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NetBSD 6.1.5 - man page for options (netbsd section 4)

OPTIONS(4)			   BSD Kernel Interfaces Manual 		       OPTIONS(4)

     options -- Miscellaneous kernel configuration options

     cinclude ...
     config ...
     [no] file-system ...
     ident ...
     include ...
     [no] makeoptions ...
     maxusers ...
     [no] options ...
     [no] pseudo-device ...

     This manual page describes a number of miscellaneous kernel configuration options that may
     be specified in a kernel config file.  See config(1) and config(5) for information on how to
     configure and build kernels.

     The no form removes a previously specified option.

     The following keywords are recognized in a kernel configuration file:

     cinclude "filename"
     Conditionally includes another kernel configuration file whose name is filename, which may
     be double-quoted and may be an explicit path or relative to the kernel source directory.
     Failure to open the named file is ignored.

     config exec_name root on rootdev [type fstype] [dumps on dumpdev]
     Defines a configuration whose kernel executable is named exec_name, normally ``netbsd'',
     with its root file system of type fstype on the device rootdev, and optionally specifying
     the location of kernel core dumps on the device dumpdev.  dev or dumpdev and fstype may be
     specified as ``?'', which is a wild card.	The root fstype and dumpdev are optional and
     assumed to be wild carded if they are not specified.

     device_instance at attachment [locators value [...]] [flags value]
     Define an instance of the device driver device_instance that attaches to the bus or device
     named attachment.	An attachment may require additional information on where the device can
     be found, such as an address, channel, function, offset, and/or slot, referred to as
     locators, whose value often may be a wild card, ``?''.  Some device drivers have one or more
     flags that can be adjusted to affect the way they operate.

     file-system fs_name [, fs_name [...]]
     Include support for the file-system fs_name.

     ident "string"
     Sets the kernel identification string to string.

     include "filename"
     Functions the same as cinclude, except failure to open filename produces a fatal error.

     options option_name [, option_name=value [...]]
     Specifies (or sets) the option, or comma-separated list of options, option_name.  Some
     options expect to be assigned a value, which may be an integer, a double-quoted word, a bare
     word, or an empty string ("").  Note that those are eventually handled by the C compiler, so
     the rules of that language apply.

     Note: Options that are not defined by device definition files are passed to the compile
     process as -D flags to the C compiler.

     makeoptions name=value
     Defines a make(1) macro name with the value value in the kernel Makefile.

     maxusers integer
     Set the maxusers variable in the kernel.

     no keyword name [arguments [...]]
     For the config(1) keywords file-system, makeoptions, options, and pseudo-device, no removes
     the file-system, makeoption, options, or pseudo-device, name.  This is useful when a kernel
     configuration file includes another which has undesired options.

     For example, a local configuration file that wanted the kitchen sink, but not COMPAT_09 or
     bridging, might be:

	   include "arch/i386/conf/GENERIC"
	   no options COMPAT_09
	   no pseudo-device bridge

     pseudo-device name [N]
     Includes support for the pseudo-device name.  Some pseudo-devices can have multiple or N

   Compatibility Options
     options COMPAT_09
     Enable binary compatibility with NetBSD 0.9.  This enables support for 16-bit user, group,
     and process IDs (following revisions support 32-bit identifiers).	It also allows the use of
     the deprecated getdomainname(3), setdomainname(3), and uname(3) syscalls.	This option also
     allows using numeric file system identifiers rather than strings.	Post NetBSD 0.9 versions
     use string identifiers.

     options COMPAT_10
     Enable binary compatibility with NetBSD 1.0.  This option allows the use of the file system
     name of ``ufs'' as an alias for ``ffs''.  The name ``ffs'' should be used post 1.0 in
     /etc/fstab and other files.  It also adds old syscalls for the AT&T System V UNIX shared
     memory interface.	This was changed post 1.0 to work on 64-bit architectures.  This option
     also enables ``sgtty'' compatibility, without which programs using the old interface produce
     an ``inappropriate ioctl'' error, and /dev/io only works when this option is set in the ker-
     nel, see io(4) on ports that support it.

     options COMPAT_11
     Enable binary compatibility with NetBSD 1.1.  This allows binaries running on the i386 port
     to gain direct access to the io ports by opening /dev/io read/write.  This functionality was
     replaced by i386_iopl(2) post 1.1.  On the Atari port, the location of the disk label was
     moved after 1.1.  When the COMPAT_11 option is set, the kernel will read (pre) 1.1 style
     disk labels as a last resort.  When a disk label is re-written, the old style label will be
     replaced with a post 1.1 style label.  This also enables the EXEC_ELF_NOTELESS option.

     options COMPAT_12
     Enable binary compatibility with NetBSD 1.2.  This allows the use of old syscalls for
     reboot() and swapon().  The syscall numbers were changed post 1.2 to add functionality to
     the reboot(2) syscall, and the new swapctl(2) interface was introduced.  This also enables
     the EXEC_ELF_NOTELESS option.

     options COMPAT_13
     Enable binary compatibility with NetBSD 1.3.  This allows the use of old syscalls for
     sigaltstack(), and also enables the old swapctl(2) command SWAP_STATS (now called
     SWAP_OSTATS), which does not include the se_path member of struct swapent.

     options COMPAT_14
     Enable binary compatibility with NetBSD 1.4.  This allows some old ioctl(2) on wscons(4) to
     be performed, and allows the NFSSVC_BIOD mode of the nfssvc(2) system call to be used for
     compatibility with the deprecated nfsiod program.

     options COMPAT_15
     Enable binary compatibility with NetBSD 1.5.  Since there were no API changes from
     NetBSD 1.5 and NetBSD 1.6, this option does nothing.

     options COMPAT_16
     Enable binary compatibility with NetBSD 1.6.  This allows the use of old signal trampoline
     code which has been deprecated with the addition of siginfo(2).

     options COMPAT_20
     Enable binary compatibility with NetBSD 2.0.  This allows the use of old syscalls for
     statfs(), fstatfs(), getfsstat() and fhstatfs(), which have been deprecated with the addi-
     tion of the statvfs(2), fstatvfs(2), getvfsstat(2) and fhstatvfs(2) system calls.

     options COMPAT_30
     Enable binary compatibility with NetBSD 3.0.  See compat_30(8) for details about the changes
     made after the NetBSD 3.0 release.

     options COMPAT_43
     Enables compatibility with 4.3BSD.  This adds an old syscall for lseek(2).  It also adds the
     ioctls for TIOCGETP and TIOCSETP.	The return values for getpid(2), getgid(2), and getuid(2)
     syscalls are modified as well, to return the parent's PID and UID as well as the current
     process's.  It also enables the deprecated NTTYDISC terminal line discipline.  It also pro-
     vides backwards compatibility with ``old'' SIOC[GS]IF{ADDR,DSTADDR,BRDADDR,NETMASK} inter-
     face ioctls, including binary compatibility with code written before the introduction of the
     sa_len field in sockaddrs.  It also enables support for some older pre 4.4BSD socket calls.

     options COMPAT_BSDPTY
     This option is currently on by default and enables the pty multiplexer ptm(4) and ptmx(4) to
     find and use ptys named /dev/ptyXX (master) and /dev/ttyXX (slave).  Eventually this option
     will become optional as ptyfs based pseudo-ttys become the default, see mount_ptyfs(8).

     options COMPAT_SVR4
     On those architectures that support it, this enables binary compatibility with AT&T System V
     Release 4 UNIX applications built for the same architecture.  This currently includes the
     i386, m68k, and sparc ports.

     options COMPAT_LINUX
     On those architectures that support it, this enables binary compatibility with Linux ELF and
     a.out(5) applications built for the same architecture.  This currently includes the alpha,
     arm, i386, m68k, mips, powerpc and x86_64 ports.

     options COMPAT_LINUX32
     On those 64 bit architectures that support it, this enables binary compatibility with 32 bit
     Linux binaries.  For now this is limited to running i386 ELF Linux binaries on amd64.

     options COMPAT_SUNOS
     On those architectures that support it, this enables binary compatibility with SunOS 4.1
     applications built for the same architecture.  This currently includes the sparc, sparc64
     and most or all m68k ports.  Note that the sparc64 requires the COMPAT_NETBSD32 option for
     64-bit kernels, in addition to this option.

     options COMPAT_ULTRIX
     On those architectures that support it, this enables binary compatibility with ULTRIX appli-
     cations built for the same architecture.  This currently is limited to the pmax.  The func-
     tionality of this option is unknown.

     options COMPAT_FREEBSD
     On those architectures that support it, this enables binary compatibility with FreeBSD
     applications built for the same architecture.  At the moment this is limited to the i386

     options COMPAT_IBCS2
     On those architectures that support it, this enables binary compatibility with iBCS2 or SVR3
     applications built for the same architecture.  This is currently limited to the i386 and vax

     options COMPAT_OSF1
     On those architectures that support it, this enables binary compatibility with Digital UNIX
     (formerly OSF/1) applications built for the same architecture.  This is currently limited to
     the alpha port.

     options COMPAT_NOMID
     Enable compatibility with a.out(5) executables that lack a machine ID.  This includes
     NetBSD 0.8's ZMAGIC format, and 386BSD and BSDI's QMAGIC, NMAGIC, and OMAGIC a.out(5) for-

     options COMPAT_NETBSD32
     On those architectures that support it, this enables binary compatibility with 32-bit appli-
     cations built for the same architecture.  This is currently limited to the amd64 and sparc64
     ports, and only applicable for 64-bit kernels.

     options COMPAT_SVR4_32
     On those architectures that support it, this enables binary compatibility with 32-bit SVR4
     applications built for the same architecture.  This is currently limited to the sparc64
     port, and only applicable for 64-bit kernels.

     options COMPAT_AOUT_M68K
     On m68k architectures which have switched to ELF, this enables binary compatibility with
     NetBSD/m68k a.out(5) executables on NetBSD/m68k ELF kernels.  This handles alignment incom-
     patibility of m68k ABI between a.out and ELF which causes the structure padding differences.
     Currently only some system calls which use struct stat are adjusted and some binaries which
     use sysctl(3) to retrieve network details would not work properly.

     options EXEC_ELF_NOTELESS
     Run unidentified ELF binaries as NetBSD binaries.	This might be needed for very old NetBSD
     ELF binaries on some archs.  These old binaries didn't contain an appropriate
     .note.netbsd.ident section, and thus can't be identified by the kernel as NetBSD binaries
     otherwise.  Beware - if this option is on, the kernel would run any unknown ELF binaries as
     if they were NetBSD binaries.

     options P1003_1B_SEMAPHORE
     Includes kernel support for the standard C library (libc) functions that implement sema-
     phores as specified in ISO/IEC 9945-1:1996 (``POSIX.1'').

   Debugging Options
     options DDB
     Compiles in a kernel debugger for diagnosing kernel problems.  See ddb(4) for details.
     NOTE: not available on all architectures.

     options DDB_FROMCONSOLE=integer
     If set to non-zero, DDB may be entered by sending a break on a serial console or by a spe-
     cial key sequence on a graphics console.  A value of "0" ignores console breaks or key
     sequences.  If not explicitly specified, the default value is "1".  Note that this sets the
     value of the ddb.fromconsole sysctl(3) variable which may be changed at run time -- see
     sysctl(8) for details.

     options DDB_HISTORY_SIZE=integer
     If this is non-zero, enable history editing in the kernel debugger and set the size of the
     history to this value.

     options DDB_ONPANIC
     The default if not specified is ``1'' - just enter into DDB.  If set to ``2'' the kernel
     will attempt to print out a stack trace before entering into DDB.	If set to ``0'' the ker-
     nel will attempt to print out a stack trace and reboot the system.  If set to ``-1'' then
     neither a stack trace is printed or DDB entered - it is as if DDB were not compiled into the
     kernel.  Note that this sets the value of the ddb.onpanic sysctl(3) variable which may be
     changed at run time -- see sysctl(8) for details.

     options DDB_COMMANDONENTER=string
     This option specify commands which will be executed on each entry to DDB.	This sets the
     default value of the ddb.commandonenter sysctl(3) variable which may be changed at run time.

     options DDB_BREAK_CHAR=integer
     This option overrides using break to enter the kernel debugger on the serial console.  The
     value given is the ASCII value to be used instead.  This is currently only supported by the
     com driver.

     options DDB_VERBOSE_HELP
     This option adds more verbose descriptions to the help command.

     options KGDB
     Compiles in a remote kernel debugger stub for diagnosing kernel problems using the ``remote
     target'' feature of gdb.  See gdb(1) for details.	NOTE: not available on all architectures.

     options KGDB_DEV
     Device number (as a dev_t) of kgdb device.

     options KGDB_DEVADDR
     Memory address of kgdb device.

     options KGDB_DEVMODE
     Permissions of kgdb device.

     options KGDB_DEVNAME
     Device name of kgdb device.

     options KGDB_DEVRATE
     Baud rate of kgdb device.

     makeoptions DEBUG="-g"
     The -g flag causes netbsd.gdb to be built in addition to netbsd.  netbsd.gdb is useful for
     debugging kernel crash dumps with gdb.  See gdb(1) for details.  This also turns on options
     DEBUG (which see).

     options DEBUG
     Turns on miscellaneous kernel debugging.  Since options are turned into preprocessor defines
     (see above), options DEBUG is equivalent to doing a #define DEBUG throughout the kernel.
     Much of the kernel has #ifdef DEBUG conditionalized debugging code.  Note that many parts of
     the kernel (typically device drivers) include their own #ifdef XXX_DEBUG conditionals
     instead.  This option also turns on certain other options, which may decrease system perfor-

     options DIAGNOSTIC
     Adds code to the kernel that does internal consistency checks.  This code will cause the
     kernel to panic if corruption of internal data structures is detected.  These checks can
     decrease performance up to 15%.

     options LOCKDEBUG
     Adds code to the kernel to detect incorrect use of locking primitives (mutex, rwlock, sim-
     plelock).	This code will cause the kernel to check for dead lock conditions.  It will also
     check for memory being freed to not contain initialised lock primitives.  Functions for use
     in ddb(4) to check lock chains etc. are also enabled.  These checks are very expensive and
     can decrease performance on multi-processor machines by a factor of three.

     Check kernel stack usage and panic if stack overflow is detected.	This check is performance
     sensitive because it scans stack on each context switch.

     options KTRACE
     Add hooks for the system call tracing facility, which allows users to watch the system call
     invocation behavior of processes.	See ktrace(1) for details.

     options MSGBUFSIZE=integer
     This option sets the size of the kernel message buffer.  This buffer holds the kernel output
     of printf() when not (yet) read by syslogd(8).  This is particularly useful when the system
     has crashed and you wish to lookup the kernel output from just before the crash.  Also,
     since the autoconfig output becomes more and more verbose, it sometimes happens that the
     message buffer overflows before syslogd(8) was able to read it.  Note that not all systems
     are capable of obtaining a variable sized message buffer.	There are also some systems on
     which memory contents are not preserved across reboots.

     options MALLOCLOG
     Enables an event log for malloc(9).  Useful for tracking down ``Data modified on freelist''
     and ``multiple free'' problems.

     options MALLOCLOGSIZE=integer
     Defines the number of entries in the malloc log.  Default is 100000 entries.

     options UVMHIST
     Enables the UVM history logs, which create in-memory traces of various UVM activities.
     These logs can be displayed be calling uvmhist_dump() or uvm_hist() with appropriate argu-
     ments from DDB.  See the kernel source file sys/uvm/uvm_stat.c for details.

     options UVMHIST_PRINT
     Prints the UVM history logs on the system console as entries are added.  Note that the out-
     put is extremely voluminous, so this option is really only useful for debugging the very
     earliest parts of kernel initialization.

   File Systems
     file-system FFS
     Includes code implementing the Berkeley Fast File System (FFS).  Most machines need this if
     they are not running diskless.

     file-system EXT2FS
     Includes code implementing the Second Extended File System (ext2), revision 0 and revision 1
     with the filetype, sparse_super and large_file options.  This is the most commonly used file
     system on the Linux operating system, and is provided here for compatibility.  Some of the
     specific features of ext2 like the "behavior on errors" are not implemented.  See
     mount_ext2fs(8) for details.

     file-system LFS
     [EXPERIMENTAL] Include the Log-structured File System (LFS).  See mount_lfs(8) and
     newfs_lfs(8) for details.

     file-system MFS
     Include the Memory File System (MFS).  This file system stores files in swappable memory,
     and produces notable performance improvements when it is used as the file store for /tmp and
     similar file systems.  See mount_mfs(8) for details.

     file-system NFS
     Include the client side of the Network File System (NFS) remote file sharing protocol.
     Although the bulk of the code implementing NFS is kernel based, several user level daemons
     are needed for it to work.  See mount_nfs(8) for details.

     file-system CD9660
     Includes code for the ISO 9660 + Rock Ridge file system, which is the standard file system
     on many CD-ROM discs.  Useful primarily if you have a CD-ROM drive.  See mount_cd9660(8) for

     file-system MSDOSFS
     Includes the MS-DOS FAT file system, which is reportedly still used by unfortunate people
     who have not heard about NetBSD.  Also implements the Windows 95 extensions to the same,
     which permit the use of longer, mixed case file names.  See mount_msdos(8) and fsck_msdos(8)
     for details.

     file-system NTFS
     [EXPERIMENTAL] Includes code for the Microsoft Windows NT file system.  See mount_ntfs(8)
     for details.

     file-system FDESC
     Includes code for a file system, conventionally mounted on /dev/fd, which permits access to
     the per-process file descriptor space via special files in the file system.  See
     mount_fdesc(8) for details.  Note that this facility is redundant, and thus unneeded on most
     NetBSD systems, since the fd(4) pseudo-device driver already provides identical functional-
     ity.  On most NetBSD systems, instances of fd(4) are mknoded under /dev/fd/ and on
     /dev/stdin, /dev/stdout, and /dev/stderr.

     file-system KERNFS
     Includes code which permits the mounting of a special file system (normally mounted on
     /kern) in which files representing various kernel variables and parameters may be found.
     See mount_kernfs(8) for details.

     file-system NULLFS
     Includes code for a loopback file system.	This permits portions of the file hierarchy to be
     re-mounted in other places.  The code really exists to provide an example of a stackable
     file system layer.  See mount_null(8) for details.

     file-system OVERLAY
     Includes code for a file system filter.  This permits the overlay file system to intercept
     all access to an underlying file system.  This file system is intended to serve as an exam-
     ple of a stacking file system which has a need to interpose itself between an underlying
     file system and all other access.	See mount_overlay(8) for details.

     file-system PROCFS
     Includes code for a special file system (conventionally mounted on /proc) in which the
     process space becomes visible in the file system.	Among other things, the memory spaces of
     processes running on the system are visible as files, and signals may be sent to processes
     by writing to ctl files in the procfs namespace.  See mount_procfs(8) for details.

     file-system UDF
     [EXPERIMENTAL] Includes code for the UDF file system commonly found on CD and DVD media but
     also on USB sticks.  Currently supports read and write access upto UDF 2.01 and somewhat
     limited write support for UDF 2.50.  It is marked experimental since there is no
     fsck_udf(8).  See mount_udf(8) for details.

     file-system UMAPFS
     Includes a loopback file system in which user and group IDs may be remapped -- this can be
     useful when mounting alien file systems with different UIDs and GIDs than the local system.
     See mount_umap(8) for details.

     file-system UNION
     [EXPERIMENTAL] Includes code for the union file system, which permits directories to be
     mounted on top of each other in such a way that both file systems remain visible -- this
     permits tricks like allowing writing (and the deleting of files) on a read-only file system
     like a CD-ROM by mounting a local writable file system on top of the read-only file system.
     See mount_union(8) for details.

     file-system CODA
     [EXPERIMENTAL] Includes code for the Coda file system.  Coda is a distributed file system
     like NFS and AFS.	It is freely available, like NFS, but it functions much like AFS in being
     a ``stateful'' file system.  Both Coda and AFS cache files on your local machine to improve
     performance.  Then Coda goes a step further than AFS by letting you access the cached files
     when there is no available network, viz. disconnected laptops and network outages.  In Coda,
     both the client and server are outside the kernel which makes them easier to experiment
     with.  Coda is available for several UNIX and non-UNIX platforms.	See
     http://www.coda.cs.cmu.edu for more details.  NOTE: You also need to enable the pseudo-
     device, vcoda, for the Coda file system to work.

     file-system SMBFS
     [EXPERIMENTAL] Includes code for the SMB/CIFS file system.  See mount_smbfs(8) for details.
     NOTE: You also need to enable the pseudo-device, nsmb, for the SMB file system to work.

     file-system PTYFS
     [EXPERIMENTAL] Includes code for a special file system (normally mounted on /dev/pts) in
     which pseudo-terminal slave devices become visible in the file system.  See mount_ptyfs(8)
     for details.

     file-system TMPFS
     Includes code for the efficient memory file system, normally used over /tmp.  See
     mount_tmpfs(8) for details.

     file-system PUFFS
     Includes kernel support for the pass-to-userspace framework file system.  It can be used to
     implement file system functionality in userspace.	See puffs(3) for more details.	This
     enables for example sshfs: mount_psshfs(8).

   File System Options
     options MAGICLINKS
     Enables the expansion of special strings (beginning with ``@'') when traversing symbolic
     links.  See symlink(7) for a list of supported strings.  Note that this option only controls
     the enabling of this feature by the kernel at boot-up.  This feature can still be manipu-
     lated with the sysctl(8) command regardless of the setting of this option.

     options NFSSERVER
     Include the server side of the NFS (Network File System) remote file sharing protocol.
     Although the bulk of the code implementing NFS is kernel based, several user level daemons
     are needed for it to work.  See mountd(8) and nfsd(8) for details.

     options QUOTA
     Enables kernel support for file system quotas.  See quotaon(8), edquota(8), and quota(1) for
     details.  Note that quotas only work on ``ffs'' file systems, although rpc.rquotad(8) per-
     mits them to be accessed over NFS.

     options QUOTA2
     Enables kernel support for the new file system quotas format.  See tunefs(8), newfs(8),
     mount_mfs(8), edquota(8), and quota(1) for details.  Note that quota2 is only supported by
     ``ffs'' and ``mfs'' file systems at this time.

     options FFS_EI
     Enable ``Endian-Independent'' FFS support.  This allows a system to mount an FFS file system
     created for another architecture, at a small performance cost for all FFS file systems.  See
     also newfs(8), fsck_ffs(8), dumpfs(8) for file system byte order status and manipulation.

     options FFS_NO_SNAPSHOT
     Disable the ``file system snapshot'' support in FFS file systems.	Maybe useful for install
     media kernels, small memory systems and embedded systems which don't require the snapshot

     options UFS_EXTATTR
     Enable extended attribute support for UFS1 filesystems.

     options WAPBL
     Enable ``Write Ahead Physical Block Logging file system journaling''.  This provides rapid
     file system consistency checking after a system outage.  It also provides better general use
     performance over regular FFS.  See also wapbl(4).

     options NVNODE=integer
     This option sets the size of the cache used by the name-to-inode translation routines,
     (a.k.a. the namei() cache, though called by many other names in the kernel source).  By
     default, this cache has NPROC (set as 20 + 16 * MAXUSERS) * (80 + NPROC / 8) entries.  A
     reasonable way to derive a value of NVNODE, should you notice a large number of namei cache
     misses with a tool such as systat(1), is to examine your system's current computed value
     with sysctl(8), (which calls this parameter "kern.maxvnodes") and to increase this value
     until either the namei cache hit rate improves or it is determined that your system does not
     benefit substantially from an increase in the size of the namei cache.

     Causes the namei cache to always enter a reverse mapping (vnode -> name) as well as a normal
     one.  Normally, this is already done for directory vnodes, to speed up the getcwd operation.
     This option will cause longer hash chains in the reverse cache, and thus slow down getcwd
     somewhat.	However, it does make vnode -> path translations possible in some cases.  For
     now, only useful if strict /proc/#/maps emulation for Linux binaries is required.

     options EXT2FS_SYSTEM_FLAGS
     This option changes the behavior of the APPEND and IMMUTABLE flags for a file on an ext2
     file system.  Without this option, the superuser or owner of the file can set and clear
     them.  With this option, only the superuser can set them, and they can't be cleared if the
     securelevel is greater than 0.  See also chflags(1) and secmodel_securelevel(9).

     options NFS_BOOT_BOOTP
     Enable use of the BOOTP protocol (RFCs 951 and 1048) to get configuration information if NFS
     is used to mount the root file system.  See diskless(8) for details.

     options NFS_BOOT_DHCP
     Same as ``NFS_BOOT_BOOTP'', but use the DHCP extensions to the BOOTP protocol (RFC 1541).

     Specifies the string sent in the bp_file field of the BOOTP / DHCP request packet.

     Enable use of the BOOTPARAM protocol, consisting of RARP and BOOTPARAM RPC, to get configu-
     ration information if NFS is used to mount the root file system.  See diskless(8) for

     options NFS_BOOT_RWSIZE=value
     Set the initial NFS read and write sizes for diskless-boot requests.  The normal default is
     8Kbytes.  This option provides a way to lower the value (e.g., to 1024 bytes) as a work-
     around for buggy network interface cards or boot PROMs.  Once booted, the read and write
     request sizes can be increased by remounting the file system.  See mount_nfs(8) for details.

     options NFS_V2_ONLY
     Reduce the size of the NFS client code by omitting code that's only required for NFSv3 and
     NQNFS support, leaving only that code required to use NFSv2 servers.

     options UFS_DIRHASH
     Increase lookup performance by maintaining in-core hash tables for large directories.

   Buffer queue strategy options
     The following options enable alternative buffer queue strategies.

     options BUFQ_READPRIO
     Enable experimental buffer queue strategy for disk I/O.  In the default strategy, outstand-
     ing disk requests are ordered by sector number and sent to the disk, regardless of whether
     the operation is a read or write; this option gives priority to issuing read requests over
     write requests.  Although requests may therefore be issued out of sector-order, causing more
     seeks and thus lower overall throughput, interactive system responsiveness under heavy disk
     I/O load may be improved, as processes blocking on disk reads are serviced sooner (file
     writes typically don't cause applications to block).  The performance effect varies greatly
     depending on the hardware, drive firmware, file system configuration, workload, and desired
     performance trade-off.  Systems using drive write-cache (most modern IDE disks, by default)
     are unlikely to benefit and may well suffer; such disks acknowledge writes very quickly, and
     optimize them internally according to physical layout.  Giving these disks as many requests
     to work with as possible (the standard strategy) will typically produce the best results,
     especially if the drive has a large cache; the drive will silently complete writes from
     cache as it seeks for reads.  Disks that support a large number of concurrent tagged
     requests (SCSI disks and many hardware RAID controllers) expose this internal scheduling
     with tagged responses, and don't block for reads; such disks may not see a noticeable dif-
     ference with either strategy.  However, if IDE disks are run with write-cache disabled for
     safety, writes are not acknowledged until actually completed, and only one request can be
     outstanding; a large number of small writes in one locality can keep the disk busy, starving
     reads elsewhere on the disk.  Such systems are likely to see the most benefit from this
     option.  Finally, the performance interaction of this option with ffs soft dependencies can
     be subtle, as that mechanism can drastically alter the workload for file system metadata

     options BUFQ_PRIOCSCAN
     Enable another buffer queue strategy for disk I/O, per-priority cyclical scan.

     options NEW_BUFQ_STRATEGY
     Synonym of BUFQ_READPRIO.

   Miscellaneous Options
     options CPU_UCODE
     Support cpu microcode loading via cpuctl(8).

     This option makes the md(4) RAM disk size dynamically sized.  It is incompatible with

     options MEMORY_DISK_HOOKS
     This option allows for some machine dependent functions to be called when the md(4) RAM disk
     driver is configured.  This can result in automatically loading a RAM disk from floppy on
     open (among other things).

     options MEMORY_DISK_IS_ROOT
     Forces the md(4) RAM disk to be the root device.  This can only be overridden when the ker-
     nel is booted in the 'ask-for-root' mode.

     options MEMORY_DISK_ROOT_SIZE=integer
     Allocates the given number of 512 byte blocks as memory for the md(4) RAM disk, to be popu-
     lated with mdsetimage(8).

     options MEMORY_DISK_SERVER=0
     Do not include the interface to a userland memory disk server process.  Per default, this
     option is set to 1, including the support code.  Useful for install media kernels.

     options MEMORY_DISK_RBFLAGS=value
     This option sets the reboot(2) flags used when booting with a memory disk as root file sys-
     tem.  Possible values include RB_AUTOBOOT (boot in the usual fashion - default value), and
     RB_SINGLE (boot in single-user mode).

     options MODULAR
     Enables the framework for kernel modules (see module(7)).

     options VND_COMPRESSION
     Enables the vnd(4) driver to also handle compressed images.  See vndcompress(1), vnd(4) and
     vnconfig(8) for more information.

     options SPLDEBUG
     Help the kernel programmer find bugs related to the interrupt priority level.  When
     spllower() or splraise() changes the current CPU's interrupt priority level to or from
     IPL_HIGH, record a backtrace.  Read return_address(9) for caveats about collecting back-
     traces.  This feature is experimental, and it is only available on i386.  See

     options TFTPROOT
     Download the root memory disk through TFTP at root mount time.  This enables the use of a
     root RAM disk without requiring it to be embedded in the kernel using mdsetimage(8).  The
     RAM disk name is obtained using DHCP's filename parameter.  This option requires

     options MALLOC_NOINLINE
     Time critical fixed size memory allocation is performed with MALLOC() and FREE().	Normally
     these expand to inline code, but with MALLOC_NOINLINE these call the normal malloc() and
     free() functions.	Useful for install media kernels, small memory systems and embedded sys-

     options HZ=integer
     On ports that support it, set the system clock frequency (see hz(9)) to the supplied value.
     Handle with care.

     options NTP
     Turns on in-kernel precision timekeeping support used by software implementing NTP (Network
     Time Protocol, RFC 1305).	The NTP option adds an in-kernel Phase-Locked Loop (PLL) for nor-
     mal NTP operation, and a Frequency-Locked Loop (FLL) for intermittently-connected operation.
     ntpd(8) will employ a user-level PLL when kernel support is unavailable, but the in-kernel
     version has lower latency and more precision, and so typically keeps much better time.

     The interface to the kernel NTP support is provided by the ntp_adjtime(2) and ntp_gettime(2)
     system calls, which are intended for use by ntpd(8) and are enabled by the option.  On sys-
     tems with sub-microsecond resolution timers, or where (HZ / 100000) is not an integer, the
     NTP option also enables extended-precision arithmetic to keep track of fractional clock
     ticks at NTP time-format precision.

     options PPS_SYNC
     This option enables a kernel serial line discipline for receiving time phase signals from an
     external reference clock such as a radio clock.  (The NTP option (which see) must be on if
     the PPS_SYNC option is used).  Some reference clocks generate a Pulse Per Second (PPS) sig-
     nal in phase with their time source.  The PPS line discipline receives this signal on either
     the data leads or the DCD control lead of a serial port.

     NTP uses the PPS signal to discipline the local clock oscillator to a high degree of preci-
     sion (typically less than 50 microseconds in time and 0.1 ppm in accuracy).  PPS can also
     generate a serial output pulse when the system receives a PPS interrupt.  This can be used
     to measure the system interrupt latency and thus calibrate NTP to account for it.	Using PPS
     usually requires a gadget box to convert from TTL to RS-232 signal levels.  The gadget box
     and PPS are described in more detail in the HTML documentation for ntpd(8) in

     NetBSD currently supports this option in com(4) and zsc(4).

     options SETUIDSCRIPTS
     Allows scripts with the setuid bit set to execute as the effective user rather than the real
     user, just like binary executables.

     NOTE: Using this option will also enable options FDSCRIPTS

     options FDSCRIPTS
     Allows execution of scripts with the execute bit set, but not the read bit, by opening the
     file and passing the file descriptor to the shell, rather than the filename.

     NOTE: Execute only (non-readable) scripts will have argv[0] set to /dev/fd/*.  What this
     option allows as far as security is concerned, is the ability to safely ensure that the cor-
     rect script is run by the interpreter, as it is passed as an already open file.

     options PUCCN
     Enables treating serial ports found on PCI boards puc(4) as potential console devices.  The
     method for choosing such a console device is port dependent.

     options RTC_OFFSET=integer
     The kernel (and typically the hardware battery backed-up clock on those machines that have
     one) keeps time in UTC (Universal Coordinated Time, once known as GMT, or Greenwich Mean
     Time) and not in the time of the local time zone.	The RTC_OFFSET option is used on some
     ports (such as the i386) to tell the kernel that the hardware clock is offset from UTC by
     the specified number of minutes.  This is typically used when a machine boots several oper-
     ating systems and one of them wants the hardware clock to run in the local time zone and not
     in UTC, e.g.  RTC_OFFSET=300 means the hardware clock is set to US Eastern Time (300 minutes
     behind UTC), and not UTC.	(Note: RTC_OFFSET is used to initialize a kernel variable named
     rtc_offset which is the source actually used to determine the clock offset, and which may be
     accessed via the kern.rtc_offset sysctl variable.	See sysctl(8) and sysctl(3) for details.
     Since the kernel clock is initialized from the hardware clock very early in the boot
     process, it is not possible to meaningfully change rtc_offset in system initialization
     scripts.  Changing this value currently may only be done at kernel compile time or by patch-
     ing the kernel and rebooting).

     NOTE: Unfortunately, in many cases where the hardware clock is kept in local time, it is
     adjusted for Daylight Savings Time; this means that attempting to use RTC_OFFSET to let
     NetBSD coexist with such an operating system, like Windows, would necessitate changing
     RTC_OFFSET twice a year.  As such, this solution is imperfect.

     options KMEMSTATS
     The kernel memory allocator, malloc(9), will keep statistics on its performance if this
     option is enabled.  Unfortunately, this option therefore essentially disables the MALLOC()
     and FREE() forms of the memory allocator, which are used to enhance the performance of cer-
     tain critical sections of code in the kernel.  This option therefore can lead to a signifi-
     cant decrease in the performance of certain code in the kernel if enabled.  Examples of such
     code include the namei() routine, the ccd(4) driver, and much of the networking code.

     options MAXUPRC=integer
     Sets the soft RLIMIT_NPROC resource limit, which specifies the maximum number of simultane-
     ous processes a user is permitted to run, for process 0; this value is inherited by its
     child processes.  It defaults to CHILD_MAX, which is currently defined to be 160.	Setting
     MAXUPRC to a value less than CHILD_MAX is not permitted, as this would result in a violation
     of the semantics of ISO/IEC 9945-1:1990 (``POSIX.1'').

     options NOFILE=integer
     Sets the soft RLIMIT_NOFILE resource limit, which specifies the maximum number of open file
     descriptors for each process; this value is inherited by its child processes.  It defaults
     to OPEN_MAX, which is currently defined to be 64.

     options MAXFILES=integer
     Sets the default value of the kern.maxfiles sysctl variable, which indicates the maximum
     number of files that may be open in the system.

     options DEFCORENAME=string
     Sets the default value of the kern.defcorename sysctl variable, otherwise it is set to
     %n.core.  See sysctl(8) and sysctl(3) for details.

     options RASOPS_CLIPPING
     Enables clipping within the rasops raster-console output system.  NOTE: only available on
     architectures that use rasops for console output.

     options RASOPS_SMALL
     Removes optimized character writing code from the rasops raster-console output system.
     NOTE: only available on architectures that use rasops for console output.

     Embeds the kernel config file used to define the kernel in the kernel binary itself.  The
     embedded data also includes any files directly included by the config file itself, e.g.
     GENERIC.local or std.$MACHINE.  The embedded config file can be extracted from the resulting
     kernel with config(1) -x, or by the following command:

	   strings netbsd | sed -n 's/^_CFG_//p' | unvis

     Similar to the above option, but includes just the actual config file, not any included

     options PIPE_SOCKETPAIR
     Use slower, but smaller socketpair(2)-based pipe implementation instead of default faster,
     but bigger one.  Primarily useful for installation kernels.

     options USERCONF
     Compiles in the in-kernel device configuration manager.  See userconf(4) for details.

     options PERFCTRS
     Compiles in kernel support for CPU performance-monitoring counters.  See pmc(1) for details.
     NOTE: not available on all architectures.

     options SYSCALL_STATS
     Count the number of times each system call number is called.  The values can be read through
     the sysctl interface and displayed using systat(1).  NOTE: not yet available on all archi-

     options SYSCALL_TIMES
     Count the time spent (using cpu_counter32()) in each system call.	NOTE: Using this option
     will also enable options SYSCALL_STATS.

     Force use of cpu_counter32() even if cpu_hascounter() reports false.  Useful for systems
     where the cycle counter doesn't run at a constant rate (e.g. Soekris boxes).

     options XSERVER_DDB
     A supplement to XSERVER that adds support for entering ddb(4) while in X11.

     options FILEASSOC
     Support for fileassoc(9).

     options FILEASSOC_NHOOKS=integer
     Number of storage slots per file for fileassoc(9).  Default is 4.

   Networking Options
     options GATEWAY
     Enables IPFORWARDING (which see) and (on most ports) increases the size of NMBCLUSTERS
     (which see).  In general, GATEWAY is used to indicate that a system should act as a router,
     and IPFORWARDING is not invoked directly.	(Note that GATEWAY has no impact on protocols
     other than IP, such as CLNP).  GATEWAY option also compiles IPv4 and IPv6 fast forwarding
     code into the kernel.

     options ICMPPRINTFS
     The ICMPPRINTFS option will enable debugging information to be printed about the icmp(4)

     options IPFORWARDING=value
     If value is 1 this enables IP routing behavior.  If value is 0 (the default), it disables
     it.  The GATEWAY option sets this to 1 automatically.  With this option enabled, the machine
     will forward IP datagrams destined for other machines between its interfaces.  Note that
     even without this option, the kernel will still forward some packets (such as source routed
     packets) -- removing GATEWAY and IPFORWARDING is insufficient to stop all routing through a
     bastion host on a firewall -- source routing is controlled independently.	To turn off
     source routing, use options IPFORWSRCRT=0 (which see).  Note that IP forwarding may be
     turned on and off independently of the setting of the IPFORWARDING option through the use of
     the net.inet.ip.forwarding sysctl variable.  If net.inet.ip.forwarding is 1, IP forwarding
     is on.  See sysctl(8) and sysctl(3) for details.

     options IPFORWSRCRT=value
     If value is set to zero, source routing of IP datagrams is turned off.  If value is set to
     one (the default) or the option is absent, source routed IP datagrams are forwarded by the
     machine.  Note that source routing of IP packets may be turned on and off independently of
     the setting of the IPFORWSRCRT option through the use of the net.inet.ip.forwsrcrt sysctl
     variable.	If net.inet.ip.forwsrcrt is 1, forwarding of source routed IP datagrams is on.
     See sysctl(8) and sysctl(3) for details.

     options IFA_STATS
     Tells the kernel to maintain per-address statistics on bytes sent and received over (cur-
     rently) Internet and AppleTalk addresses.	The option is not recommended as it degrades sys-
     tem stability.

     options IFQ_MAXLEN=value
     Increases the allowed size of the network interface packet queues.  The default queue size
     is 50 packets, and you do not normally need to increase it.

     options IPSELSRC
     Includes support for source-address selection policies.  See in_getifa(9).

     options MROUTING
     Includes support for IP multicast routers.  You certainly want INET with this.  Multicast
     routing is controlled by the mrouted(8) daemon.  See also option PIM.

     options PIM
     Includes support for Protocol Independent Multicast (PIM) routing.  You need MROUTING and
     INET with this.  Software using this can be found e.g. in pkgsrc/net/xorp.

     options INET
     Includes support for the TCP/IP protocol stack.  You almost certainly want this.  See
     inet(4) for details.

     options INET6
     Includes support for the IPv6 protocol stack.  See inet6(4) for details.  Unlike INET, INET6
     enables multicast routing code as well.  This option requires INET at this moment, but it
     should not.

     options ND6_DEBUG
     The option sets the default value of net.inet6.icmp6.nd6_debug to 1, for debugging IPv6
     neighbor discovery protocol handling.  See sysctl(3) for details.

     options IPSEC
     Includes support for the IPsec protocol, using the FAST_IPSEC implementation.  See
     fast_ipsec(4) for details.  (This option is an alias for the FAST_IPSEC option described

     options KAME_IPSEC
     Includes support for the IPsec protocol, using the KAME implementation.  See kame_ipsec(4)
     for details.

     options IPSEC_DEBUG
     Enables debugging code in IPsec stack.  See ipsec(4) for details.

     options IPSEC_ESP
     Includes support for IPsec ESP protocol, using the KAME implementation.  See kame_ipsec(4)
     for details.

     options FAST_IPSEC
     Includes support for the IPsec protocol, using the implementation derived from OpenBSD,
     relaying on opencrypto(9) to carry out cryptographic operations.  See fast_ipsec(4) for

     options IPSEC_NAT_T
     Includes support for IPsec Network Address Translator traversal (NAT-T), as described in
     RFCs 3947 and 3948.  This feature might be patent-encumbered in some countries.

     options ALTQ
     Enabled ALTQ (Alternate Queueing).  For simple rate-limiting, use tbrconfig(8) to set up the
     interface transmission rate.  To use queueing disciplines, their appropriate kernel options
     should also be defined (documented below).  Queueing disciplines are managed by altqd(8).
     See altq(9) for details.

     options ALTQ_HFSC
     Include support for ALTQ-implemented HFSC (Hierarchical Fair Service Curve) module.  HFSC
     supports both link-sharing and guaranteed real-time services.  HFSC employs a service curve
     based QoS model, and its unique feature is an ability to decouple delay and bandwidth allo-
     cation.  Requires ALTQ_RED to use the RED queueing discipline on HFSC classes, or ALTQ_RIO
     to use the RIO queueing discipline on HFSC classes.  This option assumes ALTQ.

     options ALTQ_PRIQ
     Include support for ALTQ-implemented PRIQ (Priority Queueing).  PRIQ implements a simple
     priority-based queueing discipline.  A higher priority class is always served first.
     Requires ALTQ_RED to use the RED queueing discipline on HFSC classes, or ALTQ_RIO to use the
     RIO queueing discipline on HFSC classes.  This option assumes ALTQ.

     options ALTQ_WFQ
     Include support for ALTQ-implemented WFQ (Weighted Fair Queueing).  WFQ implements a
     weighted-round robin scheduler for a set of queues.  A weight can be assigned to each queue
     to give a different proportion of the link capacity.  A hash function is used to map a flow
     to one of a set of queues.  This option assumes ALTQ.

     options ALTQ_FIFOQ
     Include support for ALTQ-implemented FIFO queueing.  FIFOQ is a simple drop-tail FIFO (First
     In, First Out) queueing discipline.  This option assumes ALTQ.

     options ALTQ_RIO
     Include support for ALTQ-implemented RIO (RED with In/Out).  The original RIO has 2 sets of
     RED parameters; one for in-profile packets and the other for out-of-profile packets.  At the
     ingress of the network, profile meters tag packets as IN or OUT based on contracted profiles
     for customers.  Inside the network, IN packets receive preferential treatment by the RIO
     dropper.  ALTQ/RIO has 3 drop precedence levels defined for the Assured Forwarding PHB of
     DiffServ (RFC 2597).  This option assumes ALTQ.

     options ALTQ_BLUE
     Include support for ALTQ-implemented Blue buffer management.  Blue is another active buffer
     management mechanism.  This option assumes ALTQ.

     options ALTQ_FLOWVALVE
     Include support for ALTQ-implemented Flowvalve.  Flowvalve is a simple implementation of a
     RED penalty box that identifies and punishes misbehaving flows.  This option requires
     ALTQ_RED and assumes ALTQ.

     options ALTQ_CDNR
     Include support for ALTQ-implemented CDNR (diffserv traffic conditioner) packet mark-
     ing/manipulation.	Traffic conditioners are components to meter, mark, or drop incoming
     packets according to some rules.  As opposed to queueing disciplines, traffic conditioners
     handle incoming packets at an input interface.  This option assumes ALTQ.

     options ALTQ_NOPCC
     Disables use of processor cycle counter to measure time in ALTQ.  This option should be
     defined for a non-Pentium i386 CPU which does not have TSC, SMP (per-CPU counters are not in
     sync), or power management which affects processor cycle counter.	This option assumes ALTQ.

     options ALTQ_IPSEC
     Include support for IPsec in IPv4 ALTQ.  This option assumes ALTQ.

     options ALTQ_JOBS
     Include support for ALTQ-implemented JoBS (Joint Buffer Management and Scheduling).  This
     option assumes ALTQ.

     options ALTQ_AFMAP
     Include support for an undocumented ALTQ feature that is used to map an IP flow to an ATM VC
     (Virtual Circuit).  This option assumes ALTQ.

     options ALTQ_LOCALQ
     Include support for ALTQ-implemented local queues.  Its practical use is undefined.  Assumes

     Sets default value for net.inet.ip.subnetsarelocal variable, which controls whether non-
     directly-connected subnets of connected networks are considered "local" for purposes of
     choosing the MSS for a TCP connection.  This is mostly present for historic reasons and com-
     pletely irrelevant if you enable Path MTU discovery.

     Sets default value for net.inet.ip.hostzerobroadcast variable, which controls whether the
     zeroth host address of each connected subnet is also considered a broadcast address.
     Default value is "1", for compatibility with old systems; if this is set to zero on all
     hosts on a subnet, you should be able to fit an extra host per subnet on the ".0" address.

     options MCLSHIFT=value
     This option is the base-2 logarithm of the size of mbuf clusters.	The BSD networking stack
     keeps network packets in a linked list, or chain, of kernel buffer objects called mbufs.
     The system provides larger mbuf clusters as an optimization for large packets, instead of
     using long chains for large packets.  The mbuf cluster size, or MCLBYTES, must be a power of
     two, and is computed as two raised to the power MCLSHIFT.	On systems with Ethernet network
     adapters, MCLSHIFT is often set to 11, giving 2048-byte mbuf clusters, large enough to hold
     a 1500-byte Ethernet frame in a single cluster.  Systems with network interfaces supporting
     larger frame sizes like ATM, FDDI, or HIPPI may perform better with MCLSHIFT set to 12 or
     13, giving mbuf cluster sizes of 4096 and 8192 bytes, respectively.

     options ISO,TPIP
     Include support for the ubiquitous OSI protocol stack.  See iso(4) for details.  This option
     assumes INET.

     options EON
     Include support for tunneling OSI protocols over IP.  Known to be broken, or at least very
     fragile, and undocumented.

     options NETATALK
     Include support for the AppleTalk protocol stack.	The kernel provides provision for the
     Datagram Delivery Protocol (DDP), providing SOCK_DGRAM support and AppleTalk routing.  This
     stack is used by the NETATALK package, which adds support for AppleTalk server services via
     user libraries and applications.

     options BLUETOOTH
     Include support for the Bluetooth protocol stack.	See bluetooth(4) for details.

     options IPNOPRIVPORTS
     Normally, only root can bind a socket descriptor to a so-called ``privileged'' TCP port,
     that is, a port number in the range 0-1023.  This option eliminates those checks from the
     kernel.  This can be useful if there is a desire to allow daemons without privileges to bind
     those ports, e.g., on firewalls.  The security tradeoffs in doing this are subtle.  This
     option should only be used by experts.

     options TCP_COMPAT_42
     TCP bug compatibility with 4.2BSD.  In 4.2BSD, TCP sequence numbers were 32-bit signed val-
     ues.  Modern implementations of TCP use unsigned values.  This option clamps the initial
     sequence number to start in the range 2^31 rather than the full unsigned range of 2^32.
     Also, under 4.2BSD, keepalive packets must contain at least one byte or else the remote end
     would not respond.

     options TCP_DEBUG
     Record the last TCP_NDEBUG TCP packets with SO_DEBUG set, and decode to the console if
     tcpconsdebug is set.

     options TCP_NDEBUG
     Number of packets to record for TCP_DEBUG.  Defaults to 100.

     options TCP_SENDSPACE=value

     options TCP_RECVSPACE=value
     These options set the max TCP window size to other sizes than the default.  The TCP window
     sizes can be altered via sysctl(8) as well.

     options TCP_INIT_WIN=value
     This option sets the initial TCP window size for non-local connections, which is used when
     the transmission starts.  The default size is 1, but if the machine should act more aggres-
     sively, the initial size can be set to some other value.  The initial TCP window size can be
     set via sysctl(8) as well.

     options PFIL_HOOKS
     This option turns on the packet filter interface hooks.  See pfil(9) for details.	This
     option assumes INET.

     options IPFILTER_LOG
     This option, in conjunction with pseudo-device ipfilter, enables logging of IP packets using

     options IPFILTER_LOOKUP
     This option enables the IP-Filter ippool(8) functionality to be enabled.

     options IPFILTER_COMPAT
     This option enables older IP-Filter binaries to work.

     This option sets the default policy of IP-Filter.	If it is set, IP-Filter will block pack-
     ets by default.

     options BRIDGE_IPF
     This option causes bridge devices to use the IP and/or IPv6 filtering hooks, forming a link-
     layer filter that uses protocol-layer rules.  This option assumes the presence of
     pseudo-device ipfilter.

     options MBUFTRACE
     This option can help track down mbuf leaks.  When enabled, mbufs are tagged with the devices
     and protocols using them, which slightly decreases network performance.  This additional
     information can be viewed with netstat(1):
	   netstat -mssv
     Not all devices or protocols support this option.

   Sysctl Related Options
     Disallows the creation or deletion of nodes from the sysctl tree, as well as the assigning
     of descriptions to nodes that lack them, by any process.  These operations are still avail-
     able to kernel sub-systems, including loadable kernel modules.

     Prevents processes from adding nodes to the sysctl tree that make existing kernel memory
     areas writable.  Sections of kernel memory can still be read and new nodes that own their
     own data may still be writable.

     Causes the SYSCTL_SETUP routines to print a brief message when they are invoked.  This is
     merely meant as an aid in determining the order in which sections of the tree are created.

     Prints a message each time sysctl_create(), the function that adds nodes to the tree, is

     Causes the kernel to include short, human readable descriptions for nodes in the sysctl
     tree.  The descriptions can be retrieved programmatically (see sysctl(3)), or by the sysctl
     binary itself (see sysctl(8)).  The descriptions are meant to give an indication of the pur-
     pose and/or effects of a given node's value, not replace the documentation for the given
     subsystem as a whole.

   System V IPC Options
     options SYSVMSG
     Includes support for AT&T System V UNIX style message queues.  See msgctl(2), msgget(2),
     msgrcv(2), msgsnd(2).

     options SYSVSEM
     Includes support for AT&T System V UNIX style semaphores.	See semctl(2), semget(2),

     options SEMMNI=value
     Sets the number of AT&T System V UNIX style semaphore identifiers.  The GENERIC config file
     for your port will have the default.

     options SEMMNS=value
     Sets the number of AT&T System V UNIX style semaphores in the system.  The GENERIC config
     file for your port will have the default.

     options SEMUME=value
     Sets the maximum number of undo entries per process for AT&T System V UNIX style semaphores.
     The GENERIC config file for your port will have the default.

     options SEMMNU=value
     Sets the number of undo structures in the system for AT&T System V UNIX style semaphores.
     The GENERIC config file for your port will have the default.

     options SYSVSHM
     Includes support for AT&T System V UNIX style shared memory.  See shmat(2), shmctl(2),
     shmdt(2), shmget(2).

     options SHMMAXPGS=value
     Sets the maximum number of AT&T System V UNIX style shared memory pages that are available
     through the shmget(2) system call.  Default value is 1024 on most ports.  See
     /usr/include/machine/vmparam.h for the default.

   VM Related Options
     options NMBCLUSTERS=value
     The number of mbuf clusters the kernel supports.  Mbuf clusters are MCLBYTES in size (usu-
     ally 2k).	This is used to compute the size of the kernel VM map mb_map, which maps mbuf
     clusters.	Default on most ports is 1024 (2048 with ``options GATEWAY'' ).  See
     /usr/include/machine/param.h for exact default information.  Increase this value if you get
     ``mclpool limit reached'' messages.

     options NKMEMPAGES=value

     options NKMEMPAGES_MIN=value

     options NKMEMPAGES_MAX=value
     Size of kernel VM map kmem_map, in PAGE_SIZE-sized chunks (the VM page size; this value may
     be read from the sysctl(8) variable hw.pagesize ).  This VM map is used to map the kernel
     malloc arena.  The kernel attempts to auto-size this map based on the amount of physical
     memory in the system.  Platform-specific code may place bounds on this computed size, which
     may be viewed with the sysctl(8) variable vm.nkmempages.  See /usr/include/machine/param.h
     for the default upper and lower bounds.  The related options 'NKMEMPAGES_MIN' and
     'NKMEMPAGES_MAX' allow the bounds to be overridden in the kernel configuration file.  These
     options are provided in the event the computed value is insufficient resulting in an ``out
     of space in kmem_map'' panic.

     options SB_MAX=value
     Sets the max size in bytes that a socket buffer is allowed to occupy.  The default is 256k,
     but sometimes it needs to be increased, for example when using large TCP windows.	This
     option can be changed via sysctl(8) as well.

     options SOMAXKVA=value
     Sets the maximum size of kernel virtual memory that the socket buffers are allowed to use.
     The default is 16MB, but in situations where for example large TCP windows are used this
     value must also be increased.  This option can be changed via sysctl(8) as well.

     options BUFCACHE=value
     Size of the buffer cache as a percentage of total available RAM.  Ignored if BUFPAGES is
     also specified.

     options NBUF=value
     Sets the number of buffer headers available, i.e., the number of open files that may have a
     buffer cache entry.  Each buffer header requires MAXBSIZE (machine dependent, but usually
     65536) bytes.  The default value is machine dependent, but is usually equal to the value of
     BUFPAGES.	If an architecture dependent VM_MAX_KERNEL_BUF constant is defined then NBUF may
     be reduced at run time so that the storage allocated for buffer headers doesn't exceed that

     options BUFPAGES=value
     These options set the number of pages available for the buffer cache.  Their default value
     is a machine dependent value, often calculated as between 5% and 10% of total available RAM.

     options MAXTSIZ=bytes
     Sets the maximum size limit of a process' text segment.  See /usr/include/machine/vmparam.h
     for the port-specific default.

     options DFLDSIZ=bytes
     Sets the default size limit of a process' data segment, the value that will be returned as
     the soft limit for RLIMIT_DATA (as returned by getrlimit(2)).  See
     /usr/include/machine/vmparam.h for the port-specific default.

     options MAXDSIZ=bytes
     Sets the maximum size limit of a process' data segment, the value that will be returned as
     the hard limit for RLIMIT_DATA (as returned by getrlimit(2)).  See
     /usr/include/machine/vmparam.h for the port-specific default.

     options DFLSSIZ=bytes
     Sets the default size limit of a process' stack segment, the value that will be returned as
     the soft limit for RLIMIT_STACK (as returned by getrlimit(2)).  See
     /usr/include/machine/vmparam.h for the port-specific default.

     options MAXSSIZ=bytes
     Sets the maximum size limit of a process' stack segment, the value that will be returned as
     the hard limit for RLIMIT_STACK (as returned by getrlimit(2)).  See
     /usr/include/machine/vmparam.h for the port-specific default.

     options DUMP_ON_PANIC=integer
     Defaults to one.  If set to zero, the kernel will not dump to the dump device when it pan-
     ics, though dumps can still be forced via ddb(4) with the ``sync'' command.  Note that this
     sets the value of the kern.dump_on_panic sysctl(3) variable which may be changed at run time
     -- see sysctl(8) for details.

     options USE_TOPDOWN_VM
     User space memory allocations (as made by mmap(2)) will be arranged in a ``top down'' fash-
     ion instead of the traditional ``upwards from MAXDSIZ + vm_daddr'' method.  This includes
     the placement of ld.so(1).  Arranging memory in this manner allows either (or both of) the
     heap or mmap(2) allocated space to grow larger than traditionally possible.  This option is
     not available on all ports, but is instead expected to be offered on a port-by-port basis,
     after which some ports will commit to using it by default.  See the files
     /usr/include/uvm/uvm_param.h for some implementation details, and
     /usr/include/machine/vmparam.h for port specific details including availability.

     options VMSWAP
     Enable paging device/file support.  This option is on by default.

     Use CLOCK-Pro, an alternative page replace policy.

   Security Options
     options INSECURE
     Hardwires the kernel security level at -1.  This means that the system always runs in secure
     level -1 mode, even when running multiuser.  See the manual page for init(8) for details on
     the implications of this.	The kernel secure level may manipulated by the superuser by
     altering the kern.securelevel sysctl(3) variable (the secure level may only be lowered by a
     call from process ID 1, i.e., init(8)).  See also secmodel_securelevel(9), sysctl(8) and

     options VERIFIED_EXEC_FP_MD5
     Enables support for MD5 hashes in Veriexec.

     options VERIFIED_EXEC_FP_SHA1
     Enables support for SHA1 hashes in Veriexec.

     options VERIFIED_EXEC_FP_RMD160
     Enables support for RMD160 hashes in Veriexec.

     options VERIFIED_EXEC_FP_SHA256
     Enables support for SHA256 hashes in Veriexec.

     options VERIFIED_EXEC_FP_SHA384
     Enables support for SHA384 hashes in Veriexec.

     options VERIFIED_EXEC_FP_SHA512
     Enables support for SHA512 hashes in Veriexec.

     options PAX_MPROTECT=value
     Enables PaX MPROTECT, mprotect(2) restrictions from the PaX project.

     The value is the default value for the global knob, see sysctl(3).  If 0, PaX MPROTECT will
     be enabled only if explicitly set on programs using paxctl(8).  If 1, PaX MPROTECT will be
     enabled for all programs.	Programs can be exempted using paxctl(8).

     See security(7) for more details.

     options PAX_SEGVGUARD=value
     Enables PaX Segvguard.

     The value is the default value for the global knob, see sysctl(3).  If 0, PaX Segvguard will
     be enabled only if explicitly set on programs using paxctl(8).  If 1, PaX Segvguard will be
     enabled to all programs, and exemption can be done using paxctl(8).

     See security(7) for more details.

     options PAX_ASLR=value
     Enables PaX ASLR.

     The value is the default value for the global knob, see sysctl(3).  If 0, PaX ASLR will be
     enabled only if explicitly set on programs using paxctl(8).  If 1, PaX ASLR will be enabled
     to all programs, and exemption can be done using paxctl(8).

     See security(7) for more details.

     options USER_VA0_DISABLE_DEFAULT=value
     Sets the initial value of the flag which controls whether user programs can map virtual
     address 0.  The flag can be changed at runtime by sysctl(3).

   amiga-specific Options
     options BB060STUPIDROM
     When the bootloader (which passes AmigaOS ROM information) claims we have a 68060 CPU with-
     out FPU, go look into the Processor Configuration Register (PCR) to find out.  You need this
     with Amiga ROMs up to (at least) V40.xxx (OS3.1), when you boot via the bootblocks and don't
     have a DraCo.

     options IOBZCLOCK=frequency
     The IOBlix boards come with two different serial master clocks: older ones use 24 MHz, newer
     ones use 22.1184 MHz.  The driver normally assumes the latter.  If your board uses 24 MHz,
     you can recompile your kernel with options IOBZCLOCK=24000000 or patch the kernel variable
     iobzclock to the same value.

     options LIMITMEM=value
     If there, limit the part of the first memory bank used by NetBSD to value megabytes.
     Default is unlimited.

     options NKPTADD=addvalue

     options NKPTADDSHIFT=shiftvalue
     The CPU specific MMU table for the kernel is pre-allocated at kernel startup time.  Part of
     it is scaled with maxproc, to have enough room to hold the user program MMU tables; the sec-
     ond part is a fixed amount for the kernel itself.

     The third part accounts for the size of the file buffer cache.  Its size is either NKPTADD
     pages (if defined) or memory size in bytes divided by two to the power of NKPTADDSHIFT.  The
     default is undefined NKPTADD and NKPTADDSHIFT=24, allowing for 16 buffers per megabyte of
     main memory (while a GENERIC kernel allocates about half of that).  When you get "can't get
     KPT page" panics, you should increase NKPTADD (if defined), or decrease NKPTADDSHIFT by one.

     options P5PPC68KBOARD
     Add special support for Phase5 mixed 68k+PPC boards.  Currently, this only affects rebooting
     from NetBSD and is only needed on 68040+PPC, not on 68060+PPC; without this, affected
     machines will hang after NetBSD has shut down and will only restart after a keyboard reset
     or a power cycle.

   arm32-specific Options
     options FRENCH_KBD
     Include translation for French keyboards when using pccons on a Shark.

     options FINNISH_KBD
     Include translation for Finnish keyboards when using pccons on a Shark.

     options GERMAN_KBD
     Include translation for German keyboards when using pccons on a Shark.

     options NORWEGIAN_KBD
     Include translation for French keyboards when using pccons on a Shark.

   atari-specific Options
     options DISKLABEL_AHDI
     Include support for AHDI (native Atari) disklabels.

     options DISKLABEL_NBDA
     Include support for NetBSD/atari labels.  If you don't set this option, it will be set auto-
     matically.  NetBSD/atari will not work without it.

     options FALCON_SCSI
     Include support for the 5380-SCSI configuration as found on the Falcon.

     options RELOC_KERNEL
     If set, the kernel will relocate itself to TT-RAM, if possible.  This will give you a
     slightly faster system.  Beware that on some TT030 systems, the system will frequently dump
     with MMU-faults with this option enabled.

     options SERCONSOLE
     Allow the modem1-port to act as the system-console.  A carrier should be active on modem1
     during system boot to active the console functionality.

     options TT_SCSI
     Include support for the 5380-SCSI configuration as found on the TT030 and Hades.

   i386-specific Options
     options CPURESET_DELAY=value
     Specifies the time (in millisecond) to wait before doing a hardware reset in the last phase
     of a reboot.  This gives the user a chance to see error messages from the shutdown opera-
     tions (like NFS unmounts, buffer cache flush, etc ...).  Setting this to 0 will disable the
     delay.  Default is 2 seconds.

     options VM86
     Include support for virtual 8086 mode, used by DOS emulators and X servers to run BIOS code,
     e.g., for some VESA routines.

     options USER_LDT
     Include i386-specific system calls for modifying the local descriptor table, used by Windows

     options PAE
     Enable PAE (Physical Address Extension) mode.  PAE permits up to 36 bits physical addressing
     (64GB of physical memory), and turns physical addresses to 64 bits entities in the memory
     management subsystem.  Userland virtual address space remains at 32 bits (4GB).  PAE mode is
     required to enable the NX/XD (No-eXecute/eXecute Disable) bit for pages, which allows mark-
     ing certain ones as not being executable.	Any attempt to execute code from such a page will
     raise an exception.

     options REALBASEMEM=integer
     Overrides the base memory size passed in from the boot block.  (Value given in kilobytes.)
     Use this option only if the boot block reports the size incorrectly.  (Note that some BIOSes
     put the extended BIOS data area at the top of base memory, and therefore report a smaller
     base memory size to prevent programs overwriting it.  This is correct behavior, and you
     should not use the REALBASEMEM option to access this memory).

     options REALEXTMEM=integer
     Overrides the extended memory size passed in from the boot block.	(Value given in kilo-
     bytes.  Extended memory does not include the first megabyte.)  Use this option only if the
     boot block reports the size incorrectly.

     Select a non-US keyboard layout for the pccons console driver.

     options CYRIX_CACHE_WORKS
     Relevant only to the Cyrix 486DLC CPU.  This option is used to turn on the cache in hold-
     flush mode.  It is not turned on by default because it is known to have problems in certain
     motherboard implementations.

     Relevant only to the Cyrix 486DLC CPU.  This option is used to turn on the cache in write-
     back mode.  It is not turned on by default because it is known to have problems in certain
     motherboard implementations.  In order for this option to take effect, option
     CYRIX_CACHE_WORKS must also be specified.

     options PCIBIOS
     Enable support for initializing the PCI bus using information from the BIOS.  See pcibios(4)
     for details.

     options KSTACK_CHECK_DR0
     Detect kernel stack overflow using DR0 register.  This option uses DR0 register exclusively
     so you can't use DR0 register for other purpose (e.g., hardware breakpoint) if you turn this

     options MTRR
     Include support for accessing MTRR registers from user-space.  See i386_get_mtrr(2).

     options BEEP_ONHALT
     Make the system speaker emit several beeps when it is completely safe to power down the com-
     puter after a halt(8) command.  Requires sysbeep(4) support.

     options BEEP_ONHALT_COUNT=times
     Number of times to beep the speaker when options BEEP_ONHALT is enabled.  Defaults to 3.

     options BEEP_ONHALT_PITCH=hz
     The tone frequency used when options BEEP_ONHALT option, in hertz.  Defaults to 1500.

     options BEEP_ONHALT_PERIOD=msecs
     The duration of each beep when options BEEP_ONHALT is enabled, in milliseconds.  Defaults to

     options MULTIBOOT
     Makes the kernel Multiboot-compliant, allowing it to be booted through a Multiboot-compliant
     boot manager such as GRUB.  See multiboot(8) for more information.

     options SPLASHSCREEN
     Display a splash screen during boot.

     Display a progress bar at the splash screen during boot.  This option requires SPLASHSCREEN.

   isa-specific Options
     Options specific to isa(4) busses.

     Control the section of IO bus space used for PCMCIA bus space mapping.  Ideally the probed
     defaults are satisfactory, however in practice that is not always the case.  See pcmcia(4)
     for details.

     options PCIC_ISA_INTR_ALLOC_MASK=mask
     Controls the allowable interrupts that may be used for PCMCIA devices.  This mask is a logi-
     cal-or of power-of-2s of allowable interrupts:

	 IRQ Val      IRQ Val	   IRQ Val	 IRQ Val
	  0  0x0001    4  0x0010    8  0x0100	 12  0x1000
	  1  0x0002    5  0x0020    9  0x0200	 13  0x2000
	  2  0x0004    6  0x0040   10  0x0400	 14  0x4000
	  3  0x0008    7  0x0080   11  0x0800	 15  0x8000

     Perform a self test of the keyboard controller before attaching it as a console.  This might
     be necessary on machines where we boot on cold iron, and pckbc refuses to talk until we
     request a self test.  Currently only the netwinder port uses it.

     If this option is set the PS/2 keyboard will not be used as the console if it cannot be
     found during boot.  This allows other keyboards, like USB, to be the console keyboard.

     options PCKBD_LAYOUT=layout
     Sets the default keyboard layout, see pckbd(4).

   m68k-specific Options
     options FPU_EMULATE
     Include support for MC68881/MC68882 emulator.

     options FPSP
     Include support for 68040 floating point.

     options M68020,M68030,M68040,M68060
     Include support for a specific CPU, at least one (the one you are using) should be speci-

     options M060SP
     Include software support for 68060.  This provides emulation of unimplemented integer
     instructions as well as emulation of unimplemented floating point instructions and data
     types and software support for floating point traps.

   powerpc-specific Options (OEA Only)
     options PMAP_MEMLIMIT=value
     Limit the amount of memory seen by the kernel to value bytes.

     options PTEGCOUNT=value
     Specify the size of the page table as value PTE groups.  Normally, one PTEG is allocated per
     physical page frame.

   sparc-specific Options
     options AUDIO_DEBUG
     Enable simple event debugging of the logging of the audio(4) device.

     options BLINK
     Enable blinking of LED.  Blink rate is full cycle every N seconds for N < then current load
     average.  See getloadavg(3).

     Count how many times the sw SCSI device has left 3, 2, 1 and 0 in the sw_3_leftover,
     sw_2_leftover, sw_1_leftover, and sw_0_leftover variables accessible from ddb(4).	See

     options DEBUG_ALIGN
     Adds debugging messages calls when user-requested alignment fault handling happens.

     options DEBUG_EMUL
     Adds debugging messages calls for emulated floating point and alignment fixing operations.

     options DEBUG_SVR4
     Prints registers messages calls for emulated SVR4 getcontext and setcontext operations.  See
     options COMPAT_SVR4.

     options EXTREME_DEBUG
     Adds debugging functions callable from ddb(4).  The debug_pagetables, test_region and
     print_fe_map functions print information about page tables for the SUN4M platforms only.

     Adds extra info to options EXTREME_DEBUG.

     options FPU_CONTEXT
     Make options COMPAT_SVR4 getcontext and setcontext include floating point registers.

     options MAGMA_DEBUG
     Adds debugging messages to the magma(4) device.

     Use the entire screen for the console.

     Use the Fixed font on the console, instead of the normal font.

     options SUN4
     Support sun4 class machines.

     options SUN4C
     Support sun4c class machines.

     options SUN4M
     Support sun4m class machines.

     options SUN4_MMU3L
     Enable support for sun4 3-level MMU machines.

     options V9
     Enable SPARC V9 assembler in ddb(4).

   sparc64-specific Options
     options AUDIO_DEBUG
     Enable simple event debugging of the logging of the audio(4) device.

     options BLINK
     Enable blinking of LED.  Blink rate is full cycle every N seconds for N < then current load
     average.  See getloadavg(3).

   x68k-specific Options
     options EXTENDED_MEMORY
     Include support for extended memory, e.g., TS-6BE16 and 060turbo on-board.

     options JUPITER
     Include support for Jupiter-X MPU accelerator

     options ZSCONSOLE,ZSCN_SPEED=value
     Use the built-in serial port as the system-console.  Speed is specified in bps, defaults to

     options ITE_KERNEL_ATTR=value
     Set the kernel message attribute for ITE.	Value, an integer, is a logical or of the follow-
     ing values:
	   1	 color inversed
	   2	 underlined
	   4	 bolded

     config(1), gdb(1), ktrace(1), pmc(1), quota(1), vndcompress(1), gettimeofday(2),
     i386_get_mtrr(2), i386_iopl(2), msgctl(2), msgget(2), msgrcv(2), msgsnd(2), ntp_adjtime(2),
     ntp_gettime(2), reboot(2), semctl(2), semget(2), semop(2), shmat(2), shmctl(2), shmdt(2),
     shmget(2), sysctl(3), apm(4), ddb(4), inet(4), iso(4), md(4), pcibios(4), pcmcia(4), ppp(4),
     userconf(4), vnd(4), wscons(4), config(5), edquota(8), init(8), mdsetimage(8),
     mount_cd9660(8), mount_fdesc(8), mount_kernfs(8), mount_lfs(8), mount_mfs(8),
     mount_msdos(8), mount_nfs(8), mount_ntfs(8), mount_null(8), mount_portal(8),
     mount_procfs(8), mount_udf(8), mount_umap(8), mount_union(8), mrouted(8), newfs_lfs(8),
     ntpd(8), quotaon(8), rpc.rquotad(8), sysctl(8), in_getifa(9)

     The options man page first appeared in NetBSD 1.3.

     The EON option should be a pseudo-device, and is also very fragile.

BSD					 January 13, 2012				      BSD

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