[apple/libc.git] / gen / sysctl.3

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.\"     @(#)sysctl.3    8.4 (Berkeley) 5/9/95
.\" $FreeBSD: src/lib/libc/gen/sysctl.3,v 1.63 2004/07/02 23:52:10 ru Exp $
.\"
.Dd January 23, 2001
.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 "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
.Ft int
.Fn sysctlbyname "const char *name" "void *oldp" "size_t *oldlenp" "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
Note:  Implementation of
.Fn printkproc
-- to print whatever data deemed necessary from the large
.Vt kinfo_proc
structure (
.In sysctl.h
) -- is left as an exercise for the reader.
.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 CTLXMACHDEP "Next level names" -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     sys/resources.h Virtual memory (struct loadavg)"
.It "CTL_VM     sys/vmmeter.h   Virtual memory (struct vmtotal)"
.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_FLOATINGPOINT   integer no"
.It "HW_MACHINE_ARCH    string  no"
.\".It "HW_DISKNAMES    integer no"
.\".It "HW_DISKSTATS    integer no"
.El
.Pp
.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 Li HW_FLOATINGPOINT
Nonzero if the floating point support is in hardware.
.It Li HW_MACHINE_ARCH
The machine dependent architecture type.
.\".It Fa HW_DISKNAMES
.\".It Fa HW_DISKSTATS
.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_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
.Pp
.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_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 the entire process table, or a subset of it.
An array of pairs of
.Va struct proc
followed by corresponding
.Va struct eproc
structures is returned,
whose size depends on the current number of such objects in the system.
The third and fourth level names are as follows:
.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
.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_MACHDEP
The set of variables defined is architecture dependent.
The following variables are defined for the i386 architecture.
.Bl -column "CONSOLE_DEVICEXXX" "struct bootinfoXXX" -offset indent
.It Sy "Second level name       Type    Changeable"
.It Li "CPU_CONSDEV     dev_t   no"
.It Li "CPU_ADJKERNTZ   int     yes"
.It Li "CPU_DISRTCSET   int     yes"
.It Li "CPU_BOOTINFO    struct bootinfo no"
.It Li "CPU_WALLCLOCK   int     yes"
.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
.Pp
.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
.Pp
.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_METER   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
.Pp
.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_METER
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 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 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 mach/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 SEE ALSO
.Xr sysconf 3 ,
.Xr sysctl 8
.Sh HISTORY
The
.Fn sysctl
function first appeared in
.Bx 4.4 .