1.\" $OpenBSD: options.4,v 1.265 2019/05/05 19:06:56 jmc 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 2019 $ 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.Li uid_t 185or 186.Li 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 FFS_SOFTUPDATES 257Enables a scheme that uses partial ordering of buffer cache operations 258to allow metadata updates in FFS to happen asynchronously, increasing write 259performance significantly. 260Normally, the FFS filesystem writes metadata updates synchronously which exacts 261a performance penalty in favor of filesystem integrity. 262With soft updates, the performance of asynchronous writes is gained while 263retaining the safety of synchronous metadata updates. 264.Pp 265Soft updates must be enabled on a per-filesystem basis. 266See 267.Xr mount 8 . 268.Pp 269Processors with a small kernel address space, such as the sun4 and sun4c, do 270not have enough kernel memory to support soft updates. 271Attempts to use this option with these CPUs will cause a kernel hang or panic 272after a short period of use as the kernel will quickly run out of memory. 273This is not related to the amount of physical memory present in the 274machine \(em it is a limitation of the CPU architecture itself. 275.It Cd option FIFO 276Adds support for 277.At V 278style FIFOs (i.e., 279.Dq named pipes ) . 280This option is recommended in almost all cases as many programs use these. 281.It Cd option NFSSERVER 282Include the server side of the 283.Em NFS 284(Network File System) remote file sharing protocol. 285Although the bulk of the code implementing 286.Em NFS 287is kernel based, several user level daemons are needed for it to 288work. 289See 290.Xr mountd 8 291and 292.Xr nfsd 8 . 293.It Cd option QUOTA 294Enables kernel support for file system quotas. 295See 296.Xr quotaon 8 , 297.Xr edquota 8 , 298.Xr repquota 8 , 299and 300.Xr quota 1 . 301Note that quotas only work on 302.Dq ffs 303file systems, although 304.Xr rpc.rquotad 8 305permits them to be accessed over 306.Em NFS . 307.It Cd option UFS_DIRHASH 308This option enables using an in memory hash table to speed lookups 309in large directories. 310.El 311.Sh MISCELLANEOUS OPTIONS 312.Bl -ohang 313.It Cd option APERTURE 314Provide in-kernel support for controlling VGA framebuffer mapping 315and PCI configuration registers by user-processes 316(such as an X Window System server). 317See 318.Xr xf86 4 . 319This option is supported on the 320.Va alpha , 321.Va amd64 , 322.Va i386 , 323.Va macppc , 324and 325.Va sparc64 326architectures. 327.It Cd option BOOT_CONFIG 328Adds support for the 329.Fl c 330boot option (User Kernel Config). 331Allows modification of kernel settings (e.g., device parameters) before 332booting the system. 333See 334.Xr boot_config 8 . 335.It Cd option CRYPTO 336Enables support for the kernel cryptographic framework. 337See 338.Xr crypto 9 . 339While not IP specific, this option is usually used in conjunction with option 340.Em IPSEC . 341.It Cd option EISAVERBOSE 342Makes the boot process more verbose for EISA peripherals. 343See 344.Xr eisa 4 . 345.It Cd option KMEMSTATS 346The kernel memory allocator, 347.Xr malloc 9 , 348will keep statistics on its performance if this option is enabled. 349.It Cd option MULTIPROCESSOR 350On those architectures that have it, this enables multiprocessor support. 351.It Cd option PCIVERBOSE 352Makes the boot process more verbose for PCI peripherals 353(vendor names and other information is printed, etc.). 354See 355.Xr pci 4 . 356.It Cd option PCMCIAVERBOSE 357Makes the boot process more verbose for PCMCIA peripherals. 358See 359.Xr pcmcia 4 . 360.It Cd option USER_PCICONF 361Enables the user level access to the PCI bus configuration space 362through ioctls on the 363.Pa /dev/pci 364device. 365It's used by 366.Xr Xorg 1 367and 368.Xr pcidump 8 . 369See 370.Xr pci 4 . 371.It Cd option UVM_SWAP_ENCRYPT 372Enables kernel support for encrypting pages that are written out to 373swap storage. 374Swap encryption prevents sensitive data from remaining 375on the disk even after the operating system has been shut down. 376This option should be turned on if cryptographic filesystems are used. 377The sysctl variable 378.Em vm.swapencrypt.enable 379controls its behaviour. 380See 381.Xr sysctl 8 382and 383.Xr sysctl 2 . 384.El 385.Sh NETWORKING OPTIONS 386.Bl -ohang 387.It Cd option ENCDEBUG 388This option permits the conditional logging of IPsec debugging information, 389and requires the 390.Em IPSEC 391option. 392Debug logging can be turned on/off through the use of the 393.Em net.inet.ip.encdebug 394sysctl variable. 395If 396.Em net.inet.ip.encdebug 397is 1, debug logging is on. 398See 399.Xr sysctl 8 400and 401.Xr sysctl 2 . 402.It Cd option INET6 403Includes support for the IPv6 protocol stack. 404See 405.Xr inet6 4 . 406.Em INET6 407enables multicast routing code as well. 408.It Cd option IPSEC 409This option enables IP security protocol support. 410See 411.Xr ipsec 4 412for more details. 413.It Cd option MROUTING 414Includes support for IP multicast routers. 415Multicast routing is controlled by the 416.Xr mrouted 8 417daemon. 418.It Cd option ND6_DEBUG 419The option sets the default value of 420.Em net.inet6.icmp6.nd6_debug 421to 1, 422for debugging IPv6 neighbor discovery protocol handling. 423See 424.Xr sysctl 2 . 425.It Cd option PIPEX 426Includes pipex in-kernel acceleration for PPPoE, L2TP or PPTP. 427See 428.Xr pipex 4 . 429.It Cd option PPP_BSDCOMP 430Enables BSD compressor for PPP connections. 431.It Cd option PPP_DEFLATE 432For use in conjunction with PPP_BSDCOMP; provides an interface to zlib for PPP 433for deflate compression/decompression. 434.It Cd option PPPOE_TERM_UNKNOWN_SESSIONS 435Send PADT to terminate open sessions before connecting. 436See 437.Xr pppoe 4 . 438.It Cd option SOCKET_SPLICE 439Enables zero-copy socket splicing in the kernel. 440See 441.Dv SO_SPLICE 442in 443.Xr setsockopt 2 444and 445.Xr sosplice 9 . 446.It Cd option TCP_ECN 447Turns on Explicit Congestion Notification (RFC 3168). 448.Em ECN 449allows intermediate routers to use the Congestion Experienced 450codepoint in the IP header as an indication of congestion, and allows 451TCP to adjust the transmission rate using this signal. 452Both communication endpoints negotiate enabling 453.Em ECN 454functionality at the TCP connection establishment. 455.It Cd option TCP_SIGNATURE 456Turns on support for the TCP MD5 Signature option (RFC 2385). 457This is used by 458Internet backbone routers to provide per-packet authentication for the TCP 459packets used to communicate BGP routing information. 460You will also need a 461routing daemon that supports this option in order to actually use it. 462.El 463.Sh OPERATION RELATED OPTIONS 464.Bl -ohang -compact 465.It Cd option BUFPAGES= Ns Ar value 466This option sets the number of pages available for the buffer cache. 467The default value is machine dependent, often calculated as 468between 5% and 10% of total available RAM. 469.Pp 470.It Cd option DST= Ns Ar value 471If 472.Ar value 473is non-zero, indicates that the hardware real-time clock device 474is one hour ahead of the offset given in 475.Sq TIMEZONE , 476due to Daylight Saving Time (DST). 477If 478.Ar value 479is zero, the hardware real-time clock device is not in Daylight Saving Time. 480.Pp 481.It Cd option NKMEMPAGES= Ns Ar value 482.It Cd option NKMEMPAGES_MAX= Ns Ar value 483Size of kernel malloc area in PAGE_SIZE-sized logical pages. 484This area is covered by the kernel submap 485.Em kmem_map . 486The kernel attempts to auto-size this map based on the amount of 487physical memory in the system. 488Platform-specific code may place bounds on this computed size, 489which may be viewed with the 490.Xr sysctl 8 491variable 492.Em vm.nkmempages . 493See 494.Pa /usr/include/machine/param.h 495for the default upper bound. 496The related option 497.Sq NKMEMPAGES_MAX 498allows the bounds to be overridden in the kernel configuration file 499in the event the computed value is insufficient resulting in an 500.Dq out of space in kmem_map 501panic. 502.Pp 503.It Cd option \&"TIMEZONE= Ns Ar value Ns Cm \&" 504.Ar value 505indicates the time zone offset of the hardware real-time clock device, 506in minutes, 507from UTC. 508It is useful when the hardware real-time clock device is configured 509with local time, 510when dual-booting 511.Ox 512with other operating systems on a single machine. 513For instance, if the hardware real-time clock is set to Tokyo time, 514.Ar value 515should be 516.Li \&-540 517as Tokyo local time is 9 hours ahead of UTC. 518Double quotes are needed when specifying a negative 519.Ar value . 520.El 521.Sh SCSI SUBSYSTEM OPTIONS 522See 523.Xr scsi 4 . 524.Bl -ohang 525.It Cd option SCSI_DELAY= Ns Ar value 526Delay for 527.Ar value 528seconds before starting to probe the first SCSI bus. 529This can be used if a SCSI device needs extra time to get ready. 530.It Cd option SCSIDEBUG 531Enable printing of SCSI subsystem debugging info to the console. 532Each of 533.Em SCSIDEBUG_LEVEL , 534.Em SCSIDEBUG_BUSES , 535.Em SCSIDEBUG_TARGETS 536and 537.Em SCSIDEBUG_LUNS 538must have non-zero values for any debugging info to be printed. 539Only 540.Em SCSIDEBUG_LEVEL 541has a default value (SDEV_DB1 | SDEV_DB2) that is non-zero. 542.It Cd option SCSIDEBUG_BUSES= Ns Ar value 543Define which SCSI buses will print debug info. 544Each bit enables debugging info for the corresponding bus. 545e.g. a value of 0x1 enables debug info for bus 0. 546.It Cd option SCSIDEBUG_LEVEL= Ns Ar value 547Define which of the four levels of debugging info are printed. 548Each bit enables a level, and multiple levels are specified by setting multiple 549bits. 550.Bd -literal -offset indent 5510x0010 (SDEV_DB1) SCSI commands, errors, and data 5520x0020 (SDEV_DB2) routine flow 5530x0040 (SDEV_DB3) routine internals 5540x0080 (SDEV_DB4) miscellaneous addition debugging 555.Ed 556.Pp 557If 558.Em SCSIDEBUG_LEVEL 559is undefined, a value of 0x0030 (SDEV_DB1|SDEV_DB2) is used. 560.It Cd option SCSIDEBUG_LUNS= Ns Ar value 561Define which SCSI luns will print debug info. 562Each bit enables debugging info for the corresponding lun. 563.It Cd option SCSIDEBUG_TARGETS= Ns Ar value 564Define which SCSI targets will print debug info. 565Each bit enables debugging info for the corresponding target. 566.It Cd option SCSITERSE 567Terser SCSI error messages. 568This omits the table for decoding ASC/ASCQ info, saving about 30KB. 569.El 570.Sh SYSTEM V IPC OPTIONS 571.Bl -ohang 572.It Cd option SEMMNI= Ns Ar value 573Number of semaphore identifiers (also called semaphore handles 574and semaphore sets) available in the system. 575Default value is 10. 576The kernel allocates memory for the control structures at startup, 577so arbitrarily large values should be avoided. 578.It Cd option SEMMNS= Ns Ar value 579Maximum number of semaphores in all sets in the system. 580Default value is 60. 581.It Cd option SEMMNU= Ns Ar value 582Maximum number of semaphore undo structures in the system. 583Default value is 30. 584.It Cd option SEMUME= Ns Ar value 585Maximum number of per-process undo operation entries in the 586system. 587Semaphore undo operations are invoked by the kernel when 588.Xr semop 2 589is called with the SEM_UNDO flag and the process holding 590the semaphores terminates unexpectedly. 591Default value is 10. 592.It Cd option SHMMAXPGS= Ns Ar value 593Sets the maximum number of 594.At V 595style shared memory pages that are available through the 596.Xr shmget 2 597system call. 598Default value is 1024 on most architectures. 599See 600.Pa /usr/include/machine/vmparam.h 601for the default. 602.It Cd option SYSVMSG 603Includes support for 604.At V 605style message queues. 606See 607.Xr msgctl 2 , 608.Xr msgget 2 , 609.Xr msgrcv 2 , 610.Xr msgsnd 2 . 611.It Cd option SYSVSEM 612Includes support for 613.At V 614style semaphores. 615See 616.Xr semctl 2 , 617.Xr semget 2 , 618.Xr semop 2 . 619.It Cd option SYSVSHM 620Includes support for 621.At V 622style shared memory. 623See 624.Xr shmat 2 , 625.Xr shmctl 2 , 626.Xr shmdt 2 , 627.Xr shmget 2 . 628.El 629.Sh SEE ALSO 630.Xr intro 4 , 631.Xr files.conf 5 , 632.Xr config 8 , 633.Xr sysctl 8 634.Sh HISTORY 635The 636.Nm 637man page first appeared in 638.Ox 2.3 . 639