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 uvm/uvm_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
The string and integer information available for the CTL_FS 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
FS_POSIX_SETUID integer yes
FS_POSIX_SETUID
When this variable is set, ownership changes on a file will cause
the S_ISUID and S_ISGID bits to be cleared. As detailed in
securelevel(7), this variable may not be changed if the se-
curelevel is > 0.
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_DISKNAMES string no
HW_DISKSTATS struct no
HW_DISKCOUNT integer no
HW_MACHINE
The machine class.
HW_MODEL
The machine model
HW_NCPU
The number of CPUs.
HW_BYTEORDER
The byteorder (4321 or 1234).
HW_PHYSMEM
The bytes of physical memory.
HW_USERMEM
The bytes of non-kernel memory.
HW_PAGESIZE
The software page size.
HW_DISKNAMES
A comma-separated list of disk names.
HW_DISKSTATS
An array of struct diskstats structures containing disk statis-
tics.
HW_DISKCOUNT
The number of disks currently attached to the system.
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_CLOCKRATE struct clockinfo no
KERN_CPTIME long[CPUSTATES] no
KERN_DOMAINNAME string yes
KERN_FILE struct file no
KERN_FSYNC integer no
KERN_FORKSTAT struct forkstat no
KERN_HOSTID integer yes
KERN_HOSTNAME string yes
KERN_JOB_CONTROL integer no
KERN_MALLOCSTATS node no
KERN_MAXFILES integer yes
KERN_MAXPARTITIONS integer no
KERN_MAXPROC integer yes
KERN_MAXVNODES integer yes
KERN_MBSTAT struct mbstat no
KERN_MSGBUFSIZE integer no
KERN_NCHSTATS struct nchstats no
KERN_NFILES integer no
KERN_NGROUPS integer no
KERN_NOSUIDCOREDUMP integer yes
KERN_NPROCS integer no
KERN_NSELCOLL integer no
KERN_NUMVNODES 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_RAWPARTITION integer no
KERN_RND struct rndstats no
KERN_SAVED_IDS integer no
KERN_SECURELVL integer raise only
KERN_SEMINFO node not applicable
KERN_SHMINFO node not applicable
KERN_SOMINCONN integer yes
KERN_SOMAXCONN integer yes
KERN_SYSVIPC_INFO node not applicable
KERN_SYSVMSG integer no
KERN_SYSVSEM integer no
KERN_SYSVSHM integer no
KERN_TTY node not applicable
KERN_TTYCOUNT integer no
KERN_USERMOUNT integer yes
KERN_VERSION string no
KERN_VNODE struct vnode no
KERN_STACKGAPRANDOM integer yes
KERN_USERASYMCRYPTO integer yes
KERN_USERCRYPTO integer yes
KERN_CRYPTODEVALLOWSOFT integer yes
KERN_PROC_ARGS node not applicable
KERN_ARGMAX
The maximum bytes of argument to exec(3).
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_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_CPTIME
An array of longs, of size CPUSTATES is returned, containing
statistics about the number of ticks spent by the system in in-
terrupt processing, user processes (niced or normal), system pro-
cessing, or idling.
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_FORKSTAT
A struct forkstat structure is returned. This structure contains
information about the number of fork(2), vfork(2), rfork(2) sys-
tem calls as well as kernel thread creations since system start-
up, and the number of pages of virtual memory involved in each.
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_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_MBSTAT
A struct mbstat structure is returned, containing statistics on
mbuf(9) usage.
KERN_MSGBUFSIZE
The size of the kernel message buffer.
KERN_NCHSTATS
A struct nchstats structure is returned. This structure contains
information the filename to inode(5) mapping cache.
KERN_NFILES
Number of open files.
KERN_NGROUPS
The maximum number of supplemental groups.
KERN_NPROCS
The number of entries in the kernel process table.
KERN_NOSUIDCOREDUMP
Programs with their set-user-ID bit set will not dump core when
this is set.
KERN_NSELCOLL
Number of select(2) collisions.
KERN_NUMVNODES
Number of vnodes in use.
KERN_OSRELEASE
The system release string.
KERN_OSREV
The system revision number.
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
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_MALLOCSTATS
Return kernel memory bucket statistics. The third level names
are detailed below. There are no changeable values in this
branch.
Third level name Type
KERN_MALLOC_BUCKETS string
KERN_MALLOC_BUCKET node
KERN_MALLOC_KMEMNAMES string
KERN_MALLOC_KMEMSTATS node
The variables are as follows:
KERN_MALLOC_BUCKETS
Return a comma-separated list of the bucket sizes used by
the kernel.
KERN_MALLOC_BUCKET.<size>
A node containing the statistics for the memory bucket of
the specified size (in decimal notation, the number of
bytes per bucket element, e.g., 16, 32, 128). Each node
returns a struct kmembuckets.
If a value is specified that does not correspond directly
to a bucket size, the statistics for the closest larger
bucket size will be returned instead.
Note that bucket sizes are typically powers of 2.
KERN_MALLOC_KERNNAMES
Return a comma-separated list of the names of the kernel
malloc(9) types.
KERN_MALLOC_KMEMSTATS
A node containing the statistics for the memory types of
the specified name. Each node returns a struct
kmemstats.
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_SEMINFO
Return the elements of struct seminfo. If the kernel is not com-
piled with System V style semaphore support, attempts to retrieve
any of the KERN_SEMINFO values will fail with EOPNOTSUPP. The
third level names for the elements of struct seminfo are detailed
below. The changeable column shows whether a process with appro-
priate privileges may change the value.
Third level name Type Changeable
KERN_SEMINFO_SEMMNI integer yes
KERN_SEMINFO_SEMMNS integer yes
KERN_SEMINFO_SEMMNU integer yes
KERN_SEMINFO_SEMMSL integer yes
KERN_SEMINFO_SEMOPM integer yes
KERN_SEMINFO_SEMUME integer no
KERN_SEMINFO_SEMUSZ integer no
KERN_SEMINFO_SEMVMX integer no
KERN_SEMINFO_SEMAEM integer no
The variables are as follows:
KERN_SEMINFO_SEMMNI
The maximum number of semaphore identifiers allowed.
KERN_SEMINFO_SEMMNS
The maximum number of semaphores allowed in the system.
KERN_SEMINFO_SEMMNU
The maximum number of semaphore undo structures allowed
in the system.
KERN_SEMINFO_SEMMSL
The maximum number of semaphores allowed per id.
KERN_SEMINFO_SEMOPM
The maximum number of operations per semop(2) call.
KERN_SEMINFO_SEMUME
The maximum number of undo entries per process.
KERN_SEMINFO_SEMUSZ
The size (in bytes) of the undo structure.
KERN_SEMINFO_SEMVMX
The semaphore maximum value.
KERN_SEMINFO_SEMAEM
The adjust on exit maximum value.
KERN_SHMINFO
Return the elements of struct shminfo. If the kernel is not com-
piled with System V style shared memory support, attempts to re-
trieve any of the KERN_SHMINFO values will fail with EOPNOTSUPP.
The third level names for the elements of struct shminfo are de-
tailed below. The changeable column shows whether a process with
appropriate privileges may change the value.
Third level name Type Changeable
KERN_SHMINFO_SHMMAX integer yes
KERN_SHMINFO_SHMMIN integer yes
KERN_SHMINFO_SHMMNI integer yes
KERN_SHMINFO_SHMSEG integer yes
KERN_SHMINFO_SHMALL integer yes
The variables are as follows:
KERN_SHMINFO_SHMMAX
The maximum shared memory segment size (in bytes).
KERN_SHMINFO_SHMMIN
The minimum shared memory segment size (in bytes).
KERN_SHMINFO_SHMMNI
The maximum number of shared memory identifiers in the
system.
KERN_SHMINFO_SHMSEG
The maximum number of shared memory segments per process.
KERN_SHMINFO_SHMALL
The maximum amount of total shared memory allowed in the
system (in pages).
KERN_SOMAXCONN
Upper bound on the number of half-open connections a process can
allow to be associated with a socket, using listen(2). The de-
fault value is 128.
KERN_SOMINCONN
Lower bound on the number of half-open connections a process can
allow to be associated with a socket, using listen(2). The de-
fault value is 80.
KERN_SYSVIPC_INFO
Return System V style IPC configuration and run-time information.
The third level name selects the System V style IPC facility.
Third level name Type
KERN_SYSVIPC_MSG_INFO struct msg_sysctl_info
KERN_SYSVIPC_SEM_INFO struct sem_sysctl_info
KERN_SYSVIPC_SHM_INFO struct shm_sysctl_info
KERN_SYSVIPC_MSG_INFO
Return information on the System V style message facili-
ty. The msg_sysctl_info structure is defined in
<sys/msg.h>.
KERN_SYSVIPC_SEM_INFO
Return information on the System V style semaphore facil-
ity. The sem_sysctl_info structure is defined in
<sys/sem.h>.
KERN_SYSVIPC_SHM_INFO
Return information on the System V style shared memory
facility. The shm_sysctl_info structure is defined in
<sys/shm.h>.
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_TTY
Return statistics information about tty input/output. The third
level names information is detailed below. The changeable column
shows whether a process with appropriate privileges may change
the value.
Third level name Type Changeable
KERN_TTY_TKNIN int64_t no
KERN_TTY_TKNOUT int64_t no
KERN_TTY_TKRAWCC int64_t no
KERN_TTY_TKCANCC int64_t no
The variables are as follows:
KERN_TTY_TKNIN
Returns the number of input characters from a tty(4).
KERN_TTY_TKNOUT
Returns the number of output characters on a tty(4).
KERN_TTY_TKRAWCC
Return the number of input characters in raw mode.
KERN_TTY_TKCANCC
Return the number of input characters in canonical mode.
KERN_TTYCOUNT
Number of available tty(4) devices.
KERN_USERMOUNT
Return non-zero if regular users can issue mount(2) requests.
The default value is 0.
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.
KERN_STACKGAPRANDOM
Sets the range of the random value added to the stack pointer on
each program execution. The random value is added to make buffer
overflow exploitation slightly harder. The bigger the number,
the harder it is to brute force this added protection, but it al-
so means bigger waste of memory.
KERN_USERASYMCRYPTO
Permits userland to use /dev/crypto for cryptographic support for
asymmetric (public) key operations via hardware cryptographic de-
vices. kern.usercrypto must also be set.
KERN_USERCRYPTO
Permits userland to use /dev/crypto for cryptographic support via
hardware cryptographic devices.
KERN_CRYPTODEVALLOWSOFT
Permits userland to use /dev/crypto even if there is no hardware
crypto accelerator in the system.
KERN_PROC_ARGS
Returns the arguments or environment of a process. The third
level name is the pid of the process. The fourth level name is
one of:
KERN_PROC_ARGV
KERN_PROC_NARGV
KERN_PROC_ENV
KERN_PROC_NENV
KERN_PROC_NARGV and KERN_PROC_NENV return the number of elements
in the argv or env array. KERN_PROC_ARG returns the argv array
and KERN_PROC_ENV returns the environ array.
KERN_WATCHDOG
If the kernel does not support a hardware watchdog timer, at-
tempts to retrieve or set any of the KERN_WATCHDOG values will
fail with EOPNOTSUPP.
Third level name Type Changeable
KERN_WATCHDOG_PERIOD integer yes
KERN_WATCHDOG_AUTO integer yes
The variables are as follows:
KERN_WATCHDOG_PERIOD
The period of the watchdog timer in seconds. Set to 0 to
disable the watchdog timer.
KERN_WATCHDOG_AUTO
If set to 1, the kernel refreshes the watchdog timer pe-
riodically. If set to 0, a userland process must ensure
that the watchdog timer gets refreshed by setting the
KERN_WATCHDOG_PERIOD variable.
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 IPv4 values yes
PF_INET6 IPv6 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:
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 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 name Variable name Type Changeable
ip forwarding integer yes
ip redirect integer yes
ip ttl integer yes
ip sourceroute integer yes
ip directed-broadcast integer yes
ip portfirst integer yes
ip portlast integer yes
ip porthifirst integer yes
ip porthilast integer yes
ip maxqueue integer yes
ip encdebug integer yes
ip ipsec-invalid-life integer yes
ip ipsec-pfs integer yes
ip ipsec-soft-allocs integer yes
ip ipsec-allocs integer yes
ip ipsec-soft-bytes integer yes
ip ipsec-bytes integer yes
ip ipsec-timeout integer yes
ip ipsec-soft-timeout integer yes
ip ipsec-soft-firstuse integer yes
ip ipsec-firstuse integer yes
ip ipsec-enc-alg string yes
ip ipsec-auth-alg string yes
ip ipsec-comp-alg string yes
ip ipsec-expire-acquire integeryes
ip mtudisc integer yes
ip mtudisctimeout integer yes
icmp maskrepl integer yes
icmp bmcastecho integer yes
icmp errppslimit integer yes
icmp rediraccept integer yes
icmp redirtimeout integer yes
icmp tstamprepl integer yes
ipip allow integer yes
tcp rfc1323 integer yes
tcp ident structure no
tcp keepinittime integer yes
tcp keepidle integer yes
tcp keepintvl integer yes
tcp slowhz integer no
tcp baddynamic array yes
tcp recvspace integer yes
tcp sendspace integer yes
tcp sack integer yes
tcp mssdflt integer yes
tcp rstppslimit integer yes
tcp ackonpush integer yes
tcp ecn integer yes
udp checksum integer yes
udp baddynamic array yes
udp recvspace integer yes
udp sendspace integer yes
gre allow integer yes
gre wccp integer yes
esp enable integer yes
ah enable integer yes
ipcomp enable integer yes
mobileip allow integer yes
etherip allow integer 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.
ip.sourceroute
Returns 1 when forwarding of source-routed packets is en-
abled for the host. This value may only be changed if
the kernel security level is less than 1.
ip.directed-broadcast
Returns 1 if directed broadcast behavior is enabled for
the host.
ip.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.
ip.ipsec-invalid-life
The lifetime of embryonic Security Associations (SAs that
key management daemons have reserved but not fully estab-
lished yet) in seconds. If set to less than or equal to
zero, embryonic SAs will not expire. The default value
is 60.
ip.ipsec-pfs
If set to any non-zero value, the kernel will ask the key
management daemons to use Perfect Forward Secrecy when
establishing IPsec Security Associations. Perfect For-
ward Secrecy makes IPsec Security Associations crypto-
graphically distinct from each other, such that breaking
the key for one such SA does not compromise any others.
Requiring PFS for every security association significant-
ly increases the computational load of isakmpd(8) ex-
changes. The default value is 1.
ip.ipsec-soft-allocs
The number of IPsec flows that can use a security associ-
ation before a message is sent by the kernel to key man-
agement for renegotiation of the security association.
If set to less than or equal to zero, no message is sent
to key management. The default value is 0.
ip.ipsec-allocs
The number of IPsec flows that can use a security associ-
ation before it will expire. If set to less than or
equal to zero, the security association will not expire
because of this counter. The default value is 0.
ip.ipsec-soft-bytes
The number of bytes that will be processed by a security
association before a message is sent by the kernel to key
management for renegotiation of the security association.
If set to less than or equal to zero, no message is sent
to key management. The default value is 0.
ip.ipsec-bytes
The number of bytes that will be processed by a security
association before it will expire. If set to less than
or equal to zero, the security association will not ex-
pire because of this counter. The default value is 0.
ip.ipsec-soft-timeout
The number of seconds after a security association is es-
tablished before a message is sent by the kernel to key
management for renegotiation of the security association.
If set to less than or equal to zero, no message is sent
to key management. The default value is 80000 seconds.
ip.ipsec-timeout
The number of seconds after a security association is es-
tablished before it will expire. If set to less than or
equal to zero, the security association will not expire
because of this timer. The default value is 86400 sec-
onds.
ip.ipsec-soft-firstuse
The number of seconds after a security association is
first used before a message is sent by the kernel to key
management for renegotiation of the security association.
If set to less than or equal to zero, no message is sent
to key management. The default value is 3600 seconds.
ip.ipsec-firstuse
The number of seconds after a security association is
first use before it will expire. If set to less than or
equal to zero, the security association will not expire
because of this timer. The default value is 7200 sec-
onds.
ip.ipsec-enc-alg
This is the default encryption algorithm the kernel will
instruct key management daemons to negotiate when estab-
lishing security associations on behalf of the kernel.
Such security associations can occur as a result of a
process having requested some security level through
setsockopt(2), or as a result of dynamic vpn(8) entries.
Supported values are des, 3des, blowfish, cast128, and
skipjack. If set to any other value, it is left to the
key management daemons to select an encryption algorithm
for the security association. The default value is 3des.
ip.ipsec-auth-alg
This is the default authentication algorithm the kernel
will instruct key management daemons to negotiate when
establishing security associations on behalf of the ker-
nel. Such security associations can occur as a result of
a process having requested some security level through
setsockopt(2), or as a result of dynamic vpn(8) entries.
Supported values are hmac-md5, hmac-sha1, and hmac-
ripemd160. If set to any other value, it is left to the
key management daemons to select an authentiction algo-
rithm for the security association. The default value is
hmac-sha1.
ip.ipsec-expire-acquire
How long should the kernel allow key management to dynam-
ically acquire security associations, before re-sending a
request. The default value is 30 seconds.
ip.ipsec-keep-invalid
How long half-created security associations should be
kept by the kernel (these are created by key management
daemons while negotiating). The default value is 60 sec-
onds.
ip.mtudisc
Returns 1 if Path MTU Discovery is enabled.
ip.mtudisctimeout
Returns the number of seconds in which a route added by
the Path MTU Discovery engine will time out. When the
route times out, the Path MTU Discovery engine will at-
tempt to probe a larger path MTU.
ipip.allow
If set to 0, incoming IP-in-IP packets will not be pro-
cessed. If set to any other value, processing will oc-
cur; furthermore, if set to 2, no checks for spoofing of
loopback addresses will be done. This is useful only for
debugging purposes, and should never be used in produc-
tion systems.
gre.allow
If set to 0, incoming GRE packets will not be processed.
If set to any other value, processing will occur.
gre.wccp
If set to 0, incoming WCCPv1-style GRE packets will not
be processed. If set to any other value, and gre.allow
allows GRE packet processing, WCCPv1-style GRE packets
will be processed.
mobileip.allow
If set to 0, incoming MobileIP encapsulated packets (RFC
2004) will not be processed. If set to any other value,
processing will occur.
etherip.allow
If set to 0, incoming Ethernet-in-IPv4 packets will not
be processed. If set to any other value, processing will
occur.
icmp.maskrepl
Returns 1 if ICMP network mask requests are to be an-
swered.
icmp.errppslimit
The variable specifies the maximum number of outgoing
ICMP error messages per second. ICMP error messages that
exceeded the value are subject to rate limitation and
will not go out from the node. Negative value disables
rate limitation.
icmp.rediraccept
If set to non-zero, the host will accept ICMP redirect
packets. Note that routers will never accept ICMP redi-
rect packets, and the variable is meaningful on IP hosts
only.
icmp.redirtimeout
The variable specifies lifetime of routing entries gener-
ated by incoming ICMP redirect. The default timeout is
10 minutes.
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.sendspace
Returns the default TCP send buffer size.
tcp.recvspace
Returns the default TCP receive buffer size.
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.
tcp.rstppslimit
The variable specifies the maximum number of outgoing TCP
RST packets per second. TCP RST packet that exceeded the
value are subject to rate limitation and will not go out
from the node. Negative value disables rate limitation.
tcp.ackonpush
Returns 1 if tcp segments with the TH_PUSH set are being
acknowledged immediately, otherwise 0.
tcp.ecn
Returns 1 if Explicit Congestion Notifications for TCP
are enabled.
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.
udp.sendspace
Returns the default UDP send buffer size.
udp.recvspace
Returns the default UDP receive buffer size.
PF_INET6
Get or set various global information about IPv6 (Internet
Protocol version 6). 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
ip6 forwarding integer yes
ip6 redirect integer yes
ip6 hlim integer yes
ip6 maxfragpackets integer yes
ip6 accept_rtadv integer yes
ip6 keepfaith integer yes
ip6 log_interval integer yes
ip6 hdrnestlimit integer yes
ip6 dad_count integer yes
ip6 auto_flowlabel integer yes
ip6 defmcasthlim integer yes
ip6 kame_version string no
ip6 use_deprecated integer yes
ip6 rr_prune integer yes
ip6 v6only integer no
ip6 maxfrags integer yes
icmp6 rediraccept integer yes
icmp6 redirtimeout integer yes
icmp6 nd6_prune integer yes
icmp6 nd6_delay integer yes
icmp6 nd6_umaxtries integer yes
icmp6 nd6_mmaxtries integer yes
icmp6 nd6_useloopback integer yes
icmp6 nodeinfo integer yes
icmp6 errppslimit integer yes
icmp6 nd6_maxnudhint integer yes
icmp6 mtudisc_hiwat integer yes
icmp6 mtudisc_lowat integer yes
icmp6 nd6_debug integer yes
The variables are as follows:
ip6.forwarding
Returns 1 when IPv6 forwarding is enabled for the node,
meaning that the node is acting as a router. Returns 0
when IPv6 forwarding is disabled for the node, meaning
that the node is acting as a host. Note that IPv6 de-
fines node behavior for the ``router'' and ``host'' cases
quite differently, and changing this variable during op-
eration may cause serious trouble. Hence, this variable
should only be set at bootstrap time.
ip6.redirect
Returns 1 when ICMPv6 redirects may be sent by the node.
This option is ignored unless the node is routing IP
packets, and should normally be enabled on all systems.
ip6.hlim
The default hop limit value for an IPv6 unicast packet
sourced by the node. This value applies to all the
transport protocols on top of IPv6. Methods for overrid-
ing this value are documented in ip6(4).
ip6.maxfragpackets
The maximum number of fragmented packets the node will
accept. 0 means that the node will not accept any frag-
mented packets. -1 means that the node will accept as
many fragmented packets as it receives. The flag is pro-
vided basically for avoiding possible DoS attacks.
ip6.accept_rtadv
If set to non-zero, the node will accept ICMPv6 router
advertisement packets and autoconfigures address prefixes
and default routers. The node must be a host (not a
router) for the option to be meaningful (see
ip6.forwarding).
ip6.keepfaith
If set to non-zero, enables the ``FAITH'' TCP relay
IPv6-to-IPv4 translator code in the kernel. Refer to
faith(4) and faithd(8) for more details.
ip6.log_interval
This variable permits adjusting the amount of logs gener-
ated by the IPv6 packet forwarding engine. The value in-
dicates the number of seconds of interval which must
elapse between log output.
ip6.hdrnestlimit
The number of IPv6 extension headers permitted on incom-
ing IPv6 packets. If set to 0, the node will accept as
many extension headers as possible.
ip6.dad_count
The variable configures the number of IPv6 DAD
(duplicated address detection) probe packets. These
packets are generated when IPv6 interfaces are first
brought up.
ip6.auto_flowlabel
On connected transport protocol packets, fill IPv6
flowlabel field to help intermediate routers identify
packet flows.
ip6.defmcasthlim
The default hop limit value for an IPv6 multicast packet
sourced by the node. This value applies to all the
transport protocols on top of IPv6. Methods for overrid-
ing this value are documented in ip6(4).
ip6.kame_version
The string identifies the version of the KAME IPv6 stack
implemented in the kernel.
ip6.use_deprecated
The variable controls use of deprecated addresses, speci-
fied in RFC2462 5.5.4.
ip6.rr_prune
The variable specifies interval between IPv6 router
renumbering prefix babysitting in seconds.
ip6.v6only
The variable specifies initial value for IPV6_V6ONLY
socket option for AF_INET6 socket. It is always 1 for
OpenBSD.
ip6.maxfrags
The maximum number of fragments the node will accept. 0
means that the node will not accept any fragments. -1
means that the node will accept as many fragments as it
receives. The flag is provided basically for avoiding
possible DoS attacks.
icmp6.rediraccept
If set to non-zero, the host will accept ICMPv6 redirect
packets. Note that IPv6 routers will never accept ICMPv6
redirect packets, so the variable is only meaningful on
IPv6 hosts, not on routers.
icmp6.redirtimeout
The variable specifies the lifetime of routing entries
generated by incoming ICMPv6 redirects.
icmp6.nd6_prune
The variable specifies interval between IPv6 neighbor
cache babysitting in seconds.
icmp6.nd6_delay
The variable specifies DELAY_FIRST_PROBE_TIME timing con-
stant in IPv6 neighbor discovery specification (RFC2461),
in seconds.
icmp6.nd6_umaxtries
The variable specifies MAX_UNICAST_SOLICIT constant in
IPv6 neighbor discovery specification (RFC2461).
icmp6.nd6_mmaxtries
The variable specifies MAX_MULTICAST_SOLICIT constant in
IPv6 neighbor discovery specification (RFC2461).
icmp6.nd6_useloopback
If set to non-zero, IPv6 will use the loopback interface
for local traffic.
icmp6.nodeinfo
The variable enables responses to ICMPv6 node information
queries. If you set the variable to 0, responses will
not be generated for ICMPv6 node information queries.
Since node information queries can have a security im-
pact, it is possible to fine tune which responses should
be answered. Two separate bits can be set.
1 Respond to ICMPv6 FQDN queries, e.g. ping6 -w.
2 Respond to ICMPv6 node addresses queries, e.g.
ping6 -a.
icmp6.errppslimit
The variable specifies the maximum number of outgoing
ICMPv6 error messages per second. ICMPv6 error messages
that exceeded the value is subject to rate limitation and
will not go out from the node. A negative value will
disable the rate limitation.
icmp6.nd6_maxnudhint
IPv6 neighbor discovery permits upper layer protocols to
supply reachability hints, to avoid unnecessary neighbor
discovery exchanges. The variable defines the number of
consecutive hints the neighbor discovery layer will take.
For example, by setting the variable to 3, neighbor dis-
covery can take take a maximum of 3 consecutive hints.
After receiving 3 hints, the neighbor discovery layer
will instead perform the normal neighbor discovery pro-
cess.
icmp6.mtudisc_hiwat
icmp6.mtudisc_lowat
These variables define the maximum number of routing
table entries, created due to path MTU discovery
(preventing denial-of-service attacks with ICMPv6 too big
messages). After IPv6 path MTU discovery happens, path
MTU information is kept in the routing table. If the
number of routing table entries exceed the value, the
kernel will not attempt to keep the path MTU information.
icmp6.mtudisc_hiwat is used when we have verified ICMPv6
too big messages. icmp6.mtudisc_lowat is used when we
have unverified ICMPv6 too big messages. Verification is
performed by using address/port pairs kept in connected
pcbs. Negative value disables the upper limit.
icmp6.nd6_debug
If set to non-zero, IPv6 neighbor discovery will generate
debugging messages. The debug outputs are useful for di-
agnosing IPv6 interoperability issues. The flag must be
set to 0 for normal operation.
We reuse net.inet.tcp and net.inet.udp for TCP/UDP over IPv6.
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_DDB
Integer information and settable variables are available for the CTL_DDB
level, as described below. More information is also available in ddb(4).
Second level name Type Changeable
DBCTL_RADIX integer yes
DBCTL_MAXWIDTH integer yes
DBCTL_TABSTOP integer yes
DBCTL_PANIC integer yes
DBCTL_CONSOLE integer yes
DBCTL_RADIX
Determines the default radix or base for non-prefixed numbers en-
tered into ddb(4). This variable is also available as the ddb
$radix variable.
DBCTL_MAXWIDTH
Determines the maximum width of a line in ddb(4). This variable
is also available as the ddb $maxwidth variable.
DBCTL_TABSTOP
Width of a tab stop in ddb(4). This variable is also available as
the ddb $tabstops variable.
DBCTL_PANIC
When this variable is set, system panics may drop into the kernel
debugger. As described in securelevel(7), a security level
greater than 1 blocks modification of this variable. ddb(4).
DBCTL_CONSOLE
When this variable is set, an architecture dependent magic key
sequence on the console or a debugger button will permit entry
into the kernel debugger. As described in securelevel(7), a se-
curity level greater than 1 blocks modification of this variable.
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_SWAPENCRYPT swap encrypt values yes
VM_UVMEXP struct uvmexp no
VM_VMMETER 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.
VM_SWAPENCRYPT
Contains statistics about swap encryption. The string and inte-
ger information available for the third level is detailed below.
Third level name Type Changeable
SWPENC_ENABLE integer yes
SWPENC_CREATED integer no
SWPENC_DELETED integer no
SWPENC_ENABLE
Set to 1 to enable swap encryption for all processes. A
0 disables swap encryption. Pages still on swap receive
a grandfather clause. Turning this option on does not
affect legacy swap data already on the disk, but all new-
ly written data will be encrypted. When swap encryption
is turned on, automatic crash(8) dumps are disabled.
SWPENC_CREATED
The number of encryption keys that have been randomly
created. The swap partition is divided into sections of
normally 512KB. Each section has its own encryption key.
SWPENC_DELETED
The number of encryption keys that have been deleted,
thus effectivly erasing the data that has been encrypted
with them. Encryption keys are deleted when their refer-
ence counter reaches zero.
VM_UVMEXP
Contains statistics about the UVM memory management system.
VM_METER:
Contains statistics about the memory management system, using the
old VM format.
CTL_VFS
The string and integer information available for the CTL_VFS 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
VFS_GENERIC vm generic info no
filesystem # filesystem info no
VFS_GENERIC
This second level identifier requests generic information about
the vfs layer. Within it, the following third level identifiers
exist:
Third level name Type Changeable
VFS_MAXTYPENUM int no
VFS_CONF struct vfsconf no
filesystem #
After finding the filesystem dependent vfc_typenum using
VFS_GENERIC with VFS_CONF, it is possible to access filesystem
dependent information.
Some filesystems may contain settings.
ffs
Third level name Type Changeable
FFS_CLUSTERREAD int yes
FFS_CLUSTERWRITE int yes
FFS_REALLOCBLOCKS int yes
FFS_ASYNCFREE int yes
nfs
Third level name Type Changeable
NFS_NFSSTATS struct nfsstats yes
NFS_NIOTHREADS int yes
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 identi-
fiers
<sys/gmon.h> definitions for third level profiling identi-
fiers
<vm/vm_param.h> definitions for second level virtual memory
identifiers
<uvm/uvm_swap_encrypt.h> definitions for third level virtual memory
identifiers
<netinet/in.h> definitions for third level IPv4/v6 identifiers
and fourth level IP and IPv6 identifiers
<netinet/icmp_var.h> definitions for fourth level ICMP identifiers
<netinet/icmp6.h> definitions for fourth level ICMPv6 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 3.3 June 4, 1993 24