Jim Mock Updated and restructured by Jake Hamby Originally contributed by kernel building a custom kernel The kernel is the core of the FreeBSD operating system. It is responsible for managing memory, enforcing security controls, networking, disk access, and much more. While more and more of FreeBSD becomes dynamically configurable it is still occasionally necessary to reconfigure and recompile your kernel. After reading this chapter, you will know: Why you might need to build a custom kernel. How to write a kernel configuration file, or alter an existing configuration file. How to use the kernel configuration file to create and build a new kernel. How to install the new kernel. How to create any entries in /dev that may be required. How to troubleshoot if things go wrong. Traditionally, FreeBSD has had what is called a monolithic kernel. This means that the kernel was one large program, supported a fixed list of devices, and if you wanted to change the kernel's behavior then you had to compile a new kernel, and then reboot your computer with the new kernel. Today, FreeBSD is rapidly moving to a model where much of the kernel's functionality is contained in modules which can be dynamically loaded and unloaded from the kernel as necessary. This allows the kernel to adapt to new hardware suddenly becoming available (such as PCMCIA cards in a laptop), or for new functionality to be brought in to the kernel that was not necessary when the kernel was originally compiled. Colloquially these are called KLDs. Despite this, it is still necessary to carry out some static kernel configuration. In some cases this is because the functionality is so tied to the kernel that it can not be made dynamically loadable. In others it may simply be because no one has yet taken the time to write a dynamic loadable kernel module for that functionality yet. Building a custom kernel is one of the most important rites of passage nearly every Unix user must endure. This process, while time consuming, will provide many benefits to your FreeBSD system. Unlike the GENERIC kernel, which must support a wide range of hardware, a custom kernel only contains support for your PC's hardware. This has a number of benefits, such as: Faster boot time. Since the kernel will only probe the hardware you have on your system, the time it takes your system to boot will decrease dramatically. Less memory usage. A custom kernel often uses less memory than the GENERIC kernel, which is important because the kernel must always be present in real memory. For this reason, a custom kernel is especially useful on a system with a small amount of RAM. Additional hardware support. A custom kernel allows you to add in support for devices such as sound cards, which are not present in the GENERIC kernel. kernel building / installing First, let us take a quick tour of the kernel build directory. All directories mentioned will be relative to the main /usr/src/sys directory, which is also accessible through /sys. There are a number of subdirectories here representing different parts of the kernel, but the most important, for our purposes, are arch/conf, where you will edit your custom kernel configuration, and compile, which is the staging area where your kernel will be built. arch represents either i386, alpha, or pc98 (an alternative development branch of PC hardware, popular in Japan). Everything inside a particular architecture's directory deals with that architecture only; the rest of the code is common to all platforms to which FreeBSD could potentially be ported. Notice the logical organization of the directory structure, with each supported device, filesystem, and option in its own subdirectory. If there is not a /usr/src/sys directory on your system, then the kernel source has not been installed. The easiest way to do this is by running /stand/sysinstall as root, choosing Configure, then Distributions, then src, then sys. If you have an aversion to sysinstall and you have access to an official FreeBSD CDROM, then you can also install the source from the command line: &prompt.root; mount /cdrom &prompt.root; mkdir -p /usr/src/sys &prompt.root; ln -s /usr/src/sys /sys &prompt.root; cat /cdrom/sys/ssys.[a-d]* | tar -xzvf Next, move to the arch/conf directory and copy the GENERIC configuration file to the name you want to give your kernel. For example: &prompt.root; cd /usr/src/sys/i386/conf &prompt.root; cp GENERIC MYKERNEL Traditionally, this name is in all capital letters and, if you are maintaining multiple FreeBSD machines with different hardware, it is a good idea to name it after your machine's hostname. We will call it MYKERNEL for the purpose of this example. Storing your kernel config file directly under /usr/src can be a bad idea. If you are experiencing problems it can be tempting to just delete /usr/src and start again. Five seconds after you do that you realize that you have deleted your custom kernel config file. You might want to keep your kernel config file elsewhere, and then create a symbolic link to the file in the i386 directory. For example: &prompt.root; cd /usr/src/sys/i386/conf &prompt.root; mkdir /root/kernels &prompt.root; cp GENERIC /root/kernels/MYKERNEL &prompt.root; ln -s /root/kernels/MYKERNEL You must execute these and all of the following commands under the root account or you will get permission denied errors. Now, edit MYKERNEL with your favorite text editor. If you are just starting out, the only editor available will probably be vi, which is too complex to explain here, but is covered well in many books in the bibliography. However, FreeBSD does offer an easier editor called ee which, if you are a beginner, should be your editor of choice. Feel free to change the comment lines at the top to reflect your configuration or the changes you have made to differentiate it from GENERIC. SunOS If you have built a kernel under SunOS or some other BSD operating system, much of this file will be very familiar to you. If you are coming from some other operating system such as DOS, on the other hand, the GENERIC configuration file might seem overwhelming to you, so follow the descriptions in the Configuration File section slowly and carefully. Be sure to always check the file /usr/src/UPDATING, before you perform any update steps, in the case you sync your source-tree with the latest sources of the FreeBSD project. In this file all important issues with updating FreeBSD are written down. /usr/src/UPDATING always fits to your version of the FreeBSD source, and is therefore more accurate for those information than the handbook. You must now compile the source code for the kernel. There are two procedures you can use to do this, and the one you will use depends on why you are rebuilding the kernel, and the version of FreeBSD you are running. If you have installed only the kernel source code, use procedure 1. If you are running a FreeBSD version prior to 4.0, and you are not upgrading to FreeBSD 4.0 or higher using the make world procedure, use procedure 1. If you are building a new kernel without updating the source code (perhaps just to add a new option, such as IPFIREWALL) you can use either procedure. If you are rebuilding the kernel as part of a make world process, use procedure 2. Run &man.config.8; to generate the kernel source code. &prompt.root; /usr/sbin/config MYKERNEL Change in to the build directory. &prompt.root; cd ../../compile/MYKERNEL Compile the kernel. &prompt.root; make depend &prompt.root; make Install the new kernel. &prompt.root; make install Change to the /usr/src directory. &prompt.root; cd /usr/src Compile the kernel. &prompt.root; make buildkernel KERNCONF=MYKERNEL Install the new kernel. &prompt.root; make installkernel KERNCONF=MYKERNEL In FreeBSD 4.2 and older you must replace KERNCONF= with KERNEL=. 4.2-STABLE that was fetched after Feb 2nd, 2001 does recognize KERNCONF=. cvsup anonymous CVS CTM CVS anonymous If you have not upgraded your source tree in any way (you have not run CVSup, CTM, or used anoncvs), then you should use the config, make depend, make, make install sequence. kernel.old The new kernel will be copied to the root directory as /kernel and the old kernel will be moved to /kernel.old. Now, shutdown the system and reboot to use your kernel. In case something goes wrong, there are some troubleshooting instructions at the end of this chapter. Be sure to read the section which explains how to recover in case your new kernel does not boot. If you have added any new devices (such as sound cards) you may have to add some device nodes to your /dev directory before you can use them. For more information, take a look at "Making Device Nodes" later on in this chapter. kernel LINT LINT kernel config file The general format of a configuration file is quite simple. Each line contains a keyword and one or more arguments. For simplicity, most lines only contain one argument. Anything following a # is considered a comment and ignored. The following sections describe each keyword, generally in the order they are listed in GENERIC, although some related keywords have been grouped together in a single section (such as Networking) even though they are actually scattered throughout the GENERIC file. An exhaustive list of options and more detailed explanations of the device lines is present in the LINT configuration file, located in the same directory as GENERIC. If you are in doubt as to the purpose or necessity of a line, check first in LINT. In all versions of FreeBSD up to and including 3.X, &man.config.8; required that any strings in the configuration file that contained numbers used as text had to be enclosed in double quotes. This requirement was removed in the 4.X branch, which this book covers, so if you are on a pre-4.X system, see the /usr/src/sys/i386/conf/LINT and /usr/src/sys/i386/conf/GENERIC files on your system for examples. kernel example config file The following is an example GENERIC kernel configuration file with various additional comments where needed for clarity. This example should match your copy in /usr/src/sys/i386/conf/GENERIC fairly closely. For details of all the possible kernel options, see /usr/src/sys/i386/conf/LINT. # # GENERIC -- Generic kernel configuration file for FreeBSD/i386 # # For more information on this file, please read the handbook section on # Kernel Configuration Files: # # http://www.FreeBSD.org/handbook/kernelconfig-config.html # # The handbook is also available locally in /usr/share/doc/handbook # if you've installed the doc distribution, otherwise always see the # FreeBSD World Wide Web server (http://www.FreeBSD.ORG/) for the # latest information. # # An exhaustive list of options and more detailed explanations of the # device lines is also present in the ./LINT configuration file. If you are # in doubt as to the purpose or necessity of a line, check first in LINT. # # $FreeBSD: src/sys/i386/conf/GENERIC,v 1.246 2000/03/09 16:32:55 jlemon Exp $ The following are the mandatory keywords required in every kernel you build: kernel options machine machine i386 This is the machine architecture. It must be either i386, alpha, or pc98. kernel options cpu cpu I386_CPU cpu I486_CPU cpu I586_CPU cpu I686_CPU The above specifies the type of CPU you have in your system. You may have multiple instances of the CPU line (i.e., you are not sure whether you should use I586_CPU or I686_CPU), however, for a custom kernel, it is best to specify only the CPU you have. If you are unsure of your CPU type, you can use the dmesg command to view your boot up messages. kernel options cpu type The Alpha architecture has different values for cpu. They include: cpu EV4 cpu EV5 If you are using an Alpha machine, you should be using one of the above CPU types. kernel options ident ident GENERIC This is the identification of the kernel. You should change this to whatever you named your kernel, as in our previous example, MYKERNEL. The value you put in the ident string will print when you boot up the kernel, so it is useful to give the new kernel a different name if you want to keep it separate from your usual kernel (i.e., you want to build an experimental kernel). kernel options maxusers maxusers n The maxusers option sets the size of a number of important system tables. This number is supposed to be roughly equal to the number of simultaneous users you expect to have on your machine. Starting with FreeBSD 4.5, the system will auto-tune this setting for you if you explicitly set it to 0 The auto-tuning algorithm sets maxuser equal to the amount of memory in the system, with a minimum of 32, and a maximum of 384.. If you are using an earlier version of FreeBSD, or you want to manage it yourself you will want to set maxusers to at least 4, especially if you are using the X Window System or compiling software. The reason is that the most important table set by maxusers is the maximum number of processes, which is set to 20 + 16 * maxusers, so if you set maxusers to 1, then you can only have 36 simultaneous processes, including the 18 or so that the system starts up at boot time, and the 15 or so you will probably create when you start the X Window System. Even a simple task like reading a manual page will start up nine processes to filter, decompress, and view it. Setting maxusers to 64 will allow you to have up to 1044 simultaneous processes, which should be enough for nearly all uses. If, however, you see the dreaded proc table full error when trying to start another program, or are running a server with a large number of simultaneous users (like ftp.FreeBSD.org), you can always increase the number and rebuild. maxusers does not limit the number of users which can log into your machine. It simply sets various table sizes to reasonable values considering the maximum number of users you will likely have on your system and how many processes each of them will be running. One keyword which does limit the number of simultaneous remote logins is pseudo-device pty 16. # Floating point support - do not disable. device npx0 at nexus? port IO_NPX irq 13 npx0 is the interface to the floating point math unit in FreeBSD, which is either the hardware co-processor or the software math emulator. This is not optional. # Pseudo devices - the number indicates how many units to allocate. pseudo-device loop # Network loopback This is the generic loopback device for TCP/IP. If you telnet or FTP to localhost (a.k.a., 127.0.0.1) it will come back at you through this pseudo-device. This is mandatory. Everything that follows is more or less optional. See the notes underneath or next to each option for more information. #makeoptions DEBUG=-g #Build kernel with gdb(1) debug symbols options MATH_EMULATE #Support for x87 emulation This line allows the kernel to simulate a math co-processor if your computer does not have one (386 or 486SX). If you have a 486DX, or a 386 or 486SX (with a separate 387 or 487 chip), or higher (Pentium, Pentium II, etc.), you can comment this line out. The normal math co-processor emulation routines that come with FreeBSD are not very accurate. If you do not have a math co-processor, and you need the best accuracy, it is recommended that you change this option to GPL_MATH_EMULATE to use the GNU math support, which is not included by default for licensing reasons. options INET #InterNETworking Networking support. Leave this in, even if you do not plan to be connected to a network. Most programs require at least loopback networking (i.e., making network connections within your PC), so this is essentially mandatory. options INET6 #IPv6 communications protocols This enables the IPv6 communication protocols. options FFS #Berkeley Fast Filesystem options FFS_ROOT #FFS usable as root device [keep this!] This is the basic hard drive filesystem. Leave it in if you boot from the hard disk. options UFS_DIRHASH #Improve performance on big directories This option includes some code to speed up disk operations on large directories, at the expense of using a some additional memory. You would normally keep this for a large server, or interactive workstation, and remove it if you are using FreeBSD on a smaller system where memory is at a premium and disk access speed is less important, such as a firewall. options SOFTUPDATES #Enable FFS soft updates support This option enables soft updates in the kernel, this will help speed up write access on the disks. They are enabled by default in the 4.X branch but may not be turned on. Review the output from &man.mount.8; to see if you have them enabled. If you do not see the soft-updates option then you will need to activate it using the &man.tunefs.8; or &man.newfs.8; for new filesystems. options MFS #Memory Filesystem options MD_ROOT #MD is a potential root device This is the memory-mapped filesystem. This is basically a RAM disk for fast storage of temporary files, useful if you have a lot of swap space that you want to take advantage of. A perfect place to mount an MFS partition is on the /tmp directory, since many programs store temporary data here. To mount an MFS RAM disk on /tmp, add the following line to /etc/fstab: /dev/ad1s2b /tmp mfs rw 0 0 Now you simply need to either reboot, or run the command mount /tmp. kernel options NFS kernel options NFS_ROOT options NFS #Network Filesystem options NFS_ROOT #NFS usable as root device, NFS required The network filesystem. Unless you plan to mount partitions from a Unix file server over TCP/IP, you can comment these out. kernel options MSDOSFS options MSDOSFS #MSDOS Filesystem The MS-DOS filesystem. Unless you plan to mount a DOS formatted hard drive partition at boot time, you can safely comment this out. It will be automatically loaded the first time you mount a DOS partition, as described above. Also, the excellent mtools software (in the ports collection) allows you to access DOS floppies without having to mount and unmount them (and does not require MSDOSFS at all). options CD9660 #ISO 9660 Filesystem options CD9660_ROOT #CD-ROM usable as root, CD9660 required The ISO 9660 filesystem for CDROMs. Comment it out if you do not have a CDROM drive or only mount data CDs occasionally (since it will be dynamically loaded the first time you mount a data CD). Audio CDs do not need this filesystem. options PROCFS #Process filesystem The process filesystem. This is a pretend filesystem mounted on /proc which allows programs like &man.ps.1; to give you more information on what processes are running. options COMPAT_43 #Compatible with BSD 4.3 [KEEP THIS!] Compatibility with 4.3BSD. Leave this in; some programs will act strangely if you comment this out. options SCSI_DELAY=15000 #Delay (in ms) before probing SCSI This causes the kernel to pause for 15 seconds before probing each SCSI device in your system. If you only have IDE hard drives, you can ignore this, otherwise you will probably want to lower this number, perhaps to 5 seconds, to speed up booting. Of course, if you do this, and FreeBSD has trouble recognizing your SCSI devices, you will have to raise it back up. options UCONSOLE #Allow users to grab the console Allow users to grab the console, which is useful for X users. For example, you can create a console xterm by typing xterm -C, which will display any write, talk, and any other messages you receive, as well as any console messages sent by the kernel. options USERCONFIG #boot -c editor This option allows you to boot the configuration editor from the boot menu. options VISUAL_USERCONFIG #visual boot -c editor This option allows you to boot the visual configuration editor from the boot menu. options KTRACE #ktrace(1) support This enables kernel process tracing, which is useful in debugging. options SYSVSHM #SYSV-style shared memory This option provides for System V shared memory. The most common use of this is the XSHM extension in X, which many graphics-intensive programs will automatically take advantage of for extra speed. If you use X, you will definitely want to include this. options SYSVSEM #SYSV-style semaphores Support for System V semaphores. Less commonly used but only adds a few hundred bytes to the kernel. options SYSVMSG #SYSV-style message queues Support for System V messages. Again, only adds a few hundred bytes to the kernel. The &man.ipcs.1; command will list any processes using each of these System V facilities. options P1003_1B #Posix P1003_1B real-time extensions options _KPOSIX_PRIORITY_SCHEDULING Real-time extensions added in the 1993 POSIX. Certain applications in the ports collection use these (such as StarOffice). kernel options ICMP_BANDLIM Denial of Service (DoS) options ICMP_BANDLIM #Rate limit bad replies This option enables ICMP error response bandwidth limiting. You typically want this option as it will help protect the machine from denial of service packet attacks. kernel options SMP # To make an SMP kernel, the next two are needed #options SMP # Symmetric MultiProcessor Kernel #options APIC_IO # Symmetric (APIC) I/O The above are both required for SMP support. device isa All PCs supported by FreeBSD have one of these. If you have an IBM PS/2 (Micro Channel Architecture), you cannot run FreeBSD at this time (support is being worked on). device eisa Include this if you have an EISA motherboard. This enables auto-detection and configuration support for all devices on the EISA bus. device pci Include this if you have a PCI motherboard. This enables auto-detection of PCI cards and gatewaying from the PCI to ISA bus. # Floppy drives device fdc0 at isa? port IO_FD1 irq 6 drq 2 device fd0 at fdc0 drive 0 device fd1 at fdc0 drive 1 This is the floppy drive controller. fd0 is the A: floppy drive, and fd1 is the B: drive. device ata This driver supports all ATA and ATAPI devices. You only need one device ata line for the kernel to detect all PCI ATA/ATAPI devices on modern machines. device atadisk # ATA disk drives This is needed along with device ata for ATAPI disk drives. device atapicd # ATAPI CDROM drives This is needed along with device ata for ATAPI CDROM drives. device atapifd # ATAPI floppy drives This is needed along with device ata for ATAPI floppy drives. device atapist # ATAPI tape drives This is needed along with device ata for ATAPI tape drives. options ATA_STATIC_ID #Static device numbering This makes the controller number static (like the old driver) or else the device numbers are dynamically allocated. # ATA and ATAPI devices device ata0 at isa? port IO_WD1 irq 14 device ata1 at isa? port IO_WD2 irq 15 Use the above for older, non-PCI systems. # SCSI Controllers device ahb # EISA AHA1742 family device ahc # AHA2940 and onboard AIC7xxx devices device amd # AMD 53C974 (Teckram DC-390(T)) device dpt # DPT Smartcache - See LINT for options! device isp # Qlogic family device ncr # NCR/Symbios Logic device sym # NCR/Symbios Logic (newer chipsets) device adv0 at isa? device adw device bt0 at isa? device aha0 at isa? device aic0 at isa? SCSI controllers. Comment out any you do not have in your system. If you have an IDE only system, you can remove these altogether. # SCSI peripherals device scbus # SCSI bus (required) device da # Direct Access (disks) device sa # Sequential Access (tape etc) device cd # CD device pass # Passthrough device (direct SCSI access) SCSI peripherals. Again, comment out any you do not have, or if you have only IDE hardware, you can remove them completely. # RAID controllers device ida # Compaq Smart RAID device amr # AMI MegaRAID device mlx # Mylex DAC960 family Supported RAID controllers. If you do not have any of these, you can comment them out or remove them. # atkbdc0 controls both the keyboard and the PS/2 mouse device atkbdc0 at isa? port IO_KBD The keyboard controller (atkbdc) provides I/O services for the AT keyboard and PS/2 style pointing devices. This controller is required by the keyboard driver (atkbd) and the PS/2 pointing device driver (psm). device atkbd0 at atkbdc? irq 1 The atkbd driver, together with atkbdc controller, provides access to the AT 84 keyboard or the AT enhanced keyboard which is connected to the AT keyboard controller. device psm0 at atkbdc? irq 12 Use this device if your mouse plugs into the PS/2 mouse port. device vga0 at isa? The video card driver. # splash screen/screen saver pseudo-device splash Splash screen at start up! Screen savers require this too. # syscons is the default console driver, resembling an SCO console device sc0 at isa? sc0 is the default console driver, which resembles a SCO console. Since most full-screen programs access the console through a terminal database library like termcap, it should not matter whether you use this or vt0, the VT220 compatible console driver. When you log in, set your TERM variable to scoansi if full-screen programs have trouble running under this console. # Enable this and PCVT_FREEBSD for pcvt vt220 compatible console driver #device vt0 at isa? #options XSERVER # support for X server on a vt console #options FAT_CURSOR # start with block cursor # If you have a ThinkPAD, uncomment this along with the rest of the PCVT lines #options PCVT_SCANSET=2 # IBM keyboards are non-std This is a VT220-compatible console driver, backward compatible to VT100/102. It works well on some laptops which have hardware incompatibilities with sc0. Also set your TERM variable to vt100 or vt220 when you log in. This driver might also prove useful when connecting to a large number of different machines over the network, where termcap or terminfo entries for the sc0 device are often not available — vt100 should be available on virtually any platform. # Power management support (see LINT for more options) device apm0 at nexus? disable flags 0x20 # Advanced Power Management Advanced Power Management support. Useful for laptops. # PCCARD (PCMCIA) support device card device pcic0 at isa? irq 10 port 0x3e0 iomem 0xd0000 device pcic1 at isa? irq 11 port 0x3e2 iomem 0xd4000 disable PCMCIA support. You want this if you are using a laptop. # Serial (COM) ports device sio0 at isa? port IO_COM1 flags 0x10 irq 4 device sio1 at isa? port IO_COM2 irq 3 device sio2 at isa? disable port IO_COM3 irq 5 device sio3 at isa? disable port IO_COM4 irq 9 These are the four serial ports referred to as COM1 through COM4 in the MS-DOS/Windows world. If you have an internal modem on COM4 and a serial port at COM2, you will have to change the IRQ of the modem to 2 (for obscure technical reasons, IRQ2 = IRQ 9) in order to access it from FreeBSD. If you have a multiport serial card, check the manual page for &man.sio.4; for more information on the proper values for these lines. Some video cards (notably those based on S3 chips) use IO addresses in the form of 0x*2e8, and since many cheap serial cards do not fully decode the 16-bit IO address space, they clash with these cards making the COM4 port practically unavailable. Each serial port is required to have a unique IRQ (unless you are using one of the multiport cards where shared interrupts are supported), so the default IRQs for COM3 and COM4 cannot be used. # Parallel port device ppc0 at isa? irq 7 This is the ISA-bus parallel port interface. device ppbus # Parallel port bus (required) Provides support for the parallel port bus. device lpt # Printer Support for parallel port printers. All three of the above are required to enable parallel printer support. device plip # TCP/IP over parallel This is the driver for the parallel network interface. device ppi # Parallel port interface device The general-purpose I/O (geek port) + IEEE1284 I/O. #device vpo # Requires scbus and da zip drive This is for an Iomega Zip drive. It requires scbus and da support. Best performance is achieved with ports in EPP 1.9 mode. # PCI Ethernet NICs. device de # DEC/Intel DC21x4x (Tulip) device fxp # Intel EtherExpress PRO/100B (82557, 82558) device tx # SMC 9432TX (83c170 EPIC) device vx # 3Com 3c590, 3c595 (Vortex) device wx # Intel Gigabit Ethernet Card (Wiseman) Various PCI network card drivers. Comment out or remove any of these not present in your system. # PCI Ethernet NICs that use the common MII bus controller code. device miibus # MII bus support MII bus support is required for some PCI 10/100 Ethernet NICs, namely those which use MII-compliant transceivers or implement transceiver control interfaces that operate like an MII. Adding device miibus to the kernel config pulls in support for the generic miibus API and all of the PHY drivers, including a generic one for PHYs that are not specifically handled by an individual driver. device dc # DEC/Intel 21143 and various workalikes device rl # RealTek 8129/8139 device sf # Adaptec AIC-6915 (Starfire) device sis # Silicon Integrated Systems SiS 900/SiS 7016 device ste # Sundance ST201 (D-Link DFE-550TX) device tl # Texas Instruments ThunderLAN device vr # VIA Rhine, Rhine II device wb # Winbond W89C840F device xl # 3Com 3c90x (Boomerang, Cyclone) Drivers that use the MII bus controller code. # ISA Ethernet NICs. device ed0 at isa? port 0x280 irq 10 iomem 0xd8000 device ex device ep # WaveLAN/IEEE 802.11 wireless NICs. Note: the WaveLAN/IEEE really # exists only as a PCMCIA device, so there is no ISA attachment needed # and resources will always be dynamically assigned by the pccard code. device wi # Aironet 4500/4800 802.11 wireless NICs. Note: the declaration below will # work for PCMCIA and PCI cards, as well as ISA cards set to ISA PnP # mode (the factory default). If you set the switches on your ISA # card for a manually chosen I/O address and IRQ, you must specify # those parameters here. device an # The probe order of these is presently determined by i386/isa/isa_compat.c. device ie0 at isa? port 0x300 irq 10 iomem 0xd0000 device fe0 at isa? port 0x300 device le0 at isa? port 0x300 irq 5 iomem 0xd0000 device lnc0 at isa? port 0x280 irq 10 drq 0 device cs0 at isa? port 0x300 device sn0 at isa? port 0x300 irq 10 # requires PCCARD (PCMCIA) support to be activated #device xe0 at isa? ISA Ethernet drivers. See /usr/src/sys/i386/conf/LINT for which cards are supported by which driver. pseudo-device ether # Ethernet support ether is only needed if you have an Ethernet card. It includes generic Ethernet protocol code. pseudo-device sl 1 # Kernel SLIP sl is for SLIP support. This has been almost entirely supplanted by PPP, which is easier to set up, better suited for modem-to-modem connection, and more powerful. The number after sl specifies how many simultaneous SLIP sessions to support. pseudo-device ppp 1 # Kernel PPP This is for kernel PPP support for dial-up connections. There is also a version of PPP implemented as a userland application that uses tun and offers more flexibility and features such as demand dialing. The number after ppp specifies how many simultaneous PPP connections to support. pseudo-device tun # Packet tunnel. This is used by the userland PPP software. A number after tun specifies the number of simultaneous PPP sessions to support. See the PPP section of this book for more information. pseudo-device pty # Pseudo-ttys (telnet etc) This is a pseudo-terminal or simulated login port. It is used by incoming telnet and rlogin sessions, xterm, and some other applications such as emacs. A number after pty indicates the number of ptys to create. If you need more than the default of 16 simultaneous xterm windows and/or remote logins, be sure to increase this number accordingly, up to a maximum of 256. pseudo-device md # Memory disks Memory disk pseudo-devices. pesudo-device gif or pseudo-device gif 4 # IPv6 and IPv4 tunneling This implements IPv6 over IPv4 tunneling, IPv4 over IPv6 tunneling, IPv4 over IPv4 tunneling, and IPv6 over IPv6 tunneling. Beginning with FreeBSD 4.4 the gif device is auto-cloning, and you should use the first example (without the number after gif). Earlier versions of FreeBSD require the number. pseudo-device faith 1 # IPv6-to-IPv4 relaying (translation) This pseudo-device captures packets that are sent to it and diverts them to the IPv4/IPv6 translation daemon. # The `bpf' pseudo-device enables the Berkeley Packet Filter. # Be aware of the administrative consequences of enabling this! pseudo-device bpf # Berkeley packet filter This is the Berkeley Packet Filter. This pseudo-device allows network interfaces to be placed in promiscuous mode, capturing every packet on a broadcast network (e.g., an Ethernet). These packets can be captured to disk and or examined with the &man.tcpdump.1; program. The bpf pseudo-device is also used by &man.dhclient.8; to obtain the IP address of the default router (gateway) and so on. If you use DHCP, leave this uncommented. # USB support #device uhci # UHCI PCI->USB interface #device ohci # OHCI PCI->USB interface #device usb # USB Bus (required) #device ugen # Generic #device uhid # Human Interface Devices #device ukbd # Keyboard #device ulpt # Printer #device umass # Disks/Mass storage - Requires scbus and da #device ums # Mouse # USB Ethernet, requires mii #device aue # ADMtek USB ethernet #device cue # CATC USB ethernet #device kue # Kawasaki LSI USB ethernet Support for various USB devices. For more information and additional devices supported by FreeBSD, see /usr/src/sys/i386/conf/LINT. device nodes MAKEDEV Almost every device in the kernel has a corresponding node entry in the /dev directory. These nodes look like regular files, but are actually special entries into the kernel which programs use to access the device. The shell script /dev/MAKEDEV, which is executed when you first install the operating system, creates nearly all of the device nodes supported. However, it does not create all of them, so when you add support for a new device, it pays to make sure that the appropriate entries are in this directory, and if not, add them. Here is a simple example: Suppose you add the IDE CD-ROM support to the kernel. The line to add is: device acd0 This means that you should look for some entries that start with acd0 in the /dev directory, possibly followed by a letter, such as c, or preceded by the letter r, which means a raw device. It turns out that those files are not there, so you must change to the /dev directory and type: MAKEDEV &prompt.root; sh MAKEDEV acd0 When this script finishes, you will find that there are now acd0c and racd0c entries in /dev so you know that it executed correctly. For sound cards, the following command creates the appropriate entries: &prompt.root; sh MAKEDEV snd0 When creating device nodes for devices such as sound cards, if other people have access to your machine, it may be desirable to protect the devices from outside access by adding them to the /etc/fbtab file. See &man.fbtab.5; for more information. Follow this simple procedure for any other non-GENERIC devices which do not have entries. All SCSI controllers use the same set of /dev entries, so you do not need to create these. Also, network cards and SLIP/PPP pseudo-devices do not have entries in /dev at all, so you do not have to worry about these either. There are five categories of trouble that can occur when building a custom kernel. They are: config fails: If the config command fails when you give it your kernel description, you have probably made a simple error somewhere. Fortunately, config will print the line number that it had trouble with, so you can quickly skip to it with vi. For example, if you see: config: line 17: syntax error You can skip to the problem in vi by typing 17G in command mode. Make sure the keyword is typed correctly, by comparing it to the GENERIC kernel or another reference. make fails: If the make command fails, it usually signals an error in your kernel description, but not severe enough for config to catch it. Again, look over your configuration, and if you still cannot resolve the problem, send mail to the &a.questions; with your kernel configuration, and it should be diagnosed very quickly. Installing the new kernel fails If the kernel compiled fine, but failed to install (the make install or make installkernel command failed), the first thing to check is if your system is running at securelevel 1 or higher (see &man.init.8;). The kernel installation tries to remove the immutable flag from your kernel and set the immutable flag on the new one. Since securelevel 1 or higher prevents unsetting the immutable flag for any files on the system, the kernel installation needs to be performed at securelevel 0 or lower. The kernel will not boot: If your new kernel does not boot, or fails to recognize your devices, do not panic! Fortunately, BSD has an excellent mechanism for recovering from incompatible kernels. Simply choose the kernel you want to boot from at the FreeBSD boot loader. You can access this when the system counts down from 10. Hit any key except for the enter key, type unload and then type boot kernel.old, or the filename of any other kernel that will boot properly. When reconfiguring a kernel, it is always a good idea to keep a kernel that is known to work on hand. After booting with a good kernel you can check over your configuration file and try to build it again. One helpful resource is the /var/log/messages file which records, among other things, all of the kernel messages from every successful boot. Also, the &man.dmesg.8; command will print the kernel messages from the current boot. If you are having trouble building a kernel, make sure to keep a GENERIC, or some other kernel that is known to work on hand as a different name that will not get erased on the next build. You cannot rely on kernel.old because when installing a new kernel, kernel.old is overwritten with the last installed kernel which may be non-functional. Also, as soon as possible, move the working kernel to the proper kernel location or commands such as &man.ps.1; will not work properly. The proper command to unlock the kernel file that make installs (in order to move another kernel back permanently) is: &prompt.root; chflags noschg /kernel If you find you cannot do this, you are probably running at a &man.securelevel.8; greater than zero. Edit kern_securelevel in /etc/rc.conf and set it to -1, then reboot. You can change it back to its previous setting when you are happy with your new kernel. And, if you want to lock your new kernel into place, or any file for that matter, so that it cannot be moved or tampered with: &prompt.root; chflags schg /kernel The kernel works, but ps does not work any more!: If you have installed a different version of the kernel from the one that the system utilities have been built with, for example, a 4.X kernel on a 3.X system, many system-status commands like &man.ps.1; and &man.vmstat.8; will not work any more. You must recompile the libkvm library as well as these utilities. This is one reason it is not normally a good idea to use a different version of the kernel from the rest of the operating system.