(Removed redundant linefeeds for neatness.)

[ikiwiki.git] / docs / newhandbook / ConfigureKernel / index.mdwn

# Configuring the DragonFly Kernel 

***Updated and restructured by Jim Mock. Originally contributed by Jake Hamby.***

[[!toc  levels=3]]

## Synopsis 

The kernel is the core of the DragonFly operating system. It is responsible for managing memory, enforcing security controls, networking, disk access, and much more. While more and more of DragonFly 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 troubleshoot if things go wrong.

## Why Build a Custom Kernel? 

Traditionally, DragonFly 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, DragonFly 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 into the kernel that was not necessary when the kernel was originally compiled. This is known as a modular kernel. 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 DragonFly 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.

## Building and Installing a Custom Kernel 

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, is `config`, where you will edit your custom kernel configuration, and `compile`, which is the staging area where your kernel will be built.  Notice the logical organization of the directory structure, with each supported device, file system, and option in its own subdirectory.

### Installing the Source

If there is ***no*** `/usr/src/sys` directory on your system, then the kernel source has not been installed. One method to do this is via git.  An alternative is to install the kernel source tree from the archive distributed on the DragonFly CD named `src-sys.tar.bz2`.  This is especially useful when you do not have ready access to the internet. Use the Makefile in `/usr` to fetch the source or to unpack the archive. When installing kernel source only, use the alternate build procedure below.

The preferred way of installing the sources is:

    # cd /usr
    # make src-create
    
This will download the whole source tree via git into /usr/src. This method also allows for easy updating of the source tree by using:

    # make src-update

### Your Custom Config File

Next, move to the `config` directory and copy the `GENERIC` configuration file to the name you want to give your kernel. For example:

    # cd /usr/src/sys/config
    # cp GENERIC MYKERNEL

Traditionally, this name is in all capital letters and, if you are maintaining multiple DragonFly 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.

**Tip:** 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. Do not edit `GENERIC` directly, as it may get overwritten the next time you [update your source tree](updating.html#UPDATING-SETUP), and your kernel modifications will be lost.  You might want to keep your kernel config file elsewhere, and then create a symbolic link to the file in the `config` directory.

For example:

    # cd /usr/src/sys/config
    # mkdir /root/kernels
    # cp GENERIC /root/kernels/MYKERNEL
    # ln -s /root/kernels/MYKERNEL

**Note:** 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](bibliography.html). However, DragonFly 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`.

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|handbook-kernelconfig-config]] section slowly and carefully.

### Building a Kernel - Full Source Tree

**Note:** Be sure to always check the file `/usr/src/UPDATING`, before you perform any update steps, in the case you [sync your source tree](updating.html#UPDATING-SETUP) with the latest sources of the DragonFly project. In this file all important issues with updating DragonFly are typed out. `/usr/src/UPDATING` always fits your version of the DragonFly source, and is therefore more accurate for new information than the handbook.

 1. Change to the `/usr/src` directory.

     

          # cd /usr/src

 1. Compile the kernel.

          # make buildkernel KERNCONF=MYKERNEL

 1. Install the new kernel.     

          # make installkernel KERNCONF=MYKERNEL

    

If you have ***not*** upgraded your source tree in any way since the last time you successfully completed a `buildworld`-`installworld` cycle (you have not run `git pull` ), then it is safe to use the `quickworld` and `quickkernel`, `buildworld`, `buildkernel` sequence.

### Building a Kernel - Kernel Source Only

When only the kernel source is installed, you need to change step 2, above, to this:
     

      # make nativekernel KERNCONF=MYKERNEL

The other steps are the same.

### Running Your New Kernel

The installer copies the new kernel and modules to `/boot/kernel/`, the kernel being `/boot/kernel/kernel` and the modules being `/boot/kernel/*.ko`. The old kernel and modules are moved to `/boot/kernel.old/`. Now, shutdown the system and reboot to use your new kernel. In case something goes wrong, there are some [troubleshooting](kernelconfig-trouble.html) 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](kernelconfig-trouble.html#KERNELCONFIG-NOBOOT).

**Note:** 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 device nodes section later on in this chapter.

## The Configuration File 
<!-- XXX: do we really want to mention all these million config options? -->
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`.

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/config/GENERIC` fairly closely. For details of all the possible kernel options, see `/usr/src/sys/config/LINT`.

    

    #

    #

    # GENERIC -- Generic kernel configuration file for DragonFly/i386

    #

    # Check the LINT configuration file in sys/config, for an

    # exhaustive list of options.

    #

    # $DragonFly: src/sys/config/GENERIC,v 1.56 2007/12/26 14:02:36 sephe Exp $

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

    

    machine         i386

This is the machine architecture. It must be `i386` at the moment.  Support for `amd64` will be added in the future.

    

    cpu          I386_CPU

    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 (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 check the `/var/run/dmesg.boot` file to view your boot up messages.

    

    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 (i.e. you want to build an experimental kernel).

    

    maxusers          0

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.

(Recommended) The system will auto-tune this setting for you if you explicitly set it to `0`[(1)](#FTN.AEN7414). If 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, 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 [kernelconfig-config.html#KERNELCONFIG-PTYS `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 DragonFly, 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 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

The normal build process of the DragonFly 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 DEVELOPMENT branch or develop changes of your own for the DragonFly 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)](http://leaf.dragonflybsd.org/cgi/web-man?command#gcc&section1).

    

    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 DragonFly 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 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 DragonFly 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. Even when this functionality is provided by the kernel, it must be turned on for specific disks. Review the output from [mount(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#mount&section8) 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)](http://leaf.dragonflybsd.org/cgi/web-man?command=tunefs&section=8) (for existing filesystems) or [newfs(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=newfs&section=8) (for new filesystems) commands.

    

    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`.

    

    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 pkgsrc®) 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)](http://leaf.dragonflybsd.org/cgi/web-man?command#ps&section1) to give you more information on what processes are running. ***

    

Compatibility with 4.3BSD. Leave this in; some programs will act strangely if you comment this out.

    

    options          SCSI_DELAY=5000    #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 five seconds (5000 ms), to speed up booting. Of course, if you do this, and DragonFly 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(1)](http://leaf.dragonflybsd.org/cgi/web-man?command#write&section1), [talk(1)](http://leaf.dragonflybsd.org/cgi/web-man?command=talk&section=1), 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.

 **Note:** The [ipcs(1)](http://leaf.dragonflybsd.org/cgi/web-man?command#ipcs&section1) 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™** ).

    

    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.

    

    device          isa

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

    

    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          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 ATA 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.

 **Note:** The USB [umass(4)](http://leaf.dragonflybsd.org/cgi/web-man?command#umass&section4) 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

    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.

 **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 DragonFly. If you have a multiport serial card, check the manual page for [sio(4)](http://leaf.dragonflybsd.org/cgi/web-man?commandsio&section=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/config/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. .

    

    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 [userppp.html 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*** after `pty` indicates the number of `pty`s 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. ***

    

Memory disk pseudo-devices.

    

    pseudo-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.

    

    pseudo-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.

    

    # The `bpf' 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)](http://leaf.dragonflybsd.org/cgi/web-man?command#tcpdump&section1) program.

 **Note:** The [bpf(4)](http://leaf.dragonflybsd.org/cgi/web-man?command#bpf&section4) device is also used by [dhclient(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=dhclient&section=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-&gt;USB interface

    #device         ohci          # OHCI PCI-&gt;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 DragonFly, see `/usr/src/sys/i386/conf/LINT`.

#### Notes 

[[!table  data="""
<tablewidth="100%"> [(1)](kernelconfig-config.html#AEN7414) | 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. |
| | 
"""]]

## Device Nodes 

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. 

These nodes are created automatically once devfs is mounted, which happens manually for the root `/dev` during boot, just after the root mount.

## If Something Goes Wrong 

 **Note:** 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 [ps(1)](http://leaf.dragonflybsd.org/cgi/web-man?command#ps&section1) will not work properly. The proper command to ***unlock*** the kernel file that `make` installs (in order to move another kernel back permanently) is:

     % chflags noschg /boot/kernel
     

If you find you cannot do this, you are probably running at a [securelevel(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#securelevel&section8) 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:

    

    % chflags schg /boot/kernel
    

There are five categories of trouble that can occur when building a custom kernel. They are:

* `config` fails: If the [config(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#config&section8) command fails when you give it your kernel description, you have probably made a simple error somewhere. Fortunately, [config(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=config&section=8) 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(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#config&section8) to catch it. Again, look over your configuration, and if you still cannot resolve the problem, send mail to the [DragonFly Bugs mailing list](http://leaf.dragonflybsd.org/mailarchive/) 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 [init(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#init&section8)). 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 does not boot: If your new kernel does not boot, or fails to recognize your devices, do not panic! Fortunately, DragonFly has an excellent mechanism for recovering from incompatible kernels. Simply choose the kernel you want to boot from at the DragonFly 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 [dmesg(8)](http://leaf.dragonflybsd.org/cgi/web-man?command#dmesg&section8) command will print the kernel messages from the current boot.

* The kernel works, but [ps(1)](http://leaf.dragonflybsd.org/cgi/web-man?command#ps&section1) 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, many system-status commands like [ps(1)](http://leaf.dragonflybsd.org/cgi/web-man?command=ps&section=1) and [vmstat(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=vmstat&section=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.