Apple

Error Configuring db46 – MacPorts

/ Felipe Alfaro Solana / 1 Comment

Recently, I could not get db46 to install from Macports:

$ sudo /opt/local/bin/port install db46
...
Error: db46 requires the Java for Mac OS X development headers.
Error: Download the Java Developer Package from:
Error: Target org.macports.configure returned: missing Java headers

The solution consists of creating symbolic link to the installed files:

sudo ln -s /Developer/SDKs/MacOSX10.6.sdk/System/Library/
  Frameworks/JavaVM.framework/Versions/CurrentJDK/Headers 
  /System/Library/Frameworks/JavaVM.framework/
  Versions/CurrentJDK/Headers

How to disable Bonjour in Mac OS X Snow Leopard

/ Felipe Alfaro Solana / 2 Comments

From Mac OS X v10.6: Disabling mDNSResponder will disable DNS I found how to disable Bonjour broadcasting without disabling mDNSResponder — because disabling mDNSResponder effectively breaks DNS name resolution.

To disable Bonjour broadcasting, just add:

<string>-NoMulticastAdvertisements</string>

to the array in the ProgramArguments section in System/Library/LaunchDaemons/com.apple.mDNSResponder.plist:

...
        <key>ProgramArguments</key>
        <array>
            <string>/usr/sbin/mDNSResponder</string>
            <string>-launchd</string>
            <string>-NoMulticastAdvertisements</string>
        </array>
...

Google Talk Video might cause up to a 30-second delay while sleeping on Snow Leopard

/ Felipe Alfaro Solana / 3 Comments

Currently available version of Google Talk Video plug-in for Mac OS X (1.0.13.1284) might cause up to a 30-second delay while putting the computer to sleep under Snow Leopard.

This has been reported and discussed in the following Apple support thread. In the end, the solution typically requires to uninstall Google Talk Video. The solution was found and reported by Snoop Dogg in that same thread.

Basically, the misbehaving process can be found by running sudo pmset -g log then looking for the process with the highest response time. In my case:

$ sudo pmset -g log
...
 * Domain: applicationresponse.timedout
 - Message: Kernel GoogleTalkPlugin com.apple.powermanagement.applicationrespons
e.timedout 30000 ms
 - Time: 9/2/09 12:42:47 AM GMT+02:00
 - Signature: GoogleTalkPlugin
 - UUID: AD1E9199-B66D-41CB-BF4F-590EF232DE79
 - Result: Noop - Response time (ms): 30000
...

Official Chromium builds for Mac OS X

/ Felipe Alfaro Solana / 9 Comments

Recently, the Chromium team has started to provide official builds of Chromium for Mac OS X. Looks to me these builds are just the output of the continuous build process — also known as waterfall.

In any case, these are good news and to me a proof that Chromium for Mac OS X keeps evolving at a fast pace and that it is making very good progress. As a consequence, a few days ago, I switched to Chromium as my main browser (also in Linux) and I must say it feels great so far.

PS: This post was written entirely under Chromium for Mac OS X. No crashes or any strange behavior were experienced.

Chromium for Mac OS X

/ Felipe Alfaro Solana / 2 Comments

Chromium is the open source browser developed by Google. The differences between Chromium and Chrome are very minimal. Chrome has custom icons and other parafernalia that, due to licensing issues, can’t be made available in Chromium. Chrome is also available as a binary for Microsoft Windows operating systems, and can be downloaded from the Google Chrome Web site.
Other than that, Chromium is a fully functional browser product that is currently available only as source code. Chromium is available for Windows, Mac OS X and Linux. The Mac OS X and Linux ports are still under heavy development but are becoming more and more usable over time.

For more than a month I’ve been tracking development of Chromium for Mac OS X. I’ve been building and testing Chromium for Mac OS X myself [1] and my general impression is that development pace is pretty fast. For example, yesterday, a mock Preferences dialog box was added. A few days ago, working support for draggable and dettachable tabs was also added (previously it was possible to detach a tab from a window but it was not possible to re-attach it to an existing window).

Overall, the Mac OS X port of Chromium is getting more and more usable and stable. I’m now able to use it for most browsing tasks. The look and feel matches perfectly Aqua but also resembles a lot its Windows counterpart. While it is true there are a few annoyances, like losing the focus on edit controls when switching tabs, or tabs crashing at times when executing a paste operation, they are getting fixed in each iteration. The browser feels extremely fast when compared to Firefox 3.0 and faster than Firefox 3.1, Safari or Safari 4 beta. Heavy and complex Web pages like Google Reader or Google Mail load almost instantly while still looking correct. Some Web pages get rendered slightly different from other browsers. As an example, Google Mail looks slightly different with bigger spacing between lines in the mail thread (main) view and also slightly smaller fonts, but these are very subtle differences that do not affect usability or readability.

I must confess I’m pretty impressed about Chromium. When Google disclosed Chrome and the initial availability for the Windows platform only I was very disappointed. I also thought that it’d take much longer to see a nearly-functional port for Mac OS X or Linux. But I was wrong. It is good to be wrong. Let’s hope the development pace keeps on the same levels 🙂

PS: By the way, this post was written entirely from Chromium in Mac OS X. The tab crashed a couple of times but WordPress has a nice auto-save feature that I really appreciate 😉

[1] http://code.google.com/p/chromium/wiki/MacBuildInstructions

Safari/MacBook security

/ Felipe Alfaro Solana / 3 Comments

It is probably not very well-known for many, and probably ignored by most, but it seems that Mac OS X and specifically Safari leaves much to be desired when talking about security.

During the Pwn2Own contest, Safari was the first browser to fall, in the order of seconds, when put under attack by Charlie Miller. This has been reported in several places, like Pwn2Own 2009: Safari/MacBook falls in seconds, or Miller: Safari on Mac First to Fall During PWN2OWN Contest, or Miller Cracks Safari Within Seconds, Wins PWN2OWN Contest. For the second year in a row, Safari/MacBook has been the browser to fall under attack the first.

So, if you are a user of Mac OS X, be very careful when using Safari. These attacks so far require you to click on links specifically crafted to cause harm to your computer, which might allow the attacker to gain total control of your machine. Hence, the importance of never running with an account that has administrative privileges.

FreeNX, usermode authentication and Mac OS X

/ Felipe Alfaro Solana / 10 Comments

I’ve always been looking for a way in NX/FreeNX to be able to authenticate using mechanisms other than username and password, like SSH private/public keys or Kerberos. Turns out that it is possible 🙂

Someone pointed me to the FreeNX 0.7.3 announcement that contains the following excerpt:


Usermode and SUID Wrapper
==================

We are now very close to login directly with users and I also heard of a C program, which can be seamlessly put between nxclient and nxssh. So with client support we now have three alternatives:

1. Login as user via ssh and connect to server with ssh command on server again.
2. Login as user and use usermode to save all sessions locally for each user.
3. Use a SUID nx (not root!) wrapper to startup a new "trusted" session.

One is error prone, two is good, but looses the central structure, three is best of both worlds and with being suid nx also has the most advantages, however not the dreaded public key problems.

_Yes_, this means if you use the suid wrapper, you still need the nx user, but you can remove the public keys and it'll still work.

The SUID wrapper is a part from the work of the redesign and thanks goes to Alistair Riddoch from Google here.

By default, NoMachine’s NX nxserver requires nxclient to login via SSH into the remote machine as user nx. As nxserver is defined as the login shell, it is run by the sshd daemon. From there on, there is a dialogue between nxclient and nxserver where nxclient supplies the user credentials (username and password that were specified in the nxclient configuration). There is, in fact, a second authentication that is performed via another SSH session to 127.0.0.1 using nxclient’s supplied credentials. If this second authentication succeeds, the NX session is activated and accessible from the NX client.

This works well for remote servers that are shared by multiple users, as the nx user and its centralized approach makes it very easy to see how many sessions are currently running (or suspended), terminate them, etc. However, for machines that are not shared by multiple users, or in those cases where authentication mechanisms other than username and password are required, this model does not work very well.

This is where FreeNX’s usermode enters the scene. Basically, what it means, is that authentication to nxserver does no longer happen as the nx user but as the end-user himself. Now, the number of SSH sessions is reduced to one that authenticates the user directly by means of SSH’s built-in authentication capabilities, and where nxserver is run under the end-user credentials instead of the nx user. This, obviously, kills the centralized approach originally envisioned by NoMachine, since now all the control and session files can’t be stored easily and securely in a central location but are now stored in the user’s home directory. But I think the upsides of the usermode support outdo the lack of centralized management. At least in my case, I don’t need centralized management since it’s me who manages all my boxes and logs into them.

How to install and configure FreeNX to support usermode

Next I describe what I had to do, both on the remote machine and also on the client, to get a working FreeNX environment that supports usermode. Other modes are also supported, like legacy nx-based, SUID and others.

Download NX4U tarball from BerliOS and extract it

$ wget http://download.berlios.de/freenx/NX4U.tar.gz
$ sudo tar -C /opt -zxf NX4U.tar.gz

NOTE: The NX4U tarball that I used can also be downloaded from this Web site here.

NOTE: The NX4U set and the nxssh wrapper are smart enough so that you can also extract the NX4U tarball in other locations. Looking at the source code for the nxssh wrapper — nxssh-4US.c — nxssh wrapper uses the following PATH to locate the nxserver binary:

#define NXSERVER_PATH 
"~/bin:
~/NX4U/:
/usr/NX/bin:
/opt/NX/bin:
/opt/NX4U/bin:
/usr/NX4U/bin:
/usr/local/NX4U/bin:
/usr/lib/nx/bin"

Compile the nxssh wrapper

First, download the source code from the SVN repository:

$ svn checkout https://developername@svn.berlios.de/svnroot/repos/freenx/trunk

NOTE: I saved a copy of the SVN repository that I used. The tarball is available in this Web site here.
Build the nxssh wrapper for Mac OS X. nxssh is a simple C program that currently compiles for me with no problems on Linux and Mac OS X:

$ cd trunk/freenx-utils/nxpublickey/
$ make nxssh

NOTE: The Makefile also has a target named nxssh.exe to compile the wrapper for Windows.

Now, let’s rename NoMachine’s nxssh binary to mxssh (the nxssh wrapper expects NoMachine’s nxssh binary to be renamed to mxssh), then install the nxssh wrapper:

$ sudo bash
# mv /usr/NX/bin/nxssh /usr/NX/bin/mxssh
# install -m755 nxssh /usr/NX/bin/nxssh
# ^D

Configure .ssh/config

What looks like a bug in NoMachine’s nxssh, will cause authentication requests using public key to fail with a "percent_expand: NULL replacement" error unless .ssh/config is modified to explicitly state the location of the public key. For example:

Host my.host.org
        IdentityFile ~/.ssh/id_dsa

Configure nxclient

In order to use usermode authentication, make sure to prepend the hostname with the @ (at) sign:

Hostname: @my.host.org

Also, make sure the username has the @ (at) sign prepended plus @U (at U) appended. These non-standard forms are parsed by the nxssh wrapper and enable usermode authentication (or other authentications like SUID):

Username: @myself@U

For more information about possible syntaxes, take a look at freenx-utils/nxpublickey/nxssh-wrapper (the shell script implementation of the nxssh wrapper).

Windows 7 Beta 1 + Apple = no sound

/ Felipe Alfaro Solana / 4 Comments

While testing Windows 7 on an Apple MacBook Pro system, I noticed that sound didn’t work at all. Of course, this was after I installed BootCamp drivers and everything was working (more or less as expected) except the sound.

What’s the solution? I found it here. In essence, the solution consists of running the RealTekSetup.exe binary from the Leopard DVD using “Troubleshoot Compatibility“, telling it that “The program worked in earlier versions of Windows” and that it worked fine in “Windows Vista“. After it has been installed no reboot it’s even needed!

iPhone OS 2.0 and jailbreaks

/ Felipe Alfaro Solana / 3 Comments

Recently I bought an iPod touch. It originally came with OS 1.1.4 and as soon as Apple made the 2.0 software available (and downloadable), I upgraded.

While the new iTunes App Store is a welcome addition, I found most of the applications not very useful to me. While some like Remote, Facebook, Last.fm or eReader are awesome, I have yet to see applications on the store that fully unleash the power of the iPhone/iPod platform. For example, I’m waiting for a PDF reader that can fetch files from the local disk.

Here comes the power of jailbreak. There are so many things one can do with a jailbroken box. For example, with OpenSSH I can upload e-books to my iPod and bypass the limitations of eBook.app (it only likes e-books purchased from two web sites, but I have a few books that I legally downloaded from manybooks.net licensed under Creative Commons). I can also install Light HTTPd to serve PDFs locally that I can browse using Safari. It is very convoluted but it works.

Apple: if you read this, please lift all the absurd restrictions from the iPhone/iPod software and let people unleash the true power of this amazing portable platform.

Kerberizing Leopard's Remote Login (built-in SSH) service

/ Felipe Alfaro Solana / 4 Comments

0. Introduction

Enabling Kerberos/GSSAPI support in Leopard’s Remote Login (SSH) service is straightforward. As Leopard’s Remote Login is built using OpenSSH, most of what is described here applies perfectly to other flavors of UNIX.

Kerberos/GSSAPI authentication allows for Single Sign-On capabilities in OpenSSH in such a way that it makes very convenient to work with or manage multiple machines while only having to authenticate to the network every certain amount (Kerberos uses a form of cached credentials that expire within hours, typically). In this document I describe how to enable support for Kerberos/GSSAPI authentication to Leopard’s implementation of OpenSSH. Leopard includes many of the tools from the MIT’s implementation of Kerberos, so this makes the whole process even easier.

The process consists on:

  1. Creating the Kerberos principal
  2. Creating /etc/krb5.conf
  3. Adding the Kerberos principal to the keytab file
  4. Reconfiguring OpenSSH to support Kerberos authentication
  5. Restarting OpenSSH
  6. Enabling Kerberos authentication on OpenSSH clients
  7. Testing

1. Creating the Kerberos principal

When a Kerberized SSH client tries to authenticate to a Kerberized OpenSSH service, the client will request a Kerberos service ticket for that specific OpenSSH service. The Kerberos service ticket contains, among other things, a shared secret (for example, a 3DES private key) that has to be distributed to both the client and the server, called Kclient,server. The KDC will generate such shared secret and will encrypt it twice. Once, with a shared secret between the KDC and the client principal, called KKDC,client, and another one with a shared secret between the KDC and the server principal, KKDC,server.

In this step, we will create the Kerberos principal that represents the OpenSSH server and consequently its shared secret, KKDC,server. Later on, we will upload this shared secret to the OpenSSH server and install it into the Keytab file, so that the OpenSSH server can access it and use it to decrypt the user’s service ticket in order to retrieve the shared secret, Kclient,server.

$ kadmin
Authenticating as principal alice/admin@LAN with password.
Password for alice/admin@LAN:
kadmin:  addprinc -randkey host/ssh.lan
WARNING: no policy specified for host/ssh.lan@LAN; defaulting to no policy
Principal "host/ssh.lan@LAN" created.

NOTE: If you are logged in as root into the KDC, you can use kadmin.local instead of kadmin if you prefer, as the former doesn’t require any authentication (being able to run it as root is enough to prove yourself authorized).

The Kerberos principal associated with the OpenSSH has been created, the shared secrets generated, stored and protected by the stash key. We can check the status of the principal using the following command:

kadmin:  getprinc host/ssh.lan
Principal: host/ssh.lan@LAN
Expiration date: [never]
Last password change: Thu Dec 06 19:42:50 CET 2007
Password expiration date: [none]
Maximum ticket life: 0 days 10:00:00
Maximum renewable life: 7 days 00:00:00
Last modified: Thu Dec 06 19:42:50 CET 2007 (root/admin@LAN)
Last successful authentication: [never]
Last failed authentication: [never]
Failed password attempts: 0
Number of keys: 2
Key: vno 5, Triple DES cbc mode with HMAC/sha1, no salt
Key: vno 5, DES cbc mode with CRC-32, no salt
Attributes:
Policy: [none]
kadmin:  exit

Now that the principal has been created, we can move onto the next step.

2. Creating /etc/krb5.conf

One of the requirements for Kerberizing OpenSSH server is configuring the Kerberos libraries via /etc/krb5.conf. These libraries are used by the OpenSSH server, kpasswd, the OpenSSH client and tools like kadmin or kinit.

This configuration file will also allow us to connect to the Kerberos administration server remotely by using kadmin, in order to download the OpenSSH shared secret. In my case, /etc/krb5.conf looks like this:

[libdefaults]
        default_realm = LAN
        dns_fallback = "no"
        default_tgs_enctypes = des-cbc-crc
        default_tkt_enctypes = des-cbc-crc

[realms]
        LAN = {
                kdc = kdc.lan:88
                admin_server = kdc.lan:749
        }

[domain_realm]
        .lan = LAN

[login]
        krb4_convert = true
        krb4_get_tickets = false

3. Adding the Kerberos principal to the keytab file

root@ssh.lan:# kadmin
Authenticating as principal root/admin@LAN with password.
Password for root/admin@LAN:
kadmin:  ktadd -k /etc/krb5.keytab host/ssh.lan@LAN
Entry for principal host/ssh.lan@LAN with kvno 7,
 encryption type Triple DES cbc mode with HMAC/sha1 added to
 keytab WRFILE:/etc/krb5.keytab.
Entry for principal host/ssh.lan@LAN with kvno 7,
 encryption type DES cbc mode with CRC-32 added to
 keytab WRFILE:/etc/krb5.keytab.

This will add the OpenSSH shared secret to the Kerberos /etc/krb5.keytab file. We need to add the shared secrets to this file properly, as Leopard has a built-in KDC service and machine-specific shared secrets in this file that are used, among others, by the Screen Sharing service, the AFP service and the SAMBA service.

To check that OpenSSH shared secret was added to the keytab file, we use ktutil to read and display the contents of the Keytab file:

root@ssh.lan:# ktutil
ktutil:  rkt /etc/krb5.keytab
ktutil:  list
slot KVNO Principal
---- ---- ---------------------------------------------------------------------
   1    3 afpserver/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   2    3 afpserver/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   3    3 afpserver/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   4    3 cifs/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   5    3 cifs/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   6    3 cifs/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   7    3 vnc/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   8    3 vnc/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
   9    3 vnc/LKDC:SHA1.E803840ADEAA3E91BF895E969F56FEDFF321BDD5@LKDC...
  10    7                      host/ssh.lan@LAN
  11    7                      host/ssh.lan@LAN

Once installed in the keytab file, OpenSSH will be able to access the shared secret, KKDC,server used to decrypt Kerberos service tickets shown by clients.

  • 4. Reconfiguring OpenSSH to support Kerberos authentication

    • It is also necessary to change OpenSSH’s server configuration file, /etc/sshd_config to explicitly enable Kerberos/GSSAPI authentication. To achieve this, modify /etc/sshd_config file and add the following lines (by default they are either uncommented or disabled):

    # GSSAPI options
GSSAPIAuthentication yes
GSSAPICleanupCredentials yes

    5. Restarting OpenSSH

    To last step on the server side requires that we restart the OpenSSH service so the previous changes are taken into effect:

    root@ssh.lan:# launchctl
aunchd% stop com.openssh.sshd
launchd% start com.openssh.sshd

    6. Enabling Kerberos authentication on OpenSSH clients

    Some OpenSSH clients have Kerberos authentication disabled by default. The easiest way to enable Kerberos/GSSAPI authentication in clients is by adding the following directives to $HOME/.ssh/config:

    Host *
        Protocol 2
        GSSAPIAuthentication yes
        GSSAPIKeyExchange yes
        GSSAPIDelegateCredentials no
        GSSAPITrustDns no

    This will enable Kerberos/GSSAPI authentication on the client side. The fact that Kerberos/GSSAPI authentication succeeds depends on several factors, like the user having a valid Kerberos TGT, the remote server having Kerberos/GSSAPI authentication enabled, and that the clocks on both the client and server machines are synced (most implementations refuse Kerberos/GSSAPI authentication if the clocks differ more than 5 minutes).

    7. Testing

    First, we need to get a TGT from the Kerberos KDC:

    $ kinit
Please enter the password for falfaro@LAN:

    To check that it worked, we list the tickets available to us, and make sure we see a ticket valid for service krbtgt/*:

    $ klist
Kerberos 5 ticket cache: 'API:Initial default ccache'
Default principal: falfaro@LAN

Valid Starting     Expires            Service Principal
12/06/07 18:06:26  12/07/07 04:06:26  krbtgt/LAN@LAN
	renew until 12/13/07 18:06:26

    Now, let’s try to log in into the OpenSSH server. Kerberos/GSSAPI authentication should be negotiated, as shown by the debugging information:

    core2:~ falfaro$ ssh -v solana
OpenSSH_4.5p1, OpenSSL 0.9.7l 28 Sep 2006
debug1: Reading configuration data /Users/falfaro/.ssh/config
debug1: Applying options for *
debug1: Reading configuration data /etc/ssh_config
debug1: Connecting to solana [10.42.242.12] port 22.
debug1: Connection established.
debug1: identity file /Users/falfaro/.ssh/id_rsa type -1
debug1: identity file /Users/falfaro/.ssh/id_dsa type 2
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.5
debug1: match: OpenSSH_4.5 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_4.5
debug1: Offering GSSAPI proposal:
 gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,
 gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==,
 gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,
 gss-gex-sha1-A/vxljAEU54gt9a48EiANQ==,
 gss-group1-sha1-A/vxljAEU54gt9a48EiANQ==,
 gss-group14-sha1-A/vxljAEU54gt9a48EiANQ==,
 gss-gex-sha1-bontcUwnM6aGfWCP21alxQ==,
 gss-group1-sha1-bontcUwnM6aGfWCP21alxQ==,
 gss-group14-sha1-bontcUwnM6aGfWCP21alxQ==
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-cbc hmac-md5 none
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'solana' is known and matches the RSA host key.
debug1: Found key in /Users/falfaro/.ssh/known_hosts:8
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue:
 publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Authentication succeeded (gssapi-with-mic).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
Last login: Thu Dec  6 20:29:59 2007 from foo.lan
$ hostname
ssh.lan
$ exit
logout
Connection to solana closed.

    If we run klist again, we will see that, in addition to the TGT we saw before, we will see the Kerberos service ticket for the OpenSSH server:

    Kerberos 5 ticket cache: 'API:Initial default ccache'
Default principal: alice@LAN

Valid Starting     Expires            Service Principal
12/06/07 18:06:26  12/07/07 04:06:26  krbtgt/LAN@LAN
	renew until 12/13/07 18:06:26
12/06/07 18:07:27  12/07/07 04:06:26  host/ssh.lan@LAN
	renew until 12/13/07 18:06:26

    8. Troubleshooting

    The GSSAPI authentication mechanism is very picky about many things, and error codes and messages are usually very cryptic but not very helpful about what the cause of the error is.

    I found that acommon source of authentication problems are entries in /etc/hosts confusing GSSAPi about the host name. For example, entries like this in /etc/hosts:

    192.168.0.1  ssh ssh.lan

    can cause SSH to think the host name is ssh instead of the expected FQDN — ssh.lan.The previous entry causes reverse name resolutions for IP 192.168.0.1 to return ssh as the host name, but not ssh.lan. Since the Kerberos keytab is host/ssh.lan but IP 192.168.0.1 is resolved to ssh this may cause authentication attempts to fail because no Kerberos keytab for host/ssh exists in /etc/krb5.keytab. The most common symptom is trying to SSH to localhost, getting a failed authentication and but ticket for the target host. Example:

    $ kinit
Password for alice@LAN:

$ klist
Ticket cache: FILE:/tmp/krb5cc_501
Default principal: alice@LAN

Valid starting     Expires            Service principal
05/31/09 01:08:21  06/01/09 01:08:20  krbtgt/LAN@LAN

    Then,

    $ ssh ssh.lan
alice@ssh.lan's password:

    But no Kerberos ticket for ssh.lan was even requested:

    $ klist
Ticket cache: FILE:/tmp/krb5cc_501
Default principal: alice@LAN

Valid starting     Expires            Service principal
05/31/09 01:08:21  06/01/09 01:08:20  krbtgt/LAN@LAN

    One possible solution consists of removing the matching entry from /etc/hosts, provided that the existing DNS name server can properly resolve the IP address of the server to the correct FQDN. If this is not possible, another solution is making sure the FQDN name is listed before the non-FQDN name in the corresponding line in /etc/hosts.

    8. References

    Some additional and very useful references:

    • Kerberos 5 setup for NFSv4.

      Describes common pitfalls, like using a non-FQDN host name in /etc/hosts or not using clock synchronization.