="#EEEEEE">
1072
$ <b>chmod go-w $HOME $HOME/.ssh</b><br>
1073
$ <b>chmod 600 $HOME/.ssh/authorized_keys</b>
1074
</td>
1075
</tr>
1076
</table>
1077
</blockquote>
1078
1079
<p>
1080
If this is not possible for some reason, an alternative is to set
1081
<b>StrictModes no</b> in <i>sshd_config</i>, however this is not
1082
recommended.
1083
1084
<h2><a name= "3.15">3.15 - OpenSSH versions and PAM behaviour.</a></h2>
1085
1086
Portable OpenSSH has a configure-time option to enable sshd's use of the
1087
<a href="http://www.opengroup.org/onlinepubs/008329799/">PAM</a>
1088
(Pluggable Authentication Modules) interface.
1089
1090
<blockquote>
1091
<table border=0 width="800">
1092
<tr>
1093
<td nowrap bgcolor="#EEEEEE">
1094
./configure --with-pam [options]
1095
</td>
1096
</tr>
1097
</table>
1098
</blockquote>
1099
1100
To use PAM at all, this option must be provided at build time.
1101
The run-time behaviour when PAM is built in varies with the version of
1102
Portable OpenSSH, and on later versions it must also be enabled by setting
1103
<b>UsePAM</b> to <b>yes</b> in <i>sshd_config</i>.
1104
1105
<p>
1106
The behaviour of the relevant authentications options when PAM support is built
1107
in is summarised by the following table.
1108
1109
<p>
1110
<table border="1">
1111
<tr> <th>Version</th> <th>UsePAM</th> <th>PasswordAuthentication</th> <th>ChallengeResponseAuthentication</th> </tr>
1112
<tr>
1113
<td><=3.6.1p2</td>
1114
<td>Not applicable</td>
1115
<td>Uses PAM</td>
1116
<td>Uses PAM if <b>PAMAuthenticationViaKbdInt</b> is enabled</td>
1117
</tr>
1118
<tr>
1119
<td>3.7p1 - 3.7.1p1</td>
1120
<td>Defaults to <b>yes</b></td>
1121
<td>Does not use PAM</td>
1122
<td>Uses PAM if <b>UsePAM</b> is enabled</td>
1123
</tr>
1124
<tr>
1125
<td>3.7.1p2 - 3.8.1p1</td>
1126
<td>Defaults to <b>no</b></td>
1127
<td>Does not use PAM <a href="#3.15fn1">[1]</a></td>
1128
<td>Uses PAM if <b>UsePAM</b> is enabled</td>
1129
</tr>
1130
<tr>
1131
<td>3.9p1</td>
1132
<td>Defaults to <b>no</b></td>
1133
<td>Uses PAM if <b>UsePAM</b> is enabled</td>
1134
<td>Uses PAM if <b>UsePAM</b> is enabled</td>
1135
</tr>
1136
</table>
1137
<p>
1138
1139
<a name= "3.15fn1">[1]</a> Some vendors, notably Redhat/Fedora, have
1140
backported the PasswordAuthentication from 3.9p1 to their 3.8x based
1141
packages. If you're using a vendor-supplied package then consult their
1142
documentation.
1143
1144
<p>
1145
OpenSSH Portable's PAM interface still has problems with a few modules,
1146
however we hope that this number will reduce in the future. As at the
1147
3.9p1 release, the known problems are:
1148
1149
<ul>
1150
<li>Modules relying on module-private data (eg pam_dhkeys, pam_krb5, AFS)
1151
may fail to correctly establish credentials (bug <a
1152
href="http://bugzilla.mindrot.org/show_bug.cgi?id=688">#688</a>) when
1153
authenticating via <b>ChallengeResponseAuthentication</b>.
1154
<b>PasswordAuthentication</b> with 3.9p1 and above should work.
1155
</ul>
1156
1157
You can also check <a
1158
href="http://bugzilla.mindrot.org/buglist.cgi?product=Portable+OpenSSH&bug_status=RESOLVED&bug_status=NEW&bug_status=ACCEPTED&component=PAM+support"
1159
>bugzilla for current PAM issues</a>.
1160
1161
<h2><a name= "3.16">3.16 - Why doesn't "w" or "who" on AIX 5.x show users
1162
logged in via ssh?</a></h2>
1163
1164
Between AIX 4.3.3 and AIX 5.x, the format of the wtmp struct changed. This
1165
means that sshd binaries built on AIX 4.x will not correctly write wtmp
1166
entries when run on AIX 5.x. This can be fixed by simply recompiling
1167
sshd on an AIX 5.x system and using that.
1168
1169
<hr>
1170
<a href="http://www.openssh.org/index.html"><img height=24 width=24 src="back.gif" border=0 alt=OpenSSH></a>
1171
<a href="mailto:www@openbsd.org">www@openbsd.org</a>
1172
<br>
1173
<small>$OpenBSD: faq.html,v 1.107 2007/06/20 18:14:15 miod Exp $</small>
1174
1175
</body>
1176
</html>
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