NAME¶
sysctl
,
sysctlbyname
,
sysctlnametomib
—
get or set system information
LIBRARY¶
Standard C Library (libc, -lc)
SYNOPSIS¶
#include
<sys/types.h>
#include
<sys/sysctl.h>
int
sysctl
(
const
int *name,
u_int
namelen,
void
*oldp,
size_t
*oldlenp,
const
void *newp,
size_t newlen);
int
sysctlbyname
(
const
char *name,
void
*oldp,
size_t
*oldlenp,
const
void *newp,
size_t newlen);
int
sysctlnametomib
(
const
char *name,
int
*mibp,
size_t
*sizep);
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(8) utility.
Unless explicitly noted below,
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
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
sysctlbyname
() function accepts an ASCII
representation of the name and internally looks up the integer name vector.
Apart from that, it behaves the same as the standard
sysctl
() function.
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 and after a call that returns with the error code
ENOMEM
. 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 the
NULL
argument 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
sysctlnametomib
() function accepts an
ASCII representation of the name, looks up the integer name vector, and
returns the numeric representation in the mib array pointed to by
mibp. The number of elements in the mib array
is given by the location specified by
sizep
before the call, and that location gives the number of entries copied after a
successful call. The resulting
mib and
size may be used in subsequent
sysctl
() calls to get the data associated
with the requested ASCII name. This interface is intended for use by
applications that want to repeatedly request the same variable (the
sysctl
() function runs in about a third the
time as the same request made via the
sysctlbyname
() function). The
sysctlnametomib
() function is also useful
for fetching mib prefixes and then adding a final component. For example, to
fetch process information for processes with pid's less than 100:
int i, mib[4];
size_t len;
struct kinfo_proc kp;
/* Fill out the first three components of the mib */
len = 4;
sysctlnametomib("kern.proc.pid", mib, &len);
/* Fetch and print entries for pid's < 100 */
for (i = 0; i < 100; i++) {
mib[3] = i;
len = sizeof(kp);
if (sysctl(mib, 4, &kp, &len, NULL, 0) == -1)
perror("sysctl");
else if (len > 0)
printkproc(&kp);
}
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_VFS |
sys/mount.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_VFS¶
A distinguished second level name, VFS_GENERIC, is used to get general
information about all file systems. One of its third level identifiers is
VFS_MAXTYPENUM that gives the highest valid file system type number. Its other
third level identifier is VFS_CONF that returns configuration information
about the file system type given as a fourth level identifier (see
getvfsbyname(3) as an example of its use). The
remaining second level identifiers are the file system type number returned by
a
statfs(2) call or from VFS_CONF. The third
level identifiers available for each file system are given in the header file
that defines the mount argument structure for that 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_FLOATINGPT |
integer |
no |
HW_MACHINE_ARCH |
string |
no |
HW_REALMEM |
integer |
no |
- Li 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.
HW_FLOATINGPT
- Nonzero if the floating point support is in hardware.
HW_MACHINE_ARCH
- The machine dependent architecture type.
HW_REALMEM
- The bytes of real memory.
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.
Second level name |
Type |
Changeable |
KERN_ARGMAX |
integer |
no |
KERN_BOOTFILE |
string |
yes |
KERN_BOOTTIME |
struct timeval |
no |
KERN_CLOCKRATE |
struct clockinfo |
no |
KERN_FILE |
struct xfile |
no |
KERN_HOSTID |
integer |
yes |
KERN_HOSTUUID |
string |
yes |
KERN_HOSTNAME |
string |
yes |
KERN_JOB_CONTROL |
integer |
no |
KERN_MAXFILES |
integer |
yes |
KERN_MAXFILESPERPROC |
integer |
yes |
KERN_MAXPROC |
integer |
no |
KERN_MAXPROCPERUID |
integer |
yes |
KERN_MAXVNODES |
integer |
yes |
KERN_NGROUPS |
integer |
no |
KERN_NISDOMAINNAME |
string |
yes |
KERN_OSRELDATE |
integer |
no |
KERN_OSRELEASE |
string |
no |
KERN_OSREV |
integer |
no |
KERN_OSTYPE |
string |
no |
KERN_POSIX1 |
integer |
no |
KERN_PROC |
node |
not applicable |
KERN_PROF |
node |
not applicable |
KERN_QUANTUM |
integer |
yes |
KERN_SAVED_IDS |
integer |
no |
KERN_SECURELVL |
integer |
raise only |
KERN_UPDATEINTERVAL |
integer |
no |
KERN_VERSION |
string |
no |
KERN_VNODE |
struct xvnode |
no |
- Li KERN_ARGMAX
- The maximum bytes of argument to
execve(2).
KERN_BOOTFILE
- The full pathname of the file from which the kernel was loaded.
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, the number of micro-seconds per hz tick and the skew
rate.
KERN_FILE
- Return the entire file table. The returned data consists of an array of
struct xfile, whose size depends on the
current number of such objects in the system.
KERN_HOSTID
- Get or set the host ID.
KERN_HOSTUUID
- Get or set the host's universally unique identifier (UUID).
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 files that may be open in the system.
KERN_MAXFILESPERPROC
- The maximum number of files that may be open for a single process. This
limit only applies to processes with an effective uid of nonzero at the
time of the open request. Files that have already been opened are not
affected if the limit or the effective uid is changed.
KERN_MAXPROC
- The maximum number of concurrent processes the system will allow.
KERN_MAXPROCPERUID
- The maximum number of concurrent processes the system will allow for a
single effective uid. This limit only applies to processes with an
effective uid of nonzero at the time of a fork request. Processes that
have already been started are not affected if the limit is changed.
KERN_MAXVNODES
- The maximum number of vnodes available on the system.
KERN_NGROUPS
- The maximum number of supplemental groups.
KERN_NISDOMAINNAME
- The name of the current YP/NIS domain.
KERN_OSRELDATE
- The kernel release version in the format
MmmRxx,
where M is the major version,
mm is the two digit minor version,
R is 0 if release branch, otherwise 1,
and xx is updated when the available APIs
change.
The userland release version is available from
<osreldate.h>
;
parse this file if you need to get the release version of the currently
installed userland.
KERN_OSRELEASE
- The system release string.
KERN_OSREV
- The system revision string.
KERN_OSTYPE
- The system type string.
KERN_POSIX1
- The version of IEEE Std 1003.1
(“POSIX.1”) with which the system attempts to
comply.
KERN_PROC
- Return selected information about specific running processes.
For the following names, an array of struct
kinfo_proc structures is returned, whose size depends on the current
number of such objects in the system.
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 |
If the third level name is KERN_PROC_ARGS
then the command line argument array is returned in a flattened form,
i.e., zero-terminated arguments follow each other. The total size of array
is returned. It is also possible for a process to set its own process
title this way. If the third level name is
KERN_PROC_PATHNAME
, the path of the
process' text file is stored. For
KERN_PROC_PATHNAME
, a process ID of
-1
implies the current process.
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
ENOENT
. 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:
- Li 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_QUANTUM
- The maximum period of time, in microseconds, for which a process is
allowed to run without being preempted if other processes are in the run
queue.
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 not be lowered.
KERN_VERSION
- The system version string.
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 consists of a struct
xvnode.
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 |
IPv4 values |
yes |
PF_INET6 |
IPv6 values |
yes |
- Li 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, sixth, and seventh level names are as
follows:
Fifth level Sixth level |
Seventh level |
NET_RT_FLAGS rtflags |
None |
NET_RT_DUMP None |
None or fib number |
NET_RT_IFLIST 0 or if_index |
None |
NET_RT_IFMALIST 0 or if_index |
None |
NET_RT_IFLISTL 0 or if_index |
None |
The NET_RT_IFMALIST
name returns
information about multicast group memberships on all interfaces if 0 is
specified, or for the interface specified by
if_index.
The NET_RT_IFLISTL
is like
NET_RT_IFLIST
, just returning message
header structs with additional fields allowing the interface to be
extended without breaking binary compatibility. The
NET_RT_IFLISTL
uses 'l' versions of the
message header structures: struct
if_msghdrl and struct
ifa_msghdrl.
PF_INET
- Get or set various global information about the IPv4 (Internet Protocol
version 4). The third level name is the protocol. The fourth level name is
the variable name. The currently defined protocols and names are:
Protocol |
Variable |
Type |
Changeable |
icmp |
bmcastecho |
integer |
yes |
icmp |
maskrepl |
integer |
yes |
ip |
forwarding |
integer |
yes |
ip |
redirect |
integer |
yes |
ip |
ttl |
integer |
yes |
udp |
checksum |
integer |
yes |
The variables are as follows:
- Li icmp.bmcastecho
- Returns 1 if an ICMP echo request to a broadcast or multicast address
is to be answered.
icmp.maskrepl
- Returns 1 if ICMP network mask requests are to be answered.
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.
udp.checksum
- Returns 1 when UDP checksums are being computed and checked. Disabling
UDP checksums is strongly discouraged.
For variables net.inet.*.ipsec, please refer to
ipsec(4).
PF_INET6
- Get or set various global information about the IPv6 (Internet Protocol
version 6). The third level name is the protocol. The fourth level name is
the variable name.
For variables net.inet6.* please refer to
inet6(4). For variables net.inet6.*.ipsec6,
please refer to ipsec(4).
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 |
- Li 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 IEEE Std 1003.2
(“POSIX.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 IEEE Std 1003.2
(“POSIX.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_TOTAL |
struct vmtotal |
no |
VM_SWAPPING_ENABLED |
integer |
maybe |
VM_V_CACHE_MAX |
integer |
yes |
VM_V_CACHE_MIN |
integer |
yes |
VM_V_FREE_MIN |
integer |
yes |
VM_V_FREE_RESERVED |
integer |
yes |
VM_V_FREE_TARGET |
integer |
yes |
VM_V_INACTIVE_TARGET |
integer |
yes |
VM_V_PAGEOUT_FREE_MIN |
integer |
yes |
- Li VM_LOADAVG
- Return the load average history. The returned data consists of a
struct loadavg.
VM_TOTAL
- Return the system wide virtual memory statistics. The returned data
consists of a struct vmtotal.
VM_SWAPPING_ENABLED
- 1 if process swapping is enabled or 0 if disabled. This variable is
permanently set to 0 if the kernel was built with swapping disabled.
VM_V_CACHE_MAX
- Maximum desired size of the cache queue.
VM_V_CACHE_MIN
- Minimum desired size of the cache queue. If the cache queue size falls
very far below this value, the pageout daemon is awakened.
VM_V_FREE_MIN
- Minimum amount of memory (cache memory plus free memory) required to be
available before a process waiting on memory will be awakened.
VM_V_FREE_RESERVED
- Processes will awaken the pageout daemon and wait for memory if the number
of free and cached pages drops below this value.
VM_V_FREE_TARGET
- The total amount of free memory (including cache memory) that the pageout
daemon tries to maintain.
VM_V_INACTIVE_TARGET
- The desired number of inactive pages that the pageout daemon should
achieve when it runs. Inactive pages can be quickly inserted into process
address space when needed.
VM_V_PAGEOUT_FREE_MIN
- If the amount of free and cache memory falls below this value, the pageout
daemon will enter "memory conserving mode" to avoid
deadlock.
RETURN VALUES¶
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable
errno is set to indicate the error.
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
<vm/vm_param.h>
- definitions for second level virtual memory identifiers
<netinet/in.h>
- definitions for third level IPv4/IPv6 identifiers and fourth level IPv4/v6
identifiers
<netinet/icmp_var.h>
- definitions for fourth level ICMP identifiers
<netinet/icmp6.h>
- definitions for fourth level ICMPv6 identifiers
<netinet/udp_var.h>
- definitions for fourth level UDP identifiers
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.
- [
ENOMEM
]
- The smaller of either the length pointed to by
oldlenp or the estimated size of the
returned data exceeds the system limit on locked memory.
- [
ENOMEM
]
- Locking the buffer oldp, or a portion of
the buffer if the estimated size of the data to be returned is smaller,
would cause the process to exceed its per-process locked memory
limit.
- [
ENOTDIR
]
- The name array specifies an intermediate
rather than terminal name.
- [
EISDIR
]
- The name array specifies a terminal name,
but the actual name is not terminal.
- [
ENOENT
]
- 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.
SEE ALSO¶
confstr(3),
kvm(3),
sysconf(3),
sysctl(8)
HISTORY¶
The
sysctl
() function first appeared in
4.4BSD.