4.4BSD/usr/share/man/cat3/sysctl.0
SYSCTL(3) BSD Programmer's Manual SYSCTL(3)
NNAAMMEE
ssyyssccttll - get or set system information
SSYYNNOOPPSSIISS
##iinncclluuddee <<ssyyss//ssyyssccttll..hh>>
_i_n_t
ssyyssccttll(_i_n_t _*_n_a_m_e, _u___i_n_t _n_a_m_e_l_e_n, _v_o_i_d _*_o_l_d_p, _s_i_z_e___t _*_o_l_d_l_e_n_p, _v_o_i_d _*_n_e_w_p,
_s_i_z_e___t _n_e_w_l_e_n);
DDEESSCCRRIIPPTTIIOONN
The ssyyssccttll function retrieves system information and allows processes
with appropriate privileges to set system information. The information
available from ssyyssccttll consists of integers, strings, and tables. Infor-
mation may be retrieved and set from the command interface using the
sysctl(1) utility.
Unless explicitly noted below, ssyyssccttll 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 ssyyssccttll are serialized 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 ssyyssccttll 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 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 in-
clude files listed here, and described in separate sections below.
_N_a_m_e _N_e_x_t _l_e_v_e_l _n_a_m_e_s _D_e_s_c_r_i_p_t_i_o_n
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 al-
lowed 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);
CCTTLL__DDEEBBUUGG
The debugging variables vary from system to system. A debugging variable
may be added or deleted without need to recompile ssyyssccttll to know about
it. Each time it runs, ssyyssccttll 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 ddeebbuugg00 through ddeebbuugg1199. They are de-
clared as separate variables so that they can be individually initialized
at the location of their associated variable. The loader prevents multi-
ple use of the same variable by issuing errors if a variable is initial-
ized in more than one place. For example, to export the variable
ddoossppeecciiaallcchheecckk as a debugging variable, the following declaration would
be used:
int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
CCTTLL__FFSS
There are currently no second level names for the file system.
CCTTLL__HHWW
The string and integer information available for the CTL_HW level is de-
tailed below. The changeable column shows whether a process with appro-
priate privilege may change the value.
_S_e_c_o_n_d _l_e_v_e_l _n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
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 (4,321, or 1,234).
HW_PHYSMEM
The bytes of physical memory.
HW_USERMEM
The bytes of non-kernel memory.
HW_PAGESIZE
The software page size.
CCTTLL__KKEERRNN
The string and integer information available for the CTL_KERN level is
detailed below. The changeable column shows whether a process with ap-
propriate 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.
_S_e_c_o_n_d _l_e_v_e_l _n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
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 integer yes
KERN_HOSTNAME string yes
KERN_JOB_CONTROL integer no
KERN_LINK_MAX integer no
KERN_MAXFILES integer yes
KERN_MAXPROC integer yes
KERN_MAXVNODES integer yes
KERN_MAX_CANON integer no
KERN_MAX_INPUT integer no
KERN_NAME_MAX integer no
KERN_NGROUPS integer no
KERN_NO_TRUNC integer no
KERN_OSRELEASE string no
KERN_OSREV integer no
KERN_OSTYPE string no
KERN_PATH_MAX integer no
KERN_PIPE_BUF integer 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_VDISABLE integer no
KERN_VERSION string no
KERN_VNODE struct vnode 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_CHOWN_RESTRICTED
Return 1 if appropriate privileges are required for the chown(2)
system call, otherwise 0.
KERN_CLOCKRATE
A _s_t_r_u_c_t _c_l_o_c_k_i_n_f_o structure is returned. This structure con-
tains the clock, statistics clock and profiling clock frequen-
cies, and the number of micro-seconds per hz tick.
KERN_FILE
Return the entire file table. The returned data consists of a
single _s_t_r_u_c_t _f_i_l_e_h_e_a_d followed by an array of _s_t_r_u_c_t _f_i_l_e, whose
size depends on the current number of such objects in the system.
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_LINK_MAX
The maximum file link count.
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 al-
low.
KERN_MAXVNODES
The maximum number of vnodes available on the system.
KERN_MAX_CANON
The maximum number of bytes in terminal canonical input line.
KERN_MAX_INPUT
The minimum maximum number of bytes for which space is available
in a terminal input queue.
KERN_NAME_MAX
The maximum number of bytes in a file name.
KERN_NGROUPS
The maximum number of supplemental groups.
KERN_NO_TRUNC
Return 1 if file names longer than KERN_NAME_MAX are truncated.
KERN_OSRELEASE
The system release string.
KERN_OSREV
The system revision string.
KERN_OSTYPE
The system type string.
KERN_PATH_MAX
The maximum number of bytes in a pathname.
KERN_PIPE_BUF
The maximum number of bytes which will be written atomically to a
pipe.
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:
_T_h_i_r_d _l_e_v_e_l _n_a_m_e _F_o_u_r_t_h _l_e_v_e_l _i_s_:
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 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 de-
tailed below. The changeable column shows whether a process with
appropriate privilege may change the value.
_T_h_i_r_d _l_e_v_e_l _n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
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_VDISABLE
Returns the terminal character disabling value.
KERN_VERSION
The system version string.
KERN_VNODE
Return the entire vnode table. Note, the vnode table is not nec-
essarily 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 _s_t_r_u_c_t _v_n_o_d_e _* followed by the vn-
ode itself _s_t_r_u_c_t _v_n_o_d_e.
CCTTLL__MMAACCHHDDEEPP
The set of variables defined is architecture dependent. Most architec-
tures define at least the following variables.
_S_e_c_o_n_d _l_e_v_e_l _n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
CPU_CONSDEV dev_t no
CCTTLL__NNEETT
The string and integer information available for the CTL_NET level is de-
tailed below. The changeable column shows whether a process with appro-
priate privilege may change the value.
_S_e_c_o_n_d _l_e_v_e_l _n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
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 al-
ways 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:
_F_i_f_t_h _l_e_v_e_l _n_a_m_e _S_i_x_t_h _l_e_v_e_l _i_s_:
NET_RT_FLAGS rtflags
NET_RT_DUMP None
NET_RT_IFLIST None
PF_INET
Get or set various global information about the internet proto-
cols. The third level name is the protocol. The fourth level
name is the variable name. The currently defined protocols and
names are:
_P_r_o_t_o_c_o_l _n_a_m_e _V_a_r_i_a_b_l_e
_n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
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 nor-
mal transport protocols, not to ICMP.
icmp.maskrepl
Returns 1 if ICMP network mask requests are to be an-
swered.
udp.checksum
Returns 1 when UDP checksums are being computed and
checked. Disabling UDP checksums is strongly discour-
aged.
CCTTLL__UUSSEERR
The string and integer information available for the CTL_USER level is
detailed below. The changeable column shows whether a process with ap-
propriate privilege may change the value.
_S_e_c_o_n_d _l_e_v_e_l _n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
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 capa-
ble of all operations described in POSIX 1003.2, otherwise 0.
USER_POSIX2_C_BIND
Return 1 if the system's C-language development facilities sup-
port the C-Language Bindings Option, otherwise 0.
USER_POSIX2_C_DEV
Return 1 if the system supports the C-Language Development Utili-
ties 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 Op-
tion, otherwise 0.
USER_POSIX2_LOCALEDEF
Return 1 if the system supports the creation of locales, other-
wise 0.
USER_POSIX2_SW_DEV
Return 1 if the system supports the Software Development Utili-
ties 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 expres-
sion 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.
CCTTLL__VVMM
The string and integer information available for the CTL_VM level is de-
tailed below. The changeable column shows whether a process with appro-
priate privilege may change the value.
_S_e_c_o_n_d _l_e_v_e_l _n_a_m_e _T_y_p_e _C_h_a_n_g_e_a_b_l_e
VM_LOADAVG struct loadavg no
VM_METER struct vmtotal no
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.
RREETTUURRNN VVAALLUUEESS
If the call to ssyyssccttll is successful, 0 is returned. Otherwise -1 is re-
turned and _e_r_r_n_o is set appropriately.
EERRRROORRSS
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 con-
tains 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 termi-
nal name.
[EOPNOTSUPP] The _n_a_m_e 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.
FFIILLEESS
<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
<vm/vm_param.h> definitions for second level virtual memory identi-
fiers
<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
SSEEEE AALLSSOO
sysctl(8)
HHIISSTTOORRYY
The ssyyssccttll function first appeared in 4.4BSD.
4.4BSD June 4, 1993 9