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(
int
*name,
u_int namelen,
void *oldp,
size_t *oldlenp,
void *newp,
size_t newlen);
int
sysctlbyname(
const
char *name,
void
*oldp,
size_t
*oldlenp,
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.
Third level name |
Fourth level is: |
KERN_PROC_ARGS |
A process ID |
KERN_PROC_PATHNAME |
A process 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
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 and sixth level names are as follows:
Fifth level name |
Sixth level is: |
NET_RT_FLAGS |
rtflags |
NET_RT_DUMP |
None |
NET_RT_IFLIST |
0 or if_index |
NET_RT_IFMALIST |
0 or if_index |
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.
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_PAGEOUT_ALGORITHM |
integer |
yes |
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_PAGEOUT_ALGORITHM
- 0 if the statistics-based page management algorithm is in
use or 1 if the near-LRU algorithm is in use.
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.