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.\" $DragonFly: src/share/man/man9/sysctl.9,v 1.6 2008/09/02 11:50:46 matthias Exp $ 28.\" 29.Dd September 2, 2008 30.Dt SYSCTL 9 31.Os 32.Sh NAME 33.Nm SYSCTL_DECL , 34.Nm SYSCTL_INT , 35.Nm SYSCTL_LONG , 36.Nm SYSCTL_QUAD , 37.Nm SYSCTL_NODE , 38.Nm SYSCTL_OPAQUE , 39.Nm SYSCTL_PROC , 40.Nm SYSCTL_STRING , 41.Nm SYSCTL_STRUCT , 42.Nm SYSCTL_UINT , 43.Nm SYSCTL_ULONG , 44.Nm SYSCTL_UQUAD 45.Nd Static sysctl declaration functions 46.Sh SYNOPSIS 47.In sys/types.h 48.In sys/sysctl.h 49.Fo SYSCTL_DECL 50.Fa "name" 51.Fc 52.Fo SYSCTL_INT 53.Fa "parent" 54.Fa "nbr" 55.Fa "name" 56.Fa "access" 57.Fa "ptr" 58.Fa "val" 59.Fa "descr" 60.Fc 61.Fo SYSCTL_LONG 62.Fa "parent" 63.Fa "nbr" 64.Fa "name" 65.Fa "access" 66.Fa "ptr" 67.Fa "val" 68.Fa "descr" 69.Fc 70.Fo SYSCTL_QUAD 71.Fa "parent" 72.Fa "nbr" 73.Fa "name" 74.Fa "access" 75.Fa "ptr" 76.Fa "val" 77.Fa "descr" 78.Fc 79.Fo SYSCTL_NODE 80.Fa "parent" 81.Fa "nbr" 82.Fa "name" 83.Fa "access" 84.Fa "handler" 85.Fa "descr" 86.Fc 87.Fo SYSCTL_OPAQUE 88.Fa "parent" 89.Fa "nbr" 90.Fa "name" 91.Fa "access" 92.Fa "ptr" 93.Fa "len" 94.Fa "fmt" 95.Fa "descr" 96.Fc 97.Fo SYSCTL_PROC 98.Fa "parent" 99.Fa "nbr" 100.Fa "name" 101.Fa "access" 102.Fa "ptr" 103.Fa "arg" 104.Fa "handler" 105.Fa "fmt" 106.Fa "descr" 107.Fc 108.Fo SYSCTL_STRING 109.Fa "parent" 110.Fa "nbr" 111.Fa "name" 112.Fa "access" 113.Fa "arg" 114.Fa "len" 115.Fa "descr" 116.Fc 117.Fo SYSCTL_STRUCT 118.Fa "parent" 119.Fa "nbr" 120.Fa "name" 121.Fa "access" 122.Fa "ptr" 123.Fa "type" 124.Fa "descr" 125.Fc 126.Fo SYSCTL_UINT 127.Fa "parent" 128.Fa "nbr" 129.Fa "name" 130.Fa "access" 131.Fa "ptr" 132.Fa "val" 133.Fa "descr" 134.Fc 135.Fo SYSCTL_ULONG 136.Fa "parent" 137.Fa "nbr" 138.Fa "name" 139.Fa "access" 140.Fa "ptr" 141.Fa "val" 142.Fa "descr" 143.Fc 144.Fo SYSCTL_UQUAD 145.Fa "parent" 146.Fa "nbr" 147.Fa "name" 148.Fa "access" 149.Fa "ptr" 150.Fa "val" 151.Fa "descr" 152.Fc 153.Sh DESCRIPTION 154The 155.Nm 156kernel interfaces allow code to statically declare 157.Xr sysctl 8 158MIB entries, which will be initialized when the kernel module containing the 159declaration is initialized. 160When the module is unloaded, the sysctl will be automatically destroyed. 161.Pp 162Sysctl nodes are created in a hierarchical tree, with all static nodes being 163represented by named C data structures; in order to create a new node under 164an existing node in the tree, the structure representing the desired parent 165node must be declared in the current context using 166.Fn SYSCTL_DECL . 167.Pp 168New nodes are declared using one of 169.Nm SYSCTL_INT , 170.Nm SYSCTL_LONG , 171.Nm SYSCTL_QUAD , 172.Nm SYSCTL_NODE , 173.Nm SYSCTL_OPAQUE , 174.Nm SYSCTL_PROC , 175.Nm SYSCTL_STRING , 176.Nm SYSCTL_STRUCT , 177.Nm SYSCTL_UINT , 178.Nm SYSCTL_ULONG , 179and 180.Nm SYSCTL_UQUAD . 181Each macro accepts a parent name, as declared using 182.Nm SYSCTL_DECL , 183an OID number, typically 184.Dv OID_AUTO , 185a node name, a set of control and access flags, and a description. 186Depending on the macro, a pointer to a variable supporting the MIB entry, a 187size, a value, and a function pointer implementing the MIB entry may also be 188present. 189.Pp 190For most of the above macros, declaring a type as part of the access flags is 191not necessary -- however, when declaring a sysctl implemented by a function, 192including a type in the access mask is required: 193.Bl -tag -width ".Dv CTLTYPE_STRING" 194.It Dv CTLTYPE_NODE 195This is a node intended to be a parent for other nodes. 196.It Dv CTLTYPE_INT 197This is a signed integer. 198.It Dv CTLTYPE_STRING 199This is a nul-terminated string stored in a character array. 200.It Dv CTLTYPE_QUAD 201This is a 64-bit signed integer. 202.It Dv CTLTYPE_OPAQUE 203This is an opaque data structure. 204.It Dv CTLTYPE_STRUCT 205Alias for 206.Dv CTLTYPE_OPAQUE . 207.It Dv CTLTYPE_UINT 208This is an unsigned integer. 209.It Dv CTLTYPE_LONG 210This is a signed long. 211.It Dv CTLTYPE_ULONG 212This is an unsigned long. 213.It Dv CTLTYPE_UQUAD 214This is a 64-bit unsigned integer. 215.El 216.Pp 217All sysctl types except for new node declarations require one or more flags 218to be set indicating the read and write disposition of the sysctl: 219.Bl -tag -width ".Dv CTLFLAG_ANYBODY" 220.It Dv CTLFLAG_RD 221This is a read-only sysctl. 222.It Dv CTLFLAG_WR 223This is a writable sysctl. 224.It Dv CTLFLAG_RW 225This sysctl is readable and writable. 226.It Dv CTLFLAG_ANYBODY 227Any user or process can write to this sysctl. 228.It Dv CTLFLAG_SECURE 229This sysctl can be written to only if the effective securelevel of the 230process is <= 0. 231.It Dv CTLFLAG_PRISON 232This sysctl can be written to by processes in 233.Xr jail 2 . 234.\".It Dv CTLFLAG_SKIP 235.\"When iterating the sysctl name space, do not list this sysctl. 236.El 237.Pp 238When creating new sysctls, careful attention should be paid to the security 239implications of the monitoring or management interface being created. 240Most sysctls present in the kernel are read-only or writable only by the 241superuser. 242Sysctls exporting extensive information on system data structures and 243operation, especially those implemented using procedures, will wish to 244implement access control to limit the undesired exposure of information about 245other processes, network connections, etc. 246.Pp 247The following top level sysctl name spaces are commonly used: 248.Bl -tag -width ".Va machdep" 249.It Va compat 250Compatibility layer information. 251.It Va debug 252Debugging information. 253Various name spaces exist under 254.Va debug . 255.It Va hw 256Hardware and device driver information. 257.It Va lwkt 258Information about the 259.Xr lwkt 9 260subsystem. 261.It Va kern 262Kernel behavior tuning; generally deprecated in favor of more specific 263name spaces. 264.It Va machdep 265Machine-dependent configuration parameters. 266.It Va net 267Network subsystem. 268Various protocols have name spaces under 269.Va net . 270.It Va sysctl 271Reserved name space for the implementation of sysctl. 272.It Va user 273Configuration settings relating to user application behavior. 274Generally, configuring applications using kernel sysctls is discouraged. 275.It Va vfs 276Virtual file system configuration and information. 277.It Va vm 278Virtual memory subsystem configuration and information. 279.El 280.Sh EXAMPLES 281Sample use of 282.Nm SYSCTL_DECL 283to declare the "machdep" sysctl tree for use by new nodes: 284.Bd -literal -offset indent 285SYSCTL_DECL(_machdep); 286.Ed 287.Pp 288Examples of integer, opaque, string, and procedure sysctls follow: 289.Bd -literal -offset indent 290/* 291 * Example of a constant integer value. Notice that the control 292 * flags are CTLFLAG_RD, the variable pointer is NULL, and the 293 * value is declared. 294 */ 295SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL, 296 sizeof(struct bio), "sizeof(struct bio)"); 297 298/* 299 * Example of a variable integer value. Notice that the control 300 * flags are CTLFLAG_RW, the variable pointer is set, and the 301 * value is 0. 302 */ 303static int doingcache = 1; /* 1 => enable the cache */ 304SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, 305 "Enable name cache"); 306 307/* 308 * Example of a variable string value. Notice that the control 309 * flags are CTLFLAG_RW, that the variable pointer and string 310 * size are set. Unlike newer sysctls, this older sysctl uses a 311 * static oid number. 312 */ 313char kernelname[MAXPATHLEN] = "/boot/kernel"; /* XXX bloat */ 314SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW, 315 kernelname, sizeof(kernelname), "Name of kernel file booted"); 316 317/* 318 * Example of an opaque data type exported by sysctl. Notice that 319 * the variable pointer and size are provided, as well as a format 320 * string for sysctl(8). 321 */ 322static l_fp pps_freq; /* scaled frequence offset (ns/s) */ 323SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, 324 &pps_freq, sizeof(pps_freq), "I", ""); 325 326/* 327 * Example of a procedure based sysctl exporting string 328 * information. Notice that the data type is declared, the NULL 329 * variable pointer and 0 size, the function pointer, and the 330 * format string for sysctl(8). 331 */ 332SYSCTL_PROC(_kern, OID_AUTO, msgbuf, CTLTYPE_STRING | CTLFLAG_RD, 333 0, 0, sysctl_kern_msgbuf, "A", "Contents of kernel message buffer"); 334.Ed 335.Pp 336When adding, modifying, or removing sysctl names, it is important to be 337aware that these interfaces may be used by users, libraries, applications, 338or documentation (such as published books), and are implicitly published 339application interfaces. 340As with other application interfaces, caution must be taken not to break 341existing applications, and to think about future use of new name spaces so as 342to avoid the need to rename or remove interfaces that might be depended on in 343the future. 344.Sh SEE ALSO 345.Xr sysctl 8 , 346.Xr sysctl_add_oid 9 , 347.Xr sysctl_ctx_free 9 , 348.Xr sysctl_ctx_init 9 , 349.Xr sysctl_remove_oid 9 350.Sh HISTORY 351.Xr sysctl 8 352first appeared in 353.Bx 4.4 . 354.Sh AUTHORS 355.An -nosplit 356The sysctl implementation originally found in 357.Bx 358has been extensively rewritten by 359.An Poul-Henning Kamp 360in order to add support for name lookups, name space iteration, and dynamic 361addition of MIB nodes. 362.Pp 363This man page was written by 364.An Robert N. M. Watson . 365