libc/gen/sysctl.3

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.\"	@(#)sysctl.3	8.4 (Berkeley) 5/9/95
.\" $FreeBSD$
.\"
.Dd February 21, 2010
.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 ``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 the
.Dv NULL
argument 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.
.Pp
.Bl -column CTLXMACHDEPXXX "Next level namesXXXXXX" -offset indent
.It Sy "Name	Next level names	Description"
.It "CTL_DEBUG	sys/sysctl.h	Debugging"
.It "CTL_VFS	sys/mount.h	File system"
.It "CTL_HW	sys/sysctl.h	Generic CPU, I/O"
.It "CTL_KERN	sys/sysctl.h	High kernel limits"
.It "CTL_MACHDEP	sys/sysctl.h	Machine dependent"
.It "CTL_NET	sys/socket.h	Networking"
.It "CTL_USER	sys/sysctl.h	User-level"
.It "CTL_VM	vm/vm_param.h	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
.Pq Vt "struct ctldebug"
variables named
.Va debug0
through
.Va 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
.Va dospecialcheck
as a debugging variable, the following declaration would be used:
.Pp
.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 file systems.
One of its third level identifiers is VFS_MAXTYPENUM
that gives the highest valid file system type number.
Its other third level identifier is VFS_CONF that
returns configuration information about the file system
type given as a fourth level identifier (see
.Xr getvfsbyname 3
as an example of its use).
The remaining second level identifiers are the
file system type number returned by a
.Xr statfs 2
call or from VFS_CONF.
The third level identifiers available for each file system
are given in the header file that defines the mount
argument structure for that file system.
.Ss CTL_HW
The string and integer information available for the 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	Type	Changeable"
.It "HW_MACHINE	string	no"
.It "HW_MODEL	string	no"
.It "HW_NCPU	integer	no"
.It "HW_BYTEORDER	integer	no"
.It "HW_PHYSMEM	integer	no"
.It "HW_USERMEM	integer	no"
.It "HW_PAGESIZE	integer	no"
.\".It "HW_DISKNAMES	integer	no"
.\".It "HW_DISKSTATS	integer	no"
.It "HW_FLOATINGPT	integer	no"
.It "HW_MACHINE_ARCH	string	no"
.It "HW_REALMEM	integer	no"
.El
.Bl -tag -width 6n
.It Li HW_MACHINE
The machine class.
.It Li HW_MODEL
The machine model
.It Li HW_NCPU
The number of cpus.
.It Li HW_BYTEORDER
The byteorder (4,321, or 1,234).
.It Li HW_PHYSMEM
The bytes of physical memory.
.It Li HW_USERMEM
The bytes of non-kernel memory.
.It Li HW_PAGESIZE
The software page size.
.\".It Fa HW_DISKNAMES
.\".It Fa HW_DISKSTATS
.It Li HW_FLOATINGPT
Nonzero if the floating point support is in hardware.
.It Li HW_MACHINE_ARCH
The machine dependent architecture type.
.It Li HW_REALMEM
The bytes of real memory.
.El
.Ss CTL_KERN
The string and integer information available for the 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 "KERNXMAXFILESPERPROCXXX" "struct clockrateXXX" -offset indent
.It Sy "Second level name	Type	Changeable"
.It "KERN_ARGMAX	integer	no"
.It "KERN_BOOTFILE	string	yes"
.It "KERN_BOOTTIME	struct timeval	no"
.It "KERN_CLOCKRATE	struct clockinfo	no"
.It "KERN_FILE	struct file	no"
.It "KERN_HOSTID	integer	yes"
.It "KERN_HOSTUUID	string	yes"
.It "KERN_HOSTNAME	string	yes"
.It "KERN_JOB_CONTROL	integer	no"
.It "KERN_MAXFILES	integer	yes"
.It "KERN_MAXFILESPERPROC	integer	yes"
.It "KERN_MAXPROC	integer	no"
.It "KERN_MAXPROCPERUID	integer	yes"
.It "KERN_MAXVNODES	integer	yes"
.It "KERN_NGROUPS	integer	no"
.It "KERN_NISDOMAINNAME	string	yes"
.It "KERN_OSRELDATE	integer	no"
.It "KERN_OSRELEASE	string	no"
.It "KERN_OSREV	integer	no"
.It "KERN_OSTYPE	string	no"
.It "KERN_POSIX1	integer	no"
.It "KERN_PROC	struct proc	no"
.It "KERN_PROF	node	not applicable"
.It "KERN_QUANTUM	integer	yes"
.It "KERN_SAVED_IDS	integer	no"
.It "KERN_SECURELVL	integer	raise only"
.It "KERN_UPDATEINTERVAL	integer	no"
.It "KERN_VERSION	string	no"
.It "KERN_VNODE	struct vnode	no"
.El
.Bl -tag -width 6n
.It Li KERN_ARGMAX
The maximum bytes of argument to
.Xr execve 2 .
.It Li KERN_BOOTFILE
The full pathname of the file from which the kernel was loaded.
.It Li KERN_BOOTTIME
A
.Va struct timeval
structure is returned.
This structure contains the time that the system was booted.
.It Li KERN_CLOCKRATE
A
.Va 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 Li KERN_FILE
Return the entire file table.
The returned data consists of a single
.Va struct filehead
followed by an array of
.Va struct file ,
whose size depends on the current number of such objects in the system.
.It Li KERN_HOSTID
Get or set the host ID.
.It Li KERN_HOSTUUID
Get or set the host's universally unique identifier (UUID).
.It Li KERN_HOSTNAME
Get or set the hostname.
.It Li KERN_JOB_CONTROL
Return 1 if job control is available on this system, otherwise 0.
.It Li KERN_MAXFILES
The maximum number of files that may be open in the system.
.It Li 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 Li KERN_MAXPROC
The maximum number of concurrent processes the system will allow.
.It Li 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 Li KERN_MAXVNODES
The maximum number of vnodes available on the system.
.It Li KERN_NGROUPS
The maximum number of supplemental groups.
.It Li KERN_NISDOMAINNAME
The name of the current YP/NIS domain.
.It Li KERN_OSRELDATE
The kernel release version in the format
.Ar M Ns Ar mm Ns Ar R Ns Ar xx ,
where
.Ar M
is the major version,
.Ar mm
is the two digit minor version,
.Ar R
is 0 if release branch, otherwise 1,
and
.Ar xx
is updated when the available APIs change.
.Pp
The userland release version is available from
.In osreldate.h ;
parse this file if you need to get the release version of
the currently installed userland.
.It Li KERN_OSRELEASE
The system release string.
.It Li KERN_OSREV
The system revision string.
.It Li KERN_OSTYPE
The system type string.
.It Li KERN_POSIX1
The version of
.St -p1003.1
with which the system
attempts to comply.
.It Li KERN_PROC
Return selected information about specific running processes.
.Pp
For the following names, an array of
.Va struct kinfo_proc
structures is returned,
whose size depends on the current number of such objects in the system.
.Bl -column "Third level nameXXXXXX" "Fourth level is:XXXXXX" -offset indent
.It "Third level name	Fourth level is:"
.It "KERN_PROC_ALL	None"
.It "KERN_PROC_PID	A process ID"
.It "KERN_PROC_PGRP	A process group"
.It "KERN_PROC_TTY	A tty device"
.It "KERN_PROC_UID	A user ID"
.It "KERN_PROC_RUID	A real user ID"
.El
.Pp
If the third level name is
.Dv KERN_PROC_ARGS
then the command line argument
array is returned in a flattened form, i.e., zero-terminated arguments
follow each other.
The total size of array is returned.
It is also possible for a process to set its own process title this way.
If the third level name is
.Dv KERN_PROC_PATHNAME ,
the path of the
process' text file is stored.
For
.Dv KERN_PROC_PATHNAME ,
a process ID of
.Li \-1
implies the current process.
.Bl -column "Third level nameXXXXXX" "Fourth level is:XXXXXX" -offset indent
.It Sy "Third level name	Fourth level is:"
.It Dv KERN_PROC_ARGS Ta "A process ID"
.It Dv KERN_PROC_PATHNAME Ta "A process ID"
.El
.It Li KERN_PROF
Return profiling information about the kernel.
If the kernel is not compiled for profiling,
attempts to retrieve any of the KERN_PROF values will
fail with
.Er ENOENT .
The third level names for the string and integer profiling information
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "GPROFXGMONPARAMXXX" "struct gmonparamXXX" -offset indent
.It Sy "Third level name	Type	Changeable"
.It "GPROF_STATE	integer	yes"
.It "GPROF_COUNT	u_short[\|]	yes"
.It "GPROF_FROMS	u_short[\|]	yes"
.It "GPROF_TOS	struct tostruct	yes"
.It "GPROF_GMONPARAM	struct gmonparam	no"
.El
.Pp
The variables are as follows:
.Bl -tag -width 6n
.It Li GPROF_STATE
Returns GMON_PROF_ON or GMON_PROF_OFF to show that profiling
is running or stopped.
.It Li GPROF_COUNT
Array of statistical program counter counts.
.It Li GPROF_FROMS
Array indexed by program counter of call-from points.
.It Li GPROF_TOS
Array of
.Va struct tostruct
describing destination of calls and their counts.
.It Li GPROF_GMONPARAM
Structure giving the sizes of the above arrays.
.El
.It Li KERN_QUANTUM
The maximum period of time, in microseconds, for which a process is allowed
to run without being preempted if other processes are in the run queue.
.It Li KERN_SAVED_IDS
Returns 1 if saved set-group and saved set-user ID is available.
.It Li KERN_SECURELVL
The system security level.
This level may be raised by processes with appropriate privilege.
It may not be lowered.
.It Li KERN_VERSION
The system version string.
.It Li 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
.Va struct vnode *
followed by the vnode itself
.Va struct vnode .
.El
.Ss CTL_NET
The string and integer information available for the 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	Type	Changeable"
.It "PF_ROUTE	routing messages	no"
.It "PF_INET	IPv4 values	yes"
.It "PF_INET6	IPv6 values	yes"
.El
.Bl -tag -width 6n
.It Li 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	Sixth level is:"
.It "NET_RT_FLAGS	rtflags"
.It "NET_RT_DUMP	None"
.It "NET_RT_IFLIST	0 or if_index"
.It "NET_RT_IFMALIST	0 or if_index"
.El
.Pp
The
.Dv NET_RT_IFMALIST
name returns information about multicast group memberships on all interfaces
if 0 is specified, or for the interface specified by
.Va if_index .
.It Li PF_INET
Get or set various global information about the IPv4
(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	Variable	Type	Changeable"
.It "icmp	bmcastecho	integer	yes"
.It "icmp	maskrepl	integer	yes"
.It "ip	forwarding	integer	yes"
.It "ip	redirect	integer	yes"
.It "ip	ttl	integer	yes"
.It "udp	checksum	integer	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.
.Pp
For variables net.inet.*.ipsec, please refer to
.Xr ipsec 4 .
.El
.It Li PF_INET6
Get or set various global information about the IPv6
(Internet Protocol version 6).
The third level name is the protocol.
The fourth level name is the variable name.
.Pp
For variables net.inet6.* please refer to
.Xr inet6 4 .
For variables net.inet6.*.ipsec6, please refer to
.Xr ipsec 4 .
.El
.Ss CTL_USER
The string and integer information available for the 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	Type	Changeable"
.It "USER_BC_BASE_MAX	integer	no"
.It "USER_BC_DIM_MAX	integer	no"
.It "USER_BC_SCALE_MAX	integer	no"
.It "USER_BC_STRING_MAX	integer	no"
.It "USER_COLL_WEIGHTS_MAX	integer	no"
.It "USER_CS_PATH	string	no"
.It "USER_EXPR_NEST_MAX	integer	no"
.It "USER_LINE_MAX	integer	no"
.It "USER_POSIX2_CHAR_TERM	integer	no"
.It "USER_POSIX2_C_BIND	integer	no"
.It "USER_POSIX2_C_DEV	integer	no"
.It "USER_POSIX2_FORT_DEV	integer	no"
.It "USER_POSIX2_FORT_RUN	integer	no"
.It "USER_POSIX2_LOCALEDEF	integer	no"
.It "USER_POSIX2_SW_DEV	integer	no"
.It "USER_POSIX2_UPE	integer	no"
.It "USER_POSIX2_VERSION	integer	no"
.It "USER_RE_DUP_MAX	integer	no"
.It "USER_STREAM_MAX	integer	no"
.It "USER_TZNAME_MAX	integer	no"
.El
.Bl -tag -width 6n
.It Li USER_BC_BASE_MAX
The maximum ibase/obase values in the
.Xr bc 1
utility.
.It Li USER_BC_DIM_MAX
The maximum array size in the
.Xr bc 1
utility.
.It Li USER_BC_SCALE_MAX
The maximum scale value in the
.Xr bc 1
utility.
.It Li USER_BC_STRING_MAX
The maximum string length in the
.Xr bc 1
utility.
.It Li USER_COLL_WEIGHTS_MAX
The maximum number of weights that can be assigned to any entry of
the LC_COLLATE order keyword in the locale definition file.
.It Li USER_CS_PATH
Return a value for the
.Ev PATH
environment variable that finds all the standard utilities.
.It Li USER_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
parenthesis by the
.Xr expr 1
utility.
.It Li USER_LINE_MAX
The maximum length in bytes of a text-processing utility's input
line.
.It Li 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 Li USER_POSIX2_C_BIND
Return 1 if the system's C-language development facilities support the
C-Language Bindings Option, otherwise 0.
.It Li USER_POSIX2_C_DEV
Return 1 if the system supports the C-Language Development Utilities Option,
otherwise 0.
.It Li USER_POSIX2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option,
otherwise 0.
.It Li USER_POSIX2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option,
otherwise 0.
.It Li USER_POSIX2_LOCALEDEF
Return 1 if the system supports the creation of locales, otherwise 0.
.It Li USER_POSIX2_SW_DEV
Return 1 if the system supports the Software Development Utilities Option,
otherwise 0.
.It Li USER_POSIX2_UPE
Return 1 if the system supports the User Portability Utilities Option,
otherwise 0.
.It Li USER_POSIX2_VERSION
The version of
.St -p1003.2
with which the system attempts to comply.
.It Li USER_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
.It Li USER_STREAM_MAX
The minimum maximum number of streams that a process may have open
at any one time.
.It Li 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 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	Type	Changeable"
.It "VM_LOADAVG	struct loadavg	no"
.It "VM_TOTAL	struct vmtotal	no"
.It "VM_PAGEOUT_ALGORITHM	integer	yes"
.It "VM_SWAPPING_ENABLED	integer	maybe"
.It "VM_V_CACHE_MAX	integer	yes"
.It "VM_V_CACHE_MIN	integer	yes"
.It "VM_V_FREE_MIN	integer	yes"
.It "VM_V_FREE_RESERVED	integer	yes"
.It "VM_V_FREE_TARGET	integer	yes"
.It "VM_V_INACTIVE_TARGET	integer	yes"
.It "VM_V_PAGEOUT_FREE_MIN	integer	yes"
.El
.Bl -tag -width 6n
.It Li VM_LOADAVG
Return the load average history.
The returned data consists of a
.Va struct loadavg .
.It Li VM_TOTAL
Return the system wide virtual memory statistics.
The returned data consists of a
.Va struct vmtotal .
.It Li 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 Li 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 Li VM_V_CACHE_MAX
Maximum desired size of the cache queue.
.It Li 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 Li 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 Li 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 Li VM_V_FREE_TARGET
The total amount of free memory (including cache memory) that the
pageout daemon tries to maintain.
.It Li 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 Li 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 <netinet/icmpXvar.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 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 ENOMEM
The smaller of either the length pointed to by
.Fa oldlenp
or the estimated size of the returned data exceeds the
system limit on locked memory.
.It Bq Er ENOMEM
Locking the buffer
.Fa oldp ,
or a portion of the buffer if the estimated size of the data
to be returned is smaller,
would cause the process to exceed its per-process locked memory limit.
.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 .