 @@ -1,2197 +1,2197 @@
-.\"	$NetBSD: options.4,v 1.517 2020/10/09 01:49:53 gutteridge Exp $
+.\"	$NetBSD: options.4,v 1.518 2021/03/14 02:56:07 rin Exp $
 .\"
 .\" Copyright (c) 1996
 .\" 	Perry E. Metzger.  All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
 .\" 3. All advertising materials mentioning features or use of this software
 .\"    must display the following acknowledgment:
 .\"	This product includes software developed for the NetBSD Project
 .\"	by Perry E. Metzger.
 .\" 4. The name of the author may not be used to endorse or promote products
 .\"    derived from this software without specific prior written permission.
 .\"
 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
 .\"
-.Dd October 9, 2020
+.Dd March 14, 2021
 .Dt OPTIONS 4
 .Os
 .Sh NAME
 .Nm options
 .Nd Miscellaneous kernel configuration options
 .Sh SYNOPSIS
 .Cd cinclude ...
 .Cd config ...
 .Cd [no] file-system ...
 .Cd ident ...
 .Cd include ...
 .Cd [no] makeoptions ...
 .Cd maxusers ...
 .Cd [no] options ...
 .Cd [no] pseudo-device ...
 .Sh DESCRIPTION
 This manual page describes a number of miscellaneous kernel
 configuration options that may be specified in a kernel config
 file.
 See
 .Xr config 1
 and
 .Xr config 5
 for information on how to configure and build kernels.
 .Pp
 The
 .Ar no
 form removes a previously specified option.
 .Ss Keywords
 The following keywords are recognized in a kernel configuration file:
 .Bl -ohang
 .It Sy cinclude Qq Ar filename
 Conditionally includes another kernel configuration file whose name is
 .Ar 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.
 .It Sy config Ar exec_name No root on Ar rootdev Oo type Ar fstype Oc \
 Oo dumps on Ar dumpdev Oc
 Defines a configuration whose kernel executable is named
 .Ar exec_name ,
 normally
 .Dq netbsd ,
 with its root file system of type
 .Ar fstype
 on the device
 .Ar rootdev ,
 and optionally specifying the location of kernel core dumps on the device
 .Ar dumpdev .
 .Ar dev
 or
 .Ar dumpdev
 and
 .Ar fstype
 may be specified as
 .Dq \&? ,
 which is a wild card.
 The root
 .Ar fstype
 and
 .Ar dumpdev
 are optional and assumed to be wild carded if they are not specified.
 .It Ar device_instance No at Ar attachment \
 Oo Ar locators value Oo ... Oc Oc Oo flags Ar value Oc
 Define an instance of the device driver
 .Ar device_instance
 that attaches to the bus or device named
 .Ar attachment .
 An
 .Ar 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
 .Ar locators ,
 whose
 .Ar value
 often may be a wild card,
 .Dq \&? .
 Some device drivers have one or more
 .Ar flags
 that can be adjusted to affect the way they operate.
 .It Sy file-system Ar fs_name Op , Ar fs_name Op ...
 Include support for the file-system
 .Ar fs_name .
 .It Sy ident Qq Ar string
 Sets the kernel identification string to
 .Ar string .
 .It Sy include Qq Ar filename
 Functions the same as
 .Ar cinclude ,
 except failure to open
 .Ar filename
 produces a fatal error.
 .It Sy makeoptions Ar name=value
 Defines a
 .Xr make 1
 macro
 .Ar name
 with the value
 .Ar value
 in the kernel Makefile.
 .It Sy maxusers Ar integer
 Set the maxusers variable in the kernel.
 .It Sy no Ar keyword Ar name Op Ar arguments Op ...
 For the
 .Xr config 1
 .Ar keywords
 file-system, makeoptions, options, and pseudo-device,
 .Ar no
 removes the file-system, makeoption, options, or pseudo-device,
 .Ar name .
 This is useful when a kernel configuration file includes another which
 has undesired options.
 .Pp
 For example, a local configuration file that wanted the kitchen sink, but
 not COMPAT_09 or bridging, might be:
 .Bd -literal -offset indent
 include "arch/i386/conf/GENERIC"
 no options COMPAT_09
 no pseudo-device bridge
 .Ed
 .It Sy options Ar option_name Op , Ar option_name=value Op ...
 Specifies (or sets) the option, or comma-separated list of options,
 .Ar 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
 .Pq Qq .
 Note that those are eventually handled by the C compiler, so the rules
 of that language apply.
 .Pp
 .Em Note :
 Options that are not defined by device definition files are passed to
 the compile process as
 .Fl D
 flags to the C compiler.
 .It Sy pseudo-device Ar name Op Ar N
 Includes support for the pseudo-device
 .Ar name .
 Some pseudo-devices can have multiple or
 .Ar N
 instances.
 .El
 .Ss Compatibility Options
 Note that compatibility options for older
 .Nx
 releases includes support for newer releases as well.
 This means that typically only one of these is necessary, with the
 .Cd COMPAT_09
 option enabling all
 .Nx
 compatibility.
 This does not include the
 .Cd COMPAT_43
 or
 .Cd COMPAT_44
 options.
 .Bl -ohang
 .It Cd options COMPAT_09
 Enable binary compatibility with
 .Nx 0.9 .
 This enables support for
 -bit user, group, and process IDs (following revisions support
 -bit identifiers).
 It also allows the use of the deprecated
 .Xr getdomainname 3 ,
 .Xr setdomainname 3 ,
 and
 .Xr uname 3
 syscalls.
 This option also allows using numeric file system identifiers rather
 than strings.
 Post
 .Nx 0.9
 versions use string identifiers.
 .It Cd options COMPAT_10
 Enable binary compatibility with
 .Nx 1.0 .
 This option allows the use of the file system name of
 .Dq ufs
 as an alias for
 .Dq ffs .
 The name
 .Dq ffs
 should be used post 1.0 in
 .Pa /etc/fstab
 and other files.
 It also adds old syscalls for the
 .At V
 shared memory interface.
 This was changed post 1.0 to work on 64-bit architectures.
 This option also enables
 .Dq sgtty
 compatibility, without which programs using the old interface produce
 an
 .Dq inappropriate ioctl
 error, and
 .Pa /dev/io
 only works when this option is set in the kernel,
 see
 .Xr io 4
 on ports that support it.
 .It Cd options COMPAT_11
 Enable binary compatibility with
 .Nx 1.1 .
 This allows binaries running on the i386 port to gain direct access to
 the io ports by opening
 .Pa /dev/io
 read/write.
 This functionality was replaced by
 .Xr i386_iopl 2
 post 1.1.
 On the Atari port, the location of the disk label was moved after 1.1.
 When the
 .Em 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
 .Em EXEC_ELF_NOTELESS
 option.
 .It Cd options COMPAT_12
 Enable binary compatibility with
 .Nx 1.2 .
 This allows the use of old syscalls for
 .Fn reboot
 and
 .Fn swapon .
 The syscall numbers were changed post 1.2 to add functionality to the
 .Xr reboot 2
 syscall, and the new
 .Xr swapctl 2
 interface was introduced.
 This also enables the
 .Em EXEC_ELF_NOTELESS
 option.
 .It Cd options COMPAT_13
 Enable binary compatibility with
 .Nx 1.3 .
 This allows the use of old syscalls for
 .Fn sigaltstack ,
 and also enables the old
 .Xr swapctl 2
 command
 .Dv SWAP_STATS
 (now called
 .Dv SWAP_OSTATS ) ,
 which does not include the
 .Fa se_path
 member of
 .Va struct swapent .
 .It Cd options COMPAT_14
 Enable binary compatibility with
 .Nx 1.4 .
 This allows some old
 .Xr ioctl 2
 on
 .Xr wscons 4
 to be performed, and allows the
 .Dv NFSSVC_BIOD
 mode of the
 .Xr nfssvc 2
 system call to be used for compatibility with the deprecated nfsiod program.
 .It Cd options COMPAT_15
 Enable binary compatibility with
 .Nx 1.5 .
 Since there were no API changes from
 .Nx 1.5
 and
 .Nx 1.6 ,
 this option does nothing.
 .It Cd options COMPAT_16
 Enable binary compatibility with
 .Nx 1.6 .
 This allows the use of old signal trampoline code which has been deprecated
 with the addition of
 .Xr siginfo 2 .
 .It Cd options COMPAT_20
 Enable binary compatibility with
 .Nx 2.0 .
 This allows the use of old syscalls for
 .Fn statfs ,
 .Fn fstatfs ,
 .Fn getfsstat
 and
 .Fn fhstatfs ,
 which have been deprecated with the addition of the
 .Xr statvfs 2 ,
 .Xr fstatvfs 2 ,
 .Xr getvfsstat 2
 and
 .Xr fhstatvfs 2
 system calls.
 .It Cd options COMPAT_30
 Enable binary compatibility with
 .Nx 3.0 .
 See
 .Xr compat_30 8
 for details about the changes made after the
 .Nx 3.0
 release.
 .It Cd options COMPAT_40
 Enable binary compatibility with
 .Nx 4.0 .
 This allows the use of old
 .Xr ptrace 2
 calls for the SH3 platform.
 It also enables the old
 .Xr mount 2
 system call that did not include the data length parameter.
 The power_event_t structure's pev_switch is filled in.
 .It Cd options COMPAT_43
 Enables compatibility with
 .Bx 4.3 .
 This adds an old syscall for
 .Xr lseek 2 .
 It also adds the ioctls for
 .Dv TIOCGETP
 and
 .Dv TIOCSETP .
 The return values for
 .Xr getpid 2 ,
 .Xr getgid 2 ,
 and
 .Xr 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
 .Dv NTTYDISC
 terminal line discipline.
 It also provides backwards compatibility with
 .Dq old
 SIOC[GS]IF{ADDR,DSTADDR,BRDADDR,NETMASK} interface 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
 .Bx 4.4
 socket calls.
 .It Cd options COMPAT_50
 Enable binary compatibility with
 .Nx 5.0 .
 This enables support for the old
 .Ft time_t
 and
 .Ft dev_t
 types as 32 bit, and all the associated kernel interface changes.
 It also enables old
 .Xr gpio 4
 and
 .Xr rnd 4
 interfaces.
 .It Cd options COMPAT_60
 Enable binary compatibility with
 .Nx 6.0 .
 This provides old
 .Xr ccd 4
 interfaces, enables support for old
 .Xr cpuctl 8
 microcode interfaces, and support for the old
 .Ft ptmget
 structure.
 .It Cd options COMPAT_70
 Enable binary compatibility with
 .Nx 7.0 .
 This provides support for old
 .Xr route 4
 interfaces.
 .It Cd options COMPAT_80
 Enable binary compatibility with
 .Nx 8.0 .
 .It Cd options COMPAT_90
 Enable binary compatibility with
 .Nx 9.0 .
 .It Cd options COMPAT_BSDPTY
 This option is currently on by default and enables the pty multiplexer
 .Xr ptm 4
 and
 .Xr ptmx 4
 to find and use ptys named
 .Pa /dev/ptyXX
 (master) and
 .Pa /dev/ttyXX
 (slave).
 Eventually this option will become optional as ptyfs based pseudo-ttys become
 the default, see
 .Xr mount_ptyfs 8 .
 .It Cd options COMPAT_LINUX
 On those architectures that support it, this enables binary
 compatibility with Linux ELF and
 .Xr a.out 5
 applications built for the same architecture.
 This currently includes the alpha, arm, i386, m68k, mips, powerpc and
 x86_64 ports.
 .It Cd 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.
 .It Cd 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
 .Em COMPAT_NETBSD32
 option for 64-bit kernels, in addition to this option.
 .It Cd options COMPAT_ULTRIX
 On those architectures that support it, this enables binary
 compatibility with ULTRIX applications built for the same architecture.
 This currently is limited to the pmax.
 The functionality of this option is unknown.
 .It Cd options COMPAT_FREEBSD
 On those architectures that support it, this enables binary
 compatibility with
 .Fx
 applications built for the same architecture.
 At the moment this is limited to the i386 port.
 .It Cd options COMPAT_NOMID
 Enable compatibility with
 .Xr a.out 5
 executables that lack a machine ID.
 This includes
 .Nx 0.8 Ns 's
 ZMAGIC format, and 386BSD and BSDI's
 QMAGIC, NMAGIC, and OMAGIC
 .Xr a.out 5
 formats.
 .It Cd options COMPAT_NETBSD32
 On those architectures that support it, this enables binary
 compatibility with 32-bit applications built for the same architecture.
 This is currently limited to the amd64 and sparc64 ports, and only
 applicable for 64-bit kernels.
 .It Cd options COMPAT_AOUT_M68K
 On m68k architectures which have switched to ELF,
 this enables binary compatibility with
 .Nx Ns /m68k
 .Xr a.out 5
 executables on
 .Nx Ns /m68k
 ELF kernels.
 This handles alignment incompatibility of m68k ABI between
 a.out and ELF which causes the structure padding differences.
 Currently only some system calls which use
 .Va struct stat
 are adjusted and some binaries which use
 .Xr sysctl 3
 to retrieve network details would not work properly.
 .It Cd options EMUL_NATIVEROOT=string
 Just like emulated binaries first try looking up files in
 an emulation root (e.g.
 .Pa /emul/linux )
 before looking them up in real root, this option causes native
 binaries to first look up files in an "emulation" directory too.
 This can be useful to test an amd64 kernel on top of an i386 system
 before full migration: by unpacking the amd64 distribution in e.g.
 .Pa /emul/netbsd64
 and specifying that location as
 .Cd EMUL_NATIVEROOT ,
 native amd64 binaries can be run while the root file system remains
 populated with i386 binaries.
 Beware of
 .Pa /dev
 incompatibilities between i386 and amd64 if you do this.
 .It Cd options EXEC_ELF_NOTELESS
 Run unidentified ELF binaries as
 .Nx
 binaries.
 This might be needed for very old
 .Nx
 ELF binaries on some archs.
 These old binaries didn't contain an appropriate
 .Li .note.netbsd.ident
 section, and thus can't be identified by the kernel as
 .Nx
 binaries otherwise.
 Beware - if this option is on, the kernel would run
 .Em any
 unknown ELF binaries as if they were
 .Nx
 binaries.
 .El
 .Ss Debugging Options
 .Bl -ohang
 .It Cd options DDB
 Compiles in a kernel debugger for diagnosing kernel problems.
 See
 .Xr ddb 4
 for details.
 .Em NOTE :
 not available on all architectures.
 .It Cd options DDB_FROMCONSOLE=integer
 If set to non-zero, DDB may be entered by sending a break on a serial
 console or by a special 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
 .Em ddb.fromconsole
 .Xr sysctl 3
 variable which may be changed at run time \(em see
 .Xr sysctl 8
 for details.
 .It Cd 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.
 .It Cd options DDB_ONPANIC
 The default if not specified is
 .Dq 1
 - just enter into DDB.
 If set to
 .Dq 0
 the kernel will attempt to print out a stack trace
 and reboot the system.
 If set to
 .Dq -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
 .Em ddb.onpanic
 .Xr sysctl 3
 variable which may be changed at run time \(em see
 .Xr sysctl 8
 for details.
 .It Cd options DDB_COMMANDONENTER=string
 This option specify commands which will be executed on each entry to DDB.
 This sets the default value of the
 .Em ddb.commandonenter
 .Xr sysctl 3
 variable which may be changed at run time.
 .It Cd 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.
 .It Cd options CNMAGIC=string
 This option overrides the
 .Xr cnmagic 9
 string used to enter the kernel debugger.
 .It Cd options DDB_VERBOSE_HELP
 This option adds more verbose descriptions to the
 .Em help
 command.
 .It Cd options DDB_PANICSTACKFRAMES=integer
 Number of stack frames to display on panic.
 Useful to avoid scrolling away the interesting frames on a glass tty.
 Default value is
 .Dv 65535
 (all frames), useful value around
 .Dv 10 .
 .It Cd options KGDB
 Compiles in a remote kernel debugger stub for diagnosing kernel problems
 using the
 .Dq remote target
 feature of gdb.
 See
 .Xr gdb 1
 for details.
 .Em NOTE :
 not available on all architectures.
 .It Cd options KGDB_DEV
 Device number
 .Po
 as a
 .Dv dev_t
 .Pc
 of kgdb device.
 .It Cd options KGDB_DEVADDR
 Memory address of kgdb device.
 .It Cd options KGDB_DEVMODE
 Permissions of kgdb device.
 .It Cd options KGDB_DEVNAME
 Device name of kgdb device.
 .It Cd options KGDB_DEVRATE
 Baud rate of kgdb device.
 .It Cd makeoptions DEBUG="-g"
 The
 .Fl g
 flag causes
 .Pa netbsd.gdb
 to be built in addition to
 .Pa netbsd .
 .Pa netbsd.gdb
 is useful for debugging kernel crash dumps with gdb.
 See
 .Xr gdb 1
 for details.
 .It Cd options DEBUG
 Turns on miscellaneous kernel debugging.
 Since options are turned into preprocessor defines (see above),
 .Em options DEBUG
 is equivalent to doing a
 .Em #define DEBUG
 throughout the kernel.
 Much of the kernel has
 .Em #ifdef DEBUG
 conditionalized debugging code.
 Note that many parts of the kernel (typically device drivers) include their own
 .Em #ifdef XXX_DEBUG
 conditionals instead.
 This option also turns on certain other options,
 which may decrease system performance.
 Systems with this option are not suitable for regular use, and are
 intended only for debugging or looking for bugs.
 .It Cd 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.
 Historically, the performance degradation is sufficiently small that
 it is reasonable for systems with
 .Em options DIAGNOSTIC
 to be in production use, with the real consideration not being
 performance but instead a preference for more panics versus continued
 operation with undetected problems.
 .It Cd options LOCKDEBUG
 Adds code to the kernel to detect incorrect use of locking primitives
 (mutex, rwlock).
 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
 .Xr 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.
 .It Cd options KDTRACE_HOOKS
 Adds hooks for the DTrace tracing facility, which allows users to
 analyze many aspects of system and application behavior.
 See
 .Xr dtrace 1
 for details.
 .It Cd options KSTACK_CHECK_MAGIC
 Check kernel stack usage and panic if stack overflow is detected.
 This check is performance sensitive because it scans stack on each context
 switch.
 .It Cd options KTRACE
 Add hooks for the system call tracing facility, which allows users to
 watch the system call invocation behavior of processes.
 See
 .Xr ktrace 1
 for details.
 .It Cd options MSGBUFSIZE=integer
 This option sets the size of the kernel message buffer.
 This buffer holds the kernel output of
 .Fn printf
 when not (yet) read by
 .Xr 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
 .Xr 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.
 .It Cd options KERNHIST
 Enables the kernel history logs, which create in-memory traces of
 various kernel activities.
 These logs can be displayed by using
 .Cm show kernhist
 from DDB.
 See the kernel source file
 .Pa sys/kern/kern_history.c
 and the
 .Xr kernhist 9
 manual for details.
 .It Cd options KERNHIST_PRINT
 Prints the kernel history logs on the system console as entries are added.
 Note that the output is
 .Em extremely
 voluminous, so this option is really only useful for debugging
 the very earliest parts of kernel initialization.
 .It Cd options UVMHIST
 Like
 .Em KERNHIST ,
 it enables the UVM history logs.
 These logs can be displayed by using
 .Cm show kernhist
 from DDB.
 See the kernel source file
 .Pa sys/uvm/uvm_stat.c
 for details.
 .It Cd options UVMHIST_PRINT
 Like
 .Em UVMHIST ,
 it prints the UVM history logs on the system console as entries are added.
 Note that the output is
 .Em extremely
 voluminous, so this option is really only useful for debugging
 the very earliest parts of kernel initialization.
 .It Cd options UVMHIST_MAPHIST_SIZE
 Set the size of the
 .Dq maphist
 kernel history.
 The default is 100.
 This option depends upon the
 .Em UVMHIST
 option.
 .It Cd options UVMHIST_PDHIST_SIZE
 Set the size of the
 .Dq pdhist
 kernel history.
 The default is 100.
 This option depends upon the
 .Em UVMHIST
 option.
 .It Cd options BIOHIST
 Like
 .Em KERNHIST ,
 it enables the BIO history logs.
 These logs can be displayed by using
 .Cm show kernhist
 from DDB, and can help in debugging problems with Buffered I/O operations.
 See the kernel source file
 .Pa sys/kern/vfs_vio.c
 for details.
 .It Cd options BIOHIST_PRINT
 Like
 .Em BIOHIST ,
 it prints the BIO history logs on the system console as entries are added.
 Note that the output is
 .Em extremely
 voluminous, so this option is really only useful for debugging
 the very earliest parts of kernel initialization.
 .It Cd options BIOHIST_SIZE
 Set the size of the
 .Dq biohist
 kernel history.
 The default is 500.
 This option depends upon the
 .Em BIOHIST
 option.
 .El
 .Ss File Systems
 .Bl -ohang
 .It Cd file-system FFS
 Includes code implementing the Berkeley Fast File System
 .Po Em FFS Pc .
 Most machines need this if they are not running diskless.
 .It Cd file-system EXT2FS
 Includes code implementing the Second Extended File System
 .Po Em ext2 Pc ,
 revision 0 and revision 1 with the
 .Em filetype ,
 .Em sparse_super
 and
 .Em 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
 .Em ext2
 like the "behavior on errors" are not implemented.
 See
 .Xr mount_ext2fs 8
 for details.
 .It Cd file-system LFS
 .Bq Em EXPERIMENTAL
 Include the Log-structured File System
 .Po Em LFS Pc .
 See
 .Xr mount_lfs 8
 and
 .Xr newfs_lfs 8
 for details.
 .It Cd file-system MFS
 Include the Memory File System
 .Po Em MFS Pc .
 This file system stores files in swappable memory, and produces
 notable performance improvements when it is used as the file store
 for
 .Pa /tmp
 and similar file systems.
 See
 .Xr mount_mfs 8
 for details.
 .It Cd 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
 .Xr mount_nfs 8
 for details.
 .It Cd 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
 .Xr mount_cd9660 8
 for details.
 .It Cd file-system MSDOSFS
 Includes the MS-DOS FAT file system, which is reportedly still used
 by unfortunate people who have not heard about
 .Nx .
 Also implements the Windows 95 extensions to the same, which permit
 the use of longer, mixed case file names.
 See
 .Xr mount_msdos 8
 and
 .Xr fsck_msdos 8
 for details.
 .It Cd file-system NTFS
 .Bq Em EXPERIMENTAL
 Includes code for the Microsoft Windows NT file system.
 See
 .Xr mount_ntfs 8
 for details.
 .It Cd file-system FDESC
 Includes code for a file system, conventionally mounted on
 .Pa /dev/fd ,
 which permits access to the per-process file descriptor space via
 special files in the file system.
 See
 .Xr mount_fdesc 8
 for details.
 Note that this facility is redundant, and thus unneeded on most
 .Nx
 systems, since the
 .Xr fd 4
 pseudo-device driver already provides identical functionality.
 On most
 .Nx
 systems, instances of
 .Xr fd 4
 are mknoded under
 .Pa /dev/fd/
 and on
 .Pa /dev/stdin ,
 .Pa /dev/stdout ,
 and
 .Pa /dev/stderr .
 .It Cd file-system KERNFS
 Includes code which permits the mounting of a special file system
 (normally mounted on
 .Pa /kern )
 in which files representing various kernel variables and parameters
 may be found.
 See
 .Xr mount_kernfs 8
 for details.
 .It Cd 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
 .Xr mount_null 8
 for details.
 .It Cd 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 example of a stacking file
 system which has a need to interpose itself between an underlying file
 system and all other access.
 See
 .Xr mount_overlay 8
 for details.
 .It Cd file-system PROCFS
 Includes code for a special file system (conventionally mounted on
 .Pa /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
 .Pa ctl
 files in the procfs namespace.
 See
 .Xr mount_procfs 8
 for details.
 .It Cd file-system UDF
 .Bq Em 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 up to UDF 2.01 and somewhat limited
 write support for UDF 2.50.
 It is marked experimental since there is no
 .Xr fsck_udf 8 .
 See
 .Xr mount_udf 8
 for details.
 .It Cd file-system UMAPFS
 Includes a loopback file system in which user and group IDs may be
 remapped \(em this can be useful when mounting alien file systems with
 different UIDs and GIDs than the local system.
 See
 .Xr mount_umap 8
 for details.
 .It Cd file-system UNION
 .Bq Em 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 \(em 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
 .Xr mount_union 8
 for details.
 .It Cd file-system CODA
 .Bq Em 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
 .Dq 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
 .Lk http://www.coda.cs.cmu.edu
 for more details.
 .Em NOTE :
 You also need to enable the pseudo-device, vcoda, for the Coda
 file system to work.
 .It Cd file-system PTYFS
 Includes code for a special file system (normally mounted on
 .Pa /dev/pts )
 in which pseudo-terminal slave devices become visible in the file system.
 See
 .Xr mount_ptyfs 8
 for details.
 .It Cd file-system TMPFS
 Includes code for the efficient memory file system, normally used over
 .Pa /tmp .
 See
 .Xr mount_tmpfs 8
 for details.
 .It Cd 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
 .Xr puffs 3
 for more details.
 This enables for example sshfs:
 .Xr mount_psshfs 8 .
 .El
 .Ss File System Options
 .Bl -ohang
 .It Cd options DISKLABEL_EI
 Enable
 .Dq Endian-Independent
 .Xr disklabel 5
 support.
 This allows a system to recognize a disklabel written in the other byte order.
 For writing, when a label already exists, its byte order is preserved.
 Otherwise, a new label is written in the native byte order.
 To specify the byte order explicitly, the
 .Fl F
 option of
 .Xr disklabel 8
 should be used with the
 .Fl B
 option in order to avoid using
 .Xr ioctl 2 ,
 which results in the default behavior explained above.
 At the moment this option is restricted to the following ports:
 amd64, bebox, emips, epoc32, evbarm, i386, ibmnws, landisk, mvmeppc, prep,
 .\" riscv,
 rs6000, sandpoint,
 .\" usermode,
 xen, and zaurus;
 also to machines of the
 evbmips and evbppc ports that support
 Master Boot Record (MBR).
 .It Cd options MAGICLINKS
 Enables the expansion of special strings
 .Po
 beginning with
 .Dq @
 .Pc
 when traversing symbolic links.
 See
 .Xr 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 manipulated with the
 .Xr sysctl 8
 command regardless of the setting of this option.
 .It Cd options NFSSERVER
 Include the server side of the
 .Em NFS
 (Network File System) remote file sharing protocol.
 Although the bulk of the code implementing
 .Em NFS
 is kernel based, several user level daemons are needed for it to
 work.
 See
 .Xr mountd 8
 and
 .Xr nfsd 8
 for details.
 .It Cd options NVNODE=integer
 This option sets the size of the cache used by the name-to-inode translation
 routines, (a.k.a. the
 .Fn namei
 cache, though called by many other names in the kernel source).
 By default, this cache has
 .Dv ( NPROC + NTEXT + 100 )
 entries (NPROC set as 20 + 16 * MAXUSERS and NTEXT as 80 + NPROC / 8).
 A reasonable way to derive a value of
 .Dv NVNODE ,
 should you notice a large number of namei cache misses with a tool such as
 .Xr systat 1 ,
 is to examine your system's current computed value with
 .Xr 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.
 .It Cd options NAMECACHE_ENTER_REVERSE
 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
 .Pa /proc/#/maps
 emulation for Linux binaries is required.
 .El
 .Ss Options for FFS/UFS File Systems
 .Bl -ohang
 .It Cd options APPLE_UFS
 Enable support for UFS file systems created on Mac OS X.
 .It Cd options FFS_EI
 Enable
 .Dq 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
 .Xr newfs 8 ,
 .Xr fsck_ffs 8 ,
 .Xr dumpfs 8
 for file system byte order status and manipulation.
 .It Cd options FFS_NO_SNAPSHOT
 Disable support for the creation of file system internal snapshot
 of FFS file systems.
 Maybe useful for install media kernels, small memory systems and
 embedded systems which don't require the snapshot support.
 .It Cd options QUOTA
 Enables kernel support for traditional quotas in FFS.
 Traditional quotas store the quota information in external files and
 require
 .Xr quotacheck 8
 and
 .Xr quotaon 8
 at boot time.
 Traditional quotas are limited to 32-bit sizes and are at this point
 considered a legacy feature.
 .It Cd options QUOTA2
 Enables kernel support for in-volume quotas in FFS.
 The quota information is file system metadata maintained by
 .Xr fsck 8
 and/or WAPBL journaling.
 MFS volumes can also use
 .Dv QUOTA2
 quotas; see
 .Xr mount_mfs 8
 for more information.
 .It Cd options UFS_DIRHASH
 Increase lookup performance by maintaining in-core hash tables
 for large directories.
 .It Cd options UFS_EXTATTR
 Enable extended attribute support for UFS1 file systems.
 .It Cd options WAPBL
 Enable
 .Dq 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
 .Xr wapbl 4 .
 .El
 .Ss Options for the LFS File System
 .Bl -ohang
 .\" .It Cd options LFS_KERNEL_RFW
 .\" There is no documentation for this. (XXX)
 .\" .It Cd options LFS_QUOTA
 .\" Enable traditional quota support for LFS.
 .\" (It is not clear if this works.)
 .\" .It Cd options LFS_QUOTA2
 .\" Enable modernized 64-bit quota support for LFS.
 .\" (This does not work yet.)
 .It Cd options LFS_EI
 Enable
 .Dq Endian-Independent
 LFS support.
 This allows (at a small performance cost) mounting an LFS file system
 created for another architecture.
 .\" .It Cd options LFS_EXTATTR
 .\" Enable extended attribute support for LFS.
 .\" (It is not clear if this works.)
 .It Cd options LFS_DIRHASH
 Increase lookup performance by maintaining in-core hash tables
 for large directories.
 .El
 .Ss Options for the ext2fs File System
 .Bl -ohang
 .It Cd options EXT2FS_SYSTEM_FLAGS
 This option changes the behavior of the APPEND and IMMUTABLE flags
 for a file on an
 .Em 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
 .Xr chflags 1
 and
 .Xr secmodel_securelevel 9 .
 .El
 .Ss Options for the NFS File System
 .Bl -ohang
 .It Cd 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
 .Xr diskless 8
 for details.
 .It Cd options NFS_BOOT_BOOTSTATIC
 Enable use of static values defined as
 .Dq NFS_BOOTSTATIC_MYIP ,
 .Dq NFS_BOOTSTATIC_GWIP ,
 .Dq NFS_BOOTSTATIC_SERVADDR ,
 and
 .Dq NFS_BOOTSTATIC_SERVER
 in kernel options to get configuration information
 if NFS is used to mount the root file system.
 .It Cd options NFS_BOOT_DHCP
 Same as
 .Dq NFS_BOOT_BOOTP ,
 but use the DHCP extensions to the
 BOOTP protocol (RFC 1541).
 .It Cd options NFS_BOOT_BOOTP_REQFILE
 Specifies the string sent in the bp_file field of the BOOTP/DHCP
 request packet.
 .It Cd options NFS_BOOT_BOOTPARAM
 Enable use of the BOOTPARAM protocol, consisting of RARP and
 BOOTPARAM RPC, to get configuration information if NFS
 is used to mount the root file system.
 See
 .Xr diskless 8
 for details.
 .It Cd 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 workaround 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
 .Xr mount_nfs 8
 for details.
 .It Cd 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.
-.It Cd options NFS_BOOT_TCP
+.It Cd options NFS_BOOT_UDP
-Use NFS over TCP instead of the default UDP, for mounting root.
+Use NFS over UDP instead of the default TCP, for mounting root.
 .El
 .Ss Buffer queue strategy options
 The following options enable alternative buffer queue strategies.
 .Bl -ohang
 .It Cd options BUFQ_READPRIO
 Enable alternate buffer queue strategy for disk I/O.
 In the default strategy, outstanding 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 difference 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 writes.
 .It Cd options BUFQ_PRIOCSCAN
 Enable another buffer queue strategy for disk I/O, per-priority cyclical scan.
 .It Cd options NEW_BUFQ_STRATEGY
 Synonym of
 .Em BUFQ_READPRIO .
 .El
 .Ss Miscellaneous Options
 .Bl -ohang
 .It Cd options CPU_UCODE
 Support cpu microcode loading via
 .Xr cpuctl 8 .
 .It Cd options MEMORY_DISK_DYNAMIC
 This option makes the
 .Xr md 4
 RAM disk size dynamically sized.
 It is incompatible with
 .Xr mdsetimage 8 .
 .It Cd options MEMORY_DISK_HOOKS
 This option allows for some machine dependent functions to be called when
 the
 .Xr md 4
 RAM disk driver is configured.
 This can result in automatically loading a RAM disk from floppy on
 open (among other things).
 .It Cd options MEMORY_DISK_IS_ROOT
 Forces the
 .Xr md 4
 RAM disk to be the root device.
 This can only be overridden when
 the kernel is booted in the 'ask-for-root' mode.
 .It Cd options MEMORY_DISK_ROOT_SIZE=integer
 Allocates the given number of 512 byte blocks as memory for the
 .Xr md 4
 RAM disk, to be populated with
 .Xr mdsetimage 8 .
 .It Cd 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.
 .It Cd options MEMORY_DISK_RBFLAGS=value
 This option sets the
 .Xr reboot 2
 flags used when booting with a memory disk as root file system.
 Possible values include
 .Dv RB_AUTOBOOT
 (boot in the usual fashion - default value), and
 .Dv RB_SINGLE
 (boot in single-user mode).
 .It Cd options MODULAR
 Enables the framework for kernel modules (see
 .Xr module 7 ) .
 .It Cd options MODULAR_DEFAULT_AUTOLOAD
 Enables the autoloading of kernel modules by default.
 This sets the default value of the
 .Em kern.module.autoload
 .Xr sysctl 3
 variable which may be changed at run time.
 .It Cd options VND_COMPRESSION
 Enables the
 .Xr vnd 4
 driver to also handle compressed images.
 See
 .Xr vndcompress 1 ,
 .Xr vnd 4
 and
 .Xr vnconfig 8
 for more information.
 .It Cd options SPLDEBUG
 Help the kernel programmer find bugs related to the interrupt priority
 level.
 When
 .Fn spllower
 or
 .Fn splraise
 changes the current CPU's interrupt priority level to or from
 .Dv IPL_HIGH ,
 record a backtrace.
 Read
 .Xr i386/return_address 9
 for caveats about collecting backtraces.
 This feature is experimental, and it is only available on i386.
 See
 .Pa sys/kern/subr_spldebug.c .
 .It Cd 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
 .Xr mdsetimage 8 .
 The RAM disk name is obtained using DHCP's filename parameter.
 This option requires
 .Em MEMORY_DISK_HOOKS
 and
 .Em MEMORY_DISK_DYNAMIC .
 It is incompatible with
 .Em MEMORY_DISK_ROOT_SIZE .
 .It Cd options HZ=integer
 On ports that support it, set the system clock frequency (see
 .Xr hz 9 )
 to the supplied value.
 Handle with care.
 .It Cd options NTP
 Turns on in-kernel precision timekeeping support used by software
 implementing
 .Em NTP
 (Network Time Protocol, RFC 1305).
 The
 .Em NTP
 option adds an in-kernel Phase-Locked Loop (PLL) for normal
 .Em NTP
 operation, and a Frequency-Locked Loop (FLL) for intermittently-connected
 operation.
 .Xr 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.
 .Pp
 The interface to the kernel
 .Em NTP
 support is provided by the
 .Xr ntp_adjtime 2
 and
 .Xr ntp_gettime 2
 system calls, which are intended for use by
 .Xr ntpd 8
 and are enabled by the option.
 On systems with sub-microsecond resolution timers, or where (HZ/100000)
 is not an integer, the
 .Em NTP
 option also enables extended-precision arithmetic to keep track of
 fractional clock ticks at NTP time-format precision.
 .It Cd 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.
 .Po
 The
 .Em NTP
 option (which see) must be on if the
 .Em PPS_SYNC
 option is used
 .Pc .
 Some reference clocks generate a Pulse Per Second (PPS) signal in
 phase with their time source.
 The
 .Em PPS
 line discipline receives this signal on either the data leads
 or the DCD control lead of a serial port.
 .Pp
 .Em NTP
 uses the PPS signal to discipline the local clock oscillator to a high
 degree of precision (typically less than 50 microseconds in time and
 .1 ppm in accuracy).
 .Em 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
 .Em NTP
 to account for it.
 Using
 .Em 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
 .Xr ntpd 8
 in
 .Pa /usr/share/doc/html/ntp .
 .Pp
 .Nx
 currently supports this option in
 .Xr com 4
 and
 .Xr zsc 4 .
 .It Cd options SETUIDSCRIPTS
 Allows scripts with the setuid bit set to execute as the effective
 user rather than the real user, just like binary executables.
 .Pp
 .Em NOTE :
 Using this option will also enable
 .Em options FDSCRIPTS
 .It Cd 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.
 .Pp
 .Em NOTE :
 Execute only (non-readable) scripts will have
 .Va argv[0]
 set to
 .Pa /dev/fd/* .
 What this option allows as far as security is
 concerned, is the ability to safely ensure that the correct script
 is run by the interpreter, as it is passed as an already open file.
 .It Cd options RTC_OFFSET=integer
 The kernel (and typically the hardware battery backed-up clock on
 those machines that have one) keeps time in
 .Em UTC
 (Universal Coordinated Time, once known as
 .Em GMT ,
 or Greenwich Mean Time)
 and not in the time of the local time zone.
 The
 .Em RTC_OFFSET
 option is used on some ports (such as the i386) to tell the kernel
 that the hardware clock is offset from
 .Em UTC
 by the specified number of minutes.
 This is typically used when a machine boots several operating
 systems and one of them wants the hardware clock to run in the
 local time zone and not in
 .Em UTC ,
 e.g.
 .Em RTC_OFFSET=300
 means
 the hardware clock is set to US Eastern Time (300 minutes behind
 .Em UTC ) ,
 and not
 .Em UTC .
 (Note:
 .Em RTC_OFFSET
 is used to initialize a kernel variable named
 .Va 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
 .Xr sysctl 8
 and
 .Xr 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
 .Va rtc_offset
 in system initialization scripts.
 Changing this value currently may only be done at kernel compile
 time or by patching the kernel and rebooting).
 .Pp
 .Em 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
 .Em RTC_OFFSET
 to let
 .Nx
 coexist with such an operating system, like Windows,
 would necessitate changing
 .Em RTC_OFFSET
 twice a year.
 As such, this solution is imperfect.
 .It Cd options MAXUPRC=integer
 Sets the soft
 .Dv RLIMIT_NPROC
 resource limit, which specifies the maximum number of simultaneous
 processes a user is permitted to run, for process 0;
 this value is inherited by its child processes.
 It defaults to
 .Em CHILD_MAX ,
 which is currently defined to be 160.
 Setting
 .Em MAXUPRC
 to a value less than
 .Em CHILD_MAX
 is not permitted, as this would result in a violation of the semantics of
 .St -p1003.1-90 .
 .It Cd options NOFILE=integer
 Sets the soft
 .Dv 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
 .Em OPEN_MAX ,
 which is currently defined to be 128.
 .It Cd options MAXFILES=integer
 Sets the default value of the
 .Em kern.maxfiles
 sysctl variable, which indicates the maximum number of files that may
 be open in the system.
 .It Cd options DEFCORENAME=string
 Sets the default value of the
 .Em kern.defcorename
 sysctl variable, otherwise it is set to
 .Nm %n.core .
 See
 .Xr sysctl 8
 and
 .Xr sysctl 3
 for details.
 .It Cd options RASOPS_CLIPPING
 Enables clipping within the
 .Nm rasops
 raster-console output system.
 .Em NOTE :
 only available on architectures that use
 .Nm rasops
 for console output.
 .It Cd options RASOPS_SMALL
 Removes optimized character writing code from the
 .Nm rasops
 raster-console output system.
 .Em NOTE :
 only available on architectures that use
 .Nm rasops
 for console output.
 .It Cd options INCLUDE_CONFIG_FILE
 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.
 .Pa GENERIC.local
 or
 .Pa std.$MACHINE .
 The embedded config file can be extracted from the resulting kernel with
 .Xr config 1
 .Fl x ,
 or by the following command:
 .Bd -literal -offset indent
 strings netbsd | sed -n 's/^_CFG_//p' | unvis
 .Ed
 .It Cd options INCLUDE_JUST_CONFIG
 Similar to the above option, but includes just the actual config file,
 not any included files.
 .It Cd options PIPE_SOCKETPAIR
 Use slower, but smaller socketpair(2)-based pipe implementation instead
 of default faster, but bigger one.
 Primarily useful for installation kernels.
 .It Cd options USERCONF
 Compiles in the in-kernel device configuration manager.
 See
 .Xr userconf 4
 for details.
 .It Cd options SCDEBUG_DEFAULT
 Used with the
 .Cd options SYSCALL_DEBUG
 described below to choose which types of events are displayed.
 .Pp
 .Bl -tag -width "SCDEBUG_KERNHIST" -compact -offset indent
 .It Dv SCDEBUG_CALLS
 Show system call entry points.
 .It Dv SCDEBUG_RETURNS
 Show system call exit points.
 .It Dv SCDEBUG_ALL
 Show all system call requests, including unimplemented calls.
 .It Dv SCDEBUG_SHOWARGS
 Show the arguments provided.
 .It Dv SCDEBUG_KERNHIST
 Store a restricted form of the system call debug in a kernel history
 instead of printing it to the console.
 This option relies upon
 .Cd options KERNHIST .
 .El
 .Pp
 The default value is
 .Dv (SCDEBUG_CALLS|SCDEBUG_RETURNS|SCDEBUG_SHOWARGS) .
 .It Cd options SYSCALL_DEBUG
 Useful for debugging system call issues, usually in early single user bringup.
 By default, writes entries to the system console for most system call events.
 Can be configured with the
 .Cd options SCDEBUG_DEFAULT
 option to to use the
 .Cd options KERNHIST
 facility instead.
 .It Cd 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
 .Xr systat 1 .
 .Em NOTE :
 not yet available on all architectures.
 .It Cd options SYSCALL_TIMES
 Count the time spent (using
 .Fn cpu_counter32 )
 in each system call.
 .Em NOTE :
 Using this option will also enable
 .Cd options SYSCALL_STATS .
 .It Cd options SYSCALL_TIMES_HASCOUNTER
 Force use of
 .Fn cpu_counter32
 even if
 .Fn cpu_hascounter
 reports false.
 Useful for systems where the cycle counter doesn't run at a constant rate
 (e.g. Soekris boxes).
 .It Cd options XSERVER_DDB
 A supplement to XSERVER that adds support for entering
 .Xr ddb 4
 while in X11.
 .It Cd options FILEASSOC
 Support for
 .Xr fileassoc 9 .
 Required for
 .Cd options PAX_SEGVGUARD
 and
 .Cd pseudo-device veriexec .
 .It Cd options FILEASSOC_NHOOKS=integer
 Number of storage slots per file for
 .Xr fileassoc 9 .
 Default is 4.
 .El
 .Ss Networking Options
 .Bl -ohang
 .It Cd options GATEWAY
 Enables
 .Em IPFORWARDING
 and (on most ports) increases the size of
 .Em NMBCLUSTERS .
 In general,
 .Em GATEWAY
 is used to indicate that a system should act as a router, and
 .Em IPFORWARDING
 is not invoked directly.
 (Note that
 .Em GATEWAY
 has no impact on protocols other than IP).
 .Em GATEWAY
 option also compiles IPv4 and IPv6 fast forwarding code into the kernel.
 .It Cd options IPFORWARDING=value
 If
 .Em value
 is 1 this enables IP routing behavior.
 If
 .Em value
 is 0 (the default), it disables it.
 The
 .Em 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) \(em removing
 .Em GATEWAY
 and
 .Em IPFORWARDING
 is insufficient to stop all routing through a bastion host on a
 firewall \(em source routing is controlled independently.
 Note that IP forwarding may be turned on and off independently of the
 setting of the
 .Em IPFORWARDING
 option through the use of the
 .Em net.inet.ip.forwarding
 sysctl variable.
 If
 .Em net.inet.ip.forwarding
 is 1, IP forwarding is on.
 See
 .Xr sysctl 8
 and
 .Xr sysctl 3
 for details.
 .It Cd options IFA_STATS
 Tells the kernel to maintain per-address statistics on bytes sent
 and received over (currently) Internet and AppleTalk addresses.
 .\"This can be a fairly expensive operation, so you probably want to
 .\"keep this disabled.
 The option is not recommended as it degrades system stability.
 .It Cd 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.
 .It Cd options IPSELSRC
 Includes support for source-address selection policies.
 See
 .Xr in_getifa 9 .
 .It Cd options MROUTING
 Includes support for IP multicast routers.
 You certainly want
 .Em INET
 with this.
 Multicast routing is controlled by the
 .Xr mrouted 8
 daemon.
 See also option
 .Cd PIM .
 .It Cd options PIM
 Includes support for Protocol Independent Multicast (PIM) routing.
 You need
 .Em MROUTING
 and
 .Em INET
 with this.
 Software using this can be found e.g. in
 .Pa pkgsrc/net/xorp .
 .It Cd options INET
 Includes support for the TCP/IP protocol stack.
 You almost certainly want this.
 See
 .Xr inet 4
 for details.
 .It Cd options INET6
 Includes support for the IPv6 protocol stack.
 See
 .Xr inet6 4
 for details.
 Unlike
 .Em INET ,
 .Em INET6
 enables multicast routing code as well.
 This option requires
 .Em INET
 at this moment, but it should not.
 .It Cd 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
 .Xr sysctl 3
 for details.
 .It Cd options IPSEC
 Includes support for the IPsec protocol, using the implementation derived from
 .Ox ,
 relying on
 .Xr opencrypto 9
 to carry out cryptographic operations.
 See
 .Xr ipsec 4
 for details.
 .It Cd options IPSEC_DEBUG
 Enables debugging code in IPsec stack.
 See
 .Xr ipsec 4
 for details.
 The
 .Cd IPSEC
 option 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.
 .It Cd options ALTQ
 Enabled ALTQ (Alternate Queueing).
 For simple rate-limiting, use
 .Xr 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
 .Xr altqd 8 .
 See
 .Xr altq 9
 for details.
 .It Cd 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 allocation.
 Requires
 .Em ALTQ_RED
 to use the RED queueing discipline on HFSC classes, or
 .Em ALTQ_RIO
 to use the RIO queueing discipline on HFSC classes.
 This option assumes
 .Em ALTQ .
 .It Cd 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
 .Em ALTQ_RED
 to use the RED queueing discipline on HFSC classes, or
 .Em ALTQ_RIO
 to use the RIO queueing discipline on HFSC classes.
 This option assumes
 .Em ALTQ .
 .It Cd 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
 .Em ALTQ .
 .It Cd 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
 .Em ALTQ .
 .It Cd 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
 .Em ALTQ .
 .It Cd options ALTQ_BLUE
 Include support for ALTQ-implemented Blue buffer management.
 Blue is another active buffer management mechanism.
 This option assumes
 .Em ALTQ .
 .It Cd 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
 .Em ALTQ_RED
 and assumes
 .Em ALTQ .
 .It Cd options ALTQ_CDNR
 Include support for ALTQ-implemented CDNR (diffserv traffic conditioner)
 packet marking/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
 .Em ALTQ .
 .It Cd 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
 .Em ALTQ .
 .It Cd options ALTQ_IPSEC
 Include support for IPsec in IPv4 ALTQ.
 This option assumes
 .Em ALTQ .
 .It Cd options ALTQ_JOBS
 Include support for ALTQ-implemented JoBS (Joint Buffer Management
 and Scheduling).
 This option assumes
 .Em ALTQ .
 .It Cd 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
 .Em ALTQ .
 .It Cd options ALTQ_LOCALQ
 Include support for ALTQ-implemented local queues.
 Its practical use is undefined.
 Assumes
 .Em ALTQ .
 .It Cd options SUBNETSARELOCAL
 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 completely irrelevant if
 you enable Path MTU discovery.
 .It Cd options HOSTZEROBROADCAST
 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.
 .It Cd options MCLSHIFT=value
 This option is the base-2 logarithm of the size of mbuf clusters.
 The
 .Bx
 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
 .Em MCLBYTES ,
 must be a power of two, and is computed as two raised to the power
 .Em MCLSHIFT .
 On systems with Ethernet network adapters,
 .Em 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
 .Em MCLSHIFT
 set to 12 or 13, giving mbuf cluster sizes of 4096 and 8192 bytes,
 respectively.
 .It Cd options NETATALK
 Include support for the AppleTalk protocol stack.
 The kernel provides provision for the
 .Em Datagram Delivery Protocol
 (DDP), providing SOCK_DGRAM support and AppleTalk routing.
 This stack is used by the
 .Em NETATALK
 package, which adds support for AppleTalk server services via user
 libraries and applications.
 .It Cd options BLUETOOTH
 Include support for the Bluetooth protocol stack.
 See
 .Xr bluetooth 4
 for details.
 .It Cd options IPNOPRIVPORTS
 Normally, only root can bind a socket descriptor to a so-called
 .Dq 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.
 .It Cd options TCP_DEBUG
 Record the last
 .Em TCP_NDEBUG
 TCP packets with SO_DEBUG set, and decode to the console if
 .Em tcpconsdebug
 is set.
 .It Cd options TCP_NDEBUG
 Number of packets to record for
 .Em TCP_DEBUG .
 Defaults to 100.
 .It Cd options TCP_SENDSPACE=value
 .It Cd 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
 .Xr sysctl 8
 as well.
 .It Cd 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 aggressively,
 the initial size can be set to some other value.
 The initial TCP window size can be set via
 .Xr sysctl 8
 as well.
 .It Cd options TCP_SIGNATURE
 Enable MD5 TCP signatures (RFC 2385) to protect BGP sessions.
 .It Cd options IPFILTER_LOG
 This option, in conjunction with
 .Em pseudo-device ipfilter ,
 enables logging of IP packets using IP-Filter.
 .It Cd options IPFILTER_LOOKUP
 This option enables the
 IP-Filter
 .Xr ippool 8
 functionality to be enabled.
 .It Cd options IPFILTER_COMPAT
 This option enables older IP-Filter binaries to work.
 .It Cd options IPFILTER_DEFAULT_BLOCK
 This option sets the default policy of IP-Filter.
 If it is set, IP-Filter will block packets by default.
 .It Cd options MBUFTRACE
 This option can help track down mbuf leaks.
 When enabled, mbufs are tagged with the devices and protocols using them.
 This can significantly decrease network performance, particularly
 on MP systems.
 This additional information can be viewed with
 .Xr netstat 1 :
 .Dl Ic netstat Fl mssv
 Not all devices or protocols support this option.
 .El
 .Ss Sysctl Related Options
 .Bl -ohang
 .It Cd options SYSCTL_DISALLOW_CREATE
 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 available to kernel sub-systems, including
 loadable kernel modules.
 .It Cd options SYSCTL_DISALLOW_KWRITE
 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.
 .It Cd options SYSCTL_DEBUG_SETUP
 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.
 .It Cd options SYSCTL_DEBUG_CREATE
 Prints a message each time
 .Fn sysctl_create ,
 the function that adds nodes to the tree, is called.
 .It Cd options SYSCTL_INCLUDE_DESCR
 Causes the kernel to include short, human readable descriptions for
 nodes in the sysctl tree.
 The descriptions can be retrieved programmatically (see
 .Xr sysctl 3 ) ,
 or by the sysctl binary itself (see
 .Xr sysctl 8 ) .
 The descriptions are meant to give an indication of the purpose and/or
 effects of a given node's value, not replace the documentation for the
 given subsystem as a whole.
 .El
 .Ss System V IPC Options
 .Bl -ohang
 .It Cd options SYSVMSG
 Includes support for
 .At V
 style message queues.
 See
 .Xr msgctl 2 ,
 .Xr msgget 2 ,
 .Xr msgrcv 2 ,
 .Xr msgsnd 2 .
 .It Cd options SYSVSEM
 Includes support for
 .At V
 style semaphores.
 See
 .Xr semctl 2 ,
 .Xr semget 2 ,
 .Xr semop 2 .
 .It Cd options SEMMNI=value
 Sets the number of
 .At V
 style semaphore identifiers.
 The GENERIC config file for your port will have the default.
 .It Cd options SEMMNS=value
 Sets the number of
 .At V
 style semaphores in the system.
 The GENERIC config file for your port will have the default.
 .It Cd options SEMUME=value
 Sets the maximum number of undo entries per process for
 .At V
 style semaphores.
 The GENERIC config file for your port will have the default.
 .It Cd options SEMMNU=value
 Sets the number of undo structures in the system for
 .At V
 style semaphores.
 The GENERIC config file for your port will have the default.
 .It Cd options SYSVSHM
 Includes support for
 .At V
 style shared memory.
 See
 .Xr shmat 2 ,
 .Xr shmctl 2 ,
 .Xr shmdt 2 ,
 .Xr shmget 2 .
 .It Cd options SHMMAXPGS=value
 Sets the maximum number of
 .At V
 style shared memory pages that are available through the
 .Xr shmget 2
 system call.
 Default value is 1024 on most ports.
 See
 .Pa /usr/include/machine/vmparam.h
 for the default.
 .El
 .Ss VM Related Options
 .Bl -ohang
 .It Cd options NMBCLUSTERS=value
 The number of mbuf clusters the kernel supports.
 Mbuf clusters are MCLBYTES in size (usually 2k).
 This is used to compute the size of the kernel VM map
 .Em mb_map ,
 which maps mbuf clusters.
 Default on most ports is 1024 (2048 with
 .Dq options GATEWAY
 ).
 See
 .Pa /usr/include/machine/param.h
 for exact default information.
 Increase this value if you get
 .Dq mclpool limit reached
 messages.
 .It Cd options NKMEMPAGES=value
 .It Cd options NKMEMPAGES_MIN=value
 .It Cd options NKMEMPAGES_MAX=value
 Size of kernel VM map
 .Em kmem_map ,
 in PAGE_SIZE-sized chunks (the VM page size; this value may be read
 from the
 .Xr sysctl 8
 variable
 .Em 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
 .Xr sysctl 8
 variable
 .Em vm.nkmempages .
 See
 .Pa /usr/include/machine/param.h
 for the default upper and lower bounds.
 The related options
 .Sq NKMEMPAGES_MIN
 and
 .Sq 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
 .Dq out of space in kmem_map
 panic.
 .It Cd 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
 .Xr sysctl 8
 as well.
 .It Cd 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
 .Xr sysctl 8
 as well.
 .It Cd options BUFCACHE=value
 Size of the buffer cache as a percentage of total available RAM.
 Ignored if BUFPAGES is also specified.
 .It Cd 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.
 .It Cd 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.
 .It Cd options MAXTSIZ=bytes
 Sets the maximum size limit of a process' text segment.
 See
 .Pa /usr/include/machine/vmparam.h
 for the port-specific default.
 .It Cd options DFLDSIZ=bytes
 Sets the default size limit of a process' data segment, the value that
 will be returned as the soft limit for
 .Dv RLIMIT_DATA
 (as returned by
 .Xr getrlimit 2 ) .
 See
 .Pa /usr/include/machine/vmparam.h
 for the port-specific default.
 .It Cd options MAXDSIZ=bytes
 Sets the maximum size limit of a process' data segment, the value that
 will be returned as the hard limit for
 .Dv RLIMIT_DATA
 (as returned by
 .Xr getrlimit 2 ) .
 See
 .Pa /usr/include/machine/vmparam.h
 for the port-specific default.
 .It Cd options DFLSSIZ=bytes
 Sets the default size limit of a process' stack segment, the value that
 will be returned as the soft limit for
 .Dv RLIMIT_STACK
 (as returned by
 .Xr getrlimit 2 ) .
 See
 .Pa /usr/include/machine/vmparam.h
 for the port-specific default.
 .It Cd options MAXSSIZ=bytes
 Sets the maximum size limit of a process' stack segment, the value that
 will be returned as the hard limit for
 .Dv RLIMIT_STACK
 (as returned by
 .Xr getrlimit 2 ) .
 See
 .Pa /usr/include/machine/vmparam.h
 for the port-specific default.
 .It Cd options DUMP_ON_PANIC=integer
 Defaults to one.
 If set to zero, the kernel will not dump to the dump device when
 it panics, though dumps can still be forced via
 .Xr ddb 4
 with the
 .Dq sync
 command.
 Note that this sets the value of the