OPTIONS(4)

NAME
options - Miscellaneous kernel configuration options

SYNOPSIS
options ...

DESCRIPTION
This manual page describes a number of miscellaneous kernel configuration options that may be specified in a kernel config file. See config(8) for information on how to configure and build kernels. Note: Options are passed to the compile process as -D flags to the C compiler.

  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 filesystem 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 filesystem 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 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.

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 disklabel is re-written, the old style label will be replaced with a post 1.1 style label.

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.

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_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 provides backwards compatibility with “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 4.4BSD socket calls.

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

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 is currently limited to the i386.

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 and most or all m68k platforms.

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.

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

options COMPAT_HPUX
On those architectures that support it, this enables binary compatibility with HP/UX applications built for the same architecture. This is limited to the hp300 port, and has some known bugs. A limited set of programs do work.

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

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, and may not even work.

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) formats.

  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 special key sequence on a graphics console. A value of "0" ignores console breaks or key sequences, It 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
If set to non-zero, the DDB will be entered upon kernel panic. The default if not specified is "1". 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 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.

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. The command
    gdb -k
invokes gdb in kernel debugger mode. 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 performance.

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.

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.

  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 (EXT2FS). 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 EXT2FS like the "behavior on errors" are not implemented. This file system can't be used with UID or GID greater than 65535. See mount_ext2fs(8) for details.

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

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 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) pseudodevice driver already provides identical functionality. 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 PORTAL
[EXPERIMENTAL] Includes the portal filesystem. This permits interesting tricks like opening TCP sockets by opening files in the file system. The portal file system is conventionally mounted on /p and is partially implemented by a special daemon. See mount_portal(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 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 filesystem to work.

  File System Options

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) permits them to be accessed over NFS.

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

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.

options EXT2FS_SYSTEM_FLAGS
This option changes the behavior of the APPEND and IMMUTABLE flags for a file on an EXT2FS filesystem. 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).

options NFS_BOOT_BOOTP
Enable use of the BOOTP protocol (RFC 951, 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).

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 diskless(8) for details.

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 filesystem. See mount_nfs(8) for details.

  Miscellaneous Options

options LKM
Enable loadable kernel modules. See lkm(4) for details. NOTE: not available on all architectures.

options INSECURE
Hardwires the kernel security level at -1. This means that the system always runs in secure level 0 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 sysctl(8) and sysctl(3).

options UCONSOLE
Normally, only the superuser can execute the TIOCCONS ioctl(2), which redirects console output to a non-console tty. See tty(4) for details. This option permits any user to execute the TIOCCONS ioctl(2). This is useful on machines such as personal workstations which run X(1) servers, where one would prefer to permit console output to be viewed in a window without requiring a suid root program to do it.

options MEMORY_DISK_HOOKS
This option allows for some machine dependent functions to be called when the 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 RAM disk to be the root device. This can only be overridden when the kernel is booted in the 'ask-for-root' mode.

options NTP
Turns on in-kernel precision timekeeping support used by software implementing NTP (Network Time Protocol, RFC1305). The NTP option adds an in-kernel Phase-Locked Loop (PLL) for normal NTP operation, and a Frequency-Locked Loop (FLL) for intermittently-connected operation. xntpd(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 xntpd(8) and are enabled by the option. On systems 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) signal 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 precision (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 shipped with the xntpd distribution.

option 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 option FDSCRIPTS

option 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 correct script is run by the interpreter, as it is passed as an already open file.

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 operating 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 patching the kernel and rebooting).

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 certain critical sections of code in the kernel. This option therefore can lead to a significant decrease in the performance of certain code in the kernel if enabled. Examples of such code include the namei() routine, the ccd(4) driver, the ncr(4) driver, and much of the networking code.

options MAXUPRC=integer
Sets the 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 CHILD_MAX, which is currently defined to be 80. Setting MAXUPRC to a value less than CHILD_MAX is not permitted, as this would result in a violation of the semantics of p1003.1-90.

options SHORTCORENAME
If set, process core dumps are named core. If not specified, they are named programname.core (the default in 4.4BSD). Note that this changes the value of the kern.shortcorename sysctl variable which may be changed at run time. See sysctl(8) and sysctl(3) for details.

  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 or XNS).

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 (currently) internet and appletalk addresses. This can be a fairly expensive operation, so you probably want to keep this disabled.

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

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

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 adaptors, 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 NS
Include support for the Xerox XNS protocol stack. See ns(4) for details.

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

options EON
Include support for tunneling OSI protocols over IP.

options CCITT,LLC,HDLC
Include support for the CCITT (nee ITU-TSS) X.25 protocol stack. The state of this code is currently unknown, and probably contains bugs.

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

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

options IPFILTER_DEFAULT_BLOCK
This option sets the default policy of ip-filter. If it is set, ip-filter will block packets by default.

options PPP_BSDCOMP
Enable support for BSD-compress (‘bsdcomp’) compression in ppp.

options PPP_DEFLATE
Enable support for deflate compression in ppp.

options PPP_FILTER
This option turns on pcap(3) based filtering for ppp connections. This option is used by pppd(8) which needs to be compiled with PPP_FILTER defined (the current default).

  System V IPC Options

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

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

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

options SHMMAXPGS=value
Sets the maximum number of AT&T 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 (usually 2k). This is used to compute the size of the kernel VM map mb_map, which maps mbuf clusters. Default on most ports is 256 (512 with “options GATEWAY” ). See /usr/include/machine/param.h for exact default information. Increase this value if you get “mb_map full” messages.

options NKMEMCLUSTERS=value
Size of kernel VM map kmem_map, in CLBYTES-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. See /usr/include/machine/param.h for the default value, which is port specific. Increase this value if you get “out of space in kmem_map” panics.

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

options NBUF=value

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.

  amiga-specific Options

options BB060STUPIDROM
When the bootloader (which passes AmigaOS ROM information) claims we have a 68060 CPU without 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 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 second 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.

  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 automatically. 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 I386_CPU,I486_CPU,I586_CPU,I686_CPU
Include support for a particular class of CPU ( i386, i486, Pentium, or Pentium Pro). If the appropriate class for your CPU is not configured, the kernel will use the highest class available that will work. In general, using the correct CPU class will result in the best performance. At least one of these options must be present.

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 operations (like NFS unmounts, buffer cache flush, etc ...). Setting this to 0 will disable the delay. Default is 2 seconds.

options MATH_EMULATE
Include the floating point emulator. This is useful only for CPUs that lack an internal Floating Point Unit (FPU) or co-processor.

options VM86
Include support for virtual 8086 mode, used by DOS emulators.

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

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 kilobytes. Extended memory does not include the first megabyte.) Use this option only if the boot block reports the size incorrectly.

options FRENCH_KBD,FINNISH_KBD,GERMAN_KBD,NORWEGIAN_KBD
Select a non-US keyboard layout for the pccons console driver.

  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 specified.

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.

  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).

options COUNT_SW_LEFTOVERS
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 accessable from ddb(4). See sw(4).

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.

options EXTREME_EXTREME_DEBUG
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.

options RASTERCONS_FULLSCREEN
Use the entire screen for the console.

options RASTERCONS_SMALLFONT
Use a 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).

  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 9600.

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

SEE ALSO
config(8), init(8), gettimeofday(2), sysctl(8), sysctl(3), xntpd(8), ntp_adjtime(2), ntp_gettime(2), i386_iopl(2), msgctl(2), msgget(2), msgrcv(2), msgsnd(2), semctl(2), semget(2), semop(2), shmat(2), shmctl(2), shmdt(2), shmget(2), ddb(4), lkm(4), inet(4), ns(4), iso(4), mrouted(8), mount_lfs(8), newlfs(8), mount_mfs(8), mount_nfs(8), mount_cd9660(8), mount_msdos(8), mount_fdesc(8), mount_kernfs(8), mount_null(8), mount_portal(8), mount_procfs(8), mount_umap(8), mount_union(8), edquota(8), quotaon(8), quota(1), rpc.rquotad(8), ktrace(1), gdb(1)

HISTORY
The options man page first appeared in NetBSD 1.3.

BUGS
The INET and the VNODEPAGER options should not be required.