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.
Quoting numbers: In all versions of FreeBSD up to and including 3.X, 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.
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:
machine i386
This is the machine architecture. It must be either i386, alpha, or pc98.
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 which type your CPU use, you can use the dmesg command to view your boot up messages.
The Alpha architecture has different values for cpu_type. They include:
cpu EV4
cpu EV5
If you are using an Alpha machine, you should be using one of the above CPU types.
ident GENERIC
This is the identification of the kernel. You should change this to whatever you named your kernel, 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 a kernel a different name if you want to keep it separate from your usual kernel (i.e., you want to build an experimental kernel).
maxusers 32
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. However, under normal circumstances, 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 man 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.
Note: 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.
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.
Note: 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_EMULATION 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 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:
Now you simply need to either reboot, or run the command mount /tmp.
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.
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 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'll 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.
Note: The ipcs(1) command will list any processes using each of these System V facilities.
options P1003_1B #Posix P1003_1B real-time extentions
options _KPOSIX_PRIORITY_SCHEDULING
Real-time extensions added in the 1993 POSIX. Certain applications in the ports collection use these (such as Star Office).
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.
# 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.
# Optionally these may need tweaked, (defaults shown):
#options NCPU=2 # number of CPUs
#options NBUS=4 # number of busses
#options NAPIC=1 # number of IO APICs
#options NINTR=24 # number of INTs
These are some additional SMP knobs.
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.
#options ATA_ENABLE_ATAPI_DMA #Enable DMA on ATAPI devices
This enables DMA on the ATAPI device. Since many ATAPI devices claim to support DMA, but it does not actually work, this is turned off by default.
# 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.
# 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.
# 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 need this if you are installing on 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.
Note: 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 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.
Note: 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
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 devices - the number indicates how many units to allocated.
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.
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. The 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. The number 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.
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.
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 tcpdump(1) program.
# 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.
For questions about FreeBSD, e-mail
<questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.