Popup notifications

I am easily distracted. If a build takes more than say, three seconds, I usually will flip to doing something else. This means that I often miss when a build is completed, and end up losing a few minutes here, a few minute there.

Well no longer. I use Zenity! What is this you ask? I didn’t know either until today. Zenity is a command line tool for making a popup window appear.

Now My build scripts look like this:

mvn -o -Pdev install
zenity –info –text “Build is completed”

This kicks off the build, and, when it is done, I get a lovely popup window telling me: the build has completed.

As the Corollary to Murphy’s law states: If its stupid, but it works, it ain’t stupid.

Why zenity? I mean, there are at least a dozen different ways to popup a window. Well, in keeping with that Cardinal programmer virtue of laziness, it is because zenity is in the Fedora11 repo, and I am running Fedora 11. yum install is my friend.

Yes, I realize that if I were cooler, I would make my script tell me success versus failure, and pop up the appropriate window for that. I’m not that cool.

OK, I wanto to be cool. Here’s the new version:

mvn -o -Pdev install && zenity –info –text “Build is completed” || zenity –warning –text “Build Failed”

This pops up a warning message box on mvn returning non-zero for failure. Note the use of the && and the ||. The evaluation of this is kind of cool: The && (logical and) has short circuit semantics, so the second portion only gets evaluated if the first part evaluates to true. However, the || (logical or) only gets evaluated if everything before it fails.

Highlander Syndrome in Package Management

Somewhere between systems work and application development lies the realm of package management. There are two main schools of thought in package management: inclusive of exclusive. If you are inclusive, you want everything inside a package management system, and everything should be inside one package management system. If you are exclusive, you want the system to provide little more than an operational environment, and you will manage your own applications thank-you-very-much.

One problem with the inclusive approach is, in the attempt to clean up old versions, you often end up with The Highlander Syndrome. There can be only one version of a library or binary installed on your system. The Exclusive approach is more end application focused. I may need to run a different version of Python than is provided by the system, and I don’t want to be locked in to using only the version installed system wide. In fact, I may require several different versions, and each of these require their own approach.

CPAN, Pear, and Maven have provide language specific approaches level APIs to resolving dependencies at the per application level. Maven is particualrly good at providing multiple versions of the API: I errs so far this way that often the same Jar file will exist multiple times in the maven repository, but under different paths.

There should be middle ground for the end user between all or nothing in package managemnt. As a system administrator, I don’t want users running “just any” software on their system, but as an end user I don’t want to be locked in to a specific version of a binary.

If the role of application maintainer is split from the role of system administrator, than the people that fill those two roles may have reason to use a different approach to package management. Since the app developer can’t be trusted, the sys admin doesn’t provide root access. With no root access, the app developer can’t deploy an RPM/Deb/MSI. The app developer doesn’t want the system administrator updating the packages that the app depends on just because there is a new bugfix/feature pack. So, the app developer doesn’t use the libraries provided by the distribution, but instead provides a limited set. Essentially, the system has two administrators, two sets of policy, and two mechanisms for applying that policy.

Each scripting language has its own package management system, but the binary languages tend to use the package management system provide by the operating system.  Most Scripting language programmers prefer to work inside their language of choice, so the Perl system is written in perl, the emacs system is written in LISP, the Python one in Python and so on.  The Wikipedia article goes into depth on the subject, so I’ll refrain from rewritintg that here.

A Package management system is really a tuple.  The variables of that system are:

  • The binary format of the package
  • The database used to track the state of the system
  • The mechanism used to fetch packages
  • The conventions for file placement

There is some redundancy in this list.  A file in the package my also be considered a capability, as is the “good name” of the package.  A package contain empty sets for some of the items in this list.  For example, an administrative package may only specify the code to be executed during install, but may not place any files on a file system.  At the other extreme, a package may provide a set of files with no executable code to be run during the install process.

Of these items, it is the conventions that really prevent interoperability.  This should come as no surprise:  It is always easier to write an adapter on top of an explicit interface than an implicit one.  The Linux Standards Base helps, as does the standards guidelines posted by Debian, Red Hat, and other distribution providers.  However, if you look at the amount of traffic on the mailing lists regarding “file X is in the wrong place for its type” you can understand why automating a cross package install is tricky.  Meta package management schemes attempt to mitigate the problem, but they can really only deal with thing that are in the right place.

Take the placement of 64 bit binaries.  For library files, Red Hat has provided a dual system:  put 32 bit libriares under /usr/lib and 64 bit librareis under /usr/lib64.  Debian puts them all into the same directory, and uses naming to keep them apart.  In neither case, however, did they provide a place to make 32 and 64 bit binaries co-exist. How much easier would migration have been if we had /usr/bin32 and /usr/bin64, with a symlink from either into /usr/bin?

Thus we see a couple of the dimensions of the problem.  An application should have a good name:  web server, mail client,  and so on.  A system should support multiple things which provide this capability, a reasonable default, and customizability for more advanced users.The system should provide protection against  applications with known security holes, but provide for the possibility of multiple implementations released at different points in time.

    An interesting take on package management comes from OSGi.  It is a language specific package management approach, specifically for Java.  It takes advantage of portions of the the Java language to allow the deployment of multiple versions of the same package inside a since Process.  When I mentioned this to some old time Linux sys admins, they blanched.  OSGi does not specify how to fetch the packages, much like RPM without YUM or DPKG  with out APT.  OSGi packages are installed into the application.  As such, they are much more like shared libraries, with specific code sections run on module load and unload.  Different OSGi container provide different sets of rules, but basically the packages must exist inside of a subset of directories in order to be available for activation.  I have heard an interesting idea that the JPackage/RPM approach and OSGi should ideally merge in the future.  To install a Jar into your OSGi container, you would have to install an RPM.

    One additional issue on the Java/RPM front is Maven.  Both Maven and RPM want to run the entire build process from start to finish.  Both have the concept of a local Database of packages to resolve dependencies.  For long term Java/RPM peaceful coexistence, RPM is going to have to treat Maven as a first class citizen, the way that it does make.  Maven should provide a means to generate a spec file that has the absolute minimum in it to track dependencies, and to kick off an RPM build of the Maven artifacts.

    interface2addr

    This little script will give you the ipv4 address for a given network interface, or list all of them if you leave the parameter blank:

    #!/bin/bash

    INTERFACE=$1

    /sbin/ifconfig $INTERFACE | grep “inet addr” | cut -d\: -f 2 | cut -d” ” -f 1

    Call it like this:

    ~/bin/interface2addr eth0

    Hacking the Palm Pre from Fedora

    My work machine is a Fedora 11 (F11) X86_64 system. The palm development SDK is distributed as a series of .deb packages, specifically targeted at an 32 bit Ubuntu 8 system. While I have the advantage of having a 32bit Debian system at home, so I was able to run through the setup process for development, ideally I would be able to attach to and control the Pre from my work machine.

    The first step is to download the .deb files onto the F11 machine. I actually only needed the novacom deb, which in my case is novacom_1.0.38_i386.deb. Deb files are accessable using ar (happy talk like a pirate day!).

    In a new and empty directory, run
    ar -vxf ~/novacom_1.0.38_i386.deb

    And you will see the three contained files:

    control.tar.gz data.tar.gz debian-binary

    Extract the data file using tar

    tar -zxf data.tar.g

    This will add a usr directory with the binaries in

    usr/local/bin/novacom{d}

    Novacom is a two piece effort: a daemon an a client. First make sure you can run the daemon.

    First, lets see the file type:

    file novacomd

    novacomd: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.8, stripped

    Let’s see what libraries it requires:

    ldd novacomd
    linux-gate.so.1 => (0x008f1000)
    libpthread.so.0 => /lib/libpthread.so.0 (0x0078a000)
    libusb-0.1.so.4 => not found
    libc.so.6 => /lib/libc.so.6 (0x00110000)
    /lib/ld-linux.so.2 (0x006ae000)

    Note that the USB library is missing. I have it installed on my system, but only the 64 bit version. To get the 32 bit version, first, figure out what the 32 bit vversion is named.

    yum search libusb

    libusb.i586

    And install

    sudo yum install libusb.i586

    F11 and the RHEL based approach for running 32bit apps on 64 makes this fairly easy to do. Unlike Debian based system which pretty much require you building a chroot if you are going to run a significant amount of 32 bit binaries, Red Hat based systems put 64 bit libraries into /usr/lib64 and 32 bit libraries int /usr/lib, so they don’t conflict. Now lddd shows we have everything:

    ldd novacomd
    linux-gate.so.1 => (0x00262000)
    libpthread.so.0 => /lib/libpthread.so.0 (0x008a5000)
    libusb-0.1.so.4 => /usr/lib/libusb-0.1.so.4 (0x00770000)
    libc.so.6 => /lib/libc.so.6 (0x00263000)
    /lib/ld-linux.so.2 (0x006ae00)

    And we can now run this. Since it is talking straight to hardware, it insists on running as root:

    ./novacomd
    [2009/9/22 11:40:48] novacomd version novacomd-62 starting…
    [2009/9/22 11:40:48] novacomctl socket ready to accept
    [2009/9/22 11:40:48] need to run as super user to access usb

    so:

    sudo ./novacomd
    [2009/9/22 11:41:11] novacomd version novacomd-62 starting…
    [2009/9/22 11:41:11] novacomctl socket ready to accept
    [2009/9/22 11:41:11] sending rst
    [2009/9/22 11:41:11] sending rst
    [2009/9/22 11:41:11] sending rst
    [2009/9/22 11:41:11] going online
    [2009/9/22 11:41:11] novacom_register_device:188: dev ‘e851588c804e8caa722490a0314ce9782dd4d9a4’ via usb type castle-linux

    No we turn our attention to the client piece.

    file novacom
    novacom: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.8, stripped
    [ayoung@ayoung novacom]$ ldd novacom
    linux-gate.so.1 =>  (0x00173000)
    libc.so.6 => /lib/libc.so.6 (0x006d2000)
    /lib/ld-linux.so.2 (0x006ae000)

    So we are ready to run.  There is no novaterm in this deb.  Instead, you run novacom in terminal mode.  A little noted line in that I will make big here is:

    ./novacom $* -t open tty://0

    Dogfooding

    When I was contracting at Sun, someone sent out a memo using the phrase “eat our own dog food.”  Scott McNeally sent out a response to the effect that Sun did not make dog food, “We Fly our own airplanes.”

    In the software world, the phrase has become so used that it has been verbed; If you work at a software company that uses its own products in house,  you are Dogfooding.

    Since so much of my professional work has been on Red Hat Enterprise, I’ve tended to run Debian based systems for my desktop, to keep abreast of what is happening in both worlds.  At Red Hat, I’ve finally had reason to run Fedora as my desktop machine, and have been enjoying the experience.  The vast majority of the Software I run now is distributed by the company I work for, and is Open Source.  It really is an amazing feeling. I am now running Fedora 11 not only on my work laptop, but my wife gave me permission to blow away the Windows install on her eeepc and install it there as well.  Fedora makes a great Netbook OS.

    However, one tenant of Software Development is to develop on the platform on which you are going to ship.  For Red Hat, that is RHEL5, and so I need access to a RHEL5 install, and in fact need both 32 and 64 bit, since the world has not completely moved to 64 bit yet.  I’ve used virtual machines in the past, but always from VMware.  Now I am running QEMU/KVM on my Laptop.  Like most things Linux-y, the command prompt method of controlling the virtual machine subsystem is a first class citizen:  I don’t need a visual console to start up a VM.  I realize this is old hat to some people, but It is new to me, and I am enjoying it.

    That is the wonderful thing about the Open Source development model:  you very quickly take ownership of the software that is essential to you.  Whenever a user becomes a contributor, that software is no longer just something out there.  It has become personal.

    Anyways. As I Fly the Red Hat virtualization airplane, I’ve learned a few things.  The GUI, Virtual Machine Manger, is great for getting over the learning curve.  The command line is virsh.  These tools are a  part of the libvirt project.  There is a command to start Qemu based vms directly, but his seems to bypass the libvirt infrastructure.  Rnning qemu-kvm allowed me to start a VM saved in /var/lib/libvirt/images, but was not able to talk to the kvm subsystem.  One thing that threw me was that connecting to the virtual shell and running the list command did not show my virtual machine;  by default, that only shows running virtual machines, and you need to add the –all option to see non-running VMs..important if you want to only run them occasionally as I do.  To connect to the system, run:

    sudo virsh -c qemu:///system

    There is also another URL qemu:///session that I am not yet familiar with.

    Working with VMware, I was comfortable with the split of the info into a vmdk and vmx files for binary data and configuration information.  IN KVM/Qemu/libvirt land, the equivalent of the VMDK is  a boot image.  This seems right to me, in keeping with the fearless Unix way of not inventing a new technology if an existing one makes sense.  The Analogue of the vmx file is in /etc/libvirt/qemu/.

    One thing I would like to get set up is bridged networking for my VMs to the corporate lan.  The base install takes the conservative view that the network should be confined to the local system.  I’ve seen some write ups to getting TAP interfaces set up to allow your virtual NICs to get packets to and from the physical NICs, but haven’t done that yet.  The configuration for the host local network can be viewed from the virtual machine manager, and it shows the range of DHCP address given out to the hosts.  It contains a wizard for adding new networks, but I am not sure if the VMware paradigm of a bridged network maps cleanly to the Linux view…I suspect not.  I see under advanced options when creating the VM that I can set the Network to bridged, but it doesn’t seem to find my DHCP server to PXE boot.  As an aside, I’d like to understand how this operates in an Ipv6 environment, as Uncle Sam is now dictating IPv6 for all new Software purchases.    So many things to learn!

    Reading the links from a webpage

    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>