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.\" $FreeBSD$ 27.\" 28.Dd September 12, 2013 29.Dt SYSCTL 9 30.Os 31.Sh NAME 32.Nm SYSCTL_DECL , 33.Nm SYSCTL_INT , 34.Nm SYSCTL_LONG , 35.Nm SYSCTL_NODE , 36.Nm SYSCTL_OPAQUE , 37.Nm SYSCTL_PROC , 38.Nm SYSCTL_QUAD , 39.Nm SYSCTL_STRING , 40.Nm SYSCTL_STRUCT , 41.Nm SYSCTL_UINT , 42.Nm SYSCTL_ULONG , 43.Nm SYSCTL_UQUAD 44.Nd Static sysctl declaration functions 45.Sh SYNOPSIS 46.In sys/types.h 47.In sys/sysctl.h 48.Fn SYSCTL_DECL name 49.Fn SYSCTL_INT parent nbr name access ptr val descr 50.Fn SYSCTL_LONG parent nbr name access ptr val descr 51.Fn SYSCTL_NODE parent nbr name access handler descr 52.Fn SYSCTL_OPAQUE parent nbr name access ptr len fmt descr 53.Fn SYSCTL_PROC parent nbr name access ptr arg handler fmt descr 54.Fn SYSCTL_QUAD parent nbr name access ptr val descr 55.Fn SYSCTL_STRING parent nbr name access arg len descr 56.Fn SYSCTL_STRUCT parent nbr name access ptr type descr 57.Fn SYSCTL_UINT parent nbr name access ptr val descr 58.Fn SYSCTL_ULONG parent nbr name access ptr val descr 59.Fn SYSCTL_UQUAD parent nbr name access ptr val descr 60.Sh DESCRIPTION 61The 62.Nm SYSCTL 63kernel interfaces allow code to statically declare 64.Xr sysctl 8 65MIB entries, which will be initialized when the kernel module containing the 66declaration is initialized. 67When the module is unloaded, the sysctl will be automatically destroyed. 68.Pp 69Sysctl nodes are created in a hierarchical tree, with all static nodes being 70represented by named C data structures; in order to create a new node under 71an existing node in the tree, the structure representing the desired parent 72node must be declared in the current context using 73.Fn SYSCTL_DECL . 74.Pp 75New nodes are declared using one of 76.Fn SYSCTL_INT , 77.Fn SYSCTL_LONG , 78.Fn SYSCTL_NODE , 79.Fn SYSCTL_OPAQUE , 80.Fn SYSCTL_PROC , 81.Fn SYSCTL_QUAD , 82.Fn SYSCTL_STRING , 83.Fn SYSCTL_STRUCT , 84.Fn SYSCTL_UINT , 85.Fn SYSCTL_ULONG , 86and 87.Fn SYSCTL_UQUAD . 88Each macro accepts a parent name, as declared using 89.Fn SYSCTL_DECL , 90an OID number, typically 91.Dv OID_AUTO , 92a node name, a set of control and access flags, and a description. 93Depending on the macro, a pointer to a variable supporting the MIB entry, a 94size, a value, and a function pointer implementing the MIB entry may also be 95present. 96.Pp 97For most of the above macros, declaring a type as part of the access flags is 98not necessary \[em] however, when declaring a sysctl implemented by a function, 99including a type in the access mask is required: 100.Bl -tag -width ".Dv CTLTYPE_STRING" 101.It Dv CTLTYPE_NODE 102This is a node intended to be a parent for other nodes. 103.It Dv CTLTYPE_INT 104This is a signed integer. 105.It Dv CTLTYPE_STRING 106This is a nul-terminated string stored in a character array. 107.It Dv CTLTYPE_S64 108This is a 64-bit signed integer. 109.It Dv CTLTYPE_OPAQUE 110This is an opaque data structure. 111.It Dv CTLTYPE_STRUCT 112Alias for 113.Dv CTLTYPE_OPAQUE . 114.It Dv CTLTYPE_UINT 115This is an unsigned integer. 116.It Dv CTLTYPE_LONG 117This is a signed long. 118.It Dv CTLTYPE_ULONG 119This is an unsigned long. 120.It Dv CTLTYPE_U64 121This is a 64-bit unsigned integer. 122.El 123.Pp 124All sysctl types except for new node declarations require one of the following 125flags to be set indicating the read and write disposition of the sysctl: 126.Bl -tag -width ".Dv CTLFLAG_ANYBODY" 127.It Dv CTLFLAG_RD 128This is a read-only sysctl. 129.It Dv CTLFLAG_RDTUN 130This is a read-only sysctl which can be set by a system tunable. 131.It Dv CTLFLAG_WR 132This is a writable sysctl. 133.It Dv CTLFLAG_RW 134This sysctl is readable and writable. 135.It Dv CTLFLAG_RWTUN 136This sysctl is readable and writable and can also be set by a system tunable. 137.El 138.Pp 139Additionally, any of the following optional flags may also be specified: 140.Bl -tag -width ".Dv CTLFLAG_ANYBODY" 141.It Dv CTLFLAG_ANYBODY 142Any user or process can write to this sysctl. 143.It Dv CTLFLAG_SECURE 144This sysctl can be written to only if the effective securelevel of the 145process is \[<=] 0. 146.It Dv CTLFLAG_PRISON 147This sysctl can be written to by processes in 148.Xr jail 2 . 149.It Dv CTLFLAG_SKIP 150When iterating the sysctl name space, do not list this sysctl. 151.It Dv CTLFLAG_TUN 152Advisory flag that a system tunable also exists for this variable. 153.El 154.Pp 155When creating new sysctls, careful attention should be paid to the security 156implications of the monitoring or management interface being created. 157Most sysctls present in the kernel are read-only or writable only by the 158superuser. 159Sysctls exporting extensive information on system data structures and 160operation, especially those implemented using procedures, will wish to 161implement access control to limit the undesired exposure of information about 162other processes, network connections, etc. 163.Pp 164The following top level sysctl name spaces are commonly used: 165.Bl -tag -width ".Va regression" 166.It Va compat 167Compatibility layer information. 168.It Va debug 169Debugging information. 170Various name spaces exist under 171.Va debug . 172.It Va hw 173Hardware and device driver information. 174.It Va kern 175Kernel behavior tuning; generally deprecated in favor of more specific 176name spaces. 177.It Va machdep 178Machine-dependent configuration parameters. 179.It Va net 180Network subsystem. 181Various protocols have name spaces under 182.Va net . 183.It Va regression 184Regression test configuration and information. 185.It Va security 186Security and security-policy configuration and information. 187.It Va sysctl 188Reserved name space for the implementation of sysctl. 189.It Va user 190Configuration settings relating to user application behavior. 191Generally, configuring applications using kernel sysctls is discouraged. 192.It Va vfs 193Virtual file system configuration and information. 194.It Va vm 195Virtual memory subsystem configuration and information. 196.El 197.Sh EXAMPLES 198Sample use of 199.Fn SYSCTL_DECL 200to declare the 201.Va security 202sysctl tree for use by new nodes: 203.Bd -literal -offset indent 204SYSCTL_DECL(_security); 205.Ed 206.Pp 207Examples of integer, opaque, string, and procedure sysctls follow: 208.Bd -literal -offset indent 209/* 210 * Example of a constant integer value. Notice that the control 211 * flags are CTLFLAG_RD, the variable pointer is NULL, and the 212 * value is declared. 213 */ 214SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL, 215 sizeof(struct bio), "sizeof(struct bio)"); 216 217/* 218 * Example of a variable integer value. Notice that the control 219 * flags are CTLFLAG_RW, the variable pointer is set, and the 220 * value is 0. 221 */ 222static int doingcache = 1; /* 1 => enable the cache */ 223SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, 224 "Enable name cache"); 225 226/* 227 * Example of a variable string value. Notice that the control 228 * flags are CTLFLAG_RW, that the variable pointer and string 229 * size are set. Unlike newer sysctls, this older sysctl uses a 230 * static oid number. 231 */ 232char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */ 233SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW, 234 kernelname, sizeof(kernelname), "Name of kernel file booted"); 235 236/* 237 * Example of an opaque data type exported by sysctl. Notice that 238 * the variable pointer and size are provided, as well as a format 239 * string for sysctl(8). 240 */ 241static l_fp pps_freq; /* scaled frequence offset (ns/s) */ 242SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, 243 &pps_freq, sizeof(pps_freq), "I", ""); 244 245/* 246 * Example of a procedure based sysctl exporting string 247 * information. Notice that the data type is declared, the NULL 248 * variable pointer and 0 size, the function pointer, and the 249 * format string for sysctl(8). 250 */ 251SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | 252 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A", 253 ""); 254.Ed 255.Sh SYSCTL NAMING 256When adding, modifying, or removing sysctl names, it is important to be 257aware that these interfaces may be used by users, libraries, applications, 258or documentation (such as published books), and are implicitly published application interfaces. 259As with other application interfaces, caution must be taken not to break 260existing applications, and to think about future use of new name spaces so as 261to avoid the need to rename or remove interfaces that might be depended on in 262the future. 263.Pp 264The semantics chosen for a new sysctl should be as clear as possible, 265and the name of the sysctl must closely reflect its semantics. 266Therefore the sysctl name deserves a fair amount of consideration. 267It should be short but yet representative of the sysctl meaning. 268If the name consists of several words, they should be separated by 269underscore characters, as in 270.Va compute_summary_at_mount . 271Underscore characters may be omitted only if the name consists of not more 272than two words, each being not longer than four characters, as in 273.Va bootfile . 274For boolean sysctls, negative logic should be totally avoided. 275That is, do not use names like 276.Va no_foobar 277or 278.Va foobar_disable . 279They are confusing and lead to configuration errors. 280Use positive logic instead: 281.Va foobar , 282.Va foobar_enable . 283.Pp 284A temporary sysctl node that should not be relied upon must be designated 285as such by a leading underscore character in its name. For example: 286.Va _dirty_hack . 287.Sh SEE ALSO 288.Xr sysctl 3 , 289.Xr sysctl 8 , 290.Xr sysctl_add_oid 9 , 291.Xr sysctl_ctx_free 9 , 292.Xr sysctl_ctx_init 9 , 293.Xr sysctl_remove_oid 9 294.Sh HISTORY 295The 296.Xr sysctl 8 297utility first appeared in 298.Bx 4.4 . 299.Sh AUTHORS 300.An -nosplit 301The 302.Nm sysctl 303implementation originally found in 304.Bx 305has been extensively rewritten by 306.An Poul-Henning Kamp 307in order to add support for name lookups, name space iteration, and dynamic 308addition of MIB nodes. 309.Pp 310This man page was written by 311.An Robert N. M. Watson . 312