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. 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 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 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 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_DDB | ddb/db_var.h | Kernel debugger
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_VFS | ufs/ffs/ffs_extern.h | Virtual file system
CTL_VM | uvm/uvm_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);
    if (sysctl(mib, 2, &maxproc, &len, NULL, 0) == -1)
    	err(1, "sysctl");

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;
    if (sysctl(mib, 2, NULL, &len, NULL, 0) == -1)
    	err(1, "sysctl");
    if ((p = malloc(len)) == NULL)
    	err(1, NULL);
    if (sysctl(mib, 2, p, &len, NULL, 0) == -1)
    	err(1, "sysctl");

  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_CONSOLE | integer | yes
DBCTL_LOG | integer | yes
DBCTL_MAXLINE | integer | yes
DBCTL_MAXWIDTH | integer | yes
DBCTL_PANIC | integer | yes
DBCTL_RADIX | integer | yes
DBCTL_TABSTOP | integer | yes
DBCTL_TRIGGER | integer | yes

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. When running with a securelevel(7) greater than 0, this variable may not be raised.

DBCTL_LOG
    When set, ddb output is also logged in the kernel message buffer.

DBCTL_MAXLINE
    Determines the number of lines to page in ddb(4). This variable is also available as the ddb $lines variable.

DBCTL_MAXWIDTH
    Determines the maximum width of a line in ddb(4). This variable is also available as the ddb $maxwidth variable.

DBCTL_PANIC
    When this variable is set, system panics may drop into the kernel debugger. When running with a securelevel(7) greater than 0, this variable may not be raised.

DBCTL_RADIX
    Determines the default radix or base for non-prefixed numbers entered into ddb(4). This variable is also available as the ddb $radix variable.

DBCTL_TABSTOP
    Width of a tab stop in ddb(4). This variable is also available as the ddb $tabstops variable.

DBCTL_TRIGGER
    When DBCTL_CONSOLE is set, writing to DBCTL_TRIGGER causes the system to enter ddb(4). If securelevel(7) is greater than 0, the process writing to this variable must be running on the console in order to enter ddb(4).

  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_FS
The string and integer information available for the CTL_FS level is detailed below. The changeable column shows whether a process with appropriate 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 securelevel is 0.

  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 privileges may change the value.
Second level name | Type | Changeable
HW_ALLOWPOWERDOWN | integer | yes
HW_BYTEORDER | integer | no
HW_CPUSPEED | integer | no
HW_DISKCOUNT | integer | no
HW_DISKNAMES | string | no
HW_DISKSTATS | struct | no
HW_MACHINE | string | no
HW_MODEL | string | no
HW_NCPU | integer | no
HW_NCPUFOUND | integer | no
HW_PAGESIZE | integer | no
HW_PHYSMEM | integer | no
HW_PHYSMEM64 | int64_t | no
HW_PRODUCT | string | no
HW_SENSORS | node | not applicable
HW_SERIALNO | string | no
HW_SETPERF | integer | yes
HW_USERMEM | integer | no
HW_USERMEM64 | int64_t | no
HW_UUID | string | no
HW_VENDOR | string | no
HW_VERSION | string | no

HW_ALLOWPOWERDOWN
    Some machines generate an interrupt when the power button is pressed and a driver can catch that interrupt. When this variable is set, such an event will cause the system to perform a regular shutdown and power off the machine. When running with a securelevel(7) greater than 0, this variable may not be changed.

HW_BYTEORDER
    The byteorder (4321 or 1234).

HW_CPUSPEED
    The current CPU frequency (in MHz).

HW_DISKCOUNT
    The number of disks currently attached to the system.

HW_DISKNAMES
    A comma-separated list of disk names.

HW_DISKSTATS
    An array of struct diskstats structures containing disk statistics.

HW_MACHINE
    The machine class.

HW_MODEL
    The machine model.

HW_NCPU
    The number of CPUs being used.

HW_NCPUFOUND
    The number of CPUs found.

HW_PAGESIZE
    The software page size.

HW_PHYSMEM
    The total physical memory, in bytes. This variable is deprecated; use HW_PHYSMEM64 instead.

HW_PHYSMEM64
    The total physical memory, in bytes.

HW_PRODUCT
    The product name of the machine.

HW_SENSORS
    Third level comprises an array of struct sensordev structures containing information about devices that may attach hardware monitoring sensors.

    Third, fourth and fifth levels together comprise an array of struct sensor structures containing snapshot readings of hardware monitoring sensors. In such usage, third level indicates the numerical representation of the sensor device name to which the sensor is attached (a device's xname and number are matched with the help of struct sensordev structure above), fourth level indicates sensor type and fifth level is an ordinal sensor number (unique to the specified sensor type on the specified sensor device).

    The sensordev and sensor structures and sensor_type enumeration are defined in <sys/sensors.h>.

HW_SERIALNO
    The serial number of the machine.

HW_SETPERF
    Current CPU performance (percentage).

HW_USERMEM
    The amount of available non-kernel memory in bytes. This variable is deprecated; use HW_USERMEM64 instead.

HW_USERMEM64
    The amount of available non-kernel memory in bytes.

HW_UUID
    The universal unique identification number assigned to the machine.

HW_VENDOR
    The vendor name for this machine.

HW_VERSION
    The version or revision of this machine.

  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 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 | char[] | no
KERN_BOOTTIME | struct timeval | no
KERN_BUFCACHEPERCENT | integer | yes
KERN_CCPU | integer | no
KERN_CLOCKRATE | struct clockinfo | no
KERN_CONSDEV | dev_t | no
KERN_CPTIME | long[CPUSTATES] | no
KERN_CPTIME2 | u_int64_t[CPUSTATES] | no
KERN_CRYPTODEVALLOWSOFT | integer | yes
KERN_DOMAINNAME | string | yes
KERN_EMUL | node | not applicable
KERN_FILE | struct file | no
KERN_FILE2 | struct kinfo_file2 | no
KERN_FORKSTAT | struct forkstat | no
KERN_FSCALE | integer | no
KERN_FSYNC | integer | no
KERN_HOSTID | integer | yes
KERN_HOSTNAME | string | yes
KERN_INTRCNT | node | not applicable
KERN_JOB_CONTROL | integer | no
KERN_MALLOCSTATS | node | no
KERN_MAXCLUSTERS | integer | yes
KERN_MAXFILES | integer | yes
KERN_MAXLOCKSPERUID | integer | yes
KERN_MAXPARTITIONS | integer | no
KERN_MAXPROC | integer | yes
KERN_MAXTHREAD | integer | yes
KERN_MAXVNODES | integer | yes
KERN_MBSTAT | struct mbstat | no
KERN_MSGBUF | char[] | 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_NTHREADS | integer | no
KERN_NUMVNODES | integer | no
KERN_OSRELEASE | string | no
KERN_OSREV | integer | no
KERN_OSTYPE | string | no
KERN_OSVERSION | string | no
KERN_POSIX1 | integer | no
KERN_PROC | struct kinfo_proc | no
KERN_PROC_ARGS | node | not applicable
KERN_PROC_CWD | string | not applicable
KERN_PROF | node | not applicable
KERN_RAWPARTITION | integer | no
KERN_RND | struct rndstats | no
KERN_RTHREADS | integer | yes
KERN_SAVED_IDS | integer | no
KERN_SECURELVL | integer | raise only
KERN_SEMINFO | node | not applicable
KERN_SHMINFO | node | not applicable
KERN_SOMAXCONN | integer | yes
KERN_SOMINCONN | integer | yes
KERN_SPLASSERT | int | yes
KERN_STACKGAPRANDOM | integer | yes
KERN_SYSVIPC_INFO | node | not applicable
KERN_SYSVMSG | integer | no
KERN_SYSVSEM | integer | no
KERN_SYSVSHM | integer | no
KERN_TIMECOUNTER | node | not applicable
KERN_TTY | node | not applicable
KERN_TTYCOUNT | integer | no
KERN_USERASYMCRYPTO | integer | yes
KERN_USERCRYPTO | integer | yes
KERN_USERMOUNT | integer | yes
KERN_VERSION | string | no
KERN_VNODE | struct e_vnode | no
KERN_WATCHDOG | node | not applicable

KERN_ARGMAX
    The maximum number of bytes allowed among the arguments to exec(3).

KERN_ARND
    Returns a maximum of 256 random bytes from the kernel using the arc4random(9) 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_BUFCACHEPERCENT
    The maximum percentage of physical memory the buffer cache may use; the default is 20%.

KERN_CCPU
    The scheduler exponential decay value.

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 clock skew rate.

KERN_CONSDEV
    The console device.

KERN_CPTIME
    An array of longs of size CPUSTATES is returned, containing statistics about the number of ticks spent by the system in interrupt processing, user processes ( nice(1) or normal), system processing, or idling.

KERN_CPTIME2
    Similar to KERN_CPTIME, but obtains information from only the single CPU specified by the third level name given.

KERN_CRYPTODEVALLOWSOFT
    Permits userland to use /dev/crypto even if there is no hardware crypto accelerator in the system.

KERN_DOMAINNAME
    Get or set the YP domain name.

KERN_EMUL
    Enable binary emulation.
    Third level name | Type | Changeable
    KERN_EMUL_ENABLED | integer | yes
    KERN_EMUL_NAME | string | no
    KERN_EMUL_NEMULS | integer | no

    Third level names in KERN_EMUL other than KERN_EMUL_NEMULS refer to a specific emulation available in the kernel. Valid values range from 1 to the return value of KERN_EMUL_NEMULS. The fourth level names available are KERN_EMUL_NAME, which returns a string with the emulation name, and KERN_EMUL_ENABLED, which is an adjustable integer.

    Note that using this interface exposes duplicate entries which are consolidated by the userland frontend.

KERN_FILE
    Return the entire file table. This name is deprecated, as the layout of the returned structures is not a stable ABI; use KERN_FILE2 instead. 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_FILE2
    Like KERN_FILE but an array of struct kinfo_file2 structures is returned. The third and fourth level names are as follows:
    Third level name | Fourth level is:
    KERN_FILE_BYFILE | Zero
    KERN_FILE_BYPID | A process ID
    KERN_FILE_BYUID | A user ID

    The fifth level name is the size of the struct kinfo_file2 and the sixth level name is the number of structures to return.

KERN_FORKSTAT
    A struct forkstat structure is returned. This structure contains information about the number of fork(2), vfork(2), and __tfork(2) system calls as well as kernel thread creations since system startup, and the number of pages of virtual memory involved in each.

KERN_FSCALE
    The kernel fixed-point scale factor.

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_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_BUCKET | node
    KERN_MALLOC_BUCKETS | string
    KERN_MALLOC_KMEMNAMES | string
    KERN_MALLOC_KMEMSTATS | node

    The variables are as follows:

    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_BUCKETS
        Return a comma-separated list of the bucket sizes used by the kernel.

    KERN_MALLOC_KMEMNAMES
        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_MAXCLUSTERS
    The maximum number of mbuf(9) clusters that may be allocated.

KERN_MAXFILES
    The maximum number of open files that may be open in the system.

KERN_MAXLOCKSPERUID
    The maximum number of file locks per user; the default is 1024.

KERN_MAXPARTITIONS
    The maximum number of partitions allowed per disk.

KERN_MAXPROC
    The maximum number of simultaneous processes the system will allow.

KERN_MAXTHREAD
    The maximum number of simultaneous threads the system will allow.

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_MSGBUF
    Returns a buffer containing kernel log messages.

KERN_MSGBUFSIZE
    The size of the kernel message buffer.

KERN_NCHSTATS
    A struct nchstats structure is returned. This structure contains information about the filename to inode(5) mapping cache.

KERN_NFILES
    Number of open files.

KERN_NGROUPS
    The maximum number of supplemental groups.

KERN_NOSUIDCOREDUMP
    Whether a process may dump core after changing user or group ID:
    value | condition | dump core to
    0 | euid == 0 | current directory
    1 | never |
    2 | always | /var/crash

KERN_NPROCS
    The number of entries in the kernel process table.

KERN_NSELCOLL
    Number of select(2) collisions.

KERN_NTHREADS
    The number of entries in the kernel thread table.

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_OSVERSION
    The kernel build version.

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_KTHREAD | A kernel thread
    KERN_PROC_PID | A process ID
    KERN_PROC_PGRP | A process group
    KERN_PROC_RUID | A real user ID
    KERN_PROC_SESSION | A session PID
    KERN_PROC_TTY | A tty device
    KERN_PROC_UID | A user ID

    The fifth level name is the size of the struct kinfo_proc and the sixth level name is the number of structures to return.

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_ENV
    KERN_PROC_NARGV
    KERN_PROC_NENV

    KERN_PROC_NARGV and KERN_PROC_NENV return the number of elements as an int in the argv or env array. KERN_PROC_ARGV returns the argv array and KERN_PROC_ENV returns the environ array. The buffer pointed to by oldp is filled with an array of char pointers followed by the strings themselves. The last char pointer is a NULL pointer.

KERN_PROC_CWD
    Return the current working directory of a process. The third level name is the target process ID. A NUL-terminated string is returned.

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 are detailed below. The changeable column shows whether a process with appropriate privileges may change the value.
    Third level name | Type | Changeable
    GPROF_COUNT | u_short[] | yes
    GPROF_FROMS | u_short[] | yes
    GPROF_GMONPARAM | struct gmonparam | no
    GPROF_STATE | integer | yes
    GPROF_TOS | struct tostruct | yes

    The variables are as follows:

    GPROF_COUNT
        Array of statistical program counter counts.

    GPROF_FROMS
        Array indexed by program counter of call-from points.

    GPROF_GMONPARAM
        Structure giving the sizes of the above arrays.

    GPROF_STATE
        Returns GMON_PROF_ON or GMON_PROF_OFF to show that profiling is running or stopped.

    GPROF_TOS
        Array of struct tostruct describing destination of calls and their counts.

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_RTHREADS
    Enable the syscalls needed for kernel level threading. Experimental.

KERN_SAVED_IDS
    Returns 1 if saved set-group-ID and saved set-user-ID are available.

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 compiled 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 appropriate privileges may change the value.
    Third level name | Type | Changeable
    KERN_SEMINFO_SEMAEM | integer | no
    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

    The variables are as follows:

    KERN_SEMINFO_SEMAEM
        The adjust on exit maximum value.

    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_SHMINFO
    Return the elements of struct shminfo. If the kernel is not compiled with System V style shared memory support, attempts to retrieve any of the KERN_SHMINFO values will fail with EOPNOTSUPP. The third level names for the elements of struct shminfo are detailed below. The changeable column shows whether a process with appropriate privileges may change the value.
    Third level name | Type | Changeable
    KERN_SHMINFO_SHMALL | integer | yes
    KERN_SHMINFO_SHMMAX | integer | yes
    KERN_SHMINFO_SHMMIN | integer | yes
    KERN_SHMINFO_SHMMNI | integer | yes
    KERN_SHMINFO_SHMSEG | integer | yes

    The variables are as follows:

    KERN_SHMINFO_SHMALL
        The maximum amount of total shared memory allowed in the system (in pages).

    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_SOMAXCONN
    Upper bound on the number of half-open connections a process can allow to be associated with a socket, using listen(2). The default 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 default value is 80.

KERN_SPLASSERT
    Modify the system interrupt priority level. Valid values are:

    0   Disable error checking.
    1   Print a message if an error is detected.
    2   Print a message if an error is detected, and a stack trace if possible.
    3   The same as 2, but also drop into the kernel debugger.

    Any other value causes a system panic on errors. See splassert(9) for more information.

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 also means bigger waste of memory.

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 facility. The msg_sysctl_info structure is defined in <sys/msg.h>.

    KERN_SYSVIPC_SEM_INFO
        Return information on the System V style semaphore facility. 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 available 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 shared memory functionality is available on this system, otherwise 0.

KERN_TIMECOUNTER
    Return statistics information about the kernel time counter. 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_TIMECOUNTER_CHOICE | string | no
    KERN_TIMECOUNTER_HARDWARE | string | yes
    KERN_TIMECOUNTER_TICK | integer | no
    KERN_TIMECOUNTER_TIMESTEPWARNINGS | integer | yes

    The variables are as follows:

    KERN_TIMECOUNTER_CHOICE
        Get the list of kernel time counter sources and their claimed quality (higher is better).

    KERN_TIMECOUNTER_HARDWARE
        Get or set the kernel time counter source by name.

    KERN_TIMECOUNTER_TICK
        Get the number of times we have reset the kernel time counter information.

    KERN_TIMECOUNTER_TIMESTEPWARNINGS
        Get or set a flag to log a message when the kernel time is stepped.

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_INFO | struct itty | no
    KERN_TTY_NPTYS | integer | no
    KERN_TTY_MAXPTYS | integer | yes
    KERN_TTY_TKCANCC | int64_t | no
    KERN_TTY_TKNIN | int64_t | no
    KERN_TTY_TKNOUT | int64_t | no
    KERN_TTY_TKRAWCC | int64_t | no

    The variables are as follows:

    KERN_TTY_INFO
        Returns an array of struct itty structures containing tty statistics.

    KERN_TTY_MAXPTYS
        The maximum number of pty(4) devices supported by the kernel. This is the upper bound on KERN_TTY_NPTYS.

    KERN_TTY_NPTYS
        The current number of pty(4) devices allocated by the kernel.

    KERN_TTY_TKCANCC
        Returns the number of input characters in canonical mode.

    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
        Returns the number of input characters in raw mode.

KERN_TTYCOUNT
    Number of available tty(4) devices.

KERN_USERASYMCRYPTO
    Permits userland to use /dev/crypto for cryptographic support for asymmetric (public) key operations via hardware cryptographic devices. KERN_USERCRYPTO (see below) must also be set.

KERN_USERCRYPTO
    Permits userland to use /dev/crypto for cryptographic support via hardware cryptographic 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 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 contains the kernel address of a vnode (struct vnode *) followed by the vnode itself (struct vnode).

KERN_WATCHDOG
    Return information on hardware watchdog timers. If the kernel does not support a hardware watchdog timer, attempts to retrieve or set any of the KERN_WATCHDOG values will fail with EOPNOTSUPP.
    Third level name | Type | Changeable
    KERN_WATCHDOG_AUTO | integer | yes
    KERN_WATCHDOG_PERIOD | integer | yes

    The variables are as follows:

    KERN_WATCHDOG_AUTO
        If set to 1, the kernel refreshes the watchdog timer periodically. If set to 0, a userland process must ensure that the watchdog timer gets refreshed by setting the KERN_WATCHDOG_PERIOD variable.

    KERN_WATCHDOG_PERIOD
        The period of the watchdog timer in seconds. Set to 0 to disable the watchdog timer.

  CTL_MACHDEP
The set of variables defined is architecture dependent. Most architectures 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 detailed below. The changeable column shows whether a process with appropriate 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_KEY | key management | no
PF_PIPEX | PIPEX 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 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_DUMP | None
    NET_RT_FLAGS | rtflags
    NET_RT_IFLIST | None
    NET_RT_STATS | None

    An optional seventh level name can be provided to select the routing table on which to run the operation. If not provided, the table with ID 0 is used.

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
    ah | enable | integer | yes
    bpf | bufsize | integer | yes
    bpf | maxbufsize | integer | yes
    carp | allow | integer | yes
    carp | log | integer | yes
    carp | preempt | integer | yes
    divert | recvspace | integer | yes
    divert | sendspace | integer | yes
    esp | enable | integer | yes
    esp | udpencap | integer | yes
    esp | udpencap_port | integer | yes
    etherip | allow | integer | yes
    gre | allow | integer | yes
    gre | wccp | integer | yes
    icmp | bmcastecho | integer | yes
    icmp | errppslimit | integer | yes
    icmp | maskrepl | integer | yes
    icmp | rediraccept | integer | yes
    icmp | redirtimeout | integer | yes
    icmp | stats | structure | no
    icmp | tstamprepl | integer | yes
    ip | directed-broadcast | integer | yes
    ip | encdebug | integer | yes
    ip | forwarding | integer | yes
    ip | ipsec-allocs | integer | yes
    ip | ipsec-auth-alg | string | yes
    ip | ipsec-bytes | integer | yes
    ip | ipsec-comp-alg | string | yes
    ip | ipsec-enc-alg | string | yes
    ip | ipsec-expire-acquire | integer | yes
    ip | ipsec-firstuse | integer | yes
    ip | ipsec-invalid-life | integer | yes
    ip | ipsec-pfs | integer | yes
    ip | ipsec-soft-allocs | integer | yes
    ip | ipsec-soft-bytes | integer | yes
    ip | ipsec-soft-firstuse | integer | yes
    ip | ipsec-soft-timeout | integer | yes
    ip | ipsec-timeout | integer | yes
    ip | maxqueue | integer | yes
    ip | mforwarding | integer | yes
    ip | mtudisc | integer | yes
    ip | mtudisctimeout | integer | yes
    ip | multipath | integer | yes
    ip | portfirst | integer | yes
    ip | porthifirst | integer | yes
    ip | porthilast | integer | yes
    ip | portlast | integer | yes
    ip | redirect | integer | yes
    ip | sourceroute | integer | yes
    ip | stats | structure | no
    ip | ttl | integer | yes
    ipcomp | enable | integer | yes
    ipip | allow | integer | yes
    mobileip | allow | integer | yes
    tcp | ackonpush | integer | yes
    tcp | always_keepalive | integer | yes
    tcp | baddynamic | array | yes
    tcp | ecn | integer | yes
    tcp | ident | structure | no
    tcp | keepidle | integer | yes
    tcp | keepinittime | integer | yes
    tcp | keepintvl | integer | yes
    tcp | mssdflt | integer | yes
    tcp | reasslimit | integer | yes
    tcp | rfc1323 | integer | yes
    tcp | rfc3390 | integer | yes
    tcp | rstppslimit | integer | yes
    tcp | sack | integer | yes
    tcp | slowhz | integer | no
    tcp | stats | structure | no
    tcp | synbucketlimit | integer | yes
    tcp | syncachelimit | integer | yes
    udp | baddynamic | array | yes
    udp | checksum | integer | yes
    udp | recvspace | integer | yes
    udp | sendspace | integer | yes
    udp | stats | structure | no

    The variables are as follows:

    ah.enable
        If set to 1, enable the Authentication Header (AH) IPsec protocol. Enabled by default. See ipsec(4) for more information.

    bpf.bufsize
        The initial size of bpf(4) buffers.

    bpf.maxbufsize
        The maximum size a user may request a bpf(4) buffer to be.

    carp.allow
        If set to 0, incoming carp(4) packets will not be processed. If set to any other value, processing will occur. Enabled by default.

    carp.log
        Controls the verbosity of carp(4) logging. May be a value between 0 and 7 corresponding with syslog(3) priorities. The default value is 2.

    carp.preempt
        If set to 0, carp(4) will not attempt to become master if it is receiving advertisements from another active master. If set to any other value, carp will become master of the virtual host if it believes it can send advertisements more frequently than the current master. Disabled by default.

    divert.recvspace
        Returns the default divert receive buffer size.

    divert.sendspace
        Returns the default divert send buffer size.

    esp.enable
        If set to 1, enable the Encapsulating Security Payload (ESP) IPsec protocol. Enabled by default. See ipsec(4) for more information.

    esp.udpencap
        If set to 1, enable processing of UDP encapsulated ESP packets. Enabled by default.

    esp.udpencap_port
        Contains the value of the UDP port that triggers decapsulation for incoming UDP encapsulated ESP packets. The default port is 4500.

    etherip.allow
        If set to 0, incoming Ethernet-in-IPv4 packets will not be processed. If set to any other value, processing will occur.

    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.

    icmp.bmcastecho
        If set to 1, respond to ICMP echo requests destined for broadcast and multicast addresses. Note, enabling this could open a system to a type of denial of service attack called "smurfing", and is thus not advised.

    icmp.errppslimit
        This variable specifies the maximum number of outgoing ICMP error messages per second. ICMP error messages exceeding this value are subject to rate limitation and will not go out from the node. A negative value disables rate limitation.

    icmp.maskrepl
        Returns 1 if ICMP network mask requests are to be answered.

    icmp.rediraccept
        If set to non-zero, the host will accept ICMP redirect packets. Note that routers will never accept ICMP redirect packets, and the variable is meaningful on IP hosts only.

    icmp.redirtimeout
        This variable specifies the lifetime of routing entries generated by incoming ICMP redirects. The default timeout is 10 minutes.

    icmp.stats
        Returns the ICMP statistics in a struct icmpstat.

    icmp.tstamprepl
        If set to 1, reply to ICMP timestamp requests. If set to 0, ignore timestamp requests.

    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.forwarding
        If set to 1, then IP forwarding is enabled for the host, indicating the host is acting as a router. If set to 2, then IP forwarding is restricted to traffic that has been IPsec encapsulated or decapsulated by the host. The default value is 0.

    ip.ipsec-allocs
        The number of IPsec flows that can use a security association before it expires. 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-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 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 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 authentication algorithm for the security association. The default value is hmac-sha1.

    ip.ipsec-bytes
        The number of bytes that will be processed by a security association before it expires. 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-comp-alg
        The compression algorithm to use with an IP Compression Association (IPCA). Possible values are “deflate” and “lzs”. Note that lzs is only available with hifn(4). See ipsecctl(8) for more information.

    ip.ipsec-enc-alg
        This is the default encryption algorithm the kernel will instruct key management daemons to negotiate when establishing 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 entries. Supported values are aes, des, 3des, blowfish and cast128. 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 aes.

    ip.ipsec-expire-acquire
        How long the kernel should allow key management to dynamically acquire security associations before re-sending a request. The default value is 30 seconds.

    ip.ipsec-firstuse
        The number of seconds after a security association is first used before it expires. If set to less than or equal to zero, the security association will not expire because of this timer. The default value is 7200 seconds.

    ip.ipsec-invalid-life
        The lifetime of embryonic Security Associations (SAs that key management daemons have reserved but not fully established 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 Forward Secrecy makes IPsec Security Associations cryptographically distinct from each other, such that breaking the key for one such SA does not compromise any others. Requiring PFS for every security association significantly increases the computational load of isakmpd(8) exchanges. The default value is 1.

    ip.ipsec-soft-allocs
        The number of IPsec flows that can use 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-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-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-soft-timeout
        The number of seconds after a security association is established 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 established 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 seconds.

    ip.maxqueue
        Fragment flood protection. Sets the maximum number of unassembled IP fragments in the fragment queue.

    ip.mforwarding
        If set to 1, then multicast forwarding is enabled for the host. The default is 0.

    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 attempt to probe a larger path MTU.

    ip.multipath
        This variable enables multipath routing for IPv4 addresses. If set to 0, only the first route selected will be used for a given destination regardless of how many routes exist in the routing table.

    ip.portfirst
        Minimum registered port number for TCP/UDP port allocation. Registered ports can be used by ordinary user processes or programs executed by ordinary users. Cannot be less than 1024 or greater than 49151. Must be less than ip.portlast.

    ip.porthifirst
        Minimum dynamic/private port number for TCP/UDP port allocation. Dynamic/private ports can be used by ordinary user processes or programs executed by ordinary users. Cannot be less than 49152 or greater than 65535. Must be less than ip.porthilast.

    ip.porthilast
        Maximum dynamic/private port number for TCP/UDP port allocation. Dynamic/private ports can be used by ordinary user processes or programs executed by ordinary users. Cannot be less than 49152 or greater than 65535. Must be greater than ip.porthifirst.

    ip.portlast
        Maximum registered port number for TCP/UDP port allocation. Registered ports can be used by ordinary user processes or programs executed by ordinary users. Cannot be less than 1024 or greater than 49151. Must be greater than ip.portfirst.

    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.sourceroute
        Returns 1 when forwarding of source-routed packets is enabled for the host. As detailed in securelevel(7), this variable may not be changed if the securelevel is 0.

    ip.stats
        Returns the IP statistics in a struct ipstat.

    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.

    ipcomp.enable
        Enable the IPComp protocol. See ipsecctl(8) for more information.

    ipip.allow
        If set to 0, incoming IP-in-IP packets will not be processed. If set to any other value, processing will occur; 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 production systems.

    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.

    tcp.ackonpush
        Returns 1 if TCP segments with the TH_PUSH flag set are being acknowledged immediately, otherwise 0.

    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.ecn
        Returns 1 if Explicit Congestion Notifications for TCP are enabled.

    tcp.ident
        A struct tcp_ident_mapping specifying a local and foreign endpoint of a TCP socket is filled in with the effective and real UIDs of the process that owns the socket. If no such socket exists, then the effective and real UID values are both set to -1.

    tcp.keepidle
        If the socket option SO_KEEPALIVE has been set on a socket, then this value specifies how much time a connection needs to be idle before keepalives are sent. See also tcp.slowhz.

    tcp.keepinittime
        Time to keep alive the initial SYN packet of a TCP handshake.

    tcp.keepintvl
        Time after a keepalive probe is sent until, in the absence of any response, another probe is sent. See also tcp.slowhz.

    tcp.always_keepalive
        Act as if the option SO_KEEPALIVE was set on all TCP sockets.

    tcp.mssdflt
        The maximum segment size that is used as default for non-local connections. The default value is 512.

    tcp.reasslimit
        The maximum number of out-of-order TCP segments the system will store for reassembly.

    tcp.rfc1323
        Returns 1 if RFC 1323 extensions to TCP are enabled.

    tcp.rfc3390
        Returns 1 if the TCP Initial Window is increased to 4 * MSS or 4380 bytes, as specified in RFC 3390. Returns 2 if the TCP Initial Window is increased to 10 * MSS or 14600 bytes, as specified in draft-ietf-tcpm-initcwnd.

    tcp.rstppslimit
        This variable specifies the maximum number of outgoing TCP RST packets per second. TCP RST packets exceeding this value are subject to rate limitation and will not go out from the node. A negative value disables rate limitation.

    tcp.sack
        Returns 1 if RFC 2018 Selective Acknowledgements are enabled.

    tcp.slowhz
        The units for tcp.keepidle and tcp.keepintvl; those variables 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.stats
        Returns the TCP statistics in a struct tcpstat.

    tcp.synbucketlimit
        The maximum number of entries allowed per hash bucket in the TCP SYN cache.

    tcp.syncachelimit
        The maximum number of entries allowed in the TCP SYN cache.

    udp.baddynamic
        Analogous to tcp.baddynamic but for UDP sockets.

    udp.checksum
        Returns 1 when UDP checksums are being computed and checked. Disabling UDP checksums is strongly discouraged.

    udp.recvspace
        Returns the default UDP receive buffer size.

    udp.sendspace
        Returns the default UDP send buffer size.

    udp.stats
        Returns the UDP statistics in a struct udpstat.

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
    icmp6 | errppslimit | integer | yes
    icmp6 | mtudisc_hiwat | integer | yes
    icmp6 | mtudisc_lowat | integer | yes
    icmp6 | nd6_debug | integer | yes
    icmp6 | nd6_delay | integer | yes
    icmp6 | nd6_maxnudhint | integer | yes
    icmp6 | nd6_mmaxtries | integer | yes
    icmp6 | nd6_prune | integer | yes
    icmp6 | nd6_umaxtries | integer | yes
    icmp6 | nd6_useloopback | integer | yes
    icmp6 | nodeinfo | integer | yes
    icmp6 | rediraccept | integer | yes
    icmp6 | redirtimeout | integer | yes
    ip6 | accept_rtadv | integer | yes
    ip6 | auto_flowlabel | integer | yes
    ip6 | dad_count | integer | yes
    ip6 | defmcasthlim | integer | yes
    ip6 | forwarding | integer | yes
    ip6 | hdrnestlimit | integer | yes
    ip6 | hlim | integer | yes
    ip6 | kame_version | string | no
    ip6 | keepfaith | integer | yes
    ip6 | log_interval | integer | yes
    ip6 | maxfragpackets | integer | yes
    ip6 | maxfrags | integer | yes
    ip6 | mforwarding | integer | yes
    ip6 | multicast_mtudisc | integer | yes
    ip6 | multipath | integer | yes
    ip6 | redirect | integer | yes
    ip6 | rr_prune | integer | yes
    ip6 | use_deprecated | integer | yes
    ip6 | v6only | integer | no

    The variables are as follows:

    icmp6.errppslimit
        This variable specifies the maximum number of outgoing ICMPv6 error messages per second. ICMPv6 error messages exceeding this value are subject to rate limitation and will not go out from the node. A negative value will disable the rate limitation.

    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 exceeds this 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. A negative value disables the upper limit.

    icmp6.nd6_debug
        If set to non-zero, IPv6 neighbor discovery will generate debugging messages. The debug output is useful for diagnosing IPv6 interoperability issues. The flag must be set to 0 for normal operation.

    icmp6.nd6_delay
        This variable specifies the DELAY_FIRST_PROBE_TIME timing constant in IPv6 neighbor discovery specification (RFC 2461), in seconds.

    icmp6.nd6_maxnudhint
        IPv6 neighbor discovery permits upper layer protocols to supply reachability hints, to avoid unnecessary neighbor discovery exchanges. This variable defines the number of consecutive hints the neighbor discovery layer will take. For example, by setting the variable to 3, neighbor discovery will take a maximum of 3 consecutive hints. After receiving 3 hints, the neighbor discovery layer will instead perform the normal neighbor discovery process.

    icmp6.nd6_mmaxtries
        This variable specifies the MAX_MULTICAST_SOLICIT constant in IPv6 neighbor discovery specification (RFC 2461).

    icmp6.nd6_prune
        This variable specifies the interval between IPv6 neighbor cache babysitting in seconds.

    icmp6.nd6_umaxtries
        This variable specifies the MAX_UNICAST_SOLICIT constant in IPv6 neighbor discovery specification (RFC 2461).

    icmp6.nd6_useloopback
        If set to non-zero, IPv6 will use the loopback interface for local traffic.

    icmp6.nodeinfo
        This variable enables responses to ICMPv6 node information queries. If set to 0, responses will not be generated for ICMPv6 node information queries. Since node information queries can have a security impact, 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.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.

    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.auto_flowlabel
        On connected transport protocol packets, fill the IPv6 flowlabel field to help intermediate routers identify packet flows.

    ip6.dad_count
        This variable configures the number of IPv6 DAD (duplicated address detection) probe packets. These packets are generated when IPv6 interfaces are first brought up.

    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 overriding this value are documented in ip6(4).

    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 defines node behavior for the “router” and “host” cases quite differently, and changing this variable during operation may cause serious trouble. Hence, this variable should only be set at bootstrap time.

    ip6.hdrnestlimit
        The number of IPv6 extension headers permitted on incoming IPv6 packets. If set to 0, the node will accept as many extension headers as possible.

    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 overriding this value are documented in ip6(4).

    ip6.kame_version
        This string identifies the version of the KAME IPv6 stack implemented in the kernel.

    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 generated by the IPv6 packet forwarding engine. The value indicates the number of seconds of interval which must elapse between log output.

    ip6.maxfragpackets
        The maximum number of fragmented packets the node will accept. 0 means that the node will not accept any fragmented packets. -1 means that the node will accept as many fragmented packets as it receives. The flag is provided basically for avoiding possible DoS attacks.

    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.

    ip6.mforwarding
        If set to 1, then multicast forwarding is enabled for the host. The default is 0.

    ip6.multicast_mtudisc
        This variable controls generation of ICMPv6 Too Big messages when the machine is performing as an IPv6 multicast router. If set to 1, an ICMPv6 Too Big message will be generated for multicast packets which were too big to be forwarded. If set to 0, the ICMPv6 Too Big message will be suppressed.

    ip6.multipath
        This variable enables multipath routing for IPv6 addresses. If set to 0, only the first route selected will be used for a given destination regardless of how many routes exist in the routing table.

    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.rr_prune
        This variable specifies the interval between IPv6 router renumbering prefix babysitting in seconds.

    ip6.use_deprecated
        This variable controls the use of deprecated addresses, specified in RFC 2462 5.5.4.

    ip6.v6only
        The variable specifies the initial value for the IPV6_V6ONLY socket option for an AF_INET6 socket. It is always 1 for OpenBSD.

    We reuse net.inet.tcp and net.inet.udp for TCP/UDP over IPv6.

PF_KEY
    Return ipsec(4) database dumps. The second level name is PF_KEY_V2. The third level name selects the database as follows:

    NET_KEY_SADB_DUMP
        Security Association database (SADB).
    NET_KEY_SPD_DUMP
        IPsec flow database (SPD).

PF_PIPEX
    Get or set global information about PIPEX.

    The currently defined variable names are:
    Third level name | Type | Changeable
    PIPEXCTL_ENABLE | integer | yes

    PIPEXCTL_ENABLE
        If set to 1, enable PIPEX processing. The default is 0.

  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 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_C_BIND | integer | no
USER_POSIX2_C_DEV | integer | no
USER_POSIX2_CHAR_TERM | 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 parentheses by the expr(1) utility.

USER_LINE_MAX
    The maximum length in bytes of a text-processing utility's input line.

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_CHAR_TERM
    Return 1 if the system supports at least one terminal type capable of all operations described in POSIX 1003.2, 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 POSIX 1003.2 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 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 time zone.

  CTL_VFS
The string and integer information available for the CTL_VFS level is detailed below. The changeable column shows whether a process with appropriate privileges may change the value.
Second level name | Type | Changeable
VFS_GENERIC | VFS 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_CONF | struct vfsconf | no
    VFS_MAXTYPENUM | int | 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_ASYNCFREE | integer | yes
        FFS_CLUSTERREAD | integer | yes
        FFS_CLUSTERWRITE | integer | yes
        FFS_DIRHASH_DIRSIZE | integer | yes
        FFS_DIRHASH_MAXMEM | integer | yes
        FFS_DIRHASH_MEM | integer | no
        FFS_MAXSOFTDEPS | integer | yes
        FFS_REALLOCBLOCKS | integer | yes
        FFS_SD_BLK_LIMIT_HIT | integer | yes
        FFS_SD_BLK_LIMIT_PUSH | integer | yes
        FFS_SD_DIR_ENTRY | integer | yes
        FFS_SD_DIRECT_BLK_PTRS | integer | yes
        FFS_SD_INDR_BLK_PTRS | integer | yes
        FFS_SD_INO_LIMIT_HIT | integer | yes
        FFS_SD_INO_LIMIT_PUSH | integer | yes
        FFS_SD_INODE_BITMAP | integer | yes
        FFS_SD_SYNC_LIMIT_HIT | integer | yes
        FFS_SD_TICKDELAY | integer | yes
        FFS_SD_WORKLIST_PUSH | integer | yes

        FFS_CLUSTERREAD
            Enable combining multiple reads into one request to improve performance.

        FFS_CLUSTERWRITE
            Enable combining multiple writes into one request.

        FFS_DIRHASH_DIRSIZE
            The minimum size of a directory, in bytes, before it is considered for hashing.

        FFS_DIRHASH_MAXMEM
            The maximum amount of memory, in bytes, to be used for storing directory hashes.

        FFS_DIRHASH_MEM
            The amount of memory currently used by all directory hashes.

        FFS_REALLOCBLOCKS
            When enabled, the kernel will attempt to relocate growing files so that they are contiguous on disk, reducing fragmentation.

    NFS
        Third level name | Type | Changeable
        NFS_NFSSTATS | struct nfsstats | yes
        NFS_NIOTHREADS | int | yes

        NFS_NIOTHREADS
            The number of NFS I/O kernel threads. Should be set high enough for the server to handle the maximum level of concurrency from its clients, typically four to six.

  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 privileges may change the value.
Second level name | Type | Changeable
VM_ANONMIN | integer | yes
VM_LOADAVG | struct loadavg | no
VM_MAXSLP | integer | no
VM_METER | struct vmtotal | no
VM_NKMEMPAGES | integer | no
VM_PSSTRINGS | struct psstrings | no
VM_SWAPENCRYPT | swap encrypt values | yes
VM_USPACE | integer | no
VM_UVMEXP | struct uvmexp | no
VM_VNODEMIN | integer | yes
VM_VTEXTMIN | integer | yes

VM_ANONMIN
    Percentage of physical memory available for pages which contain anonymous mapping.

VM_LOADAVG
    Return the load average history. The returned data consists of a struct loadavg.

VM_MAXSLP
    The time for a process to be blocked before being swappable, in seconds.

VM_METER
    Return the system wide virtual memory statistics. The returned data consists of a struct vmtotal.

VM_NKMEMPAGES
    Number of pages in kmem_map.

VM_PSSTRINGS
    Returns the address of the process struct ps_strings. The ps(1) program uses it to locate the argument and environment strings.

VM_SWAPENCRYPT
    Contains statistics about swap encryption. The string and integer information available for the third level is detailed below.
    Third level name | Type | Changeable
    SWPENC_CREATED | integer | no
    SWPENC_DELETED | integer | no
    SWPENC_ENABLE | integer | yes

    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 effectively erasing the data that has been encrypted with them. Encryption keys are deleted when their reference counter reaches zero.

    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 newly written data will be encrypted. When swap encryption is turned on, automatic crash(8) dumps are disabled.

VM_USPACE
    The number of bytes allocated for each kernel stack.

VM_UVMEXP
    Contains statistics about the UVM memory management system.

VM_VNODEMIN
    Percentage of physical memory available for pages which contain cached file data.

VM_VTEXTMIN
    Percentage of physical memory available for pages which contain cached executable data.

RETURN VALUES
If the call to sysctl() is unsuccessful, -1 is returned and errno is set appropriately.

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
<ufs/ffs/ffs_extern.h>
    definitions for third level virtual file system identifiers (ffs)
<nfs/nfs.h>
    definitions for third level virtual file system identifiers (nfs)
<uvm/uvm_param.h>
    definitions for second level virtual memory identifiers
<uvm/uvm_swap_encrypt.h>
    definitions for third level virtual memory identifiers
<net/pipex.h>
    definitions for third level PIPEX 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
<machine/cpu.h>
    definitions for second level CPU 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 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.

[ENOENT]
    The mib specified does not exist, or exceeds the range that is possible.

[ENXIO]
    If the mib is a sparsely populated array, this error may be returned instead.

[ENOTDIR]
    The name array specifies an intermediate rather than terminal 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 kernel security level is made.

[ESRCH]
    No process could be found which corresponds to the given process ID.

SEE ALSO
pathconf(2), sysconf(3), ddb(4), sysctl.conf(5), securelevel(7), sysctl(8)

HISTORY
The sysctl() function first appeared in 4.4BSD.