8.4 The Configuration File

Updated for FreeBSD 5.X by Joel Dahl.

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. For an exhaustive list of architecture dependent options and devices, see the NOTES file in the same directory as GENERIC. For architecture independent options, see /usr/src/sys/conf/NOTES.

Note: NOTES does not exist in FreeBSD 4.X. Instead, see the LINT file for detailed explanations of options and devices in GENERIC. LINT served two purposes in 4.X: to provide a reference for choosing kernel options when building a custom kernel, and to provide a kernel configuration with as many tweakable options tweaked to non-default values as possible. The reason behind this was that such a configuration helped (and still does) a lot when testing new code and changes to existing code that may cause conflicts with other parts of the kernel. However, the kernel configuration framework went through some heavy changes in 5.X; one example of this is that the driver configuration options were moved to a hints file so that they could be changed and loaded dynamically at boot time, and LINT could not contain those hints anymore. For this and other reasons, the LINT file was renamed to NOTES and retained mostly the first reason for its existence: documenting the available options for user convenience.

In FreeBSD 5.X and later versions you can still generate a buildable LINT file by typing:

# cd /usr/src/sys/i386/conf && make LINT

The following is an example of the 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.

#
# 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/doc/en_US.ISO8859-1/books/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 ../../conf/NOTES and NOTES files. 
# If you are in doubt as to the purpose or necessity of a line, check first 
# in NOTES.
#
# $FreeBSD: /repoman/r/ncvs/src/sys/i386/conf/GENERIC,v 1.413 2004/08/11 01:34:18 rwatson Exp $

The following are the mandatory keywords required in every kernel you build:

machine        i386

This is the machine architecture. It must be either alpha, amd64, i386, ia64, pc98, powerpc, or sparc64.

cpu          I486_CPU
cpu          I586_CPU
cpu          I686_CPU

The above option specifies the type of CPU you have in your system. You may have multiple instances of the CPU line (if, for example, you are not sure whether you should use I586_CPU or I686_CPU), but for a custom kernel it is best to specify only the CPU you have. If you are unsure of your CPU type, you can check the /var/run/dmesg.boot file to view your boot messages.

Support for I386_CPU is still provided in the source of FreeBSD, but it is disabled by default in both -STABLE and -CURRENT. This means that to install FreeBSD with a 386-class cpu, you now have the following options:

The first of these options is probably the easiest of all, but you will need a lot of disk space which, on a 386-class machine, may be difficult to find.

ident          GENERIC

This is the identification of the kernel. You should change this to whatever you named your kernel, i.e. MYKERNEL if you have followed the instructions of the previous examples. 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 (e.g., you want to build an experimental kernel).

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[1]. In FreeBSD 5.X and above, maxusers will default to 0 if not specified. If you are using an version of FreeBSD earlier than 4.5, 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.

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 and X terminal windows is pseudo-device pty 16. With FreeBSD 5.X, you do not have to worry about this number since the pty(4) driver is ``auto-cloning''; you simply use the line device pty in your configuration file.

# Floating point support - do not disable.
device          npx

npx 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
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 device. This is mandatory. Under FreeBSD 4.X you have to use the line pseudo-device loop.

Everything that follows is more or less optional. See the notes underneath or next to each option for more information.

#To statically compile in device wiring instead of /boot/device.hints
#hints          "GENERIC.hints"         # Default places to look for devices.

In FreeBSD 5.X and newer versions the device.hints(5) is used to configure options of the device drivers. The default location that loader(8) will check at boot time is /boot/device.hints. Using the hints option you can compile these hints statically into your kernel. Then there is no need to create a device.hints file in /boot.

#makeoptions     DEBUG=-g          # Build kernel with gdb(1) debug symbols

The normal build process of FreeBSD does not include debugging information when building the kernel and strips most symbols after the resulting kernel is linked, to save some space at the install location. If you are going to do tests of kernels in the -CURRENT branch or develop changes of your own for the FreeBSD kernel, you might want to uncomment this line. It will enable the use of the -g option which enables debugging information when passed to gcc(1). The same can be accomplished by the config(8) -g option, if you are using the ``traditional'' way for building your kernels (see Section 8.3 for more information).

options          SCHED_4BSD         # 4BSD scheduler

The traditional scheduler for FreeBSD. Depending on your system's workload, you may gain performance by using the new ULE scheduler for FreeBSD that has been designed specially for SMP, but works just fine on UP systems too. If you wish to try it out, replace SCHED_4BSD with SCHED_ULE in your configuration file.

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

This is the basic hard drive file system. Leave it in if you boot from the hard disk.

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. Even when this functionality is provided by the kernel, it must be turned on for specific disks. Review the output from mount(8) to see if Soft Updates is enabled for your system disks. If you do not see the soft-updates option then you will need to activate it using the tunefs(8) (for existing file systems) or newfs(8) (for new file systems) commands.

options          UFS_ACL           # Support for access control lists

This option, present only in FreeBSD 5.X, enables kernel support for access control lists. This relies on the use of extended attributes and UFS2, and the feature is described in detail in Section 14.12. ACLs are enabled by default and should not be disabled in the kernel if they have been used previously on a file system, as this will remove the access control lists, changing the way files are protected in unpredictable ways.

options          UFS_DIRHASH       # Improve performance on big directories

This option includes functionality to speed up disk operations on large directories, at the expense of using 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          MD_ROOT           # MD is a potential root device

This option enables support for a memory backed virtual disk used as a root device.

options          NFSCLIENT         # Network Filesystem Client
options          NFSSERVER         # Network Filesystem Server
options          NFS_ROOT          # NFS usable as /, requires NFSCLIENT

The network file system. 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® file system. 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 emulators/mtools software 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

The ISO 9660 file system 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 file system.

options          PROCFS            # Process filesystem

The process file system. This is a ``pretend'' file system mounted on /proc which allows programs like ps(1) to give you more information on what processes are running. In FreeBSD 5.X and above, use of PROCFS is not required under most circumstances, as most debugging and monitoring tools have been adapted to run without PROCFS: unlike in FreeBSD 4.X, new installations of FreeBSD 5.X will not mount the process file system by default. In addition, 6.X-CURRENT kernels making use of PROCFS must now also include support for PSEUDOFS:

options          PSEUDOFS          # Pseudo-filesystem framework

PSEUDOFS is not available in FreeBSD 4.X.

options          GEOM_GPT          # GUID Partition Tables.

This option brings the ability to have a large number of partitions on a single disk.

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          COMPAT_FREEBSD4   # Compatible with FreeBSD4

This option is required on FreeBSD 5.X i386™ and Alpha systems to support applications compiled on older versions of FreeBSD that use older system call interfaces. It is recommended that this option be used on all i386 and Alpha systems that may run older applications; platforms that gained support only in 5.X, such as ia64 and Sparc64®, do not require this option.

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 again.

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          SYSVMSG           # SYSV-style message queues

Support for System V messages. This option only adds a few hundred bytes to the kernel.

options          SYSVSEM           # SYSV-style semaphores

Support for System V semaphores. Less commonly used but only adds a few hundred bytes to the kernel.

Note: The -p option of the ipcs(1) command will list any processes using each of these System V facilities.

options         _KPOSIX_PRIORITY_SCHEDULING # POSIX P1003_1B real-time extensions

Real-time extensions added in the 1993 POSIX®. Certain applications in the Ports Collection use these (such as StarOffice).

options          KBD_INSTALL_CDEV  # install a CDEV entry in /dev

This option is related to the keyboard. It installs a CDEV entry in /dev.

options          AHC_REG_PRETTY_PRINT     # Print register bitfields in debug
                                          # output.  Adds ~128k to driver.
options          AHD_REG_PRETTY_PRINT     # Print register bitfields in debug
                                          # output.  Adds ~215k to driver.

This helps debugging by printing easier register definitions for reading.

options          ADAPTIVE_GIANT    # Giant mutex is adaptive.

Giant is the name of a mutual exclusion mechanism (a sleep mutex) that protects a large set of kernel resources. Today, this is an unacceptable performance bottleneck which is actively being replaced with locks that protect individual resources. The ADAPTIVE_GIANT option causes Giant to be included in the set of mutexes adaptively spun on. That is, when a thread wants to lock the Giant mutex, but it is already locked by a thread on another CPU, the first thread will keep running and wait for the lock to be released. Normally, the thread would instead go back to sleep and wait for its next chance to run. If you are not sure, leave this in.

device          apic               # I/O APIC

The apic device enables the use of the I/O APIC for interrupt delivery. The apic device can be used in both UP and SMP kernels, but is required for SMP kernels. Add options SMP to include support for multiple processors.

device          isa

All PCs supported by FreeBSD have one of these. Do not remove this, even if you have no ISA slots. If you have an IBM PS/2 (Micro Channel Architecture) system, FreeBSD provides only limited support at this time. For more information about the MCA support, see /usr/src/sys/i386/conf/NOTES.

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.

device          agp

Include this if you have an AGP card in the system. This will enable support for AGP, and AGP GART for boards which have these features.

# Floppy drives
device          fdc

This is the floppy drive controller.

# ATA and ATAPI devices
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 ATA disk drives.

device          ataraid                 # ATA RAID drives

This is needed along with device ata for ATA RAID 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; without this, the device numbers are dynamically allocated.

# SCSI Controllers
device          ahb        # EISA AHA1742 family
device          ahc        # AHA2940 and onboard AIC7xxx devices
device          ahd        # AHA39320/29320 and onboard AIC79xx devices
device          amd        # AMD 53C974 (Teckram DC-390(T))
device          isp        # Qlogic family
device          mpt        # LSI-Logic MPT-Fusion
#device         ncr        # NCR/Symbios Logic
device          sym        # NCR/Symbios Logic (newer chipsets)
device          trm        # Tekram DC395U/UW/F DC315U adapters

device          adv        # Advansys SCSI adapters
device          adw        # Advansys wide SCSI adapters
device          aha        # Adaptec 154x SCSI adapters
device          aic        # Adaptec 15[012]x SCSI adapters, AIC-6[23]60.
device          bt         # Buslogic/Mylex MultiMaster SCSI adapters

device          ncv        # NCR 53C500
device          nsp        # Workbit Ninja SCSI-3
device          stg        # TMC 18C30/18C50

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 for SCSI)
device          ch         # SCSI media changers
device          da         # Direct Access (disks)
device          sa         # Sequential Access (tape etc)
device          cd         # CD
device          pass       # Passthrough device (direct SCSI access)
device          ses        # SCSI Environmental Services (and SAF-TE)

SCSI peripherals. Again, comment out any you do not have, or if you have only IDE hardware, you can remove them completely.

Note: The USB umass(4) driver and a few other drivers use the SCSI subsystem even though they are not real SCSI devices. Therefore make sure not to remove SCSI support, if any such drivers are included in the kernel configuration.

# RAID controllers interfaced to the SCSI subsystem
device          amr        # AMI MegaRAID
device          asr        # DPT SmartRAID V, VI and Adaptec SCSI RAID
device          ciss       # Compaq Smart RAID 5*
device          dpt        # DPT Smartcache III, IV - See NOTES for options
device          hptmv      # Highpoint RocketRAID 182x
device          iir        # Intel Integrated RAID
device          ips        # IBM (Adaptec) ServeRAID
device          mly        # Mylex AcceleRAID/eXtremeRAID
device          twa        # 3ware 9000 series PATA/SATA RAID

# RAID controllers
device          aac        # Adaptec FSA RAID
device          aacp       # SCSI passthrough for aac (requires CAM)
device          ida        # Compaq Smart RAID
device          mlx        # Mylex DAC960 family
device          pst        # Promise Supertrak SX6000
device          twe        # 3ware ATA RAID

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          atkbdc     # AT keyboard controller

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          atkbd      # AT keyboard

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          psm        # PS/2 mouse

Use this device if your mouse plugs into the PS/2 mouse port.

device          vga        # VGA video card driver

The video card driver.

# splash screen/screen saver
device          splash     # Splash screen and screen saver support

Splash screen at start up! Screen savers require this too. Use the line pseudo-device splash with FreeBSD 4.X.

# syscons is the default console driver, resembling an SCO console
device          sc

sc is the default console driver and 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 vt, 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 for the pcvt (VT220 compatible) console driver
#device          vt
#options         XSERVER          # support for X server on a vt console
#options         FAT_CURSOR       # start with block cursor

This is a VT220-compatible console driver, backward compatible to VT100/102. It works well on some laptops which have hardware incompatibilities with sc. 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 sc device are often not available -- vt100 should be available on virtually any platform.

# Power management support (see NOTES for more options)
#device          apm

Advanced Power Management support. Useful for laptops, although in FreeBSD 5.X and above this is disabled in GENERIC by default.

# Add suspend/resume support for the i8254.
device           pmtimer

Timer device driver for power management events, such as APM and ACPI.

# PCCARD (PCMCIA) support
# PCMCIA and cardbus bridge support
device          cbb               # cardbus (yenta) bridge
device          pccard            # PC Card (16-bit) bus
device          cardbus           # CardBus (32-bit) bus

PCMCIA support. You want this if you are using a laptop.

# Serial (COM) ports
device          sio               # 8250, 16[45]50 based serial ports

These are the serial ports referred to as COM ports 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 to add to your /boot/device.hints. 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          ppc

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.

#device         puc

Uncomment this device if you have a ``dumb'' serial or parallel PCI card that is supported by the puc(4) glue driver.

# PCI Ethernet NICs.
device          de         # DEC/Intel DC21x4x (``Tulip'')
device          em         # Intel PRO/1000 adapter Gigabit Ethernet Card
device          ixgb       # Intel PRO/10GbE Ethernet Card
device          txp        # 3Com 3cR990 (``Typhoon'')
device          vx         # 3Com 3c590, 3c595 (``Vortex'')

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.
# NOTE: Be sure to keep the 'device miibus' line in order to use these NICs!
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          bfe        # Broadcom BCM440x 10/100 Ethernet
device          bge        # Broadcom BCM570xx Gigabit Ethernet
device          dc         # DEC/Intel 21143 and various workalikes
device          fxp        # Intel EtherExpress PRO/100B (82557, 82558)
device          lge        # Level 1 LXT1001 gigabit ethernet
device          nge        # NatSemi DP83820 gigabit ethernet
device          pcn        # AMD Am79C97x PCI 10/100 (precedence over 'lnc')
device          re         # RealTek 8139C+/8169/8169S/8110S
device          rl         # RealTek 8129/8139
device          sf         # Adaptec AIC-6915 (``Starfire'')
device          sis        # Silicon Integrated Systems SiS 900/SiS 7016
device          sk         # SysKonnect SK-984x & SK-982x gigabit Ethernet
device          ste        # Sundance ST201 (D-Link DFE-550TX)
device          ti         # Alteon Networks Tigon I/II gigabit Ethernet
device          tl         # Texas Instruments ThunderLAN
device          tx         # SMC EtherPower II (83c170 ``EPIC'')
device          vge        # VIA VT612x gigabit ethernet
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.  pccard NICs included.
device          cs         # Crystal Semiconductor CS89x0 NIC
# 'device ed' requires 'device miibus'
device          ed         # NE[12]000, SMC Ultra, 3c503, DS8390 cards
device          ex         # Intel EtherExpress Pro/10 and Pro/10+
device          ep         # Etherlink III based cards
device          fe         # Fujitsu MB8696x based cards
device          ie         # EtherExpress 8/16, 3C507, StarLAN 10 etc.
device          lnc        # NE2100, NE32-VL Lance Ethernet cards
device          sn         # SMC's 9000 series of Ethernet chips
device          xe         # Xircom pccard Ethernet

# ISA devices that use the old ISA shims
#device         le

ISA Ethernet drivers. See /usr/src/sys/i386/conf/NOTES for details of which cards are supported by which driver.

# Wireless NIC cards
device          wlan       # 802.11 support
device          an         # Aironet 4500/4800 802.11 wireless NICs.
device          awi        # BayStack 660 and others
device          wi         # WaveLAN/Intersil/Symbol 802.11 wireless NICs.
#device         wl         # Older non 802.11 Wavelan wireless NIC.

Support for various wireless cards.

device   mem           # Memory and kernel memory devices

The system memory devices.

device   io            # I/O device

This option allows a process to gain I/O privileges. This is useful in order to write userland programs that can handle hardware directly. This is required to run the X Window system.

device   random        # Entropy device

Cryptographically secure random number generator.

device   ether         # Ethernet support

ether is only needed if you have an Ethernet card. It includes generic Ethernet protocol code. Under FreeBSD 4.X use the line pseudo-device ether.

device   sl            # 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. With FreeBSD 4.X use the line pseudo-device sl.

device   ppp           # 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. With FreeBSD 4.X use the line pseudo-device ppp.

device   tun           # Packet tunnel.

This is used by the userland PPP software. See the PPP section of this book for more information. With FreeBSD 4.X use the line pseudo-device tun.


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.

Note: Under FreeBSD 4.X, you have to use the line pseudo-device pty number. The 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.

device   md            # Memory ``disks''

Memory disk pseudo-devices. With FreeBSD 4.X use the line pseudo-device md.

device   gif           # 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 line pseudo-device gif. Earlier versions of FreeBSD 4.X require a number, for example pseudo-device gif 4.

device   faith         # IPv6-to-IPv4 relaying (translation)

This pseudo-device captures packets that are sent to it and diverts them to the IPv4/IPv6 translation daemon. With FreeBSD 4.X use the line pseudo-device faith 1.

# The `bpf' device enables the Berkeley Packet Filter.
# Be aware of the administrative consequences of enabling this!
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. With FreeBSD 4.X use the line pseudo-device bpf.

Note: The bpf(4) device is also used by 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         udbp          # USB Double Bulk Pipe devices
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
device          urio          # Diamond Rio 500 MP3 player
device          uscanner      # Scanners
# USB Ethernet, requires mii
device          aue           # ADMtek USB Ethernet
device          axe           # ASIX Electronics USB Ethernet
device          cue           # CATC USB Ethernet
device          kue           # Kawasaki LSI USB Ethernet
device          rue           # RealTek RTL8150 USB Ethernet

Support for various USB devices.

# FireWire support
device          firewire      # FireWire bus code
device          sbp           # SCSI over FireWire (Requires scbus and da)
device          fwe           # Ethernet over FireWire (non-standard!)

Support for various Firewire devices.

For more information and additional devices supported by FreeBSD, see /usr/src/sys/i386/conf/NOTES.

8.4.1 Large Memory Configurations (PAE)

Large memory configuration machines require access to more than the 4 gigabyte limit on User+Kernel Virtual Address (KVA) space. Due to this limitation, Intel added support for 36-bit physical address space access in the Pentium® Pro and later line of CPUs.

The Physical Address Extension (PAE) capability of the Intel® Pentium Pro and later CPUs allows memory configurations of up to 64 gigabytes. FreeBSD provides support for this capability via the PAE kernel configuration option, available in the 4.X series of FreeBSD beginning with 4.9-RELEASE and in the 5.X series of FreeBSD beginning with 5.1-RELEASE. Due to the limitations of the Intel memory architecture, no distinction is made for memory above or below 4 gigabytes. Memory allocated above 4 gigabytes is simply added to the pool of available memory.

To enable PAE support in the kernel, simply add the following line to your kernel configuration file:

options            PAE

Note: The PAE support in FreeBSD is only available for Intel IA-32 processors. It should also be noted, that the PAE support in FreeBSD has not received wide testing, and should be considered beta quality compared to other stable features of FreeBSD.

PAE support in FreeBSD has a few limitations:

For performance and stability concerns, it is advised to consult the tuning(7) manual page. The pae(4) manual page contains up-to-date information on FreeBSD's PAE support.

Notes

[1]

The auto-tuning algorithm sets maxusers equal to the amount of memory in the system, with a minimum of 32, and a maximum of 384.

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.