2.11BSD/man/cat3/sysctl.0
SYSCTL(3) UNIX Programmer's Manual 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 informa-
tion. The information available from sysctl consists of
integers, strings, and tables. Information may be retrieved
and set from the command interface using the _s_y_s_c_t_l(1) util-
ity.
Unless explicitly noted below, sysctl returns a consistent
snapshot of the data requested. Calls to sysctl are serial-
ized to avoid deadlock.
The state is described using a ``Management Information
Base'' (MIB) style name, listed in _n_a_m_e , which is a _n_a_m_e_l_e_n
length array of integers.
The information is copied into the buffer specified by _o_l_d_p
. The size of the buffer is given by the location specified
by _o_l_d_l_e_n_p 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, _o_l_d_p and _o_l_d_l_e_n_p should be
set to NULL.
The size of the available data can be determined by calling
sysctl with a NULL parameter for _o_l_d_p. The size of the
available data will be returned in the location pointed to
by _o_l_d_l_e_n_p. 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, _n_e_w_p is set to point to a buffer of
length _n_e_w_l_e_n from which the requested value is to be taken.
If a new value is not to be set, _n_e_w_p should be set to NULL
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and _n_e_w_l_e_n set to 0.
The top level names are defined with a CTL_ prefix in
<_s_y_s/_s_y_s_c_t_l._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 _s_t_r_u_c_t _c_t_l_d_e_b_u_g variables named _d_e_b_u_g_0 through
_d_e_b_u_g_1_9. 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 ini-
tialized in more than one place. For example, to export the
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variable _d_o_s_p_e_c_i_a_l_c_h_e_c_k as a debugging variable, the follow-
ing declaration would be used:
int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
CTL_FS
There are currently no second level names for the file sys-
tem.
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
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process information, system inodes, the open file entries,
routing table entries, virtual memory statistics, load aver-
age 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 _s_t_r_u_c_t _t_i_m_e_v_a_l structure is returned. This structure
contains the time that the system was booted.
KERN_CLOCKRATE
A _s_t_r_u_c_t _c_l_o_c_k_i_n_f_o structure is returned. This struc-
ture 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
_f_i_l_e structures. Each element of the array contains
the kernel address of a file _s_t_r_u_c_t _i_n_o_d_e * followed by
the file itself _s_t_r_u_c_t _f_i_l_e. There can never be more
than KERN_MAXFILES inodes returned.
KERN_HOSTID
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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 _s_t_r_u_c_t _k_i_n_f_o__p_r_o_c 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
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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 infor-
mation 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 pro-
filing 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 _s_t_r_u_c_t _t_o_s_t_r_u_c_t 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
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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 _s_t_r_u_c_t
_i_n_o_d_e * followed by the inode itself _s_t_r_u_c_t _i_n_o_d_e. 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 con-
tains the kernel address of a text _s_t_r_u_c_t _t_e_x_t * followed by
the text structure itself _s_t_r_u_c_t _t_e_x_t. 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
_r_o_u_t_e(_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 fami-
lies. 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 inter-
net protocols. The third level name is the protocol.
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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
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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 _b_c(_1) utility.
USER_BC_DIM_MAX
The maximum array size in the _b_c(_1) utility.
USER_BC_SCALE_MAX
The maximum scale value in the _b_c(_1) utility.
USER_BC_STRING_MAX
The maximum string length in the _b_c(_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 _P_A_T_H 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 _e_x_p_r(_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 facili-
ties support the C-Language Bindings Option, otherwise
0.
USER_POSIX2_C_DEV
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Return 1 if the system supports the C-Language Develop-
ment 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 Develop-
ment 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
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VM_LOADAVG
Return the load average history. The returned data
consists of a _s_t_r_u_c_t _l_o_a_d_a_v_g.
VM_METER
Return the system wide virtual memory statistics. The
returned data consists of a _s_t_r_u_c_t _v_m_t_o_t_a_l.
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 alloca-
tion map is returned.
RETURN VALUES
If the call to sysctl is successful, 0 is returned. Other-
wise -1 is returned and _e_r_r_n_o is set appropriately.
ERRORS
The following errors may be reported:
EFAULT The buffer _n_a_m_e, _o_l_d_p , _n_e_w_p , or length
pointer _o_l_d_l_e_n_p contains an invalid address.
EINVAL The _n_a_m_e array is less than two or greater
than CTL_MAXNAME.
EINVAL A non-null _n_e_w_p is given and its specified
length in _n_e_w_l_e_n is too large or too small.
ENOMEM The length pointed to by _o_l_d_l_e_n_p is too short
to hold the requested value.
ENOTDIR The _n_a_m_e array specifies an intermediate
rather than terminal name.
EOPNOTSUPP The _n_a_m_e array specifies a value that is unk-
nown.
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
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<sys/socket.h> definitions for second level network identif-
iers
<sys/gmon.h> definitions for third level profiling iden-
tifiers
<sys/vmparam.h>
definitions for second level virtual memory
identifiers
<netinet/in.h> definitions for third level Internet identif-
iers 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
_s_y_s_c_t_l(_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 _s_y_s_c_t_l impl-
mentation.
Having KERN_FILE return the address of the file structure
before the actual _s_t_r_u_c_t _f_i_l_e is a 2.11BSD enhancement. The
_i_n_o_d_e (_v_n_o_d_e under 4.4) table was handled this way.
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