1.\" Copyright (c) 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)sysctl.3 8.1 (Berkeley) 6/4/93 33.\" 34.Dd "June 4, 1993" 35.Dt SYSCTL 3 36.Os 37.Sh NAME 38.Nm sysctl 39.Nd get or set system information 40.Sh SYNOPSIS 41.Fd #include <sys/types.h> 42.Fd #include <sys/sysctl.h> 43.Ft int 44.Fn sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen" 45.Sh DESCRIPTION 46The 47.Fn sysctl 48function retrieves system information and allows processes with 49appropriate privileges to set system information. 50The information available from 51.Fn sysctl 52consists of integers, strings, and tables. 53Information may be retrieved and set from the command interface 54using the 55.Xr sysctl 8 56utility. 57.Pp 58Unless explicitly noted below, 59.Fn sysctl 60returns a consistent snapshot of the data requested. 61Consistency is obtained by locking the destination 62buffer into memory so that the data may be copied out without blocking. 63Calls to 64.Fn sysctl 65are serialized to avoid deadlock. 66.Pp 67The state is described using a ``Management Information Base'' (MIB) 68style name, listed in 69.Fa name , 70which is a 71.Fa namelen 72length array of integers. 73.Pp 74The information is copied into the buffer specified by 75.Fa oldp . 76The size of the buffer is given by the location specified by 77.Fa oldlenp 78before the call, 79and that location gives the amount of data copied after a successful call 80and after a call that returns with the error code ENOMEM. 81If the amount of data available is greater 82than the size of the buffer supplied, 83the call supplies as much data as fits in the buffer provided 84and returns with the error code ENOMEM. 85If the old value is not desired, 86.Fa oldp 87and 88.Fa oldlenp 89should be set to NULL. 90.Pp 91The size of the available data can be determined by calling 92.Fn sysctl 93with a NULL parameter for 94.Fa oldp . 95The size of the available data will be returned in the location pointed to by 96.Fa oldlenp . 97For some operations, the amount of space may change often. 98For these operations, 99the system attempts to round up so that the returned size is 100large enough for a call to return the data shortly thereafter. 101.Pp 102To set a new value, 103.Fa newp 104is set to point to a buffer of length 105.Fa newlen 106from which the requested value is to be taken. 107If a new value is not to be set, 108.Fa newp 109should be set to NULL and 110.Fa newlen 111set to 0. 112.Pp 113The top level names are defined with a CTL_ prefix in 114.Pa <sys/sysctl.h> , 115and are as follows. 116The next and subsequent levels down are found in the include files 117listed here, and described in separate sections below. 118.Pp 119.Bl -column CTLXMACHDEPXXX "Next level namesXXXXXX" -offset indent 120.It Sy Pa Name Next level names Description 121.It CTL\_DEBUG sys/sysctl.h Debugging 122.It CTL\_VFS sys/sysctl.h File system 123.It CTL\_HW sys/sysctl.h Generic CPU, I/O 124.It CTL\_KERN sys/sysctl.h High kernel limits 125.It CTL\_MACHDEP sys/sysctl.h Machine dependent 126.It CTL\_NET sys/socket.h Networking 127.It CTL\_USER sys/sysctl.h User-level 128.It CTL\_VM vm/vm_param.h Virtual memory 129.El 130.Pp 131For example, the following retrieves the maximum number of processes allowed 132in the system: 133.Pp 134.Bd -literal -offset indent -compact 135int mib[2], maxproc; 136size_t len; 137 138mib[0] = CTL_KERN; 139mib[1] = KERN_MAXPROC; 140len = sizeof(maxproc); 141sysctl(mib, 2, &maxproc, &len, NULL, 0); 142.Ed 143.Pp 144To retrieve the standard search path for the system utilities: 145.Pp 146.Bd -literal -offset indent -compact 147int mib[2]; 148size_t len; 149char *p; 150 151mib[0] = CTL_USER; 152mib[1] = USER_CS_PATH; 153sysctl(mib, 2, NULL, &len, NULL, 0); 154p = malloc(len); 155sysctl(mib, 2, p, &len, NULL, 0); 156.Ed 157.Sh CTL_DEBUG 158The debugging variables vary from system to system. 159A debugging variable may be added or deleted without need to recompile 160.Fn sysctl 161to know about it. 162Each time it runs, 163.Fn sysctl 164gets the list of debugging variables from the kernel and 165displays their current values. 166The system defines twenty 167.Ns ( Va struct ctldebug ) 168variables named 169.Nm debug0 170through 171.Nm debug19 . 172They are declared as separate variables so that they can be 173individually initialized at the location of their associated variable. 174The loader prevents multiple use of the same variable by issuing errors 175if a variable is initialized in more than one place. 176For example, to export the variable 177.Nm dospecialcheck 178as a debugging variable, the following declaration would be used: 179.Bd -literal -offset indent -compact 180int dospecialcheck = 1; 181struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck }; 182.Ed 183.Sh CTL_VFS 184There are currently no second level names for the file system. 185.Sh CTL_HW 186The string and integer information available for the CTL_HW level 187is detailed below. 188The changeable column shows whether a process with appropriate 189privilege may change the value. 190.Bl -column "Second level nameXXXXXX" integerXXX -offset indent 191.It Sy Pa Second level name Type Changeable 192.It HW\_MACHINE string no 193.It HW\_MODEL string no 194.It HW\_NCPU integer no 195.It HW\_BYTEORDER integer no 196.It HW\_PHYSMEM integer no 197.It HW\_USERMEM integer no 198.It HW\_PAGESIZE integer no 199.It HW\_FLOATINGPOINT integer no 200.\".It HW\_DISKNAMES integer no 201.\".It HW\_DISKSTATS integer no 202.El 203.Pp 204.Bl -tag -width "123456" 205.It Li HW_MACHINE 206The machine class. 207.It Li HW_MODEL 208The machine model 209.It Li HW_NCPU 210The number of cpus. 211.It Li HW_BYTEORDER 212The byteorder (4,321, or 1,234). 213.It Li HW_PHYSMEM 214The bytes of physical memory. 215.It Li HW_USERMEM 216The bytes of non-kernel memory. 217.It Li HW_PAGESIZE 218The software page size. 219.It Li HW_FLOATINGPOINT 220Nonzero if the floating point support is in hardware. 221.\".It Fa HW_DISKNAMES 222.\".It Fa HW_DISKSTATS 223.El 224.Sh CTL_KERN 225The string and integer information available for the CTL_KERN level 226is detailed below. 227The changeable column shows whether a process with appropriate 228privilege may change the value. 229The types of data currently available are process information, 230system vnodes, the open file entries, routing table entries, 231virtual memory statistics, load average history, and clock rate 232information. 233.Bl -column "KERNXMAXFILESPERPROCXXX" "struct clockrateXXX" -offset indent 234.It Sy Pa Second level name Type Changeable 235.It KERN\_ARGMAX integer no 236.It KERN\_BOOTFILE string yes 237.It KERN\_BOOTTIME struct timeval no 238.It KERN\_CLOCKRATE struct clockinfo no 239.It KERN\_FILE struct file no 240.It KERN\_HOSTID integer yes 241.It KERN\_HOSTNAME string yes 242.It KERN\_JOB\_CONTROL integer no 243.It KERN\_MAXFILES integer yes 244.It KERN\_MAXFILESPERPROC integer yes 245.It KERN\_MAXPROC integer yes 246.It KERN\_MAXPROCPERUID integer yes 247.It KERN\_MAXVNODES integer yes 248.It KERN\_NGROUPS integer no 249.It KERN\_NISDOMAINNAME string yes 250.It KERN\_OSRELDATE integer no 251.It KERN\_OSRELEASE string no 252.It KERN\_OSREV integer no 253.It KERN\_OSTYPE string no 254.It KERN\_POSIX1 integer no 255.It KERN\_PROC struct proc no 256.It KERN\_PROF node not applicable 257.It KERN\_SAVED\_IDS integer no 258.It KERN\_SECURELVL integer raise only 259.It KERN\_UPDATEINTERVAL integer no 260.It KERN\_VERSION string no 261.It KERN\_VNODE struct vnode no 262.El 263.Pp 264.Bl -tag -width "123456" 265.It Li KERN_ARGMAX 266The maximum bytes of argument to 267.Xr execve 2 . 268.It Li KERN_BOOTFILE 269The full pathname of the file from which the kernel was loaded. 270.It Li KERN_BOOTTIME 271A 272.Va struct timeval 273structure is returned. 274This structure contains the time that the system was booted. 275.It Li KERN_CLOCKRATE 276A 277.Va struct clockinfo 278structure is returned. 279This structure contains the clock, statistics clock and profiling clock 280frequencies, and the number of micro-seconds per hz tick. 281.It Li KERN_FILE 282Return the entire file table. 283The returned data consists of a single 284.Va struct filehead 285followed by an array of 286.Va struct file , 287whose size depends on the current number of such objects in the system. 288.It Li KERN_HOSTID 289Get or set the host id. 290.It Li KERN_HOSTNAME 291Get or set the hostname. 292.It Li KERN_JOB_CONTROL 293Return 1 if job control is available on this system, otherwise 0. 294.It Li KERN_MAXFILES 295The maximum number of files that may be open in the system. 296.It Li KERN_MAXFILESPERPROC 297The maximum number of files that may be open for a single process. 298This limit only applies to processes with an effective uid of nonzero 299at the time of the open request. 300Files that have already been opened are not affected if the limit 301or the effective uid is changed. 302.It Li KERN_MAXPROC 303The maximum number of concurrent processes the system will allow. 304.It Li KERN_MAXPROCPERUID 305The maximum number of concurrent processes the system will allow 306for a single effective uid. 307This limit only applies to processes with an effective uid of nonzero 308at the time of a fork request. 309Processes that have already been started are not affected if the limit 310is changed. 311.It Li KERN_MAXVNODES 312The maximum number of vnodes available on the system. 313.It Li KERN_NGROUPS 314The maximum number of supplemental groups. 315.It Li KERN_NISDOMAINNAME 316The name of the current YP/NIS domain. 317.It Li KERN_OSRELDATE 318The system release date in YYYYMM format 319(January 1996 is encoded as 199601). 320.It Li KERN_OSRELEASE 321The system release string. 322.It Li KERN_OSREV 323The system revision string. 324.It Li KERN_OSTYPE 325The system type string. 326.It Li KERN_POSIX1 327The version of ISO/IEC 9945 (POSIX 1003.1) with which the system 328attempts to comply. 329.It Li KERN_PROC 330Return the entire process table, or a subset of it. 331An array of 332.Va struct kinfo_proc 333structures is returned, 334whose size depends on the current number of such objects in the system. 335The third and fourth level names are as follows: 336.Bl -column "Third level nameXXXXXX" "Fourth level is:XXXXXX" -offset indent 337.It Pa Third level name Fourth level is: 338.It KERN\_PROC\_ALL None 339.It KERN\_PROC\_PID A process ID 340.It KERN\_PROC\_PGRP A process group 341.It KERN\_PROC\_TTY A tty device 342.It KERN\_PROC\_UID A user ID 343.It KERN\_PROC\_RUID A real user ID 344.El 345.It Li KERN_PROF 346Return profiling information about the kernel. 347If the kernel is not compiled for profiling, 348attempts to retrieve any of the KERN_PROF values will 349fail with EOPNOTSUPP. 350The third level names for the string and integer profiling information 351is detailed below. 352The changeable column shows whether a process with appropriate 353privilege may change the value. 354.Bl -column "GPROFXGMONPARAMXXX" "struct gmonparamXXX" -offset indent 355.It Sy Pa Third level name Type Changeable 356.It GPROF\_STATE integer yes 357.It GPROF\_COUNT u_short[\|] yes 358.It GPROF\_FROMS u_short[\|] yes 359.It GPROF\_TOS struct tostruct yes 360.It GPROF\_GMONPARAM struct gmonparam no 361.El 362.Pp 363The variables are as follows: 364.Bl -tag -width "123456" 365.It Li GPROF_STATE 366Returns GMON_PROF_ON or GMON_PROF_OFF to show that profiling 367is running or stopped. 368.It Li GPROF_COUNT 369Array of statistical program counter counts. 370.It Li GPROF_FROMS 371Array indexed by program counter of call-from points. 372.It Li GPROF_TOS 373Array of 374.Va struct tostruct 375describing destination of calls and their counts. 376.It Li GPROF_GMONPARAM 377Structure giving the sizes of the above arrays. 378.El 379.It Li KERN_SAVED_IDS 380Returns 1 if saved set-group and saved set-user ID is available. 381.It Li KERN_SECURELVL 382The system security level. 383This level may be raised by processes with appropriate privilege. 384It may only be lowered by process 1. 385.It Li KERN_VERSION 386The system version string. 387.It Li KERN_VNODE 388Return the entire vnode table. 389Note, the vnode table is not necessarily a consistent snapshot of 390the system. 391The returned data consists of an array whose size depends on the 392current number of such objects in the system. 393Each element of the array contains the kernel address of a vnode 394.Va struct vnode * 395followed by the vnode itself 396.Va struct vnode . 397.It Li KERN_UPDATEINTERVAL 398The interval between 399.Xr sync 2 400calls in the 401.Xr update 4 402process. 403.El 404.Sh CTL_MACHDEP 405The set of variables defined is architecture dependent. 406The following variables are defined for the i386 architecture. 407.Bl -column "CONSOLE_DEVICEXXX" "struct bootinfoXXX" -offset indent 408.It Sy Pa Second level name Type Changeable 409.It Li CPU_CONSDEV dev_t no 410.It Li CPU_ADJKERNTZ int yes 411.It Li CPU_DISRTCSET int yes 412.It Li CPU_BOOTINFO struct bootinfo no 413.It Li CPU_WALLCLOCK int yes 414.El 415.Sh CTL_NET 416The string and integer information available for the CTL_NET level 417is detailed below. 418The changeable column shows whether a process with appropriate 419privilege may change the value. 420.Bl -column "Second level nameXXXXXX" "routing messagesXXX" -offset indent 421.It Sy Pa Second level name Type Changeable 422.It PF\_ROUTE routing messages no 423.It PF\_INET internet values yes 424.El 425.Pp 426.Bl -tag -width "123456" 427.It Li PF_ROUTE 428Return the entire routing table or a subset of it. 429The data is returned as a sequence of routing messages (see 430.Xr route 4 431for the header file, format and meaning). 432The length of each message is contained in the message header. 433.Pp 434The third level name is a protocol number, which is currently always 0. 435The fourth level name is an address family, which may be set to 0 to 436select all address families. 437The fifth and sixth level names are as follows: 438.Bl -column "Fifth level nameXXXXXX" "Sixth level is:XXX" -offset indent 439.It Pa Fifth level name Sixth level is: 440.It NET\_RT\_FLAGS rtflags 441.It NET\_RT\_DUMP None 442.It NET\_RT\_IFLIST None 443.El 444.It Li PF_INET 445Get or set various global information about the internet protocols. 446The third level name is the protocol. 447The fourth level name is the variable name. 448The currently defined protocols and names are: 449.Bl -column "Protocol nameXXXXXX" "Variable nameXXX" "integerXXX" -offset indent 450.It Pa Protocol name Variable name Type Changeable 451.It ip forwarding integer yes 452.It ip redirect integer yes 453.It ip ttl integer yes 454.It icmp maskrepl integer yes 455.It udp checksum integer yes 456.El 457.Pp 458The variables are as follows: 459.Bl -tag -width "123456" 460.It Li ip.forwarding 461Returns 1 when IP forwarding is enabled for the host, 462meaning that the host is acting as a router. 463.It Li ip.redirect 464Returns 1 when ICMP redirects may be sent by the host. 465This option is ignored unless the host is routing IP packets, 466and should normally be enabled on all systems. 467.It Li ip.ttl 468The maximum time-to-live (hop count) value for an IP packet sourced by 469the system. 470This value applies to normal transport protocols, not to ICMP. 471.It Li icmp.maskrepl 472Returns 1 if ICMP network mask requests are to be answered. 473.It Li udp.checksum 474Returns 1 when UDP checksums are being computed and checked. 475Disabling UDP checksums is strongly discouraged. 476.El 477.Sh CTL_USER 478The string and integer information available for the CTL_USER level 479is detailed below. 480The changeable column shows whether a process with appropriate 481privilege may change the value. 482.Bl -column "USER_COLL_WEIGHTS_MAXXXX" "integerXXX" -offset indent 483.It Sy Pa Second level name Type Changeable 484.It USER\_BC\_BASE\_MAX integer no 485.It USER\_BC\_DIM\_MAX integer no 486.It USER\_BC\_SCALE\_MAX integer no 487.It USER\_BC\_STRING\_MAX integer no 488.It USER\_COLL\_WEIGHTS\_MAX integer no 489.It USER\_CS\_PATH string no 490.It USER\_EXPR\_NEST\_MAX integer no 491.It USER\_LINE\_MAX integer no 492.It USER\_POSIX2\_CHAR\_TERM integer no 493.It USER\_POSIX2\_C\_BIND integer no 494.It USER\_POSIX2\_C\_DEV integer no 495.It USER\_POSIX2\_FORT\_DEV integer no 496.It USER\_POSIX2\_FORT\_RUN integer no 497.It USER\_POSIX2\_LOCALEDEF integer no 498.It USER\_POSIX2\_SW\_DEV integer no 499.It USER\_POSIX2\_UPE integer no 500.It USER\_POSIX2\_VERSION integer no 501.It USER\_RE\_DUP\_MAX integer no 502.It USER\_STREAM\_MAX integer no 503.It USER\_TZNAME\_MAX integer no 504.El 505.Bl -tag -width "123456" 506.Pp 507.It Li USER_BC_BASE_MAX 508The maximum ibase/obase values in the 509.Xr bc 1 510utility. 511.It Li USER_BC_DIM_MAX 512The maximum array size in the 513.Xr bc 1 514utility. 515.It Li USER_BC_SCALE_MAX 516The maximum scale value in the 517.Xr bc 1 518utility. 519.It Li USER_BC_STRING_MAX 520The maximum string length in the 521.Xr bc 1 522utility. 523.It Li USER_COLL_WEIGHTS_MAX 524The maximum number of weights that can be assigned to any entry of 525the LC_COLLATE order keyword in the locale definition file. 526.It Li USER_CS_PATH 527Return a value for the 528.Ev PATH 529environment variable that finds all the standard utilities. 530.It Li USER_EXPR_NEST_MAX 531The maximum number of expressions that can be nested within 532parenthesis by the 533.Xr expr 1 534utility. 535.It Li USER_LINE_MAX 536The maximum length in bytes of a text-processing utility's input 537line. 538.It Li USER_POSIX2_CHAR_TERM 539Return 1 if the system supports at least one terminal type capable of 540all operations described in POSIX 1003.2, otherwise 0. 541.It Li USER_POSIX2_C_BIND 542Return 1 if the system's C-language development facilities support the 543C-Language Bindings Option, otherwise 0. 544.It Li USER_POSIX2_C_DEV 545Return 1 if the system supports the C-Language Development Utilities Option, 546otherwise 0. 547.It Li USER_POSIX2_FORT_DEV 548Return 1 if the system supports the FORTRAN Development Utilities Option, 549otherwise 0. 550.It Li USER_POSIX2_FORT_RUN 551Return 1 if the system supports the FORTRAN Runtime Utilities Option, 552otherwise 0. 553.It Li USER_POSIX2_LOCALEDEF 554Return 1 if the system supports the creation of locales, otherwise 0. 555.It Li USER_POSIX2_SW_DEV 556Return 1 if the system supports the Software Development Utilities Option, 557otherwise 0. 558.It Li USER_POSIX2_UPE 559Return 1 if the system supports the User Portability Utilities Option, 560otherwise 0. 561.It Li USER_POSIX2_VERSION 562The version of POSIX 1003.2 with which the system attempts to comply. 563.It Li USER_RE_DUP_MAX 564The maximum number of repeated occurrences of a regular expression 565permitted when using interval notation. 566.It Li USER_STREAM_MAX 567The minimum maximum number of streams that a process may have open 568at any one time. 569.It Li USER_TZNAME_MAX 570The minimum maximum number of types supported for the name of a 571timezone. 572.El 573.Sh CTL_VM 574The string and integer information available for the CTL_VM level 575is detailed below. 576The changeable column shows whether a process with appropriate 577privilege may change the value. 578.Bl -column "Second level nameXXXXXX" "struct loadavgXXX" -offset indent 579.It Sy Pa Second level name Type Changeable 580.It VM\_LOADAVG struct loadavg no 581.It VM\_METER struct vmtotal no 582.El 583.Pp 584.Bl -tag -width "123456" 585.It Li VM_LOADAVG 586Return the load average history. 587The returned data consists of a 588.Va struct loadavg . 589.It Li VM_METER 590Return the system wide virtual memory statistics. 591The returned data consists of a 592.Va struct vmtotal . 593.El 594.Sh RETURN VALUES 595If the call to 596.Fn sysctl 597is successful, 0 is returned. 598Otherwise \-1 is returned and 599.Va errno 600is set appropriately. 601.Sh ERRORS 602The following errors may be reported: 603.Bl -tag -width Er 604.It Bq Er EFAULT 605The buffer 606.Fa name , 607.Fa oldp , 608.Fa newp , 609or length pointer 610.Fa oldlenp 611contains an invalid address. 612.It Bq Er EINVAL 613The 614.Fa name 615array is less than two or greater than CTL_MAXNAME. 616.It Bq Er EINVAL 617A non-null 618.Fa newp 619is given and its specified length in 620.Fa newlen 621is too large or too small. 622.It Bq Er ENOMEM 623The length pointed to by 624.Fa oldlenp 625is too short to hold the requested value. 626.It Bq Er ENOTDIR 627The 628.Fa name 629array specifies an intermediate rather than terminal name. 630.It Bq Er EOPNOTSUPP 631The 632.Fa name 633array specifies a value that is unknown. 634.It Bq Er EPERM 635An attempt is made to set a read-only value. 636.It Bq Er EPERM 637A process without appropriate privilege attempts to set a value. 638.El 639.Sh FILES 640.Bl -tag -width <netinet/icmpXvar.h> -compact 641.It Pa <sys/sysctl.h> 642definitions for top level identifiers, second level kernel and hardware 643identifiers, and user level identifiers 644.It Pa <sys/socket.h> 645definitions for second level network identifiers 646.It Pa <sys/gmon.h> 647definitions for third level profiling identifiers 648.It Pa <vm/vm_param.h> 649definitions for second level virtual memory identifiers 650.It Pa <netinet/in.h> 651definitions for third level Internet identifiers and 652fourth level IP identifiers 653.It Pa <netinet/icmp_var.h> 654definitions for fourth level ICMP identifiers 655.It Pa <netinet/udp_var.h> 656definitions for fourth level UDP identifiers 657.El 658.Sh SEE ALSO 659.Xr sysctl 8 660.Sh HISTORY 661The 662.Fn sysctl 663function first appeared in 664.Bx 4.4 . 665