1.\" 2.\" Copyright (c) 2006 Robert N. M. Watson 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/share/man/man9/sysctl.9,v 1.3 2006/04/28 23:21:36 keramida Exp $ 27.\" 28.Dd October 6, 2018 29.Dt SYSCTL 9 30.Os 31.Sh NAME 32.Nm SYSCTL_DECL , 33.Nm SYSCTL_INT , 34.Nm SYSCTL_LONG , 35.Nm SYSCTL_QUAD , 36.Nm SYSCTL_NODE , 37.Nm SYSCTL_OPAQUE , 38.Nm SYSCTL_PROC , 39.Nm SYSCTL_S8 , 40.Nm SYSCTL_S16 , 41.Nm SYSCTL_S32 , 42.Nm SYSCTL_S64 , 43.Nm SYSCTL_STRING , 44.Nm SYSCTL_STRUCT , 45.Nm SYSCTL_U8 , 46.Nm SYSCTL_U16 , 47.Nm SYSCTL_U32 , 48.Nm SYSCTL_U64 , 49.Nm SYSCTL_UINT , 50.Nm SYSCTL_ULONG , 51.Nm SYSCTL_UQUAD 52.Nd Static sysctl declaration functions 53.Sh SYNOPSIS 54.In sys/types.h 55.In sys/sysctl.h 56.Fo SYSCTL_DECL 57.Fa "name" 58.Fc 59.Fo SYSCTL_INT 60.Fa "parent" 61.Fa "nbr" 62.Fa "name" 63.Fa "access" 64.Fa "ptr" 65.Fa "val" 66.Fa "descr" 67.Fc 68.Fo SYSCTL_LONG 69.Fa "parent" 70.Fa "nbr" 71.Fa "name" 72.Fa "access" 73.Fa "ptr" 74.Fa "val" 75.Fa "descr" 76.Fc 77.Fo SYSCTL_NODE 78.Fa "parent" 79.Fa "nbr" 80.Fa "name" 81.Fa "access" 82.Fa "handler" 83.Fa "descr" 84.Fc 85.Fo SYSCTL_OPAQUE 86.Fa "parent" 87.Fa "nbr" 88.Fa "name" 89.Fa "access" 90.Fa "ptr" 91.Fa "len" 92.Fa "fmt" 93.Fa "descr" 94.Fc 95.Fo SYSCTL_PROC 96.Fa "parent" 97.Fa "nbr" 98.Fa "name" 99.Fa "access" 100.Fa "ptr" 101.Fa "arg" 102.Fa "handler" 103.Fa "fmt" 104.Fa "descr" 105.Fc 106.Fo SYSCTL_QUAD 107.Fa "parent" 108.Fa "nbr" 109.Fa "name" 110.Fa "access" 111.Fa "ptr" 112.Fa "val" 113.Fa "descr" 114.Fc 115.Fo SYSCTL_S8 116.Fa "parent" 117.Fa "number" 118.Fa "name" 119.Fa "access" 120.Fa "ptr" 121.Fa "val" 122.Fa "descr" 123.Fc 124.Fo SYSCTL_S16 125.Fa "parent" 126.Fa "number" 127.Fa "name" 128.Fa "access" 129.Fa "ptr" 130.Fa "val" 131.Fa "descr" 132.Fc 133.Fo SYSCTL_S32 134.Fa "parent" 135.Fa "number" 136.Fa "name" 137.Fa "access" 138.Fa "ptr" 139.Fa "val" 140.Fa "descr" 141.Fc 142.Fo SYSCTL_S64 143.Fa "parent" 144.Fa "number" 145.Fa "name" 146.Fa "access" 147.Fa "ptr" 148.Fa "val" 149.Fa "descr" 150.Fc 151.Fo SYSCTL_STRING 152.Fa "parent" 153.Fa "nbr" 154.Fa "name" 155.Fa "access" 156.Fa "arg" 157.Fa "len" 158.Fa "descr" 159.Fc 160.Fo SYSCTL_STRUCT 161.Fa "parent" 162.Fa "nbr" 163.Fa "name" 164.Fa "access" 165.Fa "ptr" 166.Fa "type" 167.Fa "descr" 168.Fc 169.Fo SYSCTL_U8 170.Fa "parent" 171.Fa "number" 172.Fa "name" 173.Fa "access" 174.Fa "ptr" 175.Fa "val" 176.Fa "descr" 177.Fc 178.Fo SYSCTL_U16 179.Fa "parent" 180.Fa "number" 181.Fa "name" 182.Fa "access" 183.Fa "ptr" 184.Fa "val" 185.Fa "descr" 186.Fc 187.Fo SYSCTL_U32 188.Fa "parent" 189.Fa "number" 190.Fa "name" 191.Fa "access" 192.Fa "ptr" 193.Fa "val" 194.Fa "descr" 195.Fc 196.Fo SYSCTL_U64 197.Fa "parent" 198.Fa "number" 199.Fa "name" 200.Fa "access" 201.Fa "ptr" 202.Fa "val" 203.Fa "descr" 204.Fc 205.Fo SYSCTL_UINT 206.Fa "parent" 207.Fa "nbr" 208.Fa "name" 209.Fa "access" 210.Fa "ptr" 211.Fa "val" 212.Fa "descr" 213.Fc 214.Fo SYSCTL_ULONG 215.Fa "parent" 216.Fa "nbr" 217.Fa "name" 218.Fa "access" 219.Fa "ptr" 220.Fa "val" 221.Fa "descr" 222.Fc 223.Fo SYSCTL_UQUAD 224.Fa "parent" 225.Fa "nbr" 226.Fa "name" 227.Fa "access" 228.Fa "ptr" 229.Fa "val" 230.Fa "descr" 231.Fc 232.Sh DESCRIPTION 233The 234.Nm 235kernel interfaces allow code to statically declare 236.Xr sysctl 8 237MIB entries, which will be initialized when the kernel module containing the 238declaration is initialized. 239When the module is unloaded, the sysctl will be automatically destroyed. 240.Pp 241Sysctl nodes are created in a hierarchical tree, with all static nodes being 242represented by named C data structures; in order to create a new node under 243an existing node in the tree, the structure representing the desired parent 244node must be declared in the current context using 245.Fn SYSCTL_DECL . 246.Pp 247New nodes are declared using one of 248.Nm SYSCTL_INT , 249.Nm SYSCTL_LONG , 250.Nm SYSCTL_QUAD , 251.Nm SYSCTL_NODE , 252.Nm SYSCTL_OPAQUE , 253.Nm SYSCTL_PROC , 254.Nm SYSCTL_S8 , 255.Nm SYSCTL_S16 , 256.Nm SYSCTL_S32 , 257.Nm SYSCTL_S64 , 258.Nm SYSCTL_STRING , 259.Nm SYSCTL_STRUCT , 260.Nm SYSCTL_U8 , 261.Nm SYSCTL_U16 , 262.Nm SYSCTL_U32 , 263.Nm SYSCTL_U64 , 264.Nm SYSCTL_UINT , 265.Nm SYSCTL_ULONG , 266and 267.Nm SYSCTL_UQUAD . 268Each macro accepts a parent name, as declared using 269.Nm SYSCTL_DECL , 270an OID number, typically 271.Dv OID_AUTO , 272a node name, a set of control and access flags, and a description. 273Depending on the macro, a pointer to a variable supporting the MIB entry, a 274size, a value, and a function pointer implementing the MIB entry may also be 275present. 276.Pp 277For most of the above macros, declaring a type as part of the access flags is 278not necessary -- however, when declaring a sysctl implemented by a function, 279including a type in the access mask is required: 280.Bl -tag -width ".Dv CTLTYPE_STRING" 281.It Dv CTLTYPE_NODE 282This is a node intended to be a parent for other nodes. 283.It Dv CTLTYPE_INT 284This is a signed integer. 285.It Dv CTLTYPE_S8 286This is an 8-bit signed integer. 287.It Dv CTLTYPE_S16 288This is a 16-bit signed integer. 289.It Dv CTLTYPE_S32 290This is a 32-bit signed integer. 291.It Dv CTLTYPE_S64 292This is a 64-bit signed integer. 293.It Dv CTLTYPE_STRING 294This is a nul-terminated string stored in a character array. 295.It Dv CTLTYPE_QUAD 296This is a 64-bit signed integer. 297.It Dv CTLTYPE_OPAQUE 298This is an opaque data structure. 299.It Dv CTLTYPE_STRUCT 300Alias for 301.Dv CTLTYPE_OPAQUE . 302.It Dv CTLTYPE_U8 303This is an 8-bit unsigned integer. 304.It Dv CTLTYPE_U16 305This is a 16-bit unsigned integer. 306.It Dv CTLTYPE_U32 307This is a 32-bit unsigned integer. 308.It Dv CTLTYPE_U64 309This is a 64-bit unsigned integer. 310.It Dv CTLTYPE_UINT 311This is an unsigned integer. 312.It Dv CTLTYPE_LONG 313This is a signed long. 314.It Dv CTLTYPE_ULONG 315This is an unsigned long. 316.It Dv CTLTYPE_UQUAD 317This is a 64-bit unsigned integer. 318.El 319.Pp 320All sysctl types except for new node declarations require one or more flags 321to be set indicating the read and write disposition of the sysctl: 322.Bl -tag -width ".Dv CTLFLAG_ANYBODY" 323.It Dv CTLFLAG_RD 324This is a read-only sysctl. 325.It Dv CTLFLAG_WR 326This is a writable sysctl. 327.It Dv CTLFLAG_RW 328This sysctl is readable and writable. 329.It Dv CTLFLAG_ANYBODY 330Any user or process can write to this sysctl. 331.It Dv CTLFLAG_SECURE 332This sysctl can be written to only if the effective securelevel of the 333process is <= 0. 334.It Dv CTLFLAG_PRISON 335This sysctl can be written to by processes in 336.Xr jail 2 . 337.\".It Dv CTLFLAG_SKIP 338.\"When iterating the sysctl name space, do not list this sysctl. 339.El 340.Pp 341When creating new sysctls, careful attention should be paid to the security 342implications of the monitoring or management interface being created. 343Most sysctls present in the kernel are read-only or writable only by the 344superuser. 345Sysctls exporting extensive information on system data structures and 346operation, especially those implemented using procedures, will wish to 347implement access control to limit the undesired exposure of information about 348other processes, network connections, etc. 349.Pp 350The following top level sysctl name spaces are commonly used: 351.Bl -tag -width ".Va machdep" 352.It Va compat 353Compatibility layer information. 354.It Va debug 355Debugging information. 356Various name spaces exist under 357.Va debug . 358.It Va hw 359Hardware and device driver information. 360.It Va lwkt 361Information about the 362.Xr lwkt 9 363subsystem. 364.It Va kern 365Kernel behavior tuning; generally deprecated in favor of more specific 366name spaces. 367.It Va machdep 368Machine-dependent configuration parameters. 369.It Va net 370Network subsystem. 371Various protocols have name spaces under 372.Va net . 373.It Va sysctl 374Reserved name space for the implementation of sysctl. 375.It Va user 376Configuration settings relating to user application behavior. 377Generally, configuring applications using kernel sysctls is discouraged. 378.It Va vfs 379Virtual file system configuration and information. 380.It Va vm 381Virtual memory subsystem configuration and information. 382.El 383.Sh EXAMPLES 384Sample use of 385.Nm SYSCTL_DECL 386to declare the "machdep" sysctl tree for use by new nodes: 387.Bd -literal -offset indent 388SYSCTL_DECL(_machdep); 389.Ed 390.Pp 391Examples of integer, opaque, string, and procedure sysctls follow: 392.Bd -literal -offset indent 393/* 394 * Example of a constant integer value. Notice that the control 395 * flags are CTLFLAG_RD, the variable pointer is NULL, and the 396 * value is declared. 397 */ 398SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL, 399 sizeof(struct bio), "sizeof(struct bio)"); 400 401/* 402 * Example of a variable integer value. Notice that the control 403 * flags are CTLFLAG_RW, the variable pointer is set, and the 404 * value is 0. 405 */ 406static int doingcache = 1; /* 1 => enable the cache */ 407SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, 408 "Enable name cache"); 409 410/* 411 * Example of a variable string value. Notice that the control 412 * flags are CTLFLAG_RW, that the variable pointer and string 413 * size are set. Unlike newer sysctls, this older sysctl uses a 414 * static oid number. 415 */ 416char kernelname[MAXPATHLEN] = "/boot/kernel"; /* XXX bloat */ 417SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW, 418 kernelname, sizeof(kernelname), "Name of kernel file booted"); 419 420/* 421 * Example of an opaque data type exported by sysctl. Notice that 422 * the variable pointer and size are provided, as well as a format 423 * string for sysctl(8). 424 */ 425static l_fp pps_freq; /* scaled frequency offset (ns/s) */ 426SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, 427 &pps_freq, sizeof(pps_freq), "I", ""); 428 429/* 430 * Example of a procedure based sysctl exporting string 431 * information. Notice that the data type is declared, the NULL 432 * variable pointer and 0 size, the function pointer, and the 433 * format string for sysctl(8). 434 */ 435SYSCTL_PROC(_kern, OID_AUTO, msgbuf, CTLTYPE_STRING | CTLFLAG_RD, 436 0, 0, sysctl_kern_msgbuf, "A", "Contents of kernel message buffer"); 437.Ed 438.Pp 439When adding, modifying, or removing sysctl names, it is important to be 440aware that these interfaces may be used by users, libraries, applications, 441or documentation (such as published books), and are implicitly published 442application interfaces. 443As with other application interfaces, caution must be taken not to break 444existing applications, and to think about future use of new name spaces so as 445to avoid the need to rename or remove interfaces that might be depended on in 446the future. 447.Sh SEE ALSO 448.Xr sysctl 8 , 449.Xr sysctl_add_oid 9 , 450.Xr sysctl_ctx_free 9 , 451.Xr sysctl_ctx_init 9 , 452.Xr sysctl_remove_oid 9 453.Sh HISTORY 454.Xr sysctl 8 455first appeared in 456.Bx 4.4 . 457.Sh AUTHORS 458.An -nosplit 459The sysctl implementation originally found in 460.Bx 461has been extensively rewritten by 462.An Poul-Henning Kamp 463in order to add support for name lookups, name space iteration, and dynamic 464addition of MIB nodes. 465.Pp 466This man page was written by 467.An Robert N. M. Watson . 468