Category: General

SAS & IWA: Host Name Aliases and SPNs

I’m quite keen on using host name aliases, rather than their physical host names, when referring to machines in SAS® platform installations. It does however mean a little extra configuration is required when using Integrated Windows Authentication. That is what this post is about: configuring Active Directory with additional Service Principal Names (SPNs) based on the aliases.

Host name aliases have several benefits over using physical host names. They can be easier to remember (e.g. sasmeta v.s. p106547). They can be easily redirected from primary environments to disaster recovery environments (e.g. sasmeta from p106547 to d106547) with no client reconfiguration requirements. They also allow host machines to be readily renamed if/when required with little or no changes to SAS configuration files, programs and/or metadata.

Whilst they have obvious benefits, Continue reading “SAS & IWA: Host Name Aliases and SPNs”

SAS Management Console over SSH

I was asked recently how to get SAS® Management Console to remotely access a SAS metadata server using SSH tunnels. In the absence of a VPN connection to your network, SSH can be an alternative for SAS Management Console access to a remote SAS metadata server.

I am a huge fan of SSH (Secure Shell). I have been using it several times a day for many years now. It’s great. If you haven’t heard of SSH before, take a look at the Wikipedia page for Secure Shell. Here’s a quote from the page that provides a nice intro/summary:

Secure Shell (SSH) is a network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that it connects via a secure channel over an insecure network.

Here are a couple of methods for using SAS Management Console over SSH:

1. Remote execution of SAS Management Console with X11 forwarding to the client

This method can be used when you are accessing a SAS platform installation on Linux or UNIX and have SSH client software and X server software on your remote workstation. Mac or Linux workstations are great for this since they usually have all the required software pre-installed. Windows can also be used if you obtain SSH client and X server software. I personally use Putty as an SSH client when I am working on Windows and would defintely recommend it. I have no specific recommendations for an X server on Windows since it’s been a long time since I’ve done X on Windows.

Assuming, as a SAS platform administrator, you have remote SSH access to the SAS metadata server machine then you can use SSH from your workstation to execute the SAS Management Console remotely and forward the X display to your client workstation.

Here’s an example command to do this:

ssh -X sasmeta.example.com /opt/sas93/SASManagementConsole/9.3/sasmc

Which means SSH connect, with X11 forwarding, to the machine sasmeta.example.com and then execute the SAS Management Console (/opt/sas93/SASManagementConsole/9.3/sasmc) on that remote machine sending the X windows back to the client workstation.

2. Local execution of SAS Management Console with SSH tunneling

SSH also allows you to configure a tunnel – a local port on your workstation that that forwards traffic to a designated server and port in the remote network. This tunnel can be used to make a remote service appear to be a local service. We can use it to make a remote SAS metadata server port appear to be on the local workstation so that a local installation of the SAS Management Console can connect to it as if it had a local metadata server.

Here’s an example command to do this:

ssh -L 8561:sasmeta.example.com:8561 sasmid.example.com

Which means SSH connect to the machine sasmid.example.com and establish a local machine port (8561) that forwards traffic to the remote host/port sasmeta.example.com:8561 accessible via sasmid.example.com. If you are not using public key authentication (recommended) then you will be prompted for a user id and password for the server. Once the connection is active, a local SAS Management Console can be started and will be able to access the remote SAS metadata server using a connection profile that connects to a metadata server on host/port localhost:8561. All traffic to this local port will be sent to the remote metadata server over the SSH tunnel.

Bear in mind that this only makes the metadata server port available on the local machine. So the local SAS Management Console instance can only access the metadata server. It doesn’t necessarily make the client fully functional as it may require additional connections to additional servers e.g. access to a SAS Object Spawner for a SAS Workspace Server session or a connection to the SAS Content Server. You could look into forwarding other ports and will also need to modify your local hosts file to redirect the remote host names found in metadata to the localhost interface. For anything more complex than pure metadata server access it would probably be easier and more robust to use a VPN connection (or remote access via something like X or RDP to remote network client workstations).

SAS & JBoss: Too Many Open Files

I’ve been seeing some ‘Too many open files‘ exceptions in the SAS® mid-tier JBoss logs on my Ubuntu Linux server. I was surprised about this because I remember during installation I had followed the guidance in the SAS documentation and increased the nofile limit. It turns out that verifying the ulimit from a normal console/ssh login was not sufficient, I should have also verified it from an su based login too.

These were the sorts of messages I was seeing in the JBoss logs:

2012-03-11 09:22:38,463 ERROR [org.apache.tomcat.util.net.JIoEndpoint] Socket accept failed
java.net.SocketException: Too many open files
...
2012-03-11 08:57:19,454 ERROR [org.apache.catalina.core.StandardContext] Error reading tld listeners java.io.FileNotFoundException: /opt/jboss-4.2.3.GA/server/SASServer3/work/jboss.web/localhost/SASBIDashboard/tldCache.ser (Too many open files)
...

There are some Pre-Installation Steps for JBoss for both SAS 9.3 and SAS 9.2 that should be followed during installation to avoid these errors. These were the instructions I had followed, but as you’ll see in a moment, it wasn’t quite enough for this (unsupported) Ubuntu installation.

The instructions specify to edit the /etc/security/limits.conf file directly. Rather than editing this main config file, where the settings might get forgotten or lost during an upgrade, I placed the settings I required for my SAS installation in their own dedicated config file: /etc/security/limits.d/sas.conf

# Increase the open file descriptors limit from the default of 1024 to 30720 for JBoss running web apps for SAS 9.2/9.3
* - nofile 30720

I knew that this had taken effect because I logged in, via ssh, to verify it as the sas user (I run JBoss as the sas user). Checking the ulimit I saw the following:

sas@server:~$ ulimit -Hn;ulimit -Sn
30720
30720

With nofile at 30270, how was it I was still getting ‘Too many open files‘ errors? After a quick session on Google I found a blog post suggesting the increased limits will only apply if the pam_limits PAM module is enabled.

Checking the /etc/pam.d/login file I could see the pam_limits line was already present and uncommented:
...
session required pam_limits.so
...

This made sense since the console/ssh login showed the expected numbers.

Google also led me to a stackoverflow question (how do i set hard and soft file limits for a non-root user at boot?). The answer provided there indicated that, for su commands, you also need to verify the pam_limits module is enabled in an additional su specific PAM config file, which on my machine was /etc/pam.d/su. My JBoss init script runs as root during system startup but uses su to run JBoss as the sas user. Looking in /etc/pam.d/su I could see that the pam_limits line was commented so perhaps that was the issue.

Before making the necessary changes, I verified the nofile ulimit for the sas user by running su as root:

root@server:~# su sas --login --command 'ulimit -Hn;ulimit -Sn'
1024
1024

Aha! It had the 1024 default rather then the increased value. It looked like this was indeed the problem. I uncommented the pam_limits line in /etc/pam.d/su and repeated the test:

root@server:~# su sas --login --command 'ulimit -Hn;ulimit -Sn'
30720
30720

It now shows the increased value as expected, so it looks like the problem’s fixed. I restarted JBoss and haven’t seen any ‘Too many open files‘ errors since.

SAS & IWA: Verifying Trusted for Delegation Status

Update 26Sep2018: This post is now several years old and naturally technology and security have progressed in that time. For more up to date information regarding delegation and, in particular, the requirement for constrained delegation when working with Windows Defender Credential Guard in Windows 10 and Windows Server 2016, please see Stuart Rogers’ very useful SAS Global Forum 2018 Paper: SAS 9.4 on Microsoft Windows: Unleashing Kerberos on Apache Hadoop.

I mentioned in a previous post that host machines need to be Trusted for Delegation when a SAS® software component, such as a SAS Workspace Server, needs to make outgoing connections to secondary servers when the initial incoming connection was made using Integrated Windows Authentication (IWA).

When a server needs to be Trusted for Delegation, it takes a domain administrator to change the machine account in Active Directory. I rarely have domain admin privileges when working at customer sites so I usually can’t do this for myself. :( This post describes the method I use, as a lowly domain user, to verify that a Windows server has been configured in Active Directory as Trusted for Delegation.

The screenshot below shows an example of what the domain admin might see in the Properties dialog Delegation tab for the machine account in Active Directory (via the Active Directory Users and Computers tool (under Start > All Programs > Administrative Tools).

This machine account (P1001) is not yet trusted for delegation. The domain admin would click the radio button for “Trust this computer for delegation to any service (Kerberos only)“.

Once the domain admin has advised that the change has been applied, we can test it out from the SAS platform. What happens if the test still fails? I like to double check that the server is definitely trusted for delegation before I move on to checking other things. Everyone makes mistakes from time to time, even domain admins; maybe the wrong machine account was modified (it does happen). So to avoid wasting time later on, I like to verify this pre-requisite before moving on. I could ask the domain admin to email me a screenshot of the dialog to confirm, but they’re likely very busy people, so why not do it myself? I often don’t have access to the Active Directory Users and Computers tool so I have to find another way to verify trusted for delegation. This is where the very useful AdExplorer utility helps. It’s one of the SysInternals tools available for download from Microsoft. As the name suggests it provides an explorer interface to Active Directory so you can browse the objects and attributes.

Here’s an AdExplorer screenshot showing the same machine account (P1001) from the dialog shown earlier.

I have selected the userAccessControl attribute and can see it has the value 4128. This is not good; I’ll explain why in a moment :) Essentially it means that the machine is not trusted for delegation. What I would rather see, is the next screenshot where it has the value 528416 meaning it is trusted for delegation.

So where do these magic numbers come from, and how do we know that 528416 is trusted and 4128 is not? The userAccessControl value is a bitmap value (or bit array). There are a number of possible flags that can be set in this value which are documented in the Microsoft resource How to use the UserAccountControl flags to manipulate user account properties. The main flag of interest here is TRUSTED_FOR_DELEGATION with value 0x80000 (hex) or 524288 (decimal) which is listed in the document as:

TRUSTED_FOR_DELEGATION – When this flag is set, the service account (the user or computer account) under which a service runs is trusted for Kerberos delegation. Any such service can impersonate a client requesting the service. To enable a service for Kerberos delegation, you must set this flag on the userAccountControl property of the service account.

The (trusted) decimal value 528416 (hex 0x81020) we saw above consists of TRUSTED_FOR_DELEGATION (decimal 524288 hex 0x80000) + WORKSTATION_TRUST_ACCOUNT (decimal 4096 hex 0x1000) + PASSWD_NOTREQD (decimal 32 hex 0x0020). The (untrusted) decimal value 4128 (hex 0x1020) we saw earlier only consists of WORKSTATION_TRUST_ACCOUNT (decimal hex 0x1000) + PASSWD_NOTREQD (decimal 32 hex 0x0020). It’s missing the TRUSTED_FOR_DELEGATION value. You might see other values in your environment, including other flag values, but the important thing to check is that it includes the TRUSTED_FOR_DELEGATION value.

If you know of any other ways to verify a server’s trusted for delegation status (as a normal domain user) please let me know by leaving a comment.

For more posts in this series have a look at the IWA tag.

SAS and IWA: Two Hops

Update 26Sep2018: This post is now several years old and naturally technology and security have progressed in that time. For more up to date information regarding delegation and, in particular, the requirement for constrained delegation when working with Windows Defender Credential Guard in Windows 10 and Windows Server 2016, please see Stuart Rogers’ very useful SAS Global Forum 2018 Paper: SAS 9.4 on Microsoft Windows: Unleashing Kerberos on Apache Hadoop.

In an earlier post I mentioned that I would jot down a few notes about my experiences with SAS® software and Integrated Windows Authentication (IWA). This is the first of these posts and concerns the initial configuration. Chances are, if you knew you wanted to use IWA before you installed SAS, then it would have been discussed and implemented during the initial installation and configuration. If you decided to implement IWA after the fact then you would most likely have followed the instructions from either:

A basic SAS and IWA configuration might then look something like this. In the diagram below we have a client PC (saspc001), a dedicated metadata server machine (sasmeta) and an application server machine (sasapp). This is a homogenous environment consisting of all Windows machines in the same Windows domain. Other configurations might have multiple domains that trust each other, and now with SAS 9.3, some of the SAS servers may also be UNIX based (assuming the prerequisites are met).

In the diagram above a SAS Enterprise Guide user working on the saspc001 workstation initially connects (1) to the SAS Metadata Server on sasmeta using a connection profile with IWA enabled. When they run a project, an IWA connection (2) is then made to the SAS Object Spawner on sasapp to launch a standard SAS Workspace Server to execute the SAS code. The logical SAS Workspace Server has been configured in metadata to accept IWA connections. Both of these IWA connections involve only 1-hop from the workstation: saspc001 to sasmeta, and saspc001 to sasapp.

Problems might then arise when secondary connections need to be made from the workspace server to additional servers and access denied errors are seen in the SAS log. One example of a secondary connection includes executing code on the workspace server that reads a CSV or XML file from another file server (filesrv) using a UNC path (e.g. \\filesrv\share\file.xml). Another example might be assigning a library in the workspace server session that uses SAS/ACCESS Interface to ODBC or SAS/ACCESS Interface to OLEDB to connect to a Microsoft SQL Server database on another server (sqlsrv). These examples are shown in the diagram below as (3) and (4) respectively.

Both of these example involve IWA being used in 2-hops from the client. In the first hop (2) IWA is used to connect from saspc001 to sasapp as before. In the second hops the SAS workspace server process has to then connect and authenticate to the secondary servers: sasapp to filesrv (3), and sasapp to sqlsrv (4). It is these second hops which may fail if additional measures have not been taken:

  • Trusted for Delegation: the intermediate server (sasapp in this example – where the workspace server is running) needs to configured in Active Directory as Trusted for Delegation. This must be done by a domain admin. This configuration is mentioned in the SAS Intelligence Platform: Security Administration Guide on the Windows Privileges page for both SAS 9.2 and SAS 9.3. In a future post I’ll show the method I use as a non-domain-admin to double check this as part of the troubleshooting process.
  • Force Kerberos: you also need to ensure the Kerberos protocol is used and not NTLM. Whilst you could get all of your users to configure their SAS client connection profiles to use Kerberos, it is usually preferable to leave the clients alone and instead configure the SAS servers to only offer Kerberos and not NTLM. This is documented in the in the SAS Intelligence Platform: Security Administration Guide on the How to Force Use of Kerberos page for SAS 9.2, and the How to Configure Integrated Windows Authentication page for SAS 9.3. Things can get a bit trickier when DNS host aliases (or CNAMEs) are used in environments configured for disaster recovery. In a future post I’ll show some examples of additional Service Principal Names (SPNs) that might be required in these situations.

So if you find yourself getting access denied messages when using SAS and IWA in situations where multiple hops are involved, I hope this post gives you some ideas of things to investigate further.

For more posts in this series have a look at the IWA tag.