Category Archives: Sysadmin

True Two Tiered OS Deployment

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JBoss clustering and Penguin’s Clusterware (bproc) have one thing in common: the view of the the system spans more than a single underlying system. Other systems have this concept as well, but these two are the ones I know best. Virtualization is currently changing how people do work in the datacenter. Many people have “Go virtual first” strategies: all software deployed can only be deployed inside virtual machines. While this simplifies some aspects of system administration, it complicates others: Now the system administrators need tools to manage large arrays of systems.

If you combine current virtualization practices with current cluster practices, you have an interesting sytem. Make a clustered OS instance of Virtual machines and deploy it across an array of embedded Hypervisors. Any one of the VMs that make up the clustered OS image can migrate to a different machine: after running for a length of time, no VM may be on any of the machines that were originally used to run the clustered OS Image.
Such a system would have many benefits. The virtualization technology helps minimize points of failure such that, in theory the whole system could be checkpointed and restarted from a n earlier state, assume that the networking fabric plays nice. System administration would be simplified as a unified process tree allows for killing remote processes without having to log in to each and every node to kill them. Naming service management is centralized, as is all policy for the cluster. Additionally, multiple OS images could be installed on the same physical cluster, allowing clear delineation of authority, while promoting resource sharing. Meta system administrators would see to the allocation of nodes to a clustered image, while department system admins would manage their particular cluster, without handling hardware.

Reading the links from a webpage

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I needed to see the set of RPMs in a YUM repository. I wanted to do this as part of a larger script. To do this, I fetched the page via wget, and then applied an xsl transform on it using the command line tool xsltproc.

Here is how I called it:

wget -q -O – http://spacewalk.redhat.com/yum/0.5/Fedora/10/x86_64/os/Packages/ | xsltproc –html showhrefs.xslt –

And here is the xslt file showrefs.xslt

<?xml version=”1.0″ encoding=”UTF-8″?>
<xsl:stylesheet xmlns:xsl=”http://www.w3.org/1999/XSL/Transform” version=”1.0″>
<xsl:output method=”xml” indent=”yes”/>

<!–  shut off the default matchin rule –>
<xsl:template match=”text()” />

<!– print the href value of the hyperlinks –>
<xsl:template match=”a”>
<xsl:value-of select=”@href” />
<xsl:text >
</xsl:text>

</xsl:template>

</xsl:stylesheet>

Booting into single user mode with grub

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I recently had a problem where one of the daemons run at startup would hang.  In order to disable this, I needed to boot into single user mode, and chkconfig the service off.

The key to booting into single user mode is the word ‘single’ on the kernel command line.

Heres the steps:

  1. Reboot the system
  2. At the grub screen, hit esc to stop the default boot sequence
  3. use the arrow keys select the kernel image you wish to boot
  4. type ‘e’ to edit the kernel image startup parameters
  5. on the screen use the arrow keys again to select the line with the startup parameters.  This should be the  the middle line, the one that starts with the word ‘kernel’.
  6. Type ‘e’ to edit this line
  7. append the word ‘single to the end of the line and type enter
  8. type the ‘b’ key to boot the kernel

Dependency Licenses

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The following script, when run on a RPM based system, tells you what licenses your application might trip by linking with other code.  You have to  set $MYEXE to som path to an executable.

for LIB in `ldd $MYEXE | sed -e ‘s!.*=>!!’ -e ‘s! (.*!!’` ; do rpmquery –whatprovides $LIB ; done | grep -v “any package” | sort -u | xargs rpmquery –qf %-30{NAME}:%{LICENSE}”\n

Here is a sample run for perl:

glibc                         :LGPL
perl                          :Artistic or GPL

Note that this is only for the linked files that are registered with RPM.

Small Scale High Performance Computing

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At the top end of computing there is are the Supercomputers.  At the bottom end there are embedded devices.   In between, there are a wide array of types of computer systems.  Personal computers, workstations and servers are all really just a sliding scale of the same general set of technologies.  These systems are , more and more, the building blocks of the technologies higher up on the scale. Enterprise computing typically involves high-availability and high Input/Output (I/O) based systems.  Scientific and technical computing is similar, but high availability is not as important as performance.  Three of the variables that factor into system design are parallelization, running time and (disk) storage requirements. If a job is small enough that it can run on a single machine in a reasonable amount of time, it is usually best to leave it to do so.  Any speedup you would get in parallelizing the job and distributing the workload is offset by (Amdhals law) the serial portion of the job, the added overhead of parallelization, and the fact that you could run a different job on the other machine.  If your task is parallelizable, but is very storage intensive, you need a high speed disk interconnect.  Nowadays that means fiber channel.

Only if a job takes so long that it makes sense to parallelize, and that job does not require significant access to storage does it make sense to go to a traditional Beowulf cluster.  Although Infiniband does handle the interconnect for both network and storage access, the file systems themselves do not yet handle access by large clusters.

This is the point for which we need a new term:  storage bound, single system jobs that should be run on their own machine. Examples of this abound throughout science, engineering, enterprise, and government.  Potential terms for this are:Small Scale HPC, Single System HPC,  Storage Bound HPC, but none of them really roll of the tongue.

Faking out PAM Authentication

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I am working on a server application that uses Pluggable Authentication Modules (PAM) for authentication support.  This application  must run as root. As part of development, people need to log in to this server.  I don’t want to give out the root password of my development machine to people.  My hack was to create a setup in /etc/pam.d/emo-auth that always allows the login to succeed, provided the account exists.  The emo-auth configuration is what the application looks up to authenticate network connections.

$ cat /chroot/etc/pam.d/emo-auth

account   required   pam_permit.so
auth      required pam_permit.so
session   required pam_permit.so

Now people login with root, and any password will allow them to get in.
Since this is only for development, this solution works fine, and does not require any code changes.