The random rantings of a concerned programmer.

Archive for November, 2007

Setting up Netboot

November 30th, 2007 | Category: Random

STILL WORKING OUT LOL. Process taken so far:

Okay, so I’ve been trying to get bloody netbook/diskless operation working for awhile. There’s always little pesky bugs which crop up; I almost got it running about a month ago, but I couldn’t manage to get the NFS server running correctly, and though the kernel was loaded properly on the target machine, it was unable to mount a root filesystem because NFS was broke.

So I’m starting with a clean slate, trying out FreeBSD 7.0 for the first time and documenting the steps I take so I can try to better re-create any problems I cause myself. And, lol, if I can get it working this time then having this will be handy when I need to it up again from scratch.

For the most part, the handbook entry on diskless operation is one of the best sources for the entire process; it only lacks in that it doesn’t go into much detail about each of the subsystems. It also doesn’t give any hints regarding what to do when shit goes wrong, but blah. There’s a couple of other (mostly dated) guides on the net, but there’s so many ways to do this it’s easy to get confused.

The setup I’m building is basically a Beowulf cluster – it consists of a set of machines connected on a private, internal network. Only one machine (the head or master node) is actually connected to an external network, thus the internal ones are fairly well-shielded from anything malicious from the outside.

The master node is the only machine with a drive, the rest of the nodes will boot diskless from it. The master node has two NICs – one for the external network which is DHCP-configured (or however your network works), and one for the internal network on which we’ll run a DHCP server.

Each of the nodes which will be booting diskless need special hardware to actually do it, essentially you need a NIC with a PXE-loaded bootrom (and a BIOs which will let you boot from it). A quick way to check is to see if you can boot from your network card from the BIOS – if you can, then you probably have a bootrom. I’m not going to really go into the complicated steps involved in flashing the damned things because that shit it messy. Just hope you have one already loaded with a build which works >_>

I’m using the subnet for that internal subnet; the master node will be located at, and the test diskless client I’m configuring will be at with hostname suigintou.

Configuring the Master

  1. Installed FreeBSD 7.0-BETA3, minimal distribution. I chose 7.0 because I’ve been wanting to try it out for some time, and since I was starting from scratch I didn’t have a reason not to. Most of the documentation I’m using is for 6.2, but meh it shouldn’t make a difference. It’s not like there’s that much of a change in the components this uses.
  2. Post-install configuration: get distributions: ports, man, info, doc, src, games (for fortune). Of utmost importance is that you get the entire source tree, because you’ll need it when it comes time to make distribution. And you need ports to get the dhcp server. Technically, man, info, doc and games can be omitted, but I chose not to in this run.
  3. Configure sshd’s settings in /etc/ssh/sshd and enable it in rc.conf:

    then start it

    /etc/rc.d/sshd start

    Up to this point, I was working off the actual machine. As soon as sshd was started I beheaded the machine and did the rest of the stuff remotely. Because working through putty while browsing the internet and doing other things is much more fun.

  4. Configure secondary network interface for internal LAN. You’ll need to figure out what your secondary network interface is (with ifconfig) and replace fxp0 with it, durr.
    ifconfig fxp0 inet netmask

    And add a line in rc.conf so this gets done at boot-time from now on -

    ifconfig_fxp0="inet netmask"
  5. Lay out directories for everything:
    mkdir /diskless
    mkdir /diskless/tftp
    mkdir /diskless/suigintou
  6. Re-build pxeboot from source (because I’ve had… problems with the binary that comes with the distribution for some reason) -
    cd /sys/boot

    And copy it over into the tftp folder to be served up

    cp /boot/pxeboot /diskless/tftp
  7. Install net/isc-dhcp3-server, configure rc.conf to boot it at startup only on internal interface:
  8. Configure /usr/local/etc/dhcpd.conf for each diskless host:
    default-lease-time 0;
    max-lease-time 7200;
    ddns-update-style: none;
    option domain-name-servers;
    subnet netmask {
            option subnet-mask;
            option broadcast-address;
            host suigintou {
                    hardware ethernet 00:E0:81:02:B9:92;
                    filename "/diskless/tftp/pxeboot";
                    # On another machine, this didn't work (TFTP Error: file not found)
                    # The easiest way to fix this is to tftp into the localhost and try to
                    # fetch the file by hand, then put what works into the filename.
                    option root-path "";
            # ... etc

    For each host you’re booting diskless, you’ll want to add another host{ } block. The MAC address of each block is used to associate the diskless client with a hostname. I’ll probably end up tinkering with the root-path option to specify different configurations for each diskless machine, and possibly provide swap space for them (though NFS swap is ick).

  9. Enable inetd in rc.conf:

    and have inetd start tftp when needed, for both udp (standard) and tcp (for weird PXE hardware?) connections in inetd.conf -

    tftp    dgram   udp wait    root    /usr/libexec/tftpd  tftpd -l -s /diskless/tftp
    tftp    stream  tcp wait    root    /usr/libexec/tftpd  tftpd -l -s /diskless/tftp

    and restart inetd -

    /etc/rc.d/inetd restart
  10. Enable the NFS server in rc.conf:

    and export the proper directories for each host (only 1 here) in /etc/exports:

    /diskless/suigintou -alldirs -ro

    Start up NFS with

    /etc/rc.d/rpcbind start
    /etc/rc.d/nfsd start
    /etc/rc.d/mountd start

    And verify that everything is properly mounted with showmount -e. The output should look something like this -

    # showmount -e
    Exports list on localhost:

    If there’s nothing listed there, then something isn’t set up properly and you’ll get NFS mount errors when you boot the diskless node.

  11. Prepare a DISKLESS kernel configuration, based on the GENERIC configuration. If you haven’t compiled a custom kernel before, you’ll benefit from reading the handbook article on building and installing custom kernels.
    cp /sys/i386/conf/GENERIC /sys/i386/conf/DISKLESS

    and add the following options into the DISKLESS kernel configuration:

    options     BOOTP
    options     BOOTP_NFSROOT

    The handbook article on diskless doesn’t bother to tell you that you shouldn’t modify the GENERIC configuration directly, but you shouldn’t. Always make a copy of GENERIC and work from that copy, otherwise when you break something you can always easily revert.

  12. Next, write a script to build the distribution from source -
    export DESTDIR=/diskless/suigintou/
    mkdir -p ${DESTDIR}
    cd /usr/src; make buildworld && make buildkernel KERNCONF=DISKLESS
    cd /usr/src/etc; make distribution

    I took this script straight from Diskless Operation in the handbook, but added the KERNCONF=DISKLESS to indicate that we want to use the DISKLESS kernel instead of the GENERIC kernel.

  13. And execute that script to build the distribution. This is taking forever to finish blah blah.


Okay, I think I found a fix -

  1. Build the world and the kernel. Building the world takes fucking ages to do; if you’ve done it before you shouldn’t need to do it again. Ever. You’ll need to compile the kernel in any case.

    cd /usr/src
    make buildworld
    make buildkernel KERNCONF=DISKLESS
  2. Once that’s done and over with, you need to slam that stuff into the prepared place for it -
    cd /usr/src
    make installworld DESTDIR=/diskless/suigintou
    make installkernel DESTDIR=/diskless/suigintou KERNCONF=DISKLESS
    make distribution DESTDIR=/diskless/suigintou

    As a random note, if you fuck something up and aren’t able to delete certain files anymore, it’s because the installkernel make script sets a “no change” flag on a bunch of files so you can’t accidentially fuck your system with rm -rf /*. Anyway, to kill the flag, use chflags [-R] noschg.

  3. So now we’ve got our root filesystem ready to export. Now just gotta make sure all the processes we need are running (dhcpd, inetd and nfsd), then try booting the remote system… BUM BUM BUMMMMMM

If all goes well, you should be able to boot your remote machine.

Reasons this is Fucked.

The problem is that the entire NFS filesystem will be read-only, which breaks all kinds of shit. One solution I’ve found so far is to slap a union’ed memory-based filesystem over parts of it, like

mdmfs -M -s16m -o union md1 /etc

I had to boot the machine in single-user mode to even do this, because the master.passwd requires a lock to open. Thus, we need to put a memory-backed filesystem over /etc, then touch master.passwd to copy it into the memory-backed part. unionfs is really cool…

Ideally, what I want is to be able to NFS-mount a read-only root directory, then NFS-mount with unionfs a whole filesystem over that, such that we can both modify files AND have those changes be persistant. Memory-backed file systems are great, except that they’re completely lost when you reboot…

Now to figure out how to do that…

Okay, woot figured it out. Basically, you’ll want to lay out the fstab on the client machine something like this:

# Mount the memory-backed filesystems
/dev/md0 /var  mfs rw,-M,union,-s4m 2 0
/dev/md1 /tmp  mfs rw,-M,union,-s8m 2 0

# Mount the NFS-backed filesystems /etc nfs rw /usr nfs rw

The fstab file format is really archaic: it uses a space-delimited list of things. This implies that the list of options must be comma-delimited and can CONTAIN NO SPACES. Took me a fucking half-hour to work out why mount_md was breaking shit. Anyway.

That should just about do it. I’m tired of editting this post, lawds. Now I need to find me a new CMOS battery so I can actually reboot this machine and have it load everything without me going through the BIOS menus to acknowledge that yes, I know, the battery is dead. Fucking fuckity fuck.

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November 30th, 2007 | Category: Random

lol, so something went wrong with my sleep cycle. Today is supposed to be a “sleep day”, and I should have gone to bed at 2AM this morning and been passed out until 6PM today. It’s 10AM right now, and I haven’t been able to get any sleep. I just laid in bed all night and wasn’t able to sleep.

I’m confused the fuck about this. I feel like of fatigued, but not sleepy. I’ve been awake now for about 40 hours, not sure what’s going to happen. Arguably, I needed to skip a day anyway to resync the cycle with my work week, and I’m planning on drinking pretty heavily tonight so I’ll probably just pass out from the alcohol.

Kind of weird, regardless.

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Hardware Addiction

November 29th, 2007 | Category: Random

So, I’m addicted to buying computer hardware. I’ve literally got piles of motherboards stacked beside my bed, sitting on top of both loaded and disassembled cases, memory sticks and cooling devices littering my nightstand, network hardware accumulating on my shelves. Hell, I’ve even got an old Dell Poweredge server with double-redundant power supplies (that I’ve since dived for parts).

Most of my stuff is PC100/133 Pentium 3-based, which means it’s old enough to be ridiculously cheap, but not old enough to be completely useless. I’ve had it in my mind for a while to put together a nice cluster of these machines (running FreeBSD, of course) to tinker around with. It would be fun, for example, to run a bunch of Erlang VM nodes across a cluster and be able to drastically demonstrate some of the more awesome features the language provides.

Anyway, right now everything is completely haphazard. With the exception of a single machine (and my laptop), everything lies in some state of partial-disassembly. Most of the boards don’t have a chassis, power supplies are jerry-rigged, and I’ve only got 1 working harddrive left to boot off of (I’ve got a box of bootrom NICs loaded with PXE, but I haven’t gotten bloody NFS to work straight yet). Once I get netboot working, I’ll need a way to physically structure the hardware.

So, I ended up buying two of these shiny Intel 1U cases, planning on each housing an old Tyan 2515 dual P3 board. Eventually I want to strip out those boards and swap in some Intel 7501 chipset-based boards (dual Xeons, 400/533 FSB) since the processors are really cheap, but those boards cost ~$40/each and the PC2100 RAM is tricky to get (most of the stuff I’ve found is unbuffered, which is useless).

The trick is, those chassis are 1U rack-mountable, and I might be able to convince some people at school to let me house them in some of the half-empty racks they leave lying around unlocked. I thought about just secretly stashing my stuff in there (since the combined cost of each machine is only around ~$50 anyway), but I figured I might get in more trouble than just hardware confiscation for fsking around with their stuff.

Anyway, hopefully I’ll eventually have something to show for all this time and money spent on this project. At the very least, I’d like a nice multi-machine platform to run my happy little Erlang programs on <3

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Erlang MUD II

November 29th, 2007 | Category: Random

Okay, so there’s a shitton of stuff I need to plan out for a MUD. MUDs are XBOX HUEG things, I realized. It’s the technology behind them that’s typically less than other projects.

So far, I’ve written a simple non-persistent talker throwaway prototype to become acquainted with the gen_tcp module. It works, but it isn’t good enough to use for anything but the most basic of references. The source can be found here.

In addition to better working out the overall program structure, there’s a couple more things I need to be better acquainted with, like Mnesia, the Erlang distributed database backend.

I think my next project is to write another prototype, adding additional features like:

  • Persistent player state.
  • Emotes and player-defined emotes.
  • Rooms (ugh, you’ll hear more about rooms).

And I think one of my routers just crashed. Motherfucker.

Anyway, that’s probably enough for me to bite off for now, and should provide both some experience working with Mnesia and have some reference example to work on future prototypes.

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Erlang MUD I

November 28th, 2007 | Category: Random

I’ve been tinkering with the idea of writing a MUD in Erlang, a functional language which is focused for concurrent fault-tolerant applications and supports distributed systems out of the box. It’s a pretty nifty language, after using it for a couple of small random things, I wouldn’t really think about using anything else for small projects involving networks or threads.

You can’t change a variable.

Program structure in Erlang is a bit different from imperative languages in that you’re not really thinking about code in a flowing manner, but rather thinking in terms of processes and their interactions. The Erlang VM implements it’s own lightweight process system. Processes interact through messaging rather than shared memory, which is really nice.

Erlang also has a nice built-in database back-end, Mnesia. It’s nice because it seems pretty simple to use, and can be spread over multiple physical nodes (since it’s written in Erlang) for added redundancy. Should be fun.

The way I think I’m going to structure my MUD server is as such – each client has two separate processes. One of these processes is a message producer, it just sits on the socket and waits for data to come in, passing it to the second process. The second process also has access to the client socket, and is responsible for sending stuff. So when it receives the parsed data from the first socket, it can either send the client an “invalid message” string, or it can send another message to a higher structure, or alter the player’s state, or whatever.

That’s just the basics really. I need to sit down and actually work out the design of the MUD before I commit to any program structures, because MUDs are one of the types of games in which a lot can be done (in terms of gameplay). MUDs are so different from modern games that I don’t really want to take concepts from graphical games and just slap them around until they work in a text-environment. I want to develop my core mechanics with the environmental limitations in mind.

lol, so I’m basically still at square 1, “CHOOSE TECHNOLOGY”. Which arguably isn’t even a very good square to start with in some situations, but probably is just fine for this one.


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