The Secure Shell ^TM Frequently Asked Questions

0. Meta-info

• 0.1. Where can I get this document?
• 0.2. Who maintains this document?
• 0.3. Where do I send questions, additions, corrections etc. about this document?
• 0.4. Revision history
• 0.5. Legalese
• 0.6. Trademarks
• 0.7. Credits

1. About Secure Shell

• 1.1. What is Secure Shell?
• 1.2. How widespread is its use?
• 1.3. What protocols does it use?
• 1.4. What encryption algorithms does Secure Shell use?
• 1.5. How does Secure Shell authenticate?
• 1.6. What does Secure Shell protect against?
• 1.7. What doens't Secure Shell protect against?
• 1.8. What is the difference between SSH1 and SSH2?
• 1.9. Who maintains Secure Shell?
• 1.10. Can I run Secure Shell legally?
• 1.10.1. Licensing
• 1.10.2. Cryptography laws
• 1.10.3. Patents on cryptographic algorithms
• 1.11. What operating systems does Secure Shell run on?
• 1.12. Shouldn't I be using only SSH2?

2. Getting Secure Shell

• 2.1. Where is the official Secure Shell distribution and mirror sites?
• 2.1.1. Official Site
• 2.1.2. Mirrors
• 2.2. How about getting other relatively free versions of Secure Shell?
• 2.2.1. UNIX
• 2.2.2. Java
• 2.2.3. Windows
• 2.2.4. Macintosh
• 2.2.5. OpenVMS
• 2.2.6. Handheld devices
• 2.2.7. BeOS
• 2.2.8. OS/2
• 2.2.9. DOS
• 2.3. How about getting commerically supported versions of Secure Shell?
• 2.3.1. SSH Secure Shell
• 2.3.2. Van Dyke Software SecureCRT
• 2.3.3. F-Secure Tunnel and Terminal
• 2.3.4. Appgate Client and Server
• 2.3.5. EmTec ZOC

3. Installing Secure Shell

• 3.1. What is the latest version of Secure Shell?
• 3.2. How do I install Secure Shell?
• 3.3. Does it make sense to install Secure Shell as a non-root user on UNIX?
• 3.4. Where do I get pre-compiled binaries for Secure Shell?

4. Running Secure Shell

• 4.1. How do I run SSH1?
• 4.1.1. ssh1
• 4.1.2. scp1
• 4.1.3. sshd1
• 4.1.4. ssh-agent1
• 4.1.5. ssh-add1
• 4.2. How do I run SSH2?
• 4.2.1. ssh2
• 4.2.2. scp2
• 4.2.3. sshd2
• 4.2.4. ssh-agent2
• 4.2.5. ssh-add2
• 4.2.6. sftp2
• 4.3. How do I administer Secure Shell after I have the daemon running?
• 4.4. How do I get hostbased authentication to work with SSH2?
• 4.5. How do I get user public key authentication to work with SSH2?
• 4.6. Can I run Secure Shell from inetd?

5. Secure Shell and other applications

• 5.1. Can I run backups over ssh?
• 5.2. Can I use ssh to communicate across a firewall?
• 5.3. Can I use rdist or rsync with ssh?
• 5.4. Can I use ssh to securely connect two subnets across the Internet?
• 5.5. Can I use ssh to securely forward UDP-based services, such as NFS or NIS?
• 5.6. Can I use ssh to protect services like ftp or POP?
• 5.7. Can I use ssh across a Socks firewall?
• 5.8. Is there ssh support for AFS/Kerberos?
• 5.9. Can I use TCP wrappers for added security on Secure Shell?
• 5.10. How do I tunnel X through Secure Shell?
• 5.10.1. Basic configuration
• 5.10.2. Can I configure XDM to go through Secure Shell?
• 5.11 Can I forward SGI GL connections over ssh?
• 5.12 Does Secure Shell support digital certificates?
• 5.13 Does Secure Shell work with PGP keys?

6. Patches for Secure Shell

• 6.1. Applying patches for Secure Shell
• 6.2. Official patch distribution from Secure Shell Communications Security
• 6.3. Other patch distributions

7. Troubleshooting Secure Shell

• 7.1. Common compiling problems
• 7.1.1. Compiling fails with some error messages from the assembler.
• 7.1.2. The configure process cannot find xauth!
• 7.1.3. The configure process cannot find nm
• 7.2. General troubleshooting tips
• 7.2.1. Ssh is doing wrong things for multi-homed hosts!
• 7.2.2. Ssh asks me for passwords despite .rhosts!
• 7.2.3. Why does ssh loop with "Secure connection refused'?
• 7.2.4. ssh hangs when forwarding multiple TCP connections.
• 7.2.5. I still see cleartext packages on the net when I run ssh!
• 7.2.6. I have problems with RSAREF, something to do with too many bits!
• 7.2.7. Connections are forwarded as root by ssh!
• 7.2.8. Why do I get a connection refused message?
• 7.3. X11 Forwarding problems
• 7.3.1 ssh otherhosh xclient & does not work
• 7.3.2 ssh-agent does not work with rxvt!
• 7.3.3 X authorization always fails.
• 7.3.4 What does Warning: remote host denied X11 forwarding mean?
• 7.4. Linux
• 7.4.1 X11 forwarding does not work for an SCO binary with the iBCS2 emulator under Linux.
• 7.4.2 On Linux, compilation aborts with some error message about libc.so.4
• 7.5. Solaris
• 7.5.1 Compiling with Solaris 2.5 fails!
• 7.5.2 Ssh fails with "Resource temporarily unavailable" for Solaris
• 7.5.3 Sshd hangs under Solaris 2.5!
• 7.5.4 ssh-keygen dumps core on Solaris or SunOS
• 7.5.5 I can't get TCP wrappers to work under Solaris
• 7.6. Other operating systems
• 7.6.1 ssh-keygen dumps core on Alpha OSF!
• 7.6.2 On HP-UX 9, X authorization sometimes fails.
• 7.6.3 Userid swapping is broken under AIX!

8. Getting support for Secure Shell

• 8.1. Who provides support for Secure Shell?
• 8.1.1. What groups can help me with the "free" versions?
• 8.1.2. How can I get commercial support for UNIX Secure Shell?
• 8.2. So, I'm confused. If Datafellows sells Secure Shell, what does SSH Communications Security do?
• 8.3. Secure Shell Mailing list
• 8.4. Tutorials
• 8.5. Web pages
• 8.6. Publications

9. Tips and Tricks of Secure Shell

• 9.1. Making Secure Shell more transparent to users
• 9.2. How do I find out which version of Secure Shell is running at the remote end?
• 9.3. How do I get SSH2 to compile on a MacOSX server?
• 9.4. Running SSH2 With SSH1 Compatibility
• 9.4.1 What Is SSH1 Compatibility?
• 9.4.2 Setting Up Compatibility
• 9.4.3 About TCP Wrappers and SSH1 Compatibility
• 9.4.4 Authentication in Compatibility Mode
• 9.4.5 How do I get hostbased authentication to work with SSH2 and SSH1?

10. The ever-popular miscellaneous section

• 10.1. Should I turn encryption off, for performance reasons?
• 10.2. Known security bugs with Secure Shell
• 10.3. I don't like the commercial aspects of Secure Shell.
• 10.4. Alternatives to Secure Shell