gen/FreeBSD/sysctl.3

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  32 .\"     @(#)sysctl.3    8.4 (Berkeley) 5/9/95
  33 .\" $FreeBSD: src/lib/libc/gen/sysctl.3,v 1.63 2004/07/02 23:52:10 ru Exp $
  34 .\"
  35 .Dd October 21, 2008
  36 .Dt SYSCTL 3
  37 .Os
  38 .Sh NAME
  39 .Nm sysctl ,
  40 .Nm sysctlbyname ,
  41 .Nm sysctlnametomib
  42 .Nd get or set system information
  43 .Sh LIBRARY
  44 .Lb libc
  45 .Sh SYNOPSIS
  46 .In sys/types.h
  47 .In sys/sysctl.h
  48 .Ft int
  49 .Fn sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
  50 .Ft int
  51 .Fn sysctlbyname "const char *name" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
  52 .Ft int
  53 .Fn sysctlnametomib "const char *name" "int *mibp" "size_t *sizep"
  54 .Sh DESCRIPTION
  55 The
  56 .Fn sysctl
  57 function retrieves system information and allows processes with
  58 appropriate privileges to set system information.
  59 The information available from
  60 .Fn sysctl
  61 consists of integers, strings, and tables.
  62 Information may be retrieved and set from the command interface
  63 using the
  64 .Xr sysctl 8
  65 utility.
  66 .Pp
  67 Unless explicitly noted below,
  68 .Fn sysctl
  69 returns a consistent snapshot of the data requested.
  70 Consistency is obtained by locking the destination
  71 buffer into memory so that the data may be copied out without blocking.
  72 Calls to
  73 .Fn sysctl
  74 are serialized to avoid deadlock.
  75 .Pp
  76 The state is described using a ``Management Information Base'' (MIB)
  77 style name, listed in
  78 .Fa name ,
  79 which is a
  80 .Fa namelen
  81 length array of integers.
  82 .Pp
  83 The
  84 .Fn sysctlbyname
  85 function accepts an ASCII representation of the name and internally
  86 looks up the integer name vector.
  87 Apart from that, it behaves the same
  88 as the standard
  89 .Fn sysctl
  90 function.
  91 .Pp
  92 The information is copied into the buffer specified by
  93 .Fa oldp .
  94 The size of the buffer is given by the location specified by
  95 .Fa oldlenp
  96 before the call,
  97 and that location gives the amount of data copied after a successful call
  98 and after a call that returns with the error code
  99 .Er ENOMEM .
 100 If the amount of data available is greater
 101 than the size of the buffer supplied,
 102 the call supplies as much data as fits in the buffer provided
 103 and returns with the error code
 104 .Er ENOMEM .
 105 If the old value is not desired,
 106 .Fa oldp
 107 and
 108 .Fa oldlenp
 109 should be set to NULL.
 110 .Pp
 111 The size of the available data can be determined by calling
 112 .Fn sysctl
 113 with the
 114 .Dv NULL
 115 argument for
 116 .Fa oldp .
 117 The size of the available data will be returned in the location pointed to by
 118 .Fa oldlenp .
 119 For some operations, the amount of space may change often.
 120 For these operations,
 121 the system attempts to round up so that the returned size is
 122 large enough for a call to return the data shortly thereafter.
 123 .Pp
 124 To set a new value,
 125 .Fa newp
 126 is set to point to a buffer of length
 127 .Fa newlen
 128 from which the requested value is to be taken.
 129 If a new value is not to be set,
 130 .Fa newp
 131 should be set to NULL and
 132 .Fa newlen
 133 set to 0.
 134 .Pp
 135 The
 136 .Fn sysctlnametomib
 137 function accepts an ASCII representation of the name,
 138 looks up the integer name vector,
 139 and returns the numeric representation in the mib array pointed to by
 140 .Fa mibp .
 141 The number of elements in the mib array is given by the location specified by
 142 .Fa sizep
 143 before the call,
 144 and that location gives the number of entries copied after a successful call.
 145 The resulting
 146 .Fa mib
 147 and
 148 .Fa size
 149 may be used in subsequent
 150 .Fn sysctl
 151 calls to get the data associated with the requested ASCII name.
 152 This interface is intended for use by applications that want to
 153 repeatedly request the same variable (the
 154 .Fn sysctl
 155 function runs in about a third the time as the same request made via the
 156 .Fn sysctlbyname
 157 function).
 158 The
 159 .Fn sysctlnametomib
 160 function is also useful for fetching mib prefixes and then adding
 161 a final component.
 162 For example, to fetch process information
 163 for processes with pid's less than 100:
 164 .Pp
 165 .Bd -literal -offset indent -compact
 166 int i, mib[4];
 167 size_t len;
 168 struct kinfo_proc kp;
 169
 170 /* Fill out the first three components of the mib */
 171 len = 4;
 172 sysctlnametomib("kern.proc.pid", mib, &len);
 173
 174 /* Fetch and print entries for pid's < 100 */
 175 for (i = 0; i < 100; i++) {
 176         mib[3] = i;
 177         len = sizeof(kp);
 178         if (sysctl(mib, 4, &kp, &len, NULL, 0) == -1)
 179                 perror("sysctl");
 180         else if (len > 0)
 181                 printkproc(&kp);
 182 }
 183 .Ed
 184 .Pp
 185 Note:  Implementation of
 186 .Fn printkproc
 187 -- to print whatever data deemed necessary from the large
 188 .Vt kinfo_proc
 189 structure (
 190 .In sys/sysctl.h
 191 ) -- is left as an exercise for the reader.
 192 .Pp
 193 The top level names are defined with a CTL_ prefix in
 194 .In sys/sysctl.h ,
 195 and are as follows.
 196 The next and subsequent levels down are found in the include files
 197 listed here, and described in separate sections below.
 198 .Pp
 199 .Bl -column CTLXMACHDEP "Next level names" -offset indent
 200 .It Sy "Name    Next level names        Description"
 201 .It "CTL_DEBUG  sys/sysctl.h    Debugging"
 202 .It "CTL_VFS    sys/mount.h     File system"
 203 .It "CTL_HW     sys/sysctl.h    Generic CPU, I/O"
 204 .It "CTL_KERN   sys/sysctl.h    High kernel limits"
 205 .It "CTL_MACHDEP        sys/sysctl.h    Machine dependent"
 206 .It "CTL_NET    sys/socket.h    Networking"
 207 .It "CTL_USER   sys/sysctl.h    User-level"
 208 .It "CTL_VM     sys/resources.h Virtual memory (struct loadavg)"
 209 .It "CTL_VM     sys/vmmeter.h   Virtual memory (struct vmtotal)"
 210 .El
 211 .Pp
 212 For example, the following retrieves the maximum number of processes allowed
 213 in the system:
 214 .Pp
 215 .Bd -literal -offset indent -compact
 216 int mib[2], maxproc;
 217 size_t len;
 218
 219 mib[0] = CTL_KERN;
 220 mib[1] = KERN_MAXPROC;
 221 len = sizeof(maxproc);
 222 sysctl(mib, 2, &maxproc, &len, NULL, 0);
 223 .Ed
 224 .Pp
 225 To retrieve the standard search path for the system utilities:
 226 .Pp
 227 .Bd -literal -offset indent -compact
 228 int mib[2];
 229 size_t len;
 230 char *p;
 231
 232 mib[0] = CTL_USER;
 233 mib[1] = USER_CS_PATH;
 234 sysctl(mib, 2, NULL, &len, NULL, 0);
 235 p = malloc(len);
 236 sysctl(mib, 2, p, &len, NULL, 0);
 237 .Ed
 238 .Ss CTL_DEBUG
 239 The debugging variables vary from system to system.
 240 A debugging variable may be added or deleted without need to recompile
 241 .Fn sysctl
 242 to know about it.
 243 Each time it runs,
 244 .Fn sysctl
 245 gets the list of debugging variables from the kernel and
 246 displays their current values.
 247 The system defines twenty
 248 .Pq Vt "struct ctldebug"
 249 variables named
 250 .Va debug0
 251 through
 252 .Va debug19 .
 253 They are declared as separate variables so that they can be
 254 individually initialized at the location of their associated variable.
 255 The loader prevents multiple use of the same variable by issuing errors
 256 if a variable is initialized in more than one place.
 257 For example, to export the variable
 258 .Va dospecialcheck
 259 as a debugging variable, the following declaration would be used:
 260 .Pp
 261 .Bd -literal -offset indent -compact
 262 int dospecialcheck = 1;
 263 struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
 264 .Ed
 265 .Ss CTL_VFS
 266 A distinguished second level name, VFS_GENERIC,
 267 is used to get general information about all file systems.
 268 One of its third level identifiers is VFS_MAXTYPENUM
 269 that gives the highest valid file system type number.
 270 Its other third level identifier is VFS_CONF that
 271 returns configuration information about the file system
 272 type given as a fourth level identifier (see
 273 .Xr getvfsbyname 3
 274 as an example of its use).
 275 The remaining second level identifiers are the
 276 file system type number returned by a
 277 .Xr statfs 2
 278 call or from VFS_CONF.
 279 The third level identifiers available for each file system
 280 are given in the header file that defines the mount
 281 argument structure for that file system.
 282 .Ss CTL_HW
 283 The string and integer information available for the CTL_HW level
 284 is detailed below.
 285 The changeable column shows whether a process with appropriate
 286 privilege may change the value.
 287 .Bl -column "Second level nameXXXXXX" integerXXX -offset indent
 288 .It Sy "Second level name       Type    Changeable"
 289 .It "HW_MACHINE string  no"
 290 .It "HW_MODEL   string  no"
 291 .It "HW_NCPU    integer no (DEPRECATED)"
 292 .It "HW_BYTEORDER       integer no"
 293 .It "HW_PHYSMEM integer no"
 294 .It "HW_MEMSIZE integer no"
 295 .It "HW_USERMEM integer no"
 296 .It "HW_PAGESIZE        integer no"
 297 .It "HW_FLOATINGPOINT   integer no"
 298 .It "HW_MACHINE_ARCH    string  no"
 299 .\".It "HW_DISKNAMES    integer no"
 300 .\".It "HW_DISKSTATS    integer no"
 301 .El
 302 .Pp
 303 .Bl -tag -width 6n
 304 .It Li HW_MACHINE
 305 The machine class.
 306 .It Li HW_MODEL
 307 The machine model
 308 .It Li HW_NCPU (DEPRECATED)
 309 The number of cpus.  It is recommended that you use "hw.physicalcpu" "hw.physicalcpu_max" "hw.logicalcpu" or "hw.logicalcpu_max" instead.
 310 .It Li "hw.physicalcpu"
 311 The number of physical processors available in the current power management mode.
 312 .It Li "hw.physicalcpu_max"
 313 The maximum number of physical processors that could be available this boot.
 314 .It Li "hw.logicalcpu"
 315 The number of logical processors available in the current power management mode.
 316 .It Li "hw.logicalcpu_max"
 317 The maximum number of logical processors that could be available this boot.
 318 .It Li HW_BYTEORDER
 319 The byteorder (4,321, or 1,234).
 320 .It Li HW_PHYSMEM
 321 The bytes of physical memory represented by a 32-bit integer (for backward compatibility). Use HW_MEMSIZE instead.
 322 .It Li HW_MEMSIZE
 323 The bytes of physical memory represented by a 64-bit integer.
 324 .It Li HW_USERMEM
 325 The bytes of non-kernel memory.
 326 .It Li HW_PAGESIZE
 327 The software page size.
 328 .It Li HW_FLOATINGPOINT
 329 Nonzero if the floating point support is in hardware.
 330 .It Li HW_MACHINE_ARCH
 331 The machine dependent architecture type.
 332 .\".It Fa HW_DISKNAMES
 333 .\".It Fa HW_DISKSTATS
 334 .El
 335 .Ss CTL_KERN
 336 The string and integer information available for the CTL_KERN level
 337 is detailed below.
 338 The changeable column shows whether a process with appropriate
 339 privilege may change the value.
 340 The types of data currently available are process information,
 341 system vnodes, the open file entries, routing table entries,
 342 virtual memory statistics, load average history, and clock rate
 343 information.
 344 .Bl -column "KERNXMAXFILESPERPROCXXX" "struct clockrateXXX" -offset indent
 345 .It Sy "Second level name       Type    Changeable"
 346 .It "KERN_ARGMAX        integer no"
 347 .It "KERN_BOOTFILE      string  yes"
 348 .It "KERN_BOOTTIME      struct timeval  no"
 349 .It "KERN_CLOCKRATE     struct clockinfo        no"
 350 .It "KERN_FILE  struct file     no"
 351 .It "KERN_HOSTID        integer yes"
 352 .It "KERN_HOSTNAME      string  yes"
 353 .It "KERN_JOB_CONTROL   integer no"
 354 .It "KERN_MAXFILES      integer yes"
 355 .It "KERN_MAXFILESPERPROC       integer yes"
 356 .It "KERN_MAXPROC       integer no"
 357 .It "KERN_MAXPROCPERUID integer yes"
 358 .It "KERN_MAXVNODES     integer yes"
 359 .It "KERN_NGROUPS       integer no"
 360 .It "KERN_NISDOMAINNAME string  yes"
 361 .It "KERN_OSRELDATE     integer no"
 362 .It "KERN_OSRELEASE     string  no"
 363 .It "KERN_OSREV integer no"
 364 .It "KERN_OSTYPE        string  no"
 365 .It "KERN_POSIX1        integer no"
 366 .It "KERN_PROC  struct kinfo_proc       no"
 367 .It "KERN_PROF  node    not applicable"
 368 .It "KERN_QUANTUM       integer yes"
 369 .It "KERN_SAVED_IDS     integer no"
 370 .It "KERN_SECURELVL     integer raise only"
 371 .It "KERN_UPDATEINTERVAL        integer no"
 372 .It "KERN_VERSION       string  no"
 373 .It "KERN_VNODE struct vnode    no"
 374 .El
 375 .Pp
 376 .Bl -tag -width 6n
 377 .It Li KERN_ARGMAX
 378 The maximum bytes of argument to
 379 .Xr execve 2 .
 380 .It Li KERN_BOOTFILE
 381 The full pathname of the file from which the kernel was loaded.
 382 .It Li KERN_BOOTTIME
 383 A
 384 .Va struct timeval
 385 structure is returned.
 386 This structure contains the time that the system was booted.
 387 .It Li KERN_CLOCKRATE
 388 A
 389 .Va struct clockinfo
 390 structure is returned.
 391 This structure contains the clock, statistics clock and profiling clock
 392 frequencies, the number of micro-seconds per hz tick and the skew rate.
 393 .It Li KERN_FILE
 394 Return the entire file table.
 395 The returned data consists of a single
 396 .Va struct filehead
 397 followed by an array of
 398 .Va struct file ,
 399 whose size depends on the current number of such objects in the system.
 400 .It Li KERN_HOSTID
 401 Get or set the host id.
 402 .It Li KERN_HOSTNAME
 403 Get or set the hostname.
 404 .It Li KERN_JOB_CONTROL
 405 Return 1 if job control is available on this system, otherwise 0.
 406 .It Li KERN_MAXFILES
 407 The maximum number of files that may be open in the system.
 408 .It Li KERN_MAXFILESPERPROC
 409 The maximum number of files that may be open for a single process.
 410 This limit only applies to processes with an effective uid of nonzero
 411 at the time of the open request.
 412 Files that have already been opened are not affected if the limit
 413 or the effective uid is changed.
 414 .It Li KERN_MAXPROC
 415 The maximum number of concurrent processes the system will allow.
 416 .It Li KERN_MAXPROCPERUID
 417 The maximum number of concurrent processes the system will allow
 418 for a single effective uid.
 419 This limit only applies to processes with an effective uid of nonzero
 420 at the time of a fork request.
 421 Processes that have already been started are not affected if the limit
 422 is changed.
 423 .It Li KERN_MAXVNODES
 424 The maximum number of vnodes available on the system.
 425 .It Li KERN_NGROUPS
 426 The maximum number of supplemental groups.
 427 .It Li KERN_NISDOMAINNAME
 428 The name of the current YP/NIS domain.
 429 .It Li KERN_OSRELDATE
 430 The kernel release version in the format
 431 .Ar M Ns Ar mm Ns Ar R Ns Ar xx ,
 432 where
 433 .Ar M
 434 is the major version,
 435 .Ar mm
 436 is the two digit minor version,
 437 .Ar R
 438 is 0 if release branch, otherwise 1,
 439 and
 440 .Ar xx
 441 is updated when the available APIs change.
 442 .Pp
 443 The userland release version is available from
 444 .In osreldate.h ;
 445 parse this file if you need to get the release version of
 446 the currently installed userland.
 447 .It Li KERN_OSRELEASE
 448 The system release string.
 449 .It Li KERN_OSREV
 450 The system revision string.
 451 .It Li KERN_OSTYPE
 452 The system type string.
 453 .It Li KERN_POSIX1
 454 The version of
 455 .St -p1003.1
 456 with which the system
 457 attempts to comply.
 458 .It Li KERN_PROC
 459 Return the entire process table, or a subset of it.
 460 An array of
 461 .Va struct kinfo_proc
 462 structures is returned,
 463 whose size depends on the current number of such objects in the system.
 464 The third and fourth level names are as follows:
 465 .Bl -column "Third level nameXXXXXX" "Fourth level is:XXXXXX" -offset indent
 466 .It "Third level name   Fourth level is:"
 467 .It "KERN_PROC_ALL      None"
 468 .It "KERN_PROC_PID      A process ID"
 469 .It "KERN_PROC_PGRP     A process group"
 470 .It "KERN_PROC_TTY      A tty device"
 471 .It "KERN_PROC_UID      A user ID"
 472 .It "KERN_PROC_RUID     A real user ID"
 473 .El
 474 .It Li KERN_PROF
 475 Return profiling information about the kernel.
 476 If the kernel is not compiled for profiling,
 477 attempts to retrieve any of the KERN_PROF values will
 478 fail with
 479 .Er ENOENT .
 480 The third level names for the string and integer profiling information
 481 is detailed below.
 482 The changeable column shows whether a process with appropriate
 483 privilege may change the value.
 484 .Bl -column "GPROFXGMONPARAMXXX" "struct gmonparamXXX" -offset indent
 485 .It Sy "Third level name        Type    Changeable"
 486 .It "GPROF_STATE        integer yes"
 487 .It "GPROF_COUNT        u_short[\|]     yes"
 488 .It "GPROF_FROMS        u_short[\|]     yes"
 489 .It "GPROF_TOS  struct tostruct yes"
 490 .It "GPROF_GMONPARAM    struct gmonparam        no"
 491 .El
 492 .Pp
 493 The variables are as follows:
 494 .Bl -tag -width 6n
 495 .It Li GPROF_STATE
 496 Returns GMON_PROF_ON or GMON_PROF_OFF to show that profiling
 497 is running or stopped.
 498 .It Li GPROF_COUNT
 499 Array of statistical program counter counts.
 500 .It Li GPROF_FROMS
 501 Array indexed by program counter of call-from points.
 502 .It Li GPROF_TOS
 503 Array of
 504 .Va struct tostruct
 505 describing destination of calls and their counts.
 506 .It Li GPROF_GMONPARAM
 507 Structure giving the sizes of the above arrays.
 508 .El
 509 .It Li KERN_QUANTUM
 510 The maximum period of time, in microseconds, for which a process is allowed
 511 to run without being preempted if other processes are in the run queue.
 512 .It Li KERN_SAVED_IDS
 513 Returns 1 if saved set-group and saved set-user ID is available.
 514 .It Li KERN_SECURELVL
 515 The system security level.
 516 This level may be raised by processes with appropriate privilege.
 517 It may not be lowered.
 518 .It Li KERN_VERSION
 519 The system version string.
 520 .It Li KERN_VNODE
 521 Return the entire vnode table.
 522 Note, the vnode table is not necessarily a consistent snapshot of
 523 the system.
 524 The returned data consists of an array whose size depends on the
 525 current number of such objects in the system.
 526 Each element of the array contains the kernel address of a vnode
 527 .Va struct vnode *
 528 followed by the vnode itself
 529 .Va struct vnode .
 530 .El
 531 .Ss CTL_MACHDEP
 532 The set of variables defined is architecture dependent.
 533 The following variables are defined for the i386 architecture.
 534 .Bl -column "CONSOLE_DEVICEXXX" "struct bootinfoXXX" -offset indent
 535 .It Sy "Second level name       Type    Changeable"
 536 .It Li "CPU_CONSDEV     dev_t   no"
 537 .It Li "CPU_ADJKERNTZ   int     yes"
 538 .It Li "CPU_DISRTCSET   int     yes"
 539 .It Li "CPU_BOOTINFO    struct bootinfo no"
 540 .It Li "CPU_WALLCLOCK   int     yes"
 541 .El
 542 .Ss CTL_NET
 543 The string and integer information available for the CTL_NET level
 544 is detailed below.
 545 The changeable column shows whether a process with appropriate
 546 privilege may change the value.
 547 .Bl -column "Second level nameXXXXXX" "routing messagesXXX" -offset indent
 548 .It Sy "Second level name       Type    Changeable"
 549 .It "PF_ROUTE   routing messages        no"
 550 .It "PF_INET    IPv4 values     yes"
 551 .It "PF_INET6   IPv6 values     yes"
 552 .El
 553 .Pp
 554 .Bl -tag -width 6n
 555 .It Li PF_ROUTE
 556 Return the entire routing table or a subset of it.
 557 The data is returned as a sequence of routing messages (see
 558 .Xr route 4
 559 for the header file, format and meaning).
 560 The length of each message is contained in the message header.
 561 .Pp
 562 The third level name is a protocol number, which is currently always 0.
 563 The fourth level name is an address family, which may be set to 0 to
 564 select all address families.
 565 The fifth and sixth level names are as follows:
 566 .Bl -column "Fifth level nameXXXXXX" "Sixth level is:XXX" -offset indent
 567 .It Sy "Fifth level name        Sixth level is:"
 568 .It "NET_RT_FLAGS       rtflags"
 569 .It "NET_RT_DUMP        None"
 570 .It "NET_RT_IFLIST      0 or if_index"
 571 .It "NET_RT_IFMALIST    0 or if_index"
 572 .El
 573 .Pp
 574 The
 575 .Dv NET_RT_IFMALIST
 576 name returns information about multicast group memberships on all interfaces
 577 if 0 is specified, or for the interface specified by
 578 .Va if_index .
 579 .It Li PF_INET
 580 Get or set various global information about the IPv4
 581 (Internet Protocol version 4).
 582 The third level name is the protocol.
 583 The fourth level name is the variable name.
 584 The currently defined protocols and names are:
 585 .Bl -column ProtocolXX VariableXX TypeXX ChangeableXX
 586 .It Sy "Protocol        Variable        Type    Changeable"
 587 .It "icmp       bmcastecho      integer yes"
 588 .It "icmp       maskrepl        integer yes"
 589 .It "ip forwarding      integer yes"
 590 .It "ip redirect        integer yes"
 591 .It "ip ttl     integer yes"
 592 .It "udp        checksum        integer yes"
 593 .El
 594 .Pp
 595 The variables are as follows:
 596 .Bl -tag -width 6n
 597 .It Li icmp.bmcastecho
 598 Returns 1 if an ICMP echo request to a broadcast or multicast address is
 599 to be answered.
 600 .It Li icmp.maskrepl
 601 Returns 1 if ICMP network mask requests are to be answered.
 602 .It Li ip.forwarding
 603 Returns 1 when IP forwarding is enabled for the host,
 604 meaning that the host is acting as a router.
 605 .It Li ip.redirect
 606 Returns 1 when ICMP redirects may be sent by the host.
 607 This option is ignored unless the host is routing IP packets,
 608 and should normally be enabled on all systems.
 609 .It Li ip.ttl
 610 The maximum time-to-live (hop count) value for an IP packet sourced by
 611 the system.
 612 This value applies to normal transport protocols, not to ICMP.
 613 .It Li udp.checksum
 614 Returns 1 when UDP checksums are being computed and checked.
 615 Disabling UDP checksums is strongly discouraged.
 616 .Pp
 617 For variables net.inet.*.ipsec, please refer to
 618 .Xr ipsec 4 .
 619 .El
 620 .It Li PF_INET6
 621 Get or set various global information about the IPv6
 622 (Internet Protocol version 6).
 623 The third level name is the protocol.
 624 The fourth level name is the variable name.
 625 .Pp
 626 For variables net.inet6.* please refer to
 627 .Xr inet6 4 .
 628 For variables net.inet6.*.ipsec6, please refer to
 629 .Xr ipsec 4 .
 630 .El
 631 .Ss CTL_USER
 632 The string and integer information available for the CTL_USER level
 633 is detailed below.
 634 The changeable column shows whether a process with appropriate
 635 privilege may change the value.
 636 .Bl -column "USER_COLL_WEIGHTS_MAXXXX" "integerXXX" -offset indent
 637 .It Sy "Second level name       Type    Changeable"
 638 .It "USER_BC_BASE_MAX   integer no"
 639 .It "USER_BC_DIM_MAX    integer no"
 640 .It "USER_BC_SCALE_MAX  integer no"
 641 .It "USER_BC_STRING_MAX integer no"
 642 .It "USER_COLL_WEIGHTS_MAX      integer no"
 643 .It "USER_CS_PATH       string  no"
 644 .It "USER_EXPR_NEST_MAX integer no"
 645 .It "USER_LINE_MAX      integer no"
 646 .It "USER_POSIX2_CHAR_TERM      integer no"
 647 .It "USER_POSIX2_C_BIND integer no"
 648 .It "USER_POSIX2_C_DEV  integer no"
 649 .It "USER_POSIX2_FORT_DEV       integer no"
 650 .It "USER_POSIX2_FORT_RUN       integer no"
 651 .It "USER_POSIX2_LOCALEDEF      integer no"
 652 .It "USER_POSIX2_SW_DEV integer no"
 653 .It "USER_POSIX2_UPE    integer no"
 654 .It "USER_POSIX2_VERSION        integer no"
 655 .It "USER_RE_DUP_MAX    integer no"
 656 .It "USER_STREAM_MAX    integer no"
 657 .It "USER_TZNAME_MAX    integer no"
 658 .El
 659 .Bl -tag -width 6n
 660 .Pp
 661 .It Li USER_BC_BASE_MAX
 662 The maximum ibase/obase values in the
 663 .Xr bc 1
 664 utility.
 665 .It Li USER_BC_DIM_MAX
 666 The maximum array size in the
 667 .Xr bc 1
 668 utility.
 669 .It Li USER_BC_SCALE_MAX
 670 The maximum scale value in the
 671 .Xr bc 1
 672 utility.
 673 .It Li USER_BC_STRING_MAX
 674 The maximum string length in the
 675 .Xr bc 1
 676 utility.
 677 .It Li USER_COLL_WEIGHTS_MAX
 678 The maximum number of weights that can be assigned to any entry of
 679 the LC_COLLATE order keyword in the locale definition file.
 680 .It Li USER_CS_PATH
 681 Return a value for the
 682 .Ev PATH
 683 environment variable that finds all the standard utilities.
 684 .It Li USER_EXPR_NEST_MAX
 685 The maximum number of expressions that can be nested within
 686 parenthesis by the
 687 .Xr expr 1
 688 utility.
 689 .It Li USER_LINE_MAX
 690 The maximum length in bytes of a text-processing utility's input
 691 line.
 692 .It Li USER_POSIX2_CHAR_TERM
 693 Return 1 if the system supports at least one terminal type capable of
 694 all operations described in
 695 .St -p1003.2 ,
 696 otherwise 0.
 697 .It Li USER_POSIX2_C_BIND
 698 Return 1 if the system's C-language development facilities support the
 699 C-Language Bindings Option, otherwise 0.
 700 .It Li USER_POSIX2_C_DEV
 701 Return 1 if the system supports the C-Language Development Utilities Option,
 702 otherwise 0.
 703 .It Li USER_POSIX2_FORT_DEV
 704 Return 1 if the system supports the FORTRAN Development Utilities Option,
 705 otherwise 0.
 706 .It Li USER_POSIX2_FORT_RUN
 707 Return 1 if the system supports the FORTRAN Runtime Utilities Option,
 708 otherwise 0.
 709 .It Li USER_POSIX2_LOCALEDEF
 710 Return 1 if the system supports the creation of locales, otherwise 0.
 711 .It Li USER_POSIX2_SW_DEV
 712 Return 1 if the system supports the Software Development Utilities Option,
 713 otherwise 0.
 714 .It Li USER_POSIX2_UPE
 715 Return 1 if the system supports the User Portability Utilities Option,
 716 otherwise 0.
 717 .It Li USER_POSIX2_VERSION
 718 The version of
 719 .St -p1003.2
 720 with which the system attempts to comply.
 721 .It Li USER_RE_DUP_MAX
 722 The maximum number of repeated occurrences of a regular expression
 723 permitted when using interval notation.
 724 .It Li USER_STREAM_MAX
 725 The minimum maximum number of streams that a process may have open
 726 at any one time.
 727 .It Li USER_TZNAME_MAX
 728 The minimum maximum number of types supported for the name of a
 729 timezone.
 730 .El
 731 .Ss CTL_VM
 732 The string and integer information available for the CTL_VM level
 733 is detailed below.
 734 The changeable column shows whether a process with appropriate
 735 privilege may change the value.
 736 .Bl -column "Second level nameXXXXXX" "struct loadavgXXX" -offset indent
 737 .It Sy "Second level name       Type    Changeable"
 738 .It "VM_LOADAVG struct loadavg  no"
 739 .It "VM_PAGEOUT_ALGORITHM       integer yes"
 740 .It "VM_SWAPPING_ENABLED        integer maybe"
 741 .It "VM_V_CACHE_MAX     integer yes"
 742 .It "VM_V_CACHE_MIN     integer yes"
 743 .It "VM_V_FREE_MIN      integer yes"
 744 .It "VM_V_FREE_RESERVED integer yes"
 745 .It "VM_V_FREE_TARGET   integer yes"
 746 .It "VM_V_INACTIVE_TARGET       integer yes"
 747 .It "VM_V_PAGEOUT_FREE_MIN      integer yes"
 748 .El
 749 .Pp
 750 .Bl -tag -width 6n
 751 .It Li VM_LOADAVG
 752 Return the load average history.
 753 The returned data consists of a
 754 .Va struct loadavg .
 755 .It Li VM_PAGEOUT_ALGORITHM
 756 0 if the statistics-based page management algorithm is in use
 757 or 1 if the near-LRU algorithm is in use.
 758 .It Li VM_SWAPPING_ENABLED
 759 1 if process swapping is enabled or 0 if disabled.
 760 This variable is
 761 permanently set to 0 if the kernel was built with swapping disabled.
 762 .It Li VM_V_CACHE_MAX
 763 Maximum desired size of the cache queue.
 764 .It Li VM_V_CACHE_MIN
 765 Minimum desired size of the cache queue.
 766 If the cache queue size
 767 falls very far below this value, the pageout daemon is awakened.
 768 .It Li VM_V_FREE_MIN
 769 Minimum amount of memory (cache memory plus free memory)
 770 required to be available before a process waiting on memory will be
 771 awakened.
 772 .It Li VM_V_FREE_RESERVED
 773 Processes will awaken the pageout daemon and wait for memory if the
 774 number of free and cached pages drops below this value.
 775 .It Li VM_V_FREE_TARGET
 776 The total amount of free memory (including cache memory) that the
 777 pageout daemon tries to maintain.
 778 .It Li VM_V_INACTIVE_TARGET
 779 The desired number of inactive pages that the pageout daemon should
 780 achieve when it runs.
 781 Inactive pages can be quickly inserted into
 782 process address space when needed.
 783 .It Li VM_V_PAGEOUT_FREE_MIN
 784 If the amount of free and cache memory falls below this value, the
 785 pageout daemon will enter "memory conserving mode" to avoid deadlock.
 786 .El
 787 .Sh RETURN VALUES
 788 .Rv -std
 789 .Sh ERRORS
 790 The following errors may be reported:
 791 .Bl -tag -width Er
 792 .It Bq Er EFAULT
 793 The buffer
 794 .Fa name ,
 795 .Fa oldp ,
 796 .Fa newp ,
 797 or length pointer
 798 .Fa oldlenp
 799 contains an invalid address.
 800 .It Bq Er EINVAL
 801 The
 802 .Fa name
 803 array is less than two or greater than CTL_MAXNAME.
 804 .It Bq Er EINVAL
 805 A non-null
 806 .Fa newp
 807 is given and its specified length in
 808 .Fa newlen
 809 is too large or too small.
 810 .It Bq Er ENOMEM
 811 The length pointed to by
 812 .Fa oldlenp
 813 is too short to hold the requested value.
 814 .It Bq Er ENOMEM
 815 The smaller of either the length pointed to by
 816 .Fa oldlenp
 817 or the estimated size of the returned data exceeds the
 818 system limit on locked memory.
 819 .It Bq Er ENOMEM
 820 Locking the buffer
 821 .Fa oldp ,
 822 or a portion of the buffer if the estimated size of the data
 823 to be returned is smaller,
 824 would cause the process to exceed its per-process locked memory limit.
 825 .It Bq Er ENOTDIR
 826 The
 827 .Fa name
 828 array specifies an intermediate rather than terminal name.
 829 .It Bq Er EISDIR
 830 The
 831 .Fa name
 832 array specifies a terminal name, but the actual name is not terminal.
 833 .It Bq Er ENOENT
 834 The
 835 .Fa name
 836 array specifies a value that is unknown.
 837 .It Bq Er EPERM
 838 An attempt is made to set a read-only value.
 839 .It Bq Er EPERM
 840 A process without appropriate privilege attempts to set a value.
 841 .El
 842 .Sh FILES
 843 .Bl -tag -width <netinet/icmpXvar.h> -compact
 844 .It In sys/sysctl.h
 845 definitions for top level identifiers, second level kernel and hardware
 846 identifiers, and user level identifiers
 847 .It In sys/socket.h
 848 definitions for second level network identifiers
 849 .It In sys/gmon.h
 850 definitions for third level profiling identifiers
 851 .It In mach/vm_param.h
 852 definitions for second level virtual memory identifiers
 853 .It In netinet/in.h
 854 definitions for third level IPv4/IPv6 identifiers and
 855 fourth level IPv4/v6 identifiers
 856 .It In netinet/icmp_var.h
 857 definitions for fourth level ICMP identifiers
 858 .It In netinet/icmp6.h
 859 definitions for fourth level ICMPv6 identifiers
 860 .It In netinet/udp_var.h
 861 definitions for fourth level UDP identifiers
 862 .El
 863 .Sh SEE ALSO
 864 .Xr sysconf 3 ,
 865 .Xr sysctl 8
 866 .Sh HISTORY
 867 The
 868 .Fn sysctl
 869 function first appeared in
 870 .Bx 4.4 .