libc/gen/sysctl.3

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.\"	@(#)sysctl.3	8.4 (Berkeley) 5/9/95
.\" $FreeBSD: src/lib/libc/gen/sysctl.3,v 1.33.2.13 2002/04/07 04:57:14 dd Exp $
.\"
.Dd January 5, 2019
.Dt SYSCTL 3
.Os
.Sh NAME
.Nm sysctl ,
.Nm sysctlbyname ,
.Nm sysctlnametomib
.Nd get or set system information
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/sysctl.h
.Ft int
.Fn sysctl "const int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "const void *newp" "size_t newlen"
.Ft int
.Fn sysctlbyname "const char *name" "void *oldp" "size_t *oldlenp" "const void *newp" "size_t newlen"
.Ft int
.Fn sysctlnametomib "const char *name" "int *mibp" "size_t *sizep"
.Sh DESCRIPTION
The
.Fn sysctl
function retrieves system information and allows processes with
appropriate privileges to set system information.
The information available from
.Fn sysctl
consists of integers, strings, and tables.
Information may be retrieved and set from the command interface
using the
.Xr sysctl 8
utility.
.Pp
Unless explicitly noted below,
.Fn sysctl
returns a consistent snapshot of the data requested.
Consistency is obtained by locking the destination
buffer into memory so that the data may be copied out without blocking.
Calls to
.Fn sysctl
are serialized to avoid deadlock.
.Pp
The state is described using a
.Dq Management Information Base (MIB)
style name, listed in
.Fa name ,
which is a
.Fa namelen
length array of integers.
.Pp
The
.Fn sysctlbyname
function accepts an ASCII representation of the name and internally
looks up the integer name vector.  Apart from that, it behaves the same
as the standard
.Fn sysctl
function.
.Pp
The information is copied into the buffer specified by
.Fa oldp .
The size of the buffer is given by the location specified by
.Fa oldlenp
before the call,
and that location gives the amount of data copied after a successful call
and after a call that returns with the error code
.Er ENOMEM .
If the amount of data available is greater
than the size of the buffer supplied,
the call supplies as much data as fits in the buffer provided
and returns with the error code
.Er ENOMEM .
If the old value is not desired,
.Fa oldp
and
.Fa oldlenp
should be set to NULL.
.Pp
The size of the available data can be determined by calling
.Fn sysctl
with a NULL parameter for
.Fa oldp .
The size of the available data will be returned in the location pointed to by
.Fa oldlenp .
For some operations, the amount of space may change often.
For these operations,
the system attempts to round up so that the returned size is
large enough for a call to return the data shortly thereafter.
.Pp
To set a new value,
.Fa newp
is set to point to a buffer of length
.Fa newlen
from which the requested value is to be taken.
If a new value is not to be set,
.Fa newp
should be set to NULL and
.Fa newlen
set to 0.
.Pp
The
.Fn sysctlnametomib
function accepts an ASCII representation of the name,
looks up the integer name vector,
and returns the numeric representation in the mib array pointed to by
.Fa mibp .
The number of elements in the mib array is given by the location specified by
.Fa sizep
before the call,
and that location gives the number of entries copied after a successful call.
The resulting
.Fa mib
and
.Fa size
may be used in subsequent
.Fn sysctl
calls to get the data associated with the requested ASCII name.
This interface is intended for use by applications that want to
repeatedly request the same variable (the
.Fn sysctl
function runs in about a third the time as the same request made via the
.Fn sysctlbyname
function).
The
.Fn sysctlnametomib
function is also useful for fetching mib prefixes and then adding
a final component.
For example, to fetch process information
for processes with pid's less than 100:
.Pp
.Bd -literal -offset indent -compact
int i, mib[4];
size_t len;
struct kinfo_proc kp;

/* Fill out the first three components of the mib */
len = 4;
sysctlnametomib("kern.proc.pid", mib, &len);

/* Fetch and print entries for pid's < 100 */
for (i = 0; i < 100; i++) {
	mib[3] = i;
	len = sizeof(kp);
	if (sysctl(mib, 4, &kp, &len, NULL, 0) == -1)
		perror("sysctl");
	else if (len > 0)
		printkproc(&kp);
}
.Ed
.Pp
The top level names are defined with a CTL_ prefix in
.In sys/sysctl.h ,
and are as follows.
The next and subsequent levels down are found in the include files
listed here, and described in separate sections below.
.Bl -column CTLXMACHDEPXXX "Next level namesXXXXXX" -offset indent
.It Sy "Name" Ta Sy "Next level names" Ta Sy "Description"
.It Dv CTL_DEBUG Ta "sys/sysctl.h" Ta "Debugging"
.It Dv CTL_VFS Ta "sys/mount.h" Ta "Filesystem"
.It Dv CTL_HW Ta "sys/sysctl.h" Ta "Generic CPU, I/O"
.It Dv CTL_KERN Ta "sys/sysctl.h" Ta "High kernel limits"
.It Dv CTL_MACHDEP Ta "sys/sysctl.h" Ta "Machine dependent"
.It Dv CTL_NET Ta "sys/socket.h" Ta "Networking"
.It Dv CTL_USER Ta "sys/sysctl.h" Ta "User-level"
.It Dv CTL_VM Ta "vm/vm_param.h" Ta "Virtual memory"
.El
.Pp
For example, the following retrieves the maximum number of processes allowed
in the system:
.Pp
.Bd -literal -offset indent -compact
int mib[2], maxproc;
size_t len;

mib[0] = CTL_KERN;
mib[1] = KERN_MAXPROC;
len = sizeof(maxproc);
sysctl(mib, 2, &maxproc, &len, NULL, 0);
.Ed
.Pp
To retrieve the standard search path for the system utilities:
.Pp
.Bd -literal -offset indent -compact
int mib[2];
size_t len;
char *p;

mib[0] = CTL_USER;
mib[1] = USER_CS_PATH;
sysctl(mib, 2, NULL, &len, NULL, 0);
p = malloc(len);
sysctl(mib, 2, p, &len, NULL, 0);
.Ed
.Ss CTL_DEBUG
The debugging variables vary from system to system.
A debugging variable may be added or deleted without need to recompile
.Fn sysctl
to know about it.
Each time it runs,
.Fn sysctl
gets the list of debugging variables from the kernel and
displays their current values.
The system defines twenty
.Vt struct ctldebug
variables named
.Nm debug0
through
.Nm debug19 .
They are declared as separate variables so that they can be
individually initialized at the location of their associated variable.
The loader prevents multiple use of the same variable by issuing errors
if a variable is initialized in more than one place.
For example, to export the variable
.Nm dospecialcheck
as a debugging variable, the following declaration would be used:
.Bd -literal -offset indent -compact
int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
.Ed
.Ss CTL_VFS
A distinguished second level name, VFS_GENERIC,
is used to get general information about all filesystems.
One of its third level identifiers is VFS_MAXTYPENUM
that gives the highest valid filesystem type number.
Its other third level identifier is VFS_CONF that
returns configuration information about the filesystem
type given as a fourth level identifier (see
.Xr getvfsbyname 3
as an example of its use).
The remaining second level identifiers are the
filesystem type number returned by a
.Xr statfs 2
call or from VFS_CONF.
The third level identifiers available for each filesystem
are given in the header file that defines the mount
argument structure for that filesystem.
.Ss CTL_HW
The string and integer information available for the
.Dv CTL_HW
level
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "Second level nameXXXXXX" integerXXX -offset indent
.It Sy "Second level name" Ta Sy "Type" Ta Sy "Changeable"
.It Dv HW_MACHINE Ta "string" Ta "no"
.It Dv HW_MODEL Ta "string" Ta "no"
.It Dv HW_NCPU Ta "integer" Ta "no"
.It Dv HW_BYTEORDER Ta "integer" Ta "no"
.It Dv HW_PHYSMEM Ta "integer" Ta "no"
.It Dv HW_USERMEM Ta "integer" Ta "no"
.It Dv HW_PAGESIZE Ta "integer" Ta "no"
.It Dv HW_FLOATINGPT Ta "integer" Ta "no"
.It Dv HW_MACHINE_ARCH Ta "string" Ta "no"
.It Dv HW_MACHINE_PLATFORM Ta "string" Ta "no"
.\".It Dv HW_DISKNAMES Ta "integer" Ta "no"
.\".It Dv HW_DISKSTATS Ta "integer" Ta "no"
.It Dv HW_SENSORS Ta "node" Ta "not applicable"
.El
.Bl -tag -width 6n
.It Dv HW_MACHINE
The machine class.
.It Dv HW_MODEL
The machine model
.It Dv HW_NCPU
The number of cpus.
.It Dv HW_BYTEORDER
The byteorder (4321, or 1234).
.It Dv HW_PHYSMEM
The bytes of physical memory.
.It Dv HW_USERMEM
The bytes of non-kernel memory.
.It Dv HW_PAGESIZE
The software page size.
.It Dv HW_FLOATINGPT
Nonzero if the floating point support is in hardware.
.It Dv HW_MACHINE_ARCH
The machine dependent architecture type.
.It Dv HW_MACHINE_PLATFORM
The platform architecture type.
.\".It Dv HW_DISKNAMES
.\".It Dv HW_DISKSTATS
.It Dv HW_SENSORS
Third level comprises an array of
.Vt "struct sensordev"
structures containing information about devices
that may attach hardware monitoring sensors.
.Pp
Third, fourth and fifth levels together comprise an array of
.Vt "struct sensor"
structures containing snapshot readings of hardware monitoring sensors.
In such usage, third level indicates the numerical representation
of the sensor device name to which the sensor is attached
(device's
.Va xname
and number shall be matched with the help of
.Vt "struct sensordev"
structure above),
fourth level indicates sensor type and
fifth level is an ordinal sensor number (unique to
the specified sensor type on the specified sensor device).
.Pp
The
.Vt sensordev
and
.Vt sensor
structures
and
.Vt sensor_type
enumeration
are defined in
.In sys/sensors.h .
.El
.Ss CTL_KERN
The string and integer information available for the
.Dv CTL_KERN
level
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
The types of data currently available are process information,
system vnodes, the open file entries, routing table entries,
virtual memory statistics, load average history, and clock rate
information.
.Bl -column "KERNXMAXPOSIXLOCKSPERUIDXXX" "struct clockrateXXX" -offset indent
.It Sy "Second level name" Ta Sy "Type" Ta Sy "Changeable"
.It Dv KERN_ARGMAX Ta "integer" Ta "no"
.It Dv KERN_BOOTFILE Ta "string" Ta "yes"
.It Dv KERN_BOOTTIME Ta "struct timespec" Ta "no"
.It Dv KERN_CLOCKRATE Ta "struct clockinfo" Ta "no"
.It Dv KERN_FILE Ta "struct kinfo_file" Ta "no"
.It Dv KERN_HOSTID Ta "integer" Ta "yes"
.It Dv KERN_HOSTNAME Ta "string" Ta "yes"
.It Dv KERN_JOB_CONTROL Ta "integer" Ta "no"
.It Dv KERN_MAXFILES Ta "integer" Ta "yes"
.It Dv KERN_MAXFILESPERPROC Ta "integer" Ta "yes"
.It Dv KERN_MAXPOSIXLOCKSPERUID Ta "integer" Ta "yes"
.It Dv KERN_MAXPROC Ta "integer" Ta "no"
.It Dv KERN_MAXPROCPERUID Ta "integer" Ta "yes"
.It Dv KERN_MAXVNODES Ta "integer" Ta "yes"
.It Dv KERN_NGROUPS Ta "integer" Ta "no"
.It Dv KERN_NISDOMAINNAME Ta "string" Ta "yes"
.It Dv KERN_OSRELDATE Ta "integer" Ta "no"
.It Dv KERN_OSRELEASE Ta "string" Ta "no"
.It Dv KERN_OSREV Ta "integer" Ta "no"
.It Dv KERN_OSTYPE Ta "string" Ta "no"
.It Dv KERN_POSIX1 Ta "integer" Ta "no"
.It Dv KERN_PROC Ta "struct kinfo_proc" Ta "no"
.It Dv KERN_SAVED_IDS Ta "integer" Ta "no"
.It Dv KERN_SECURELVL Ta "integer" Ta "raise only"
.It Dv KERN_VERSION Ta "string" Ta "no"
.It Dv KERN_VNODE Ta "struct vnode" Ta "no"
.El
.Bl -tag -width 6n
.It Dv KERN_ARGMAX
The maximum bytes of argument to
.Xr execve 2 .
.It Dv KERN_BOOTFILE
The full pathname of the file from which the kernel was loaded.
.It Dv KERN_BOOTTIME
A
.Vt struct timespec
structure is returned.
This structure contains the time that the system was booted.
.It Dv KERN_CLOCKRATE
A
.Vt struct clockinfo
structure is returned.
This structure contains the clock, statistics clock and profiling clock
frequencies, the number of micro-seconds per hz tick and the skew rate.
.It Dv KERN_FILE
Return the entire file table.
The returned data consists of an array of
.Vt struct kinfo_file ,
whose size depends on the current number of such objects in the system.
.It Dv KERN_HOSTID
Get or set the host id.
.It Dv KERN_HOSTNAME
Get or set the hostname.
.It Dv KERN_JOB_CONTROL
Return 1 if job control is available on this system, otherwise 0.
.It Dv KERN_MAXFILES
The maximum number of files that may be open in the system.
.It Dv KERN_MAXFILESPERPROC
The maximum number of files that may be open for a single process.
This limit only applies to processes with an effective uid of nonzero
at the time of the open request.
Files that have already been opened are not affected if the limit
or the effective uid is changed.
.It Dv KERN_MAXPROC
The maximum number of concurrent processes the system will allow.
.It Dv KERN_MAXPROCPERUID
The maximum number of concurrent processes the system will allow
for a single effective uid.
This limit only applies to processes with an effective uid of nonzero
at the time of a fork request.
Processes that have already been started are not affected if the limit
is changed.
.It Dv KERN_MAXVNODES
The maximum number of vnodes available on the system.
.It Dv KERN_NGROUPS
The maximum number of supplemental groups.
.It Dv KERN_NISDOMAINNAME
The name of the current YP/NIS domain.
.It Dv KERN_OSRELDATE
The system release date in YYYYMM format
(January 1996 is encoded as 199601).
.It Dv KERN_OSRELEASE
The system release string.
.It Dv KERN_OSREV
The system revision string.
.It Dv KERN_OSTYPE
The system type string.
.It Dv KERN_POSIX1
The version of
.St -p1003.1
with which the system
attempts to comply.
.It Dv KERN_PROC
Return selected information about specific running processes.
.Pp
For the following names, an array of
.Vt struct kinfo_proc
structures is returned,
whose size depends on the current number of such objects in the system.
Adding the flag
.Dv KERN_PROC_FLAG_LWP
to the third level name signals that information about all
light weight processes of the selected processes should be returned.
.Bl -column "Third level nameXXXXXX" "Fourth level is:XXXXXX" -offset indent
.It Sy "Third level name" Ta Sy "Fourth level is:"
.It Dv KERN_PROC_ALL Ta "None"
.It Dv KERN_PROC_PID Ta "A process ID"
.It Dv KERN_PROC_PGRP Ta "A process group"
.It Dv KERN_PROC_TTY Ta "A tty device"
.It Dv KERN_PROC_UID Ta "A user ID"
.It Dv KERN_PROC_RUID Ta "A real user ID"
.El
.Pp
For the following names, a NUL-terminated string is returned.
.Bl -column "Third level nameXXXXXX" "Fourth level is:XXXXXX" -offset indent
.It Sy "Third level name" Ta Sy "Fourth level is:"
.It Dv KERN_PROC_ARGS Ta "A process ID"
.It Dv KERN_PROC_CWD Ta "A process ID"
.It Dv KERN_PROC_PATHNAME Ta "A process ID"
.El
.Pp
The variables are as follows:
.Bl -tag -width 6n
.It Dv KERN_PROC_ARGS
Returns the command line argument array of a process, in a flattened form,
i.e. NUL-terminated arguments follow each other.
A process can set its own process title by changing this value.
.It Dv KERN_PROC_CWD
Returns the current working directory of a process.
.It Dv KERN_PROC_PATHNAME
Returns the path of a process' text file.
A process ID of
.Li \-1
implies the current process.
.El
.It Dv KERN_SAVED_IDS
Returns 1 if saved set-group and saved set-user ID is available.
.It Dv KERN_SECURELVL
The system security level.
This level may be raised by processes with appropriate privilege.
It may not be lowered.
.It Dv KERN_VERSION
The system version string.
.It Dv KERN_VNODE
Return the entire vnode table.
Note, the vnode table is not necessarily a consistent snapshot of
the system.
The returned data consists of an array whose size depends on the
current number of such objects in the system.
Each element of the array contains the kernel address of a vnode
.Vt struct vnode *
followed by the vnode itself
.Vt struct vnode .
.El
.Ss CTL_MACHDEP
The set of variables defined is architecture dependent.
The following variables are defined for the x86_64 architecture.
.Bl -column "CONSOLE_DEVICEXXX" "struct bootinfoXXX" -offset indent
.It Sy "Second level name" Ta Sy "Type" Ta Sy "Changeable"
.It Dv CPU_CONSDEV Ta "dev_t" Ta "no"
.It Dv CPU_ADJKERNTZ Ta "int" Ta "yes"
.It Dv CPU_DISRTCSET Ta "int" Ta "yes"
.It Dv CPU_BOOTINFO Ta "struct bootinfo" Ta "no"
.It Dv CPU_WALLCLOCK Ta "int" Ta "yes"
.El
.Ss CTL_NET
The string and integer information available for the
.Dv CTL_NET
level is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "Second level nameXXXXXX" "routing messagesXXX" -offset indent
.It Sy "Second level name" Ta Sy "Type" Ta Sy "Changeable"
.It Dv PF_ROUTE Ta "routing messages" Ta "no"
.It Dv PF_INET Ta "IPv4 values" Ta "yes"
.It Dv PF_INET6 Ta "IPv6 values" Ta "yes"
.El
.Bl -tag -width 6n
.It Dv PF_ROUTE
Return the entire routing table or a subset of it.
The data is returned as a sequence of routing messages (see
.Xr route 4
for the header file, format and meaning).
The length of each message is contained in the message header.
.Pp
The third level name is a protocol number, which is currently always 0.
The fourth level name is an address family, which may be set to 0 to
select all address families.
The fifth and sixth level names are as follows:
.Bl -column "Fifth level nameXXXXXX" "Sixth level is:XXX" -offset indent
.It Sy "Fifth level name" Ta Sy "Sixth level is:"
.It Dv NET_RT_FLAGS Ta "rtflags"
.It Dv NET_RT_DUMP Ta "None"
.It Dv NET_RT_IFLIST Ta "None"
.El
.It Dv PF_INET
Get or set various global information about the IPv4
.Pq Internet Protocol version 4 .
The third level name is the protocol.
The fourth level name is the variable name.
The currently defined protocols and names are:
.Bl -column ProtocolXX VariableXX TypeXX ChangeableXX
.It Sy "Protocol" Ta Sy "Variable" Ta Sy "Type" Ta Sy "Changeable"
.It icmp Ta bmcastecho Ta integer Ta yes
.It icmp Ta maskrepl Ta integer Ta yes
.It ip Ta forwarding Ta integer Ta yes
.It ip Ta redirect Ta integer Ta yes
.It ip Ta ttl Ta integer Ta yes
.It udp Ta checksum Ta integer Ta yes
.El
.Pp
The variables are as follows:
.Bl -tag -width 6n
.It Li icmp.bmcastecho
Returns 1 if an ICMP echo request to a broadcast or multicast address is
to be answered.
.It Li icmp.maskrepl
Returns 1 if ICMP network mask requests are to be answered.
.It Li ip.forwarding
Returns 1 when IP forwarding is enabled for the host,
meaning that the host is acting as a router.
.It Li ip.redirect
Returns 1 when ICMP redirects may be sent by the host.
This option is ignored unless the host is routing IP packets,
and should normally be enabled on all systems.
.It Li ip.ttl
The maximum time-to-live (hop count) value for an IP packet sourced by
the system.
This value applies to normal transport protocols, not to ICMP.
.It Li udp.checksum
Returns 1 when UDP checksums are being computed and checked.
Disabling UDP checksums is strongly discouraged.
.El
.It Dv PF_INET6
Get or set various global information about IPv6
.Pq Internet Protocol version 6 .
The third level name is the protocol.
The fourth level name is the variable name.
.Pp
For variables
.Li net.inet6.* ,
please refer to
.Xr inet6 4 .
.El
.Ss CTL_USER
The string and integer information available for the
.Dv CTL_USER
level is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "USER_COLL_WEIGHTS_MAXXXX" "integerXXX" -offset indent
.It Sy "Second level name" Ta Sy "Type" Ta Sy "Changeable"
.It Dv USER_BC_BASE_MAX Ta integer Ta no
.It Dv USER_BC_DIM_MAX Ta integer Ta no
.It Dv USER_BC_SCALE_MAX Ta integer Ta no
.It Dv USER_BC_STRING_MAX Ta integer Ta no
.It Dv USER_COLL_WEIGHTS_MAX Ta integer Ta no
.It Dv USER_CS_PATH Ta string Ta no
.It Dv USER_EXPR_NEST_MAX Ta integer Ta no
.It Dv USER_LINE_MAX Ta integer Ta no
.It Dv USER_POSIX2_CHAR_TERM Ta integer Ta no
.It Dv USER_POSIX2_C_BIND Ta integer Ta no
.It Dv USER_POSIX2_C_DEV Ta integer Ta no
.It Dv USER_POSIX2_FORT_DEV Ta integer Ta no
.It Dv USER_POSIX2_FORT_RUN Ta integer Ta no
.It Dv USER_POSIX2_LOCALEDEF Ta integer Ta no
.It Dv USER_POSIX2_SW_DEV Ta integer Ta no
.It Dv USER_POSIX2_UPE Ta integer Ta no
.It Dv USER_POSIX2_VERSION Ta integer Ta no
.It Dv USER_RE_DUP_MAX Ta integer Ta no
.It Dv USER_STREAM_MAX Ta integer Ta no
.It Dv USER_TZNAME_MAX Ta integer Ta no
.El
.Bl -tag -width 6n
.It Dv USER_BC_BASE_MAX
The maximum ibase/obase values in the
.Xr bc 1
utility.
.It Dv USER_BC_DIM_MAX
The maximum array size in the
.Xr bc 1
utility.
.It Dv USER_BC_SCALE_MAX
The maximum scale value in the
.Xr bc 1
utility.
.It Dv USER_BC_STRING_MAX
The maximum string length in the
.Xr bc 1
utility.
.It Dv USER_COLL_WEIGHTS_MAX
The maximum number of weights that can be assigned to any entry of the
.Dv LC_COLLATE
order keyword in the locale definition file.
.It Dv USER_CS_PATH
Return a value for the
.Ev PATH
environment variable that finds all the standard utilities.
.It Dv USER_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
parenthesis by the
.Xr expr 1
utility.
.It Dv USER_LINE_MAX
The maximum length in bytes of a text-processing utility's input line.
.It Dv USER_POSIX2_CHAR_TERM
Return 1 if the system supports at least one terminal type capable of
all operations described in
.St -p1003.2 ,
otherwise 0.
.It Dv USER_POSIX2_C_BIND
Return 1 if the system's C-language development facilities support the
C-Language Bindings Option, otherwise 0.
.It Dv USER_POSIX2_C_DEV
Return 1 if the system supports the C-Language Development Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_LOCALEDEF
Return 1 if the system supports the creation of locales, otherwise 0.
.It Dv USER_POSIX2_SW_DEV
Return 1 if the system supports the Software Development Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_UPE
Return 1 if the system supports the User Portability Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_VERSION
The version of
.St -p1003.2
with which the system attempts to comply.
.It Dv USER_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
.It Dv USER_STREAM_MAX
The minimum maximum number of streams that a process may have open
at any one time.
.It Dv USER_TZNAME_MAX
The minimum maximum number of types supported for the name of a timezone.
.El
.Ss CTL_VM
The string and integer information available for the
.Dv CTL_VM
level is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "Second level nameXXXXXX" "struct loadavgXXX" -offset indent
.It Sy "Second level name" Ta Sy "Type" Ta Sy "Changeable"
.It Dv VM_LOADAVG Ta struct loadavg Ta no
.It Dv VM_METER Ta struct vmtotal Ta no
.It Dv VM_PAGEOUT_ALGORITHM Ta integer Ta yes
.It Dv VM_SWAPPING_ENABLED Ta integer Ta maybe
.It Dv VM_V_CACHE_MAX Ta integer Ta yes
.It Dv VM_V_CACHE_MIN Ta integer Ta yes
.It Dv VM_V_FREE_MIN Ta integer Ta yes
.It Dv VM_V_FREE_RESERVED Ta integer Ta yes
.It Dv VM_V_FREE_TARGET Ta integer Ta yes
.It Dv VM_V_INACTIVE_TARGET Ta integer Ta yes
.It Dv VM_V_PAGEOUT_FREE_MIN Ta integer Ta yes
.El
.Bl -tag -width 6n
.It Dv VM_LOADAVG
Return the load average history.
The returned data consists of a
.Vt struct loadavg .
.It Dv VM_METER
Return the system wide virtual memory statistics.
The returned data consists of a
.Vt struct vmtotal .
.It Dv VM_PAGEOUT_ALGORITHM
0 if the statistics-based page management algorithm is in use
or 1 if the near-LRU algorithm is in use.
.It Dv VM_SWAPPING_ENABLED
1 if process swapping is enabled or 0 if disabled.  This variable is
permanently set to 0 if the kernel was built with swapping disabled.
.It Dv VM_V_CACHE_MAX
Maximum desired size of the cache queue.
.It Dv VM_V_CACHE_MIN
Minimum desired size of the cache queue.  If the cache queue size
falls very far below this value, the pageout daemon is awakened.
.It Dv VM_V_FREE_MIN
Minimum amount of memory (cache memory plus free memory)
required to be available before a process waiting on memory will be
awakened.
.It Dv VM_V_FREE_RESERVED
Processes will awaken the pageout daemon and wait for memory if the
number of free and cached pages drops below this value.
.It Dv VM_V_FREE_TARGET
The total amount of free memory (including cache memory) that the
pageout daemon tries to maintain.
.It Dv VM_V_INACTIVE_TARGET
The desired number of inactive pages that the pageout daemon should
achieve when it runs.  Inactive pages can be quickly inserted into
process address space when needed.
.It Dv VM_V_PAGEOUT_FREE_MIN
If the amount of free and cache memory falls below this value, the
pageout daemon will enter "memory conserving mode" to avoid deadlock.
.El
.Sh RETURN VALUES
.Rv -std
.Sh FILES
.Bl -tag -width ".In netinet/icmp_var.h" -compact
.It In sys/sysctl.h
definitions for top level identifiers, second level kernel and hardware
identifiers, and user level identifiers
.It In sys/socket.h
definitions for second level network identifiers
.It In sys/gmon.h
definitions for third level profiling identifiers
.It In vm/vm_param.h
definitions for second level virtual memory identifiers
.It In netinet/in.h
definitions for third level IPv4/IPv6 identifiers and
fourth level IPv4/v6 identifiers
.It In netinet/icmp_var.h
definitions for fourth level ICMP identifiers
.It In netinet/icmp6.h
definitions for fourth level ICMPv6 identifiers
.It In netinet/udp_var.h
definitions for fourth level UDP identifiers
.El
.Sh ERRORS
The following errors may be reported:
.Bl -tag -width Er
.It Bq Er EFAULT
The buffer
.Fa name ,
.Fa oldp ,
.Fa newp ,
or length pointer
.Fa oldlenp
contains an invalid address.
.It Bq Er EINVAL
The
.Fa name
array is less than two or greater than
.Dv CTL_MAXNAME .
.It Bq Er EINVAL
A non-null
.Fa newp
is given and its specified length in
.Fa newlen
is too large or too small.
.It Bq Er ENOMEM
The length pointed to by
.Fa oldlenp
is too short to hold the requested value.
.It Bq Er ENOTDIR
The
.Fa name
array specifies an intermediate rather than terminal name.
.It Bq Er EISDIR
The
.Fa name
array specifies a terminal name, but the actual name is not terminal.
.It Bq Er ENOENT
The
.Fa name
array specifies a value that is unknown.
.It Bq Er EPERM
An attempt is made to set a read-only value.
.It Bq Er EPERM
A process without appropriate privilege attempts to set a value.
.El
.Sh SEE ALSO
.Xr sysconf 3 ,
.Xr sysctl 8
.Sh HISTORY
The
.Fn sysctl
function first appeared in
.Bx 4.4 .