Ssh (Secure Shell) FAQ - Frequently asked questions

by Thomas König Thomas.Koenig@ciw.uni-karlsruhe.de

1. Meta-questions

• 1.1 Where do I get this document?
• 1.2 Where do I send questions, corrections etc. about this document?

2. Ssh basics

• 2.1 What is ssh?
• 2.2 Why should I use it?
• 2.3 What kinds of attacks does ssh protect against?
• 2.4 What kind of attacks does ssh not protect against?
• 2.5 How does it work?

3. Obtaining and installing ssh

• 3.1 What is the latest version of ssh?
• 3.2 May I legally run ssh?
• 3.3 What about commercial use of ssh?
• 3.4 Where can I obtain ssh?
• 3.5 How do I install it?
• 3.6 Does it make sense to install ssh as non-root under UNIX?
• 3.7 Where do I get help?
• 3.8 Are there any versions for other operating systems than UNIX?
• 3.9 What about administration of ssh?

4. Ssh Applications

• 4.1 Can I run backups over ssh?
• 4.2 Should I turn encryption off, for performance reasons?
• 4.3 Can I use ssh to communicate across a firewall?
• 4.4 Can I use rdist with ssh?
• 4.5 Can I use ssh to securely connect two subnets across the Internet?
• 4.6 Can I use ssh to securely forward UDP-based services, such as NFS or NIS?
• 4.7 Can I forward SGI GL connections over ssh?
• 4.8 Can I use ssh to protect services like ftp or POP?
• 4.9 Can I use ssh across a Socks firewall?
• 4.10 Is there ssh support for AFS/Kerberos?

5. Problems

• 5.1 ssh otherhost xclient & does not work!
• 5.2 Ssh fails with "Resource temporarily unavailable" for Solaris
• 5.3 Sshd hangs under Solaris 2.5!
• 5.4 X11 forwarding does not work for an SCO binary with the iBCS2 emulator under Linux.
• 5.5 Ssh is doing wrong things for multi-homed hosts!
• 5.6 Userid swapping is broken under AIX!
• 5.7 ssh-keygen dumps core on Alpha OSF!
• 5.8 ssh-keygen dumps core on Solaris or SunOS
• 5.9 On Linux, compilation aborts with some error message about libc.so.4
• 5.10 X authorization sometimes fails.
• 5.11 Ssh asks me for passwords despite .rhosts!
• 5.12 Why does ssh loop with "Secure connection refused'?
• 5.13 ssh-agent does not work with rxvt!
• 5.14 X authorization always fails.
• 5.15 ssh hangs when forwarding multiple TCP connections.
• 5.16 What does Warning: remote host denied X11 forwarding mean?
• 5.17 I still see cleartext packages on the net when I run ssh!
• 5.18 I have problems with RSAREF, something to do with too many bits!
• 5.19 Compiling fails with some error messages from the assembler.
• 5.20 Compiling with Solaris 2.5 fails!
• 5.21 Ssh suddenly drops connections!
• 5.22 Connections are forwarded as root by ssh!

6. Miscellaneous

• 6.1 What known security bugs exist in which versions of ssh?
• 6.2 How widespread is use of ssh?
• 6.3 I don't like the commercial aspects of ssh.
• 6.4 Credits