SSH

Secure Shell, of course. Besides the obvious OpenSSH link, this page will hold some of the less obvious (and more useful) stuff:

Resources:

Essentials:

• DenyHosts – block script kiddies and other pests from trying to do dictionary-based attacks on your server (on the internet, nobody knows that you only use key-based authentication – not even morons).

HOWTOs:

• An Illustrated Guide to SSH Agent Forwarding – everything but SOCKS, but pretty useful to hand out to newbies.
• Restricted Shell for scp/sftp
• scponly
• Using ssh-agent

Tools:

• Gnome SSH Tunnel Manager

Clients:

• PuTTY, Symbian port (updated on Mar 5 for S60)
• SSH Tools – includes a secure VNC client in Java, sources
• MindTerm – oldie but goodie Java applet
• JavaSSH – another (smaller) applet
• MIDP SSH

Libraries:

• org.keyphrene – Python wrapper
• sshfs, a FUSE / VFS -based filesystem layer atop SSH (FUSE has a BSD port, and there are now plenty of equivalents for Mac OS X)

Useful tricks:

Automatic session forwarding

If you routinely need to access a host behind another (or a VM inside a host), this is a relatively painless way to do so (won’t allow you to do SFTP, though, since that’s a different subsystem):

cat ~/.ssh/authorized_keys | grep command
command="ssh user@host" ...rest of key

Keepalives

Using the built-in keepalive feature to maintain tunnels with a TCP keepalive and a 30s internal (in-band) client active check (will try 10 times before disconnecting):

KeepAlive yes
ClientAliveInterval 30
ClientAliveCountMax 10

Speeding up connections to the same host (thanks to Melo):

$ head -3 ~/.ssh/config
Host *
  ControlMaster auto
  ControlPath /tmp/501/mux-%h-%p-%r

(on my machine the socket file is in 502 – more similar tips here)