1.\" $OpenBSD: options.4,v 1.271 2024/05/05 07:26:58 jsg Exp $ 2.\" $NetBSD: options.4,v 1.21 1997/06/25 03:13:00 thorpej Exp $ 3.\" 4.\" Copyright (c) 1998 Theo de Raadt 5.\" Copyright (c) 1998 Todd Miller 6.\" Copyright (c) 1998 Gene Skonicki 7.\" Copyright (c) 1996 8.\" Perry E. Metzger. All rights reserved. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. All advertising materials mentioning features or use of this software 19.\" must display the following acknowledgment: 20.\" This product includes software developed for the NetBSD Project 21.\" by Perry E. Metzger. 22.\" 4. The name of the author may not be used to endorse or promote products 23.\" derived from this software without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 26.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 27.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 28.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 29.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 30.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 31.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 32.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 33.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 34.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 35.\" 36.\" 37.Dd $Mdocdate: May 5 2024 $ 38.Dt OPTIONS 4 39.Os 40.Sh NAME 41.Nm options 42.Nd kernel configuration options 43.Sh SYNOPSIS 44.Cd option ... 45.Sh DESCRIPTION 46This manual page describes a number of miscellaneous kernel 47configuration options that may be specified in a kernel config file. 48See 49.Xr config 8 50for information on how to configure and build kernels. 51.Em Note : 52options are passed to the compile process as 53.Fl D 54flags to the C compiler. 55.Sh DEBUGGING OPTIONS 56.Bl -ohang 57.It Cd makeoptions DEBUG="" 58Do not build the debug kernel 59.Pa bsd.gdb . 60Normally, 61.Pa bsd.gdb 62is built 63(in addition to the regular 64.Pa bsd 65kernel) 66and is used for debugging kernels and their crash dumps with 67.Xr gdb 1 . 68A crash dump can be debugged by starting gdb with 69.Pa bsd.gdb 70as an argument (no core file) and then using the gdb command 71.Dq target kvm COREFILE . 72.It Cd makeoptions PROF="-pg" 73The 74.Fl pg 75flag causes the kernel to be compiled with support for profiling. 76The 77.Cm option GPROF 78is required for the kernel compile to succeed. 79.It Cd option ACCOUNTING 80Adds support for the 81.Xr acct 2 82system call. 83.It Cd option DDB 84Compiles in a kernel debugger for diagnosing kernel problems. 85See 86.Xr ddb 4 . 87.It Cd option DDB_SAFE_CONSOLE 88Allows a break into the kernel debugger during boot. 89Useful when debugging problems that can cause 90.Xr init 8 91to fail. 92.It Cd option DEBUG 93Turns on miscellaneous kernel debugging. 94Since options are turned into preprocessor defines (see above), 95.Cm option DEBUG 96is equivalent to doing a 97.Em #define DEBUG 98throughout the kernel. 99Much of the kernel has 100.Em #ifdef DEBUG 101conditional debugging code. 102Note that many parts of the kernel (typically device drivers) include their own 103.Em #ifdef XXX_DEBUG 104conditionals instead. 105.It Cd option DIAGNOSTIC 106Adds code to the kernel that does internal consistency checks. 107This code will cause the kernel to panic if corruption of internal data 108structures is detected. 109.It Cd option GPROF 110Adds code to the kernel for kernel profiling with 111.Xr kgmon 8 . 112.It Cd option KTRACE 113Adds hooks for the system call tracing facility, which allows users to 114watch the system call invocation behavior of processes. 115See 116.Xr ktrace 1 . 117.It Cd option KUBSAN 118Detect undefined behavior in the kernel. 119See 120.Xr kubsan 4 . 121.It Cd option NO_PROPOLICE 122Do not compile the kernel with the ProPolice stack protection. 123See 124.Xr gcc-local 1 125for more information about ProPolice. 126.It Cd option PTRACE 127Adds hooks for the process tracing facility, allowing a process to 128control and observe another process. 129See 130.Xr ptrace 2 . 131.It Cd option SMALL_KERNEL 132Removes some features and some optimizations from the kernel to reduce the 133size of the resulting kernel binary. 134This option is used on some installation media and should not be used 135for general purpose kernels. 136.It Cd option VFSLCKDEBUG 137Turns on debugging for the Virtual File System interface. 138See 139.Xr vfs 9 . 140.It Cd option WITNESS 141Compiles in a lock checker for detecting lock order violations in the kernel. 142See 143.Xr witness 4 . 144.It Cd option WITNESS_COUNT= Ns Ar integer 145Maximum number of lock types that are tracked by 146.Xr witness 4 . 147It defaults to 1536. 148.It Cd option WITNESS_LOCKTRACE 149Enable 150.Xr witness 4 151lock stack trace saving at boot. 152The feature is disabled by default and has to be enabled by setting the 153.Va kern.witness.locktrace 154.Xr sysctl 8 155variable. 156.It Cd option WITNESS_WATCH 157Enable 158.Xr witness 4 159at boot. 160By default, the subsystem is disabled and has to be enabled at runtime 161by raising the 162.Va kern.witness.watch 163.Xr sysctl 8 164variable. 165.El 166.Sh FILE SYSTEMS 167.Bl -ohang 168.It Cd option CD9660 169Includes code for the ISO 9660 + Rock Ridge file system, which is the 170standard file system used on many CD-ROMs. 171It also supports Joliet extensions. 172See 173.Xr mount_cd9660 8 . 174.It Cd option EXT2FS 175Includes code implementing the Second Extended File System 176.Em ( EXT2FS ) , 177commonly used on the Linux operating system. 178This option is provided here for compatibility. 179Some specific features of 180.Em EXT2FS 181like the "behavior on errors" are not implemented. 182This file system 183can't be used with 184.Vt uid_t 185or 186.Vt gid_t 187values greater than 65535. 188Also, the filesystem will not function correctly on architectures with 189differing byte-orders. 190That is, a big-endian machine will not be able to read an 191ext2fs filesystem created on an i386 or other little-endian machine. 192See 193.Xr mount_ext2fs 8 . 194.It Cd option FFS 195Includes code implementing the Berkeley Fast File System 196.Em ( FFS ) . 197Most machines need this if they are not running diskless. 198.It Cd option FFS2 199Includes code implementing the enhanced Fast File System 200.Em ( FFS2 ) . 201.It Cd option MFS 202Include the memory file system 203.Em ( MFS ) . 204This file system stores files in swappable memory, and produces 205notable performance improvements when it is used as the file store 206for 207.Pa /tmp 208or similar mount points. 209See 210.Xr mount_mfs 8 . 211.It Cd option MSDOSFS 212Includes support for the MS-DOS FAT file system. 213The kernel also implements the Windows 95 214extensions which permit the use of longer, mixed-case file names. 215See 216.Xr mount_msdos 8 217and 218.Xr fsck_msdos 8 . 219.It Cd option NFSCLIENT 220Include the client side of the 221.Em NFS 222(Network File System) remote file sharing protocol. 223Although the bulk of the code implementing 224.Em NFS 225is kernel based, several user level daemons are needed for it to work. 226See 227.Xr mount_nfs 8 228for details on NFS. 229.It Cd option NTFS 230Includes support for reading NTFS file systems. 231See 232.Xr mount_ntfs 8 . 233.It Cd option UDF 234Includes code for the UDF file systems typically found on DVD discs. 235See 236.Xr mount_udf 8 . 237.It Cd option TMPFS 238Includes code for the TMPFS efficient memory file system. 239See 240.Xr mount_tmpfs 8 . 241.El 242.Sh FILE SYSTEM OPTIONS 243.Bl -ohang 244.It Cd option BUFCACHEPERCENT= Ns Ar integer 245The maximum percentage of DMA-reachable physical memory the buffer cache may use. 246.It Cd option EXT2FS_SYSTEM_FLAGS 247This option changes the behavior of the APPEND and IMMUTABLE flags 248for a file on an 249.Em EXT2FS 250filesystem. 251Without this option, the superuser or owner of the file can set and clear them. 252With this option, only the superuser can set them, and they can't be cleared 253if the securelevel is greater than 0. 254See also 255.Xr chflags 1 . 256.It Cd option FIFO 257Adds support for 258.At V 259style FIFOs (i.e., 260.Dq named pipes ) . 261This option is recommended in almost all cases as many programs use these. 262.It Cd option NFSSERVER 263Include the server side of the 264.Em NFS 265(Network File System) remote file sharing protocol. 266Although the bulk of the code implementing 267.Em NFS 268is kernel based, several user level daemons are needed for it to 269work. 270See 271.Xr mountd 8 272and 273.Xr nfsd 8 . 274.It Cd option QUOTA 275Enables kernel support for file system quotas. 276See 277.Xr quotaon 8 , 278.Xr edquota 8 , 279.Xr repquota 8 , 280and 281.Xr quota 1 . 282Note that quotas only work on 283.Dq ffs 284file systems, although 285.Xr rpc.rquotad 8 286permits them to be accessed over 287.Em NFS . 288.It Cd option UFS_DIRHASH 289This option enables using an in memory hash table to speed lookups 290in large directories. 291.El 292.Sh MISCELLANEOUS OPTIONS 293.Bl -ohang 294.It Cd option APERTURE 295Provide in-kernel support for controlling VGA framebuffer mapping 296and PCI configuration registers by user-processes 297(such as an X Window System server). 298See 299.Xr xf86 4 . 300This option is supported on the 301.Va alpha , 302.Va amd64 , 303.Va i386 , 304.Va macppc , 305and 306.Va sparc64 307architectures. 308.It Cd option BOOT_CONFIG 309Adds support for the 310.Fl c 311boot option (User Kernel Config). 312Allows modification of kernel settings (e.g., device parameters) before 313booting the system. 314See 315.Xr boot_config 8 . 316.It Cd option CRYPTO 317Enables support for the kernel cryptographic framework. 318See 319.Xr crypto 9 . 320While not IP specific, this option is usually used in conjunction with option 321.Em IPSEC . 322.It Cd option EISAVERBOSE 323Makes the boot process more verbose for EISA peripherals. 324See 325.Xr eisa 4 . 326.It Cd option KMEMSTATS 327The kernel memory allocator, 328.Xr malloc 9 , 329will keep statistics on its performance if this option is enabled. 330.It Cd option MULTIPROCESSOR 331On those architectures that have it, this enables multiprocessor support. 332.It Cd option PCIVERBOSE 333Makes the boot process more verbose for PCI peripherals 334(vendor names and other information is printed, etc.). 335See 336.Xr pci 4 . 337.It Cd option PCMCIAVERBOSE 338Makes the boot process more verbose for PCMCIA peripherals. 339See 340.Xr pcmcia 4 . 341.It Cd option USER_PCICONF 342Enables the user level access to the PCI bus configuration space 343through ioctls on the 344.Pa /dev/pci 345device. 346It's used by 347.Xr Xorg 1 348and 349.Xr pcidump 8 . 350See 351.Xr pci 4 . 352.It Cd option UVM_SWAP_ENCRYPT 353Enables kernel support for encrypting pages that are written out to 354swap storage. 355Swap encryption prevents sensitive data from remaining 356on the disk even after the operating system has been shut down. 357This option should be turned on if cryptographic filesystems are used. 358The sysctl variable 359.Em vm.swapencrypt.enable 360controls its behaviour. 361See 362.Xr sysctl 8 363and 364.Xr sysctl 2 . 365.El 366.Sh NETWORKING OPTIONS 367.Bl -ohang 368.It Cd option ENCDEBUG 369This option permits the conditional logging of IPsec debugging information, 370and requires the 371.Em IPSEC 372option. 373Debug logging can be turned on/off through the use of the 374.Em net.inet.ip.encdebug 375sysctl variable. 376If 377.Em net.inet.ip.encdebug 378is 1, debug logging is on. 379See 380.Xr sysctl 8 381and 382.Xr sysctl 2 . 383.It Cd option INET6 384Includes support for the IPv6 protocol stack. 385See 386.Xr inet6 4 . 387.Em INET6 388enables multicast routing code as well. 389.It Cd option IPSEC 390This option enables IP security protocol support. 391See 392.Xr ipsec 4 393for more details. 394.It Cd option MROUTING 395Includes support for IP multicast routers. 396Multicast routing is controlled by the 397.Xr mrouted 8 398daemon. 399.It Cd option ND6_DEBUG 400The option sets the default value of 401.Em net.inet6.icmp6.nd6_debug 402to 1, 403for debugging IPv6 neighbor discovery protocol handling. 404See 405.Xr sysctl 2 . 406.It Cd option PIPEX 407Includes pipex in-kernel acceleration for PPPoE, L2TP or PPTP. 408See 409.Xr pipex 4 . 410.It Cd option PPP_BSDCOMP 411Enables BSD compressor for PPP connections. 412.It Cd option PPP_DEFLATE 413For use in conjunction with PPP_BSDCOMP; provides an interface to zlib for PPP 414for deflate compression/decompression. 415.It Cd option PPPOE_TERM_UNKNOWN_SESSIONS 416Send PADT to terminate open sessions before connecting. 417See 418.Xr pppoe 4 . 419.It Cd option SOCKET_SPLICE 420Enables zero-copy socket splicing in the kernel. 421See 422.Dv SO_SPLICE 423in 424.Xr setsockopt 2 425and 426.Xr sosplice 9 . 427.It Cd option TCP_ECN 428Turns on Explicit Congestion Notification (RFC 3168). 429.Em ECN 430allows intermediate routers to use the Congestion Experienced 431codepoint in the IP header as an indication of congestion, and allows 432TCP to adjust the transmission rate using this signal. 433Both communication endpoints negotiate enabling 434.Em ECN 435functionality at the TCP connection establishment. 436.It Cd option TCP_SIGNATURE 437Turns on support for the TCP MD5 Signature option (RFC 2385). 438This is used by 439Internet backbone routers to provide per-packet authentication for the TCP 440packets used to communicate BGP routing information. 441You will also need a 442routing daemon that supports this option in order to actually use it. 443.El 444.Sh OPERATION RELATED OPTIONS 445.Bl -ohang -compact 446.It Cd option BUFPAGES= Ns Ar value 447This option sets the number of pages available for the buffer cache. 448The default value is machine dependent, often calculated as 449between 5% and 10% of total available RAM. 450.Pp 451.It Cd option NKMEMPAGES= Ns Ar value 452Size of kernel malloc area in PAGE_SIZE-sized logical pages. 453This area is covered by the kernel submap 454.Em kmem_map . 455The kernel attempts to auto-size this map based on the amount of 456physical memory in the system. 457Platform-specific code may place bounds on this computed size, 458which may be viewed with the 459.Xr sysctl 8 460variable 461.Em vm.nkmempages . 462.El 463.Sh SCSI SUBSYSTEM OPTIONS 464See 465.Xr scsi 4 . 466.Bl -ohang 467.It Cd option SCSI_DELAY= Ns Ar value 468Delay for 469.Ar value 470seconds before starting to probe the first SCSI bus. 471This can be used if a SCSI device needs extra time to get ready. 472.It Cd option SCSIDEBUG 473Enable printing of SCSI subsystem debugging info to the console. 474Debugging info on the probing and attachment of all SCSI devices will 475be printed. 476.Pp 477Additional information can be requested by setting 478.Em SCSIDEBUG_BUSES , 479.Em SCSIDEBUG_LEVEL , 480.Em SCSIDEBUG_LUNS 481and 482.Em SCSIDEBUG_TARGETS . 483.It Cd option SCSIDEBUG_BUSES= Ns Ar value 484Define which SCSI buses will print debug info. 485Each bit enables debugging info for the corresponding bus. 486e.g. a value of 0x1 enables debug info for bus 0. 487.It Cd option SCSIDEBUG_LEVEL= Ns Ar value 488Define which of the four levels of debugging info are printed. 489Each bit enables a level, and multiple levels are specified by setting multiple 490bits. 491.Bd -literal -offset indent 4920x0010 (SDEV_DB1) SCSI commands, errors, and data 4930x0020 (SDEV_DB2) routine flow 4940x0040 (SDEV_DB3) routine internals 4950x0080 (SDEV_DB4) miscellaneous addition debugging 496.Ed 497.Pp 498.Em SCSIDEBUG_LEVEL 499defaults to a value of 0x0030 (SDEV_DB1|SDEV_DB2). 500.It Cd option SCSIDEBUG_LUNS= Ns Ar value 501Define which SCSI luns will print debug info. 502Each bit enables debugging info for the corresponding lun. 503.It Cd option SCSIDEBUG_TARGETS= Ns Ar value 504Define which SCSI targets will print debug info. 505Each bit enables debugging info for the corresponding target. 506.It Cd option SCSITERSE 507Terser SCSI error messages. 508This omits the table for decoding ASC/ASCQ info, saving about 30KB. 509.El 510.Sh SYSTEM V IPC OPTIONS 511.Bl -ohang 512.It Cd option SEMMNI= Ns Ar value 513Number of semaphore identifiers (also called semaphore handles 514and semaphore sets) available in the system. 515Default value is 10. 516The kernel allocates memory for the control structures at startup, 517so arbitrarily large values should be avoided. 518.It Cd option SEMMNS= Ns Ar value 519Maximum number of semaphores in all sets in the system. 520Default value is 60. 521.It Cd option SEMMNU= Ns Ar value 522Maximum number of semaphore undo structures in the system. 523Default value is 30. 524.It Cd option SEMUME= Ns Ar value 525Maximum number of per-process undo operation entries in the 526system. 527Semaphore undo operations are invoked by the kernel when 528.Xr semop 2 529is called with the SEM_UNDO flag and the process holding 530the semaphores terminates unexpectedly. 531Default value is 10. 532.It Cd option SHMMAXPGS= Ns Ar value 533Sets the maximum number of 534.At V 535style shared memory pages that are available through the 536.Xr shmget 2 537system call. 538Default value is 1024 on most architectures. 539See 540.Pa /usr/include/machine/vmparam.h 541for the default. 542.It Cd option SYSVMSG 543Includes support for 544.At V 545style message queues. 546See 547.Xr msgctl 2 , 548.Xr msgget 2 , 549.Xr msgrcv 2 , 550.Xr msgsnd 2 . 551.It Cd option SYSVSEM 552Includes support for 553.At V 554style semaphores. 555See 556.Xr semctl 2 , 557.Xr semget 2 , 558.Xr semop 2 . 559.It Cd option SYSVSHM 560Includes support for 561.At V 562style shared memory. 563See 564.Xr shmat 2 , 565.Xr shmctl 2 , 566.Xr shmdt 2 , 567.Xr shmget 2 . 568.El 569.Sh SEE ALSO 570.Xr intro 4 , 571.Xr files.conf 5 , 572.Xr config 8 , 573.Xr sysctl 8 574.Sh HISTORY 575The 576.Nm 577man page first appeared in 578.Ox 2.3 . 579