SYSCTL(3)

NAME
sysctl - get or set system information

SYNOPSIS
#include <sys/sysctl.h>
int
sysctl(name, namelen, oldp, *oldlenp, *newp, newlen)
   int *name;
   u_int namelen;
   void *oldp;
   size_t *oldlenp;
   void *newp;
   size_t newlen

DESCRIPTION
The sysctl function retrieves system information and allows processes with appropriate privileges to set system information. The information available from sysctl consists of integers, strings, and tables. Information may be retrieved and set from the command interface using the sysctl(1) utility.

Unless explicitly noted below, sysctl returns a consistent snapshot of the data requested. Calls to sysctl are serialized to avoid deadlock.

The state is described using a ``Management Information Base'' (MIB) style name, listed in name , which is a namelen length array of integers.

The information is copied into the buffer specified by oldp . The size of the buffer is given by the location specified by 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, oldp and oldlenp should be set to NULL.

The size of the available data can be determined by calling sysctl with a NULL parameter for oldp. The size of the available data will be returned in the location pointed to by 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.

To set a new value, newp is set to point to a buffer of length newlen from which the requested value is to be taken. If a new value is not to be set, newp should be set to NULL and newlen set to 0.

The top level names are defined with a CTL_ prefix 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.

	Name	Next level names	Description
	CTL_DEBUG	sys/sysctl.h	Debugging
	CTL_FS	sys/sysctl.h	File system
	CTL_HW	sys/sysctl.h	Generic CPU, I/O
	CTL_KERN	sys/sysctl.h	High kernel limits
	CTL_MACHDEP	sys/sysctl.h	Machine dependent
	CTL_NET	sys/socket.h	Networking
	CTL_USER	sys/sysctl.h	User-level
	CTL_VM	vm/vm_param.h	Virtual memory

For example, the following retrieves the maximum number of processes allowed in the system:

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);

To retrieve the standard search path for the system utilities:

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);

CTL_DEBUG
The debugging variables vary from system to system. A debugging variable may be added or deleted without need to recompile sysctl to know about it. Each time it runs, sysctl gets the list of debugging variables from the kernel and displays their current values. The system defines twenty struct ctldebug variables named debug0 through 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 dospecialcheck as a debugging variable, the following declaration would be used:

int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };

CTL_FS
There are currently no second level names for the file system.

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.

	Second level name	Type	Changeable
	HW_MACHINE	string	no
	HW_MODEL	string	no
	HW_NCPU	integer	no
	HW_BYTEORDER	integer	no
	HW_PHYSMEM	integer	no
	HW_USERMEM	integer	no
	HW_PAGESIZE	integer	no

HW_MACHINE
    The machine class.

HW_MODEL
    The machine model

HW_NCPU
    The number of cpus.

HW_BYTEORDER
    The byteorder (3412, 4321, or 1234).

HW_PHYSMEM
    The bytes of physical memory.

HW_USERMEM
    The bytes of non-kernel memory.

HW_PAGESIZE
    The software page size.

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 inodes, the open file entries, routing table entries, virtual memory statistics, load average history, and clock rate information.

	Second level name	Type	Changeable
	KERN_ARGMAX	integer	no
	KERN_BOOTTIME	struct timeval	no
	KERN_CHOWN_RESTRICTED	integer	no
	KERN_CLOCKRATE	struct clockinfo	no
	KERN_FILE	struct file	no
	KERN_HOSTID	long	yes
	KERN_HOSTNAME	string	yes
	KERN_JOB_CONTROL	integer	no
	KERN_MAXFILES	integer	no
	KERN_MAXPROC	integer	no
	KERN_MAXINODES	integer	no
	KERN_MAXTEXTS	integer	no
	KERN_NGROUPS	integer	no
	KERN_OSRELEASE	string	no
	KERN_OSREV	integer	no
	KERN_OSTYPE	string	no
	KERN_POSIX1	integer	no
	KERN_PROC	struct proc	no
	KERN_PROF	node	not applicable
	KERN_SAVED_IDS	integer	no
	KERN_SECURELVL	integer	raise only
	KERN_TEXT	struct text	no
	KERN_VERSION	string	no
	KERN_INODE	struct inode	no

KERN_ARGMAX
The maximum bytes of argument to exec(2).

KERN_BOOTTIME
A struct timeval structure is returned. This structure contains the time that the system was booted.

KERN_CLOCKRATE
A 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.

KERN_FILE
Return the entire file table as an array of extended file structures. Each element of the array contains the kernel address of a file struct inode * followed by the file itself struct file. There can never be more than KERN_MAXFILES inodes returned.

KERN_HOSTID
Get or set the host id.

KERN_HOSTNAME
Get or set the hostname.

KERN_JOB_CONTROL
Return 1 if job control is available on this system, otherwise 0.

KERN_MAXFILES
The maximum number of open files that may be open in the system.

KERN_MAXPROC
The maximum number of simultaneous processes the system will allow.

KERN_MAXINODES
The maximum number of inodes available on the system.

KERN_MAXTEXTS
The maximum number of text structures available on the system.

KERN_NGROUPS
The maximum number of supplemental groups.

KERN_OSRELEASE
The system release string.

KERN_OSREV
The system revision string.

KERN_OSTYPE
The system type string.

KERN_POSIX1
The version of ISO/IEC 9945 (POSIX 1003.1) with which the system attempts to comply.

KERN_PROC
Return the entire process table, or a subset of it. An array of 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:

	Third level name	Fourth level is:
	KERN_PROC_ALL	None
	KERN_PROC_PID	A process ID
	KERN_PROC_PGRP	A process group
	KERN_PROC_TTY	A tty device
	KERN_PROC_UID	A user ID
	KERN_PROC_RUID	A real user ID
	KERN_PROF	Return kernel profiling information.

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.

Third level name	Type	Changeable
	GPROF_STATE	integer	yes
	GPROF_COUNT	u_short[]	yes
	GPROF_FROMS	u_short[]	yes
	GPROF_TOS	struct tostruct	yes
	GPROF_GMONPARAM	struct gmonparam	no

The variables are as follows:

GPROF_STATE
Returns GMON_PROF_ON or GMON_PROF_OFF to show that profiling is running or stopped.

GPROF_COUNT
Array of statistical program counter counts.

GPROF_FROMS
Array indexed by program counter of call-from points.

GPROF_TOS
Array of struct tostruct describing destination of calls and their counts.

GPROF_GMONPARAM
Structure giving the sizes of the above arrays.

KERN_SAVED_IDS
Returns 1 if saved set-group and saved set-user ID is available.

KERN_SECURELVL
The system security level. This level may be raised by processes with appropriate privilege. It may only be lowered by process 1.

KERN_VERSION
The system version string.

KERN_INODE
Return the entire inode table. Note, the inode 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 inode struct inode * followed by the inode itself struct inode. There can never be more than KERN_MAXINODES inodes returned.

KERN_TEXT
Return the entire text table. The returned data consists of an array whose size depends on the current number of such objects active in the system. Each element of the array contains the kernel address of a text struct text * followed by the text structure itself struct text. There can never be more structures than returned by KERN_MAXTEXTS.

CTL_MACHDEP
The set of variables defined is architecture dependent. Most architectures define at least the following variables.

	Second level name	Type	Changeable
	CPU_CONSDEV	dev_t	no

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.

	Second level name	Type	Changeable
	PF_ROUTE	routing messages	no
	PF_INET	internet values	yes

PF_ROUTE
Return the entire routing table or a subset of it. The data is returned as a sequence of routing messages (see route(4) 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:

	Fifth level name	Sixth level is:
	NET_RT_FLAGS	rtflags
	NET_RT_DUMP	None
	NET_RT_IFLIST	None

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:

	Protocol name	Variable name	Type	Changeable
	ip	forwarding	integer	yes
	ip	redirect	integer	yes
	ip	ttl	integer	yes
	icmp	maskrepl	integer	yes
	udp	checksum	integer	yes

The variables are as follows:

ip.forwarding
Returns 1 when IP forwarding is enabled for the host, meaning that the host is acting as a router.

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.

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.

icmp.maskrepl
Returns 1 if ICMP network mask requests are to be answered.

udp.checksum
Returns 1 when UDP checksums are being computed and checked. Disabling UDP checksums is strongly discouraged.

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.

	Second level name	Type	Changeable
	USER_BC_BASE_MAX	integer	no
	USER_BC_DIM_MAX	integer	no
	USER_BC_SCALE_MAX	integer	no
	USER_BC_STRING_MAX	integer	no
	USER_COLL_WEIGHTS_MAX	integer	no
	USER_CS_PATH	string	no
	USER_EXPR_NEST_MAX	integer	no
	USER_LINE_MAX	integer	no
	USER_POSIX2_CHAR_TERM	integer	no
	USER_POSIX2_C_BIND	integer	no
	USER_POSIX2_C_DEV	integer	no
	USER_POSIX2_FORT_DEV	integer	no
	USER_POSIX2_FORT_RUN	integer	no
	USER_POSIX2_LOCALEDEF	integer	no
	USER_POSIX2_SW_DEV	integer	no
	USER_POSIX2_UPE	integer	no
	USER_POSIX2_VERSION	integer	no
	USER_RE_DUP_MAX	integer	no
	USER_STREAM_MAX	integer	no
	USER_TZNAME_MAX	integer	no

USER_BC_BASE_MAX
The maximum ibase/obase values in the bc(1) utility.

USER_BC_DIM_MAX
The maximum array size in the bc(1) utility.

USER_BC_SCALE_MAX
The maximum scale value in the bc(1) utility.

USER_BC_STRING_MAX
The maximum string length in the bc(1) utility.

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.

USER_CS_PATH
Return a value for the PATH environment variable that finds all the standard utilities.

USER_EXPR_NEST_MAX
The maximum number of expressions that can be nested within parenthesis by the expr(1) utility.

USER_LINE_MAX
The maximum length in bytes of a text-processing utility's input line.

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.

USER_POSIX2_C_BIND
Return 1 if the system's C-language development facilities support the C-Language Bindings Option, otherwise 0.

USER_POSIX2_C_DEV
Return 1 if the system supports the C-Language Development Utilities Option, otherwise 0.

USER_POSIX2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option, otherwise 0.

USER_POSIX2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option, otherwise 0.

USER_POSIX2_LOCALEDEF
Return 1 if the system supports the creation of locales, otherwise 0.

USER_POSIX2_SW_DEV
Return 1 if the system supports the Software Development Utilities Option, otherwise 0.

USER_POSIX2_UPE
Return 1 if the system supports the User Portability Utilities Option, otherwise 0.

USER_POSIX2_VERSION
The version of POSIX 1003.2 with which the system attempts to comply.

USER_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression permitted when using interval notation.

USER_STREAM_MAX
The minimum maximum number of streams that a process may have open at any one time.

USER_TZNAME_MAX
The minimum maximum number of types supported for the name of a timezone.

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.

	Second level name	Type	Changeable
	VM_LOADAVG	struct loadavg	no
	VM_METER	struct vmtotal	no
	VM_SWAPMAP	struct map	no
	VM_COREMAP	struct map	no

VM_LOADAVG
Return the load average history. The returned data consists of a struct loadavg.

VM_METER
Return the system wide virtual memory statistics. The returned data consists of a struct vmtotal.

VM_SWAPMAP
Return the swapmap. The size of this structure is fixed and may be determined by specifying a oldlenp initialized to zero, the kernel will fill in the size of the swapmap.

VM_COREMAP
Same as for swapmap above except that the core allocation map is returned.

RETURN VALUES
If the call to sysctl is successful, 0 is returned. Otherwise -1 is returned and errno is set appropriately.

ERRORS
The following errors may be reported:

EFAULT
    The buffer name, oldp , newp , or length pointer oldlenp contains an invalid address.

EINVAL
    The name array is less than two or greater than CTL_MAXNAME.

EINVAL
    A non-null newp is given and its specified length in newlen is too large or too small.

ENOMEM
    The length pointed to by oldlenp is too short to hold the requested value.

ENOTDIR
    The name array specifies an intermediate rather than terminal name.

EOPNOTSUPP
    The name array specifies a value that is unknown.

EPERM
    An attempt is made to set a read-only value.

EPERM
    A process without appropriate privilege attempts to set a value.

FILES

<sys/sysctl.h>
    definitions for top level identifiers, second level kernel and hardware identifiers, and user level identifiers

<sys/socket.h>
    definitions for second level network identifiers

<sys/gmon.h>
    definitions for third level profiling identifiers

<sys/vmparam.h>
    definitions for second level virtual memory identifiers

<netinet/in.h>
    definitions for third level Internet identifiers and fourth level IP identifiers

<netinet/icmp_var.h>
    definitions for fourth level ICMP identifiers

<netinet/udp_var.h>
    definitions for fourth level UDP identifiers

SEE ALSO
sysctl(8)

HISTORY
The sysctl function first appeared in 4.4BSD.

The KERN_TEXT, KERN_MAXTEXTS, VM_SWAPMAP, VM_COREMAP options are 2.11BSD specific extensions to the 4.4BSD sysctl implmentation.

Having KERN_FILE return the address of the file structure before the actual struct file is a 2.11BSD enhancement. The inode (vnode under 4.4) table was handled this way.