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SYSCTL(3) OpenBSD Programmer's Manual SYSCTL(3)
NAME
sysctl - get or set system information
SYNOPSIS
#include <sys/param.h>
#include <sys/sysctl.h>
int
sysctl(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. In-
formation 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 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 re-
turned in the location pointed to by oldlenp. For some operations, the
amount of space may change often. For these operations, the system at-
tempts 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 in-
clude 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 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);
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 initial-
ized 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 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 de-
tailed below. The changeable column shows whether a process with appro-
priate privileges 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 (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.
CTL_KERN
The string and integer information available for the CTL_KERN level is
detailed below. The changeable column shows whether a process with ap-
propriate privileges 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_ARND integer no
KERN_BOOTTIME struct timeval no
KERN_CHOWN_RESTRICTED integer no
KERN_CLOCKRATE struct clockinfo no
KERN_DOMAINNAME string yes
KERN_FILE struct file no
KERN_FSYNC integer no
KERN_HOSTID integer yes
KERN_HOSTNAME string yes
KERN_JOB_CONTROL integer no
KERN_LINK_MAX integer no
KERN_MAXFILES integer yes
KERN_MAXPARTITIONS integer no
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_NOSUIDCOREDUMP integer yes
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_RAWPARTITION integer no
KERN_RND struct rndstats no
KERN_SAVED_IDS integer no
KERN_SECURELVL integer raise only
KERN_SYSVMSG integer no
KERN_SYSVSEM integer no
KERN_SYSVSHM integer no
KERN_VDISABLE integer no
KERN_VERSION string no
KERN_VNODE struct vnode no
KERN_ARGMAX
The maximum bytes of argument to exec(2).
KERN_ARND
Returns a random integer from the kernel arc4random() function.
This can be useful if /dev/arandom is not available (see
random(4)).
KERN_BOOTTIME
A struct timeval 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 struct clockinfo structure is returned. This structure con-
tains the clock, statistics clock and profiling clock frequen-
cies, the number of micro-seconds per hz tick, and the clock skew
rate.
KERN_DOMAINNAME
Get or set the YP domain name.
KERN_FILE
Return the entire file table. The returned data consists of a
single struct filehead followed by an array of struct file, whose
size depends on the current number of such objects in the system.
KERN_FSYNC
Return 1 if the File Synchronisation Option is available on this
system, otherwise 0.
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_MAXPARTITIONS
The maximum number of partitions allowed per disk.
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_NOSUIDCOREDUMP
Programs with their set-user-ID bit set will not dump core when
this is set.
KERN_OSRELEASE
The system release string.
KERN_OSREV
The system revision number.
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
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 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 detailed be-
low. The changeable column shows whether a process with appro-
priate privileges 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 struct tostruct describing destination of calls
and their counts.
GPROF_GMONPARAM
Structure giving the sizes of the above arrays.
KERN_RAWPARTITION
The raw partition of a disk (a == 0).
KERN_RND
Returns statistics about the /dev/random device in a struct
rndstats structure.
KERN_SAVED_IDS
Returns 1 if saved set-group-ID and saved set-user-ID are avail-
able.
KERN_SECURELVL
The system security level. This level may be raised by processes
with appropriate privileges. It may only be lowered by process
1.
KERN_SYSVMSG
Returns 1 if System V style message queue functionality is avail-
able on this system, otherwise 0.
KERN_SYSVSEM
Returns 1 if System V style semaphore functionality is available
on this system, otherwise 0.
KERN_SYSVSHM
Returns 1 if System V style share memory functionality is avail-
able on this system, otherwise 0.
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 struct vnode * followed by the vn-
ode itself struct vnode.
CTL_MACHDEP
The set of variables defined is architecture dependent. Most architec-
tures 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 de-
tailed below. The changeable column shows whether a process with appro-
priate privileges may change the value.
Second level name Type Changeable
PF_ROUTE routing messages no
PF_INET internet values yes
PF_ENCAP IPsec values yes
PF_ENCAP
Get or set various global information about the IP security pro-
tocols. 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
encap encdebug integer yes
The variables are as follows:
encap.encdebug
Returns 1 when error message reporting is enabled for the
host. If the kernel has been compiled with the ENCDEBUG
option, then debugging information will also be reported
when this variable is set.
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:
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 proto-
cols. 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
tcp rfc1323 integer yes
tcp baddynamic array yes
tcp ident structure no
tcp keepidle integer yes
tcp keepintvl integer yes
tcp slowhz integer yes
tcp sack integer yes
tcp mssdflt integer yes
udp checksum integer yes
udp baddynamic array yes
The variables are as follows:
ip.forwarding
Returns 1 when IP forwarding is enabled for the host, in-
dicating 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.
tcp.rfc1323
Returns 1 if RFC1323 extensions to TCP are enabled.
tcp.baddynamic
An array of in_port_t is returned specifying the bitmask
of TCP ports between 512 and 1023 inclusive that should
not be allocated dynamically by the kernel (i.e., they
must be bound specifically by port number).
tcp.ident
A structure struct tcp_ident_mapping specifying a local
and foreign endpoint of a TCP socket is filled in with
the euid and ruid of the process that owns the socket.
If no such socket exists then the euid and ruid values
are both set to -1.
tcp.keepidle
If the socket option SO_KEEPALIVE has been set, time a
connection needs to be idle before keepalives are sent.
See also tcp.slowhz.
tcp.keepintvl
Time after a keepalive probe is sent until, in the ab-
sence of any response, another probe is sent. See also
tcp.slowhz.
tcp.slowhz
The units for tcp.keepidle and tcp.keepintvl; those vari-
ables are in ticks of a clock that ticks tcp.slowhz times
per second. (That is, their values must be divided by
the tcp.slowhz value to get times in seconds.)
tcp.sack
Returns 1 if RFC2018 Selective Acknowledgements are en-
abled.
tcp.mssdflt
The maximum segment size that is used as default for non
local connections. The default value is 512.
udp.checksum
Returns 1 when UDP checksums are being computed and
checked. Disabling UDP checksums is strongly discour-
aged.
udp.baddynamic
Analogous to tcp.baddynamic but for UDP sockets.
CTL_USER
The string and integer information available for the CTL_USER level is
detailed below. The changeable column shows whether a process with ap-
propriate privileges 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 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 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 de-
tailed below. The changeable column shows whether a process with appro-
priate privileges may change the value.
Second level name Type Changeable
VM_LOADAVG struct loadavg no
VM_METER struct vmtotal 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.
RETURN VALUES
If the call to sysctl() is unsuccessful, -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 con-
tains an invalid address.
[EINVAL] The name array is less than two or greater than
CTL_MAXNAME.
[EINVAL] A non-null newp pointer 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 termi-
nal 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 privileges attempts to set a
value.
[EPERM] An attempt to change a value protected by the current ker-
nel security level is made.
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 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/tcp_var.h> definitions for fourth level TCP identifiers
<netinet/udp_var.h> definitions for fourth level UDP identifiers
SEE ALSO
sysctl(8)
HISTORY
The sysctl() function first appeared in 4.4BSD.
OpenBSD 2.6 June 4, 1993 11
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others. |
(Corrections, notes, and links courtesy of RocketAware.com)
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