This page explains how to log in to our servers without having to type in a password. We use kerberos for this rather than RSA/DSA public keys. The main reason for doing so is MemberManual/DistributedSecurity; please see that page if you feel that the procedures described below are unduly cumbersome.

An extra benefit is that passwordless logins using kerberos are noticably faster than passwordless logins using public key authentication. This is because kerberos uses symmetric cryptography (which is faster) and requires fewer round-trips during the authentication process.

These instructions have been tested with the major unix variants (Debian, RedHat, Fedora, Ubuntu, MacOSX, etc). There are reports that the ssh client in certain minor distributions (ArchLinux, for one) does not support this.

Prerequisites

You must have openssh client 4.3 or later. Other versions may work, but we make no guarantees. You will also want the krb5-user package if you are using Debian or Ubuntu. For Mac OS X 10.5 and later no additional software is required for the instructions below to work; earlier versions of Mac OS X might work if you install the MacPorts version of kerberos+ssh (but no guarantees!). For further details, check out MemberManual/TransferringFiles/OpenAFS, and follow just the Kerberos instructions.

Instructions

Once a Kerberos client hsa been installed, you must obtain Kerberos tickets. If your username is "fred", you would do this by typing:

kinit -f fred@HCOOP.NET

Then type your password when prompted. Note that you must capitalize HCOOP.NET and you must not capitalize your user name. This is important.

Next, make sure you have your tickets. To do this, type

klist

You should see your tickets and their expiration dates.

Last, type

ssh -oGSSAPIAuthentication=yes -oGSSAPIDelegateCredentials=yes fred@mire.hcoop.net

GSSAPI is the "generic name" for Kerberos-like authentication protocols. The first option tells your ssh client to use your Kerberos tickets to prove your identity to the hcoop servers. The second option tells your ssh client that it is safe to entrust the hcoop servers with a copy of your tickets once you have authenticated.

Automating things

If you do this a lot, you can include the GSSAPIAuthentication and GSSAPIDelegateCredentials options in your ~/.ssh/config file. But you should NOT turn on GSSAPIDelegateCredentials for arbitrary hosts. Make sure you only enable it for HCOOP hosts! You should never, ever use GSSAPIDelegateCredentials on a machine which is operated by somebody other than yourself and HCoop.

Here is an example entry for ~/.ssh/config:

Host hcoop
  HostName mire.hcoop.net
  GSSAPIAuthentication yes
  GSSAPIDelegateCredentials yes
  User fred

This will allow you to type the following, instead of the longer command above.

ssh hcoop

Troubleshooting

Adding "-vvv" to the ssh command line makes it spit out lots of useful debugging information.

If you see something like the following in the output:

debug1: Unspecified GSS failure.  Minor code may provide more information
Server not found in Kerberos database

check to see if you have an /etc/hosts file with the host that you're trying to reach in it. If there is an entry for this host, make sure that the fully-qualified domain name is listed first, before any aliases that you may be using.

If it still doesn't work

See the Troubleshooting Kerberos page for more diagnostics. You may also send the output of your ssh command with the "'-vvv'" to hcoop-help and we'll try to figure things out from there.