libc/gen/sysctl.3

.\" Copyright (c) 1993 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.roff%
.\"
.\"	@(#)sysctl.3	6.7 (Berkeley) 05/20/93
.\"
.Dd ""
.Dt SYSCTL 3
.Os
.Sh NAME
.Nm sysctl
.Nd get or set system information
.Sh SYNOPSIS
.Fd #include <sys/sysctl.h>
.Ft int
.Fn sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
.Sh DESCRIPTION
The
.Nm sysctl
function retrieves system information and allows processes with
appropriate privileges to set system information.
The information available from
.Nm sysctl
consists of integers, strings, and tables.
Information may be retrieved and set from the command interface
using the
.Xr sysctl 1
utility.
.Pp
Unless explicitly noted below,
.Nm 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
.Nm 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 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.
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,
.Fa oldp
and
.Fa oldlenp
should be set to NULL.
.Pp
The size of the available data can be determined by calling
.Nm 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 top level names are defined with a CTL_ prefix in
.Pa <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 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: processes, 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:
.Bd -literal -offset indent -compact
int mib[2], maxproc;
size_t len;
.sp
mib[0] = CTL_KERN;
mib[1] = KERN_MAXPROC;
len = sizeof(maxproc);
sysctl(mib, 2, &maxproc, &len, NULL, 0);
.Ed
.sp
To retrieve the standard search path for the system utilities:
.Bd -literal -offset indent -compact
int mib[2];
size_t len;
char *p;
.sp
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
.Sh CTL_DEBUG
The debugging variables vary from system to system.
A debugging variable may be added or deleted without need to recompile
.Nm sysctl
to know about it.
Each time it runs,
.Nm sysctl
gets the list of debugging variables from the kernel and
displays their current values.
The system defines twenty
.Ns ( Va 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
.Sh CTL_FS
There are currently no second level names for the file system.
.Sh 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 Pa 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
.El
.Pp
.Bl -tag -width "123456"
.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
.El
.Sh 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 "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
.El
.Pp
.Bl -tag -width "123456"
.It Li KERN_ARGMAX
Maximum bytes of argument to exec.
.It Li KERN_BOOTTIME
A
.Va struct timeval
structure is returned.
This structure contains the time that the system was booted.
.It Li KERN_CHOWN_RESTRICTED
Return 1 if appropriate privileges are required for the
.Xr chown 2
system call, otherwise 0.
.It Li KERN_CLOCKRATE
A
.Va struct clockinfo
structure is returned.
This structure contains the clock, statistics clock and profiling clock
frequencies, and the number of micro-seconds per hz tick.
.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_LINK_MAX
The maximum file link count.
.It Li KERN_MAXFILES
The maximum number of open files that may be open in the system.
.It Li KERN_MAXPROC
The maximum number of simultaneous processes the system will allow.
.It Li KERN_MAXVNODES
The maximum number of vnodes available on the system.
.It Li KERN_MAX_CANON
The maximum number of bytes in terminal canonical input line.
.It Li KERN_MAX_INPUT
The minimum number of bytes for which space is available in
a terminal input queue.
.It Li KERN_NAME_MAX
The maximum number of bytes in a file name.
.It Li KERN_NGROUPS
The maximum number of supplemental groups.
.It Li KERN_NO_TRUNC
Return 1 if file names longer than KERN_NAME_MAX are truncated.
.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_PATH_MAX
The maximum number of bytes in a pathname.
.It Li KERN_PIPE_BUF
The maximum number of bytes which will be written atomically to a pipe.
.It Li KERN_POSIX1
The POSIX 1003.1 version with which the system attempts to comply.
.It Li KERN_PROC
Return the entire process table, or a subset of it.
An array of
.Va struct kinfo_proc
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 Pa 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 EOPNOTSUPP.
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 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
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.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_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 only be lowered by process 1.
.It Li KERN_VDISABLE
Returns the terminal character disabling value.
.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
.Sh CTL_MACHDEP
There are currently no second level names for the machine dependent
interface.
.Sh 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 Pa Second level name	Type	Changeable
.It PF\_ROUTE	routing messages	no
.It PF\_INET	internet values	yes
.El
.Pp
.Bl -tag -width "123456"
.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 Pa Fifth level name	Sixth level is:
.It NET\_RT\_FLAGS	rtflags
.It NET\_RT\_DUMP	None
.It NET\_RT\_IFLIST	None
.El
.It Li PF_INET
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 ip	ttl	integer	yes
.It icmp	maskrepl	integer	yes
.It udp	checksum	integer	yes
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.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 icmp.maskrepl
Returns 1 if ICMP network mask requests are to be answered.
.It Li udp.checksum
Returns 1 when UDP checksums are being computed and checked.
Disabling UDP checksums is strongly discouraged.
.El
.Sh 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 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
.El
.Bl -tag -width "123456"
.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 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.
.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 POSIX 1003.2 version 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.
.El
.Sh 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 Pa Second level name	Type	Changeable
.It VM\_LOADAVG	struct loadavg	no
.It VM\_METER	struct vmtotal	no
.El
.Pp
.Bl -tag -width "123456"
.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 .
.El
.Sh RETURN VALUES
If the call to
.Nm sysctl
is successful, 0 is returned.
Otherwise \-1 is returned and
.Va errno
is set appropriately.
.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 ENOTDIR
The
.Fa name
array specifies an intermediate rather than terminal name.
.It Bq Er EOPNOTSUPP
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 Pa <sys/sysctl.h>
definitions for top level identifiers, second level kernel and hardware
identifiers, and user level identifiers
.It Pa <sys/socket.h>
definitions for second level network identifiers
.It Pa <sys/gmon.h>
definitions for third level profiling identifiers
.It Pa <vm/vm_param.h>
definitions for second level virtual memory identifiers
.It Pa <netinet/in.h>
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
.El
.Sh SEE ALSO
.Xr sysctl 8
.Sh HISTORY
The
.Nm sysctl
function first appeared in 4.4BSD.