.\" Copyright (c) 1993 The Regents of the University of California.
.\" %sccs.include.redist.roff%
.\" @(#)sysctl.3 6.11 (Berkeley) %G%
.Nd get or set system information
.Fd #include <sys/sysctl.h>
.Fn sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
function retrieves system information and allows processes with
appropriate privileges to set system information.
The information available from
consists of integers, strings, and tables.
Information may be retrieved and set from the command interface
Unless explicitly noted below,
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.
are serialized to avoid deadlock.
The state is described using a ``Management Information Base'' (MIB)
length array of integers.
The information is copied into the buffer specified by
The size of the buffer is given by the location specified by
and that location gives the amount of data copied after a successful call.
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 ENOMEM.
If the old value is not desired,
The size of the available data can be determined by calling
with a NULL parameter for
The size of the available data will be returned in the location pointed to by
For some operations, the amount of space may change often.
the system attempts to round up so that the returned size is
large enough for a call to return the data shortly thereafter.
is set to point to a buffer of length
from which the requested value is to be taken.
If a new value is not to be set,
should be set to NULL and
The top level names are defined with a CTL_ prefix in
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 Pa Name Next level names Description
.It CTL\_DEBUG sys/sysctl.h Debugging
.It CTL\_FS sys/sysctl.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
For example, the following retrieves the maximum number of processes allowed
.Bd -literal -offset indent -compact
sysctl(mib, 2, &maxproc, &len, NULL, 0);
To retrieve the standard search path for the system utilities:
.Bd -literal -offset indent -compact
sysctl(mib, 2, NULL, &len, NULL, 0);
sysctl(mib, 2, p, &len, NULL, 0);
The debugging variables vary from system to system.
A debugging variable may be added or deleted without need to recompile
gets the list of debugging variables from the kernel and
displays their current values.
The system defines twenty
.Ns ( Va struct ctldebug )
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
as a debugging variable, the following declaration would be used:
.Bd -literal -offset indent -compact
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
There are currently no second level names for the file system.
The string and integer information available for the CTL_HW level
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "Second level nameXXXXXX" integerXXX -offset indent
.It Sy Pa Second level name Type Changeable
.It HW\_MACHINE string 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
The byteorder (4,321, or 1,234).
The bytes of physical memory.
The bytes of non-kernel memory.
The string and integer information available for the CTL_KERN level
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
.Bl -column "KERNXCHOWNXRESTRICTEDXXX" "struct clockrateXXX" -offset indent
.It Sy Pa Second level name Type Changeable
.It KERN\_ARGMAX integer no
.It KERN\_BOOTTIME struct timeval no
.It KERN\_CHOWN\_RESTRICTED integer 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\_LINK\_MAX integer no
.It KERN\_MAXFILES integer yes
.It KERN\_MAXPROC integer yes
.It KERN\_MAXVNODES integer yes
.It KERN\_MAX\_CANON integer no
.It KERN\_MAX\_INPUT integer no
.It KERN\_NAME\_MAX integer no
.It KERN\_NGROUPS integer no
.It KERN\_NO\_TRUNC integer no
.It KERN\_OSRELEASE string no
.It KERN\_OSREV integer no
.It KERN\_OSTYPE string no
.It KERN\_PATH\_MAX integer no
.It KERN\_PIPE\_BUF integer no
.It KERN\_POSIX1 integer no
.It KERN\_PROC struct proc no
.It KERN\_PROF node not applicable
.It KERN\_SAVED\_IDS integer no
.It KERN\_SECURELVL integer raise only
.It KERN\_VDISABLE integer no
.It KERN\_VERSION string no
.It KERN\_VNODE struct vnode no
The maximum bytes of argument to
This structure contains the time that the system was booted.
.It Li KERN_CHOWN_RESTRICTED
Return 1 if appropriate privileges are required for the
system call, otherwise 0.
This structure contains the clock, statistics clock and profiling clock
frequencies, and the number of micro-seconds per hz tick.
Return the entire file table.
The returned data consists of a single
whose size depends on the current number of such objects in the system.
Return 1 if job control is available on this system, otherwise 0.
The maximum file link count.
The maximum number of open files that may be open in the system.
The maximum number of simultaneous processes the system will allow.
The maximum number of vnodes available on the system.
The maximum number of bytes in terminal canonical input line.
The minimum maximum number of bytes for which space is available in
The maximum number of bytes in a file name.
The maximum number of supplemental groups.
Return 1 if file names longer than KERN_NAME_MAX are truncated.
The system release string.
The system revision string.
The maximum number of bytes in a pathname.
The maximum number of bytes which will be written atomically to a pipe.
The version of ISO/IEC 9945 (POSIX 1003.1) with which the system
Return the entire process table, or a subset of it.
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 Pa Third level name Fourth level is:
.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
Return profiling information about the kernel.
If the kernel is not compiled for profiling,
attempts to retrieve any of the KERN_PROF values will
The third level names for the string and integer profiling information
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "GPROFXGMONPARAMXXX" "struct gmonparamXXX" -offset indent
.It Sy Pa 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
The variables are as follows:
Returns GMON_PROF_ON or GMON_PROF_OFF to show that profiling
Array of statistical program counter counts.
Array indexed by program counter of call-from points.
describing destination of calls and their counts.
Structure giving the sizes of the above arrays.
Returns 1 if saved set-group and saved set-user ID is available.
The system security level.
This level may be raised by processes with appropriate privilege.
It may only be lowered by process 1.
Returns the terminal character disabling value.
The system version string.
Return the entire vnode table.
Note, the vnode table is not necessarily a consistent snapshot of
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
followed by the vnode itself
The set of variables defined is architecture dependent.
Most architectures define at least the following variables.
.Bl -column "CONSOLE_DEVICEXXX" "integerXXX" -offset indent
.It Sy Pa Second level name Type Changeable
.It Li CPU_CONSDEV dev_t no
The string and integer information available for the CTL_NET level
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 Pa Second level name Type Changeable
.It PF\_ROUTE routing messages no
.It PF\_INET internet values yes
Return the entire routing table or a subset of it.
The data is returned as a sequence of routing messages (see
for the header file, format and meaning).
The length of each message is contained in the message header.
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 Pa Fifth level name Sixth level is:
.It NET\_RT\_FLAGS rtflags
Get or set various global information about the internet protocols.
The third level name is the protocol.
The fourth level name is the variable name.
The currently defined protocols and names are:
.Bl -column "Protocol nameXXXXXX" "Variable nameXXX" "integerXXX" -offset indent
.It Pa Protocol name Variable name Type Changeable
.It ip forwarding integer yes
.It ip redirect integer yes
.It icmp maskrepl integer yes
.It udp checksum integer yes
The variables are as follows:
Returns 1 when IP forwarding is enabled for the host,
meaning that the host is acting as a router.
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.
The maximum time-to-live (hop count) value for an IP packet sourced by
This value applies to normal transport protocols, not to ICMP.
Returns 1 if ICMP network mask requests are to be answered.
Returns 1 when UDP checksums are being computed and checked.
Disabling UDP checksums is strongly discouraged.
The string and integer information available for the CTL_USER level
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 Pa 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
The maximum ibase/obase values in the
The maximum array size in the
The maximum scale value in the
.It Li USER_BC_STRING_MAX
The maximum string length in the
.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.
environment variable that finds all the standard utilities.
.It Li USER_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
The maximum length in bytes of a text-processing utility's input
.It Li USER_POSIX2_CHAR_TERM
Return 1 if the system supports at least one terminal type capable of
all operations described in POSIX 1003.2, 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.
Return 1 if the system supports the C-Language Development Utilities Option,
.It Li USER_POSIX2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option,
.It Li USER_POSIX2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option,
.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,
Return 1 if the system supports the User Portability Utilities Option,
.It Li USER_POSIX2_VERSION
The version of POSIX 1003.2 with which the system attempts to comply.
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
The minimum maximum number of streams that a process may have open
The minimum maximum number of types supported for the name of a
The string and integer information available for the CTL_VM level
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 Pa Second level name Type Changeable
.It VM\_LOADAVG struct loadavg no
.It VM\_METER struct vmtotal no
Return the load average history.
The returned data consists of a
Return the system wide virtual memory statistics.
The returned data consists of a
is successful, 0 is returned.
Otherwise \-1 is returned and
The following errors may be reported:
contains an invalid address.
array is less than two or greater than CTL_MAXNAME.
is given and its specified length in
is too large or too small.
is too short to hold the requested value.
array specifies an intermediate rather than terminal name.
array specifies a value that is unknown.
An attempt is made to set a read-only value.
A process without appropriate privilege attempts to set a value.
.Bl -tag -width <netinet/icmpXvar.h> -compact
definitions for top level identifiers, second level kernel and hardware
identifiers, and user level identifiers
definitions for second level network identifiers
definitions for third level profiling identifiers
definitions for second level virtual memory identifiers
definitions for third level Internet identifiers and
fourth level IP identifiers
.It Pa <netinet/icmp_var.h>
definitions for fourth level ICMP identifiers
.It Pa <netinet/udp_var.h>
definitions for fourth level UDP identifiers
function first appeared in 4.4BSD.
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