Diskless, LowFormFactor OpenBSD SystemsUnix系统 电脑资料

Diskless, LowFormFactor OpenBSD SystemsUnix系统 电脑资料 In a previous articlewe built a tiny OpenBSD system out of a Soekris miniature PC, abootstrap workstation, and a Compact Flash (CF) card. While thisbination works nicely for many purposes, once you have Soekriiscattered all around your n Your server must be a NFS server capable of runningdhcpd(8),rarpd(8), andtftpd(8). The server operatingsystemis irrelevant; any BSD, Linux, or even a mercial UNIX will work. Ichose touse a FreeBSD server, simply because I had spare capacity on aserver-gradesystem. (My OpenBSD bootstrap station is a Celeron 433 with a 10GB harddrive. The original desktop user plained that it was unusable, butthe problems disappeared when we removed the original operating system.Its perfectly adequate for any free UNIX, but not exactly what youwant in a server.) Experimenting with an NFS server,rarpd, andtftpdprobably wont affect your environment, but doing unfamiliar things tothe DHCPserver most certainly can, so the main corporate LAN might not be awise choicefor your test bed. For my initial experiments in diskless booting, Iinstalled asecond work card in my diskless server and ran a crossover cablebetweenthat NIC and the Soekris box. Running a private DHCP server on thatinterfaceallowed me to experiment freely without corrupting the corporatework.While developers asking, Why did my machine boot something other thanWindows? would be amusing, it would cause too many meetings. To configure your Soekris box to run properly diskless, you need the MACaddress of its Ether port. Find this by booting the Soekris with a CFcard and runningifconfig(8), or by using a packet sniffer such astcpdumpor Ethereal. When the Soekris boots, it will attempt to grab its IPaddress via DHCP; you can always watch the DHCP logs. All of the rest of our work takes place on the server. (Thats kind of the point, you know.) In the first stage of a diskless boot (as described indiskless(8),a PROM or stage-1 bootstrap fetches a boot program from the diskless bootserver. Where can you find such a bootstrap for OpenBSD/i386? Google revealsa variety of sources, but I chose to go with GRUB for OpenBSD. Cedric Berger has patched GRUB modified to disklessly boot OpenBSD.(This site also has GRUB versions modified to boot OpenBSD on anIntel fxp work card, if youre interested in playing with disklessoperations on a standard PC.) Grab thepxegrub.sis-tty-19200file and put it somewhere safe. The Soekris will use bothdhcpd(8)andrarpd(8)todo its initial configuration.rarpdwill provide the basic IPaddress information, whiledhcpdwill provide boot-timeconfiguration information. Lets start by configuringrarpd. rarpd(8)handles reverse ARP requests. In a normal ARPrequest, a machine has an IP address and requests the matching Ether MACaddress. In reverse ARP, a machine has a MAC address and requests thecorresponding IP address. The Soekris knows its own Ether MAC address andwants an IP address. Differentrarpd(8)implementations have different features andrequirements; cursory checks for FreeBSD, OpenBSD, and Red Hat Linux showdifferent behaviors and different mand-line flags. For example, the FreeBSDrarpdI used expected to be able to provide a boot loader to theclient, and by default ignored requests for which it had no boot loader. Idont want to userarpd(8)to provide the loader information, so Ihad to use the-smand-line switch to tell the program toprovide answers only for those MAC addresses for which it had a mapping. Red HatLinux also defaults to checking for a bootable image, but uses a differentmand-line switch to just provide service. OpenBSDsrarpd(8)simply provides the RARP mapping service without trying to provide a bootableimage. I wont discuss differences in every program we require under everyoperating system; the point is, check your serversmanpages! All monrarpd(8)implementations use/etc/ethersto map MAC addresses to hostnames. My/etc/etherscontains the single line: The hostnamesoekris-diskless.blackhelicoptersmust beavailable in either DNS or/etc/hosts, so that the RARP server can getthe information. Next, the diskless machine will attempt to fetch its boot loader informationfrom the DHCP server. Here, Im usingisc-dhcpd3. While we dont need to group all of our diskless clients together, it will make further expansion simpler. Thefilenamekeyword means you should go grab this file from the TFTP server. Allof our Soekrii need to know about it, so it goes under the groupheading. Each diskless client also needs a separate entry for its MAC address and itsIP address. Once the diskless Soekris has figured out its IP address and whereto getits boot loader, it will attempt to grab that boot loader via TFTP. Allmodern, free, UNIX-like operating systems include a TFTPimplementation, usually run out ofid(8). Again, the manual pages for all of thetftpd(8)servers I checked have slightly different options. On myFreeBSD server, I decided to use/var/tftpbootas the TFTP rootdirectory, symlinked/tftpbootto it, and then set up/etc/id.conflike this: The-lflag tellstftpd(8)to log all requests,which is very helpful when debugging. The-schrootstftpd(8), and the-ntellstftpdto be as quiet as possible. Now, copypxegrub.sis-tty-19200into thetftpbootdirectory. The DHCP server will tell the Soekris to grab and run this file.pxegrubneeds a configuration file:grub.conf.Heres a working example. While you shouldnt have to change any of this for a Soekris, you might wishto edit thekernelline. This example makespxegrublook for a file calledbsdon thetftpdserver andattempt to load it as the kernel. Switch between kernels by changing thisentry. If youre not using a Soekris and wish to change some of the settings (forexample, to use the monitor and keyboard instead of a serial console), checkthe GRUB configuration manual for guidance. Note that the default GRUB configuration file is calledmenu.lst, notgrub.conf;whilepxegrubhas changed the configuration file name, thesettings within the file are all identical to standard GRUB. The kernel will boot the system and should recognize its basic hardware. Atthe point that it needs to mount a root file system, the system will automaticallybroadcast a request for its boot parameters across the local work. Your NFSserver needs to respond to this request viabootparamd(8).bootparamds entire reason for being is to answer broadcastconfiguration requests. These configurations are stored in/etc/bootparams. The first entry on a line is the fully qualified host name of the disklessmachine. In this example, our second entry is the path to the NFS-exportedroot directory for the diskless machine. You can also export swap and dumpdevice information, but we only need the root directory to start. bootparamd(8)requiresrpcbind(8). On FreeBSD, Irun both of these daemons with the-sflag, which causes them todrop privileges as soon as possible. (One mistake I made initially was to haverpcbindattach only to the IP address of the server machine, whichprecludes it from answering broadcast requests. The lesson is, dont be toosecure too quickly when youre trying to make this work!) Exports? Thats right, we need NFS! Fortunately, this is very easy to setup for a single client. The root of our file system is in/var/obsd/diskless-soekris/rootand we only need to export it to asingle host. Heres an/etc/exportsfor our FreeBSD server. Well also have to start the NFS server daemons at boot. By the time weredone, the FreeBSD server has the following set in/etc/rc.conf: Put the proper interface name in therarpd_flagsfield for yourserver. You then need an OpenBSD file system under your exported root. Thatsactually quite easy to do. You could just mount the root directory from yourOpenBSD bootstrap station and copy the entire system withtar-xvpf, but that will give you everything on your bootstrap station.(The-pflag is important; it preserves ownership information.)Another way to get a small image is to use the file system prepared for aCompact Flash system; youll have only the minimal files required, but caneasily add more. Copy over the/etc/rc.*files from yourbootstrap station anyway, as OpenBSDs startup system has specific features fordiskless operations. You will also have to do some debugging of the startupprocess, however, and create some directories under/varif youchoose this option. Finally, you could simply extract some OpenBSDdistribution tarballs in that directory and install vital/etcfiles from your bootstrap station. OpenBSD provides a kernel configuration specifically for i386 disklessoperations. Its called DISKLESS. Remember, the OpenBSD folks are primarilyinterested in supporting the GENERIC kernel; youll have minimal support if youuse a non-GENERIC kernel. However, in my experience, the DISKLESS kernel configurationis quite stable and reliable. As long as youre on a custom kernel anyway, you can make your life a littleeasier by equalizing the serial console speeds. The Soekris uses a serialconsole speed of 19200, while OpenBSD defaults to 9600. If you connect to theserial console at 19200, the Soekris boot messages will be legible, but theO