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 January 16, 2010 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_STRING , 39.Nm SYSCTL_STRUCT , 40.Nm SYSCTL_UINT , 41.Nm SYSCTL_ULONG , 42.Nm SYSCTL_QUAD 43.Nd Static sysctl declaration functions 44.Sh SYNOPSIS 45.In sys/types.h 46.In sys/sysctl.h 47.Fn SYSCTL_DECL name 48.Fn SYSCTL_INT parent nbr name access ptr val descr 49.Fn SYSCTL_LONG parent nbr name access ptr val descr 50.Fn SYSCTL_NODE parent nbr name access handler descr 51.Fn SYSCTL_OPAQUE parent nbr name access ptr len fmt descr 52.Fn SYSCTL_PROC parent nbr name access ptr arg handler fmt descr 53.Fn SYSCTL_STRING parent nbr name access arg len descr 54.Fn SYSCTL_STRUCT parent nbr name access ptr type descr 55.Fn SYSCTL_UINT parent nbr name access ptr val descr 56.Fn SYSCTL_ULONG parent nbr name access ptr val descr 57.Fn SYSCTL_QUAD parent nbr name access ptr val descr 58.Sh DESCRIPTION 59The 60.Nm SYSCTL 61kernel interfaces allow code to statically declare 62.Xr sysctl 8 63MIB entries, which will be initialized when the kernel module containing the 64declaration is initialized. 65When the module is unloaded, the sysctl will be automatically destroyed. 66.Pp 67Sysctl nodes are created in a hierarchical tree, with all static nodes being 68represented by named C data structures; in order to create a new node under 69an existing node in the tree, the structure representing the desired parent 70node must be declared in the current context using 71.Fn SYSCTL_DECL . 72.Pp 73New nodes are declared using one of 74.Fn SYSCTL_INT , 75.Fn SYSCTL_LONG , 76.Fn SYSCTL_NODE , 77.Fn SYSCTL_OPAQUE , 78.Fn SYSCTL_PROC , 79.Fn SYSCTL_STRING , 80.Fn SYSCTL_STRUCT , 81.Fn SYSCTL_UINT , 82.Fn SYSCTL_ULONG , 83and 84.Fn SYSCTL_QUAD . 85Each macro accepts a parent name, as declared using 86.Fn SYSCTL_DECL , 87an OID number, typically 88.Dv OID_AUTO , 89a node name, a set of control and access flags, and a description. 90Depending on the macro, a pointer to a variable supporting the MIB entry, a 91size, a value, and a function pointer implementing the MIB entry may also be 92present. 93.Pp 94For most of the above macros, declaring a type as part of the access flags is 95not necessary \[em] however, when declaring a sysctl implemented by a function, 96including a type in the access mask is required: 97.Bl -tag -width ".Dv CTLTYPE_STRING" 98.It Dv CTLTYPE_NODE 99This is a node intended to be a parent for other nodes. 100.It Dv CTLTYPE_INT 101This is a signed integer. 102.It Dv CTLTYPE_STRING 103This is a nul-terminated string stored in a character array. 104.It Dv CTLTYPE_S64 105This is a 64-bit signed integer. 106.It Dv CTLTYPE_OPAQUE 107This is an opaque data structure. 108.It Dv CTLTYPE_STRUCT 109Alias for 110.Dv CTLTYPE_OPAQUE. 111.It Dv CTLTYPE_UINT 112This is an unsigned integer. 113.It Dv CTLTYPE_LONG 114This is a signed long. 115.It Dv CTLTYPE_ULONG 116This is an unsigned long. 117.It Dv CTLTYPE_U64 118This is a 64-bit unsigned integer. 119.El 120.Pp 121All sysctl types except for new node declarations require one or more flags 122to be set indicating the read and write disposition of the sysctl: 123.Bl -tag -width ".Dv CTLFLAG_ANYBODY" 124.It Dv CTLFLAG_RD 125This is a read-only sysctl. 126.It Dv CTLFLAG_WR 127This is a writable sysctl. 128.It Dv CTLFLAG_RW 129This sysctl is readable and writable. 130.It Dv CTLFLAG_ANYBODY 131Any user or process can write to this sysctl. 132.It Dv CTLFLAG_SECURE 133This sysctl can be written to only if the effective securelevel of the 134process is \[<=] 0. 135.It Dv CTLFLAG_PRISON 136This sysctl can be written to by processes in 137.Xr jail 2 . 138.It Dv CTLFLAG_SKIP 139When iterating the sysctl name space, do not list this sysctl. 140.It Dv CTLFLAG_TUN 141Also declare a system tunable with the same name to initialize this variable. 142.It Dv CTLFLAG_RDTUN 143Also declare a system tunable with the same name to initialize this variable; 144however, the run-time variable is read-only. 145.El 146.Pp 147When creating new sysctls, careful attention should be paid to the security 148implications of the monitoring or management interface being created. 149Most sysctls present in the kernel are read-only or writable only by the 150superuser. 151Sysctls exporting extensive information on system data structures and 152operation, especially those implemented using procedures, will wish to 153implement access control to limit the undesired exposure of information about 154other processes, network connections, etc. 155.Pp 156The following top level sysctl name spaces are commonly used: 157.Bl -tag -width ".Va regression" 158.It Va compat 159Compatibility layer information. 160.It Va debug 161Debugging information. 162Various name spaces exist under 163.Va debug . 164.It Va hw 165Hardware and device driver information. 166.It Va kern 167Kernel behavior tuning; generally deprecated in favor of more specific 168name spaces. 169.It Va machdep 170Machine-dependent configuration parameters. 171.It Va net 172Network subsystem. 173Various protocols have name spaces under 174.Va net . 175.It Va regression 176Regression test configuration and information. 177.It Va security 178Security and security-policy configuration and information. 179.It Va sysctl 180Reserved name space for the implementation of sysctl. 181.It Va user 182Configuration settings relating to user application behavior. 183Generally, configuring applications using kernel sysctls is discouraged. 184.It Va vfs 185Virtual file system configuration and information. 186.It Va vm 187Virtual memory subsystem configuration and information. 188.El 189.Sh EXAMPLES 190Sample use of 191.Fn SYSCTL_DECL 192to declare the 193.Va security 194sysctl tree for use by new nodes: 195.Bd -literal -offset indent 196SYSCTL_DECL(_security); 197.Ed 198.Pp 199Examples of integer, opaque, string, and procedure sysctls follow: 200.Bd -literal -offset indent 201/* 202 * Example of a constant integer value. Notice that the control 203 * flags are CTLFLAG_RD, the variable pointer is NULL, and the 204 * value is declared. 205 */ 206SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, NULL, 207 sizeof(struct bio), "sizeof(struct bio)"); 208 209/* 210 * Example of a variable integer value. Notice that the control 211 * flags are CTLFLAG_RW, the variable pointer is set, and the 212 * value is 0. 213 */ 214static int doingcache = 1; /* 1 => enable the cache */ 215SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0, 216 "Enable name cache"); 217 218/* 219 * Example of a variable string value. Notice that the control 220 * flags are CTLFLAG_RW, that the variable pointer and string 221 * size are set. Unlike newer sysctls, this older sysctl uses a 222 * static oid number. 223 */ 224char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */ 225SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW, 226 kernelname, sizeof(kernelname), "Name of kernel file booted"); 227 228/* 229 * Example of an opaque data type exported by sysctl. Notice that 230 * the variable pointer and size are provided, as well as a format 231 * string for sysctl(8). 232 */ 233static l_fp pps_freq; /* scaled frequence offset (ns/s) */ 234SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, 235 &pps_freq, sizeof(pps_freq), "I", ""); 236 237/* 238 * Example of a procedure based sysctl exporting string 239 * information. Notice that the data type is declared, the NULL 240 * variable pointer and 0 size, the function pointer, and the 241 * format string for sysctl(8). 242 */ 243SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | 244 CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A", 245 ""); 246.Ed 247.Sh SYSCTL NAMING 248When adding, modifying, or removing sysctl names, it is important to be 249aware that these interfaces may be used by users, libraries, applications, 250or documentation (such as published books), and are implicitly published application interfaces. 251As with other application interfaces, caution must be taken not to break 252existing applications, and to think about future use of new name spaces so as 253to avoid the need to rename or remove interfaces that might be depended on in 254the future. 255.Pp 256The semantics chosen for a new sysctl should be as clear as possible, 257and the name of the sysctl must closely reflect its semantics. 258Therefore the sysctl name deserves a fair amount of consideration. 259It should be short but yet representative of the sysctl meaning. 260If the name consists of several words, they should be separated by 261underscore characters, as in 262.Va compute_summary_at_mount . 263Underscore characters may be omitted only if the name consists of not more 264than two words, each being not longer than four characters, as in 265.Va bootfile . 266For boolean sysctls, negative logic should be totally avoided. 267That is, do not use names like 268.Va no_foobar 269or 270.Va foobar_disable . 271They are confusing and lead to configuration errors. 272Use positive logic instead: 273.Va foobar , 274.Va foobar_enable . 275.Pp 276A temporary sysctl node that should not be relied upon must be designated 277as such by a leading underscore character in its name. For example: 278.Va _dirty_hack . 279.Sh SEE ALSO 280.Xr sysctl 3 , 281.Xr sysctl 8 , 282.Xr sysctl_add_oid 9 , 283.Xr sysctl_ctx_free 9 , 284.Xr sysctl_ctx_init 9 , 285.Xr sysctl_remove_oid 9 286.Sh HISTORY 287The 288.Xr sysctl 8 289utility first appeared in 290.Bx 4.4 . 291.Sh AUTHORS 292.An -nosplit 293The 294.Nm sysctl 295implementation originally found in 296.Bx 297has been extensively rewritten by 298.An Poul-Henning Kamp 299in order to add support for name lookups, name space iteration, and dynamic 300addition of MIB nodes. 301.Pp 302This man page was written by 303.An Robert N. M. Watson . 304