SYSCTL(7)

NAME
sysctl - system information variables

DESCRIPTION
The sysctl(3) library function and the sysctl(8) utility are used to get and set values of system variables, maintained by the kernel. The variables are organized in a tree and identified by a sequence of numbers, conventionally separated by dots with the topmost identifier at the left side. The numbers have corresponding text names. The sysctlnametomib(3) function or the -M argument to the sysctl(8) utility can be used to convert the text representation to the numeric one.

The individual sysctl variables are described below, both the textual and numeric form where applicable. The textual names can be used as argument to the sysctl(8) utility and in the file /etc/sysctl.conf. The numeric names are usually defined as preprocessor constants and are intended for use by programs. Every such constant expands to one integer, which identifies the sysctl variable relative to the upper level of the tree. See the sysctl(3) manual page for programming examples.

  Top level names
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 | Constant | Next level names | Description
kern | CTL_KERN | <sys/sysctl.h> | High kernel limits
vm | CTL_VM | <uvm/uvm_param.h> | Virtual memory
vfs | CTL_VFS | <sys/mount.h> | Filesystem
net | CTL_NET | <sys/socket.h> | Networking
debug | CTL_DEBUG | <sys/sysctl.h> | Debugging
hw | CTL_HW | <sys/sysctl.h> | Generic CPU, I/O
machdep | CTL_MACHDEP | <sys/sysctl.h> | Machine dependent
user | CTL_USER | <sys/sysctl.h> | User-level
ddb | CTL_DDB | <sys/sysctl.h> | In-kernel debugger
proc | CTL_PROC | <sys/sysctl.h> | Per-process
vendor | CTL_VENDOR |? | Vendor specific
emul | CTL_EMUL | <sys/sysctl.h> | Emulation settings
security | CTL_SECURITY | <sys/sysctl.h> | Security settings

  The debug.* subtree
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 };

Note that the dynamic implementation of sysctl currently in use largely makes this particular sysctl interface obsolete. See sysctl(8) for more information.

  The vfs.* subtree
A distinguished second level name, vfs.generic (VFS_GENERIC), is used to get general information about all file systems. It has the following third level identifiers:

vfs.generic.maxtypenum (VFS_MAXTYPENUM)
    The highest valid file system type number.

vfs.generic.conf (VFS_CONF)
    Returns configuration information about the file system type given as a fourth level identifier.

vfs.generic.usermount (VFS_USERMOUNT)
    Controls whether users other than the super-user can mount file systems. Defaults to 0, so only the super-user can mount file systems.

    File systems mounted by unprivileged users must be mounted with the nodev and nosuid mount(8) options.

vfs.generic.magiclinks (VFS_MAGICLINKS)
    Controls whether expansion of variables is going to be performed on pathnames or not. Defaults to 0, no variable expansion. Variables are of the form @name and the variables supported are described in symlink(7) under “MAGIC SYMLINKS”.

A second level name for controlling the wapbl(4) (Write Ahead Physical Block Logging file system journaling) capabilities with the following third level identifiers:

vfs.wapbl.flush_disk_cache
    Controls whether to attempt to flush the disk cache on each commit. It defaults to 1 and it should always be on to ensure integrity of file system metadata in the event of a power loss. For slow disks, turning it off can improve performance.

vfs.wapbl.verbose_commit
    For each transaction log commit, print the number of bytes written and the time it took to commit as seconds.nanoseconds.

The remaining second level identifiers are the file system names, identified by the type number returned by a statvfs(2) call or from vfs.generic.conf.

The third level identifiers available for each file system are given in the header file that defines the mount argument structure for that file system.

  The hw.* subtree
The string and integer information available for the hw level is detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
Second level name | Type | Changeable
hw.alignbytes integer no
hw.byteorder integer no
hw.cnmagic string yes
hw.disknames string no
hw.diskstats struct no
hw.machine string no
hw.machine_arch string no
hw.model string no
hw.ncpu integer no
hw.ncpuonline integer no
hw.pagesize integer no
hw.physmem integer no
hw.physmem64 quad no
hw.usermem integer no
hw.usermem64 quad no

hw.alignbytes (HW_ALIGNBYTES)
    Alignment constraint for all possible data types. This shows the value ALIGNBYTES in <machine/param.h>, at the kernel compilation time.

hw.byteorder (HW_BYTEORDER)
    The byteorder (4321, or 1234).

hw.cnmagic (HW_CNMAGIC)
    The console magic key sequence.

hw.disknames (HW_DISKNAMES)
    The list of (space separated) disk device names on the system.

hw.iostatnames (HW_IOSTATNAMES)
    A space separated list of devices that will have I/O statistics collected on them.

hw.iostats (HW_IOSTATS)
    Return statistical information on the NFS mounts, disk and tape devices on the system. An array of struct io_sysctl structures is returned, whose size depends on the current number of such objects in the system. The third level name is the size of the struct io_sysctl. The type of object can be determined by examining the type element of struct io_sysctl. Which can be IOSTAT_DISK (disk drive), IOSTAT_TAPE (tape drive), or IOSTAT_NFS (NFS mount).

hw.machine (HW_MACHINE)
    The machine class.

hw.machine_arch (HW_MACHINE_ARCH)
    The machine CPU class.

hw.model (HW_MODEL)
    The machine model.

hw.ncpu (HW_NCPU)
    The number of CPUs configured.

hw.ncpuonline (HW_NCPUONLINE)
    The number of CPUs online.

hw.pagesize (HW_PAGESIZE)
    The software page size.

hw.physmem (HW_PHYSMEM)
    The bytes of physical memory as a 32-bit integer.

hw.physmem64 (HW_PHYSMEM64)
    The bytes of physical memory as a 64-bit integer.

hw.usermem (HW_USERMEM)
    The bytes of non-kernel memory as a 32-bit integer.

hw.usermem64 (HW_USERMEM64)
    The bytes of non-kernel memory as a 64-bit integer.

  The kern.* subtree
This subtree includes data generally related to the kernel. The string and integer information available for the kern level is detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
Second level name | Type | Changeable
kern.aio_listio_max integer yes
kern.aio_max integer yes
kern.arandom integer no
kern.argmax integer no
kern.boothowto integer no
kern.boottime struct timespec no
kern.buildinfo string no
kern.ccpu integer no
kern.clockrate struct clockinfo no
kern.consdev integer no
kern.coredump node not applicable
kern.cp_id struct no
kern.cp_time uint64_t[] no
kern.cryptodevallowsoft integer yes
kern.defcorename string yes
kern.detachall integer yes
kern.domainname string yes
kern.drivers struct kinfo_drivers no
kern.dump_on_panic integer yes
kern.expose_address integer yes
kern.file struct file no
kern.forkfsleep integer yes
kern.fscale integer no
kern.fsync integer no
kern.hardclock_ticks integer no
kern.heartbeat.max_period integer yes
kern.hostid integer yes
kern.hostname string yes
kern.iov_max integer no
kern.ipc node not applicable
kern.job_control integer no
kern.labeloffset integer no
kern.labelsector integer no
kern.login_name_max integer no
kern.logsigexit integer yes
kern.lwp struct kinfo_lwp yes
kern.mapped_files integer no
kern.maxfiles integer yes
kern.maxlwp integer yes
kern.maxpartitions integer no
kern.maxphys integer no
kern.maxproc integer yes
kern.maxptys integer yes
kern.maxvnodes integer yes
kern.messages integer yes
kern.mbuf node not applicable
kern.memlock integer no
kern.memlock_range integer no
kern.memory_protection integer no
kern.module node not applicable
kern.monotonic_clock integer no
kern.mqueue node not applicable
kern.msgbuf integer no
kern.msgbufsize integer no
kern.ngroups integer no
kern.ntptime struct ntptimeval no
kern.osrelease string no
kern.osrevision integer no
kern.ostype string no
kern.pipe node not applicable
kern.pool struct pool_sysctl no
kern.posix1version integer no
kern.posix_aio integer no
kern.posix_barriers integer no
kern.posix_reader_writer_locks integer no
kern.posix_semaphores integer no
kern.posix_spin_locks integer no
kern.posix_threads integer no
kern.posix_timers integer no
kern.proc struct kinfo_proc no
kern.proc2 struct kinfo_proc2 no
kern.proc_args string no
kern.profiling node not applicable
kern.rawpartition integer no
kern.root_device string no
kern.root_partition integer no
kern.rtc_offset integer yes
kern.saved_ids integer no
kern.sbmax integer yes
kern.sched node not applicable
kern.securelevel integer raise only
kern.sofixedbuf boolean yes
kern.somaxkva integer yes
kern.sooptions integer yes
kern.synchronized_io integer no
kern.timecounter node not applicable
kern.timex struct no
kern.tkstat node not applicable
kern.tty node not applicable
kern.urandom integer no
kern.usercrypto integer yes
kern.userasymcrypto integer yes
kern.veriexec node not applicable
kern.version string no
kern.vnode struct vnode no

kern.aio_listio_max
    The maximum number of asynchronous I/O operations in a single list I/O call. Like with all variables related to aio(3), the variable may be created and removed dynamically upon loading or unloading the corresponding kernel module.

kern.aio_max
    The maximum number of asynchronous I/O operations.

kern.arandom (KERN_ARND)
    Returns independent uniformly distributed bytes at random each time, as many as requested up to 256, derived from the system entropy pool; see rnd(4).

    Reading kern.arandom is equivalent to reading up to 256 bytes at a time from /dev/urandom: reading kern.arandom never blocks, and once the system entropy pool has full entropy, output subsequently read from kern.arandom is fit for use as cryptographic key material. For example, the arc4random(3) library routine uses kern.arandom internally to seed a cryptographic pseudorandom number generator.

kern.argmax (KERN_ARGMAX)
    The maximum bytes of argument to execve(2).

kern.boothowto
    Flags passed from the boot loader; see reboot(2) for the meanings of the flags.

kern.boottime (KERN_BOOTTIME)
    A struct timespec structure is returned. This structure contains the time that the system was booted. That time is defined (for this purpose) to be the time at which the kernel first started accumulating clock ticks.

kern.bufq
    This variable contains information on the bufq(9) subsystem. Currently, the only third level name implemented is kern.bufq.strategies which provides a list of buffer queue strategies currently available.

kern.buildinfo
    When the kernel is built, the build environment may optionally provide arbitrary information to be stored in this variable.

kern.ccpu (KERN_CCPU)
    The scheduler exponential decay value.

kern.clockrate (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. Refer to hz(9) for additional details.

kern.consdev (KERN_CONSDEV)
    Console device.

kern.coredump
    Settings related to set-id processes coredumps. By default, set-id processes do not dump core in situations where other processes would. The settings in this node allows an administrator to change this behavior.

    The third level name is kern.coredump.setid and fourth level variables are described below.
    Fourth level name | Type | Changeable
    kern.coredump.setid.dump integer yes
    kern.coredump.setid.group integer yes
    kern.coredump.setid.mode integer yes
    kern.coredump.setid.owner integer yes
    kern.coredump.setid.path string yes

    kern.coredump.setid.dump
        If non-zero, set-id processes will dump core.

    kern.coredump.setid.group
        The group-id for the set-id processes' coredump.

    kern.coredump.setid.mode
        The mode for the set-id processes' coredump. See chmod(1).

    kern.coredump.setid.owner
        The user-id that will be used as the owner of the set-id processes' coredump.

    kern.coredump.setid.path
        The path to which set-id processes' coredumps will be saved to. Same syntax as kern.defcorename.

kern.cp_id (KERN_CP_ID)
    Mapping of CPU number to CPU id.

kern.cp_time (KERN_CP_TIME)
    Returns an array of CPUSTATES uint64_ts. This array contains the number of clock ticks spent in different CPU states. On multi-processor systems, the sum across all CPUs is returned unless appropriate space is given for one data set for each CPU. Data for a specific CPU can also be obtained by adding the number of the CPU at the end of the MIB, enlarging it by one.

kern.cryptodevallowsoft
    This variable controls userland access to hardware versus software transforms in the crypto(4) system. The available values are as follows:

    < 0 Always force userlevel requests to use software transforms.

    = 0 If present, use hardware and grant userlevel requests for non-accelerated transforms (handling the latter in software).

    > 0 Allow user requests only for transforms which are hardware-accelerated.

kern.defcorename (KERN_DEFCORENAME)
    Default template for the name of core dump files (see also proc.pid.corename in the per-process variables proc.*, and core(5) for format of this template). The default value is %n.core and can be changed with the kernel configuration option options DEFCORENAME (see options(4) ).

kern.detachall
    Detach all devices at shutdown.

kern.domainname (KERN_DOMAINNAME)
    Get or set the YP domain name.

kern.drivers (KERN_DRIVERS)
    Return an array of struct kinfo_drivers that contains the name and major device numbers of all the device drivers in the current kernel. The d_name field is always a NUL terminated string. The d_bmajor field will be set to -1 if the driver doesn't have a block device.

kern.expose_address
    Expose kernel addresses in sysctl(3) calls used by fstat(1) and sockstat(1). If it is set to 0 access is not allowed. If it is set to 1 then only processes that have opened /dev/kmem can have access. If it is set to 2 every process is allowed. Defaults to 0 for KASLR kernels and 1 otherwise. Allowing general access renders KASLR ineffective; allowing only kmem accessing programs weakens KASLR if those programs can be subverted to leak the addresses.

kern.dump_on_panic (KERN_DUMP_ON_PANIC)
    Perform a crash dump on system panic(9).

kern.file (KERN_FILE)
    Return the entire file table. The returned data consists of a single struct filelist followed by an array of struct file, whose size depends on the current number of such objects in the system.

kern.forkfsleep (KERN_FORKFSLEEP)
    If fork(2) system call fails due to limit on number of processes (either the global maxproc limit or user's one), wait for this many milliseconds before returning EAGAIN error to process. Useful to keep heavily forking runaway processes in bay. Default zero (no sleep). Maximum is 20 seconds.

kern.fscale (KERN_FSCALE)
    The kernel fixed-point scale factor.

kern.fsync (KERN_FSYNC)
    Return 1 if the p1003.1b-93 File Synchronization Option is available on this system, otherwise 0.

kern.hardclock_ticks (KERN_HARDCLOCK_TICKS)
    Returns the number of hardclock(9) ticks.

kern.heartbeat.max_period
    Time in seconds since the last options HEARTBEAT progress check has passed before it will trigger a panic. See options(4).

kern.hist
    This variable contains kernel history data if the kernel was configured for any of the options UVHMIST, USB_DEBUG, BIOHIST, or SCDEBUG. (See options(4) for more details.) The third-level names correspond to each available history table. The values of the history tables are in an internal format, and can be decoded by the vmstat(1) utility's -U and -u options; the -l option can be used to see which tables are available.

kern.hostid (KERN_HOSTID)
    Get or set the host identifier. This is aimed to replace the legacy gethostid(3) and sethostid(3) system calls.

kern.hostname (KERN_HOSTNAME)
    Get or set the hostname(1).

kern.iov_max (KERN_IOV_MAX)
    Return the maximum number of iovec structures that a process has available for use with preadv(2), pwritev(2), readv(2), recvmsg(2), sendmsg(2) and writev(2).

kern.ipc (KERN_SYSVIPC)
    Return information about the SysV IPC parameters. The third level names for the ipc variables are detailed below.
    Third level name | Type | Changeable
    kern.ipc.sysvmsg integer no
    kern.ipc.sysvsem integer no
    kern.ipc.sysvshm integer no
    kern.ipc.sysvipc_info struct no
    kern.ipc.shmmax integer yes
    kern.ipc.shmmni integer yes
    kern.ipc.shmseg integer yes
    kern.ipc.shmmaxpgs integer yes
    kern.ipc.shm_use_phys integer yes
    kern.ipc.msgmni integer yes
    kern.ipc.msgseg integer yes
    kern.ipc.semmni integer yes
    kern.ipc.semmns integer yes
    kern.ipc.semmnu integer yes

    kern.ipc.sysvmsg (KERN_SYSVIPC_MSG)
        Returns 1 if System V style message queue functionality is available on this system, otherwise 0.

    kern.ipc.sysvsem (KERN_SYSVIPC_SEM)
        Returns 1 if System V style semaphore functionality is available on this system, otherwise 0.

    kern.ipc.sysvshm (KERN_SYSVIPC_SHM)
        Returns 1 if System V style share memory functionality is available on this system, otherwise 0.

    kern.ipc.sysvipc_info (KERN_SYSVIPC_INFO)
        Return System V style IPC configuration and run-time information. The fourth level name selects the System V style IPC facility.
        Fourth 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.ipc.shmmax (KERN_SYSVIPC_SHMMAX)
        Max shared memory segment size in bytes.

    kern.ipc.shmmni (KERN_SYSVIPC_SHMMNI)
        Max number of shared memory identifiers.

    kern.ipc.shmseg (KERN_SYSVIPC_SHMSEG)
        Max shared memory segments per process.

    kern.ipc.shmmaxpgs (KERN_SYSVIPC_SHMMAXPGS)
        Max amount of shared memory in pages.

    kern.ipc.shm_use_phys (KERN_SYSVIPC_SHMUSEPHYS)
        Locking of shared memory in physical memory. If 0, memory can be swapped out, otherwise it will be locked in physical memory.

    kern.ipc.msgmni
        Max number of message queue identifiers.

    kern.ipc.msgseg
        Max number of number of message segments.

    kern.ipc.semmni
        Max number of number of semaphore identifiers.

    kern.ipc.semmns
        Max number of number of semaphores in system.

    kern.ipc.semmnu
        Max number of undo structures in system.

kern.job_control (KERN_JOB_CONTROL)
    Return 1 if job control is available on this system, otherwise 0.

kern.labeloffset (KERN_LABELOFFSET)
    The offset within the sector specified by KERN_LABELSECTOR of the disklabel(5).

kern.labelsector (KERN_LABELSECTOR)
    The sector number containing the disklabel(5).

kern.login_name_max (KERN_LOGIN_NAME_MAX)
    The size of the storage required for a login name, in bytes, including the terminating NUL.

kern.logsigexit (KERN_LOGSIGEXIT)
    If this flag is non-zero, the kernel will log(9) all process exits due to signals which create a core(5) file, and whether the coredump was created.

kern.lwp (KERN_LWP)
    Returns information about the current light-weight process. The kinfo_lwp structure is defined in <sys/sysctl.h>.

kern.mapped_files (KERN_MAPPED_FILES)
    Returns 1 if the p1003.1b-93 Memory Mapped Files Option is available on this system, otherwise 0.

kern.maxfiles (KERN_MAXFILES)
    The maximum number of open files that may be open in the system. This also controls the maximum file locks per unprivileged user enforced by fcntl(2) and flock(2).

kern.maxpartitions (KERN_MAXPARTITIONS)
    The maximum number of partitions allowed per disk.

kern.maxlwp
    The maximum number of Lightweight Processes (threads) the system allows per uid.

kern.maxphys (KERN_MAXPHYS)
    Maximum raw I/O transfer size.

kern.maxproc (KERN_MAXPROC)
    The maximum number of simultaneous processes the system will allow.

kern.maxptys (KERN_MAXPTYS)
    The maximum number of pseudo terminals. This value can be both raised and lowered, though it cannot be set lower than number of currently used ptys. See also pty(4).

kern.maxvnodes (KERN_MAXVNODES)
    The maximum number of vnodes available on the system. This cannot be lowered below the number of currently active vnodes.

kern.mbuf (KERN_MBUF)
    Return information about the mbuf control variables. Mbufs are data structures which store network packets and other data structures in the networking code, see mbuf(9). The third level names for the mbuf variables are detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
    Third level name | Type | Changeable
    kern.mbuf.mblowat integer yes
    kern.mbuf.mclbytes integer yes
    kern.mbuf.mcllowat integer yes
    kern.mbuf.msize integer yes
    kern.mbuf.nmbclusters integer yes
    kern.mbuf.nmbclusters_limit integer no

    The variables are as follows:

    kern.mbuf.mblowat (MBUF_MBLOWAT)
        The mbuf low water mark.

    kern.mbuf.mclbytes (MBUF_MCLBYTES)
        The mbuf cluster size.

    kern.mbuf.mcllowat (MBUF_MCLLOWAT)
        The mbuf cluster low water mark.

    kern.mbuf.msize (MBUF_MSIZE)
        The mbuf base size.

    kern.mbuf.nmbclusters (MBUF_NMBCLUSTERS)
        The limit on the number of mbuf clusters. The variable can only be increased, and only increased on machines with direct-mapped pool pages.

    kern.mbuf.nmbclusters_limit (MBUF_NMBCLUSTERS_LIMIT)
        The limit of nmbclusters.

kern.memlock (KERN_MEMLOCK)
    Returns 1 if the p1003.1b-93 Process Memory Locking Option is available on this system, otherwise 0.

kern.memlock_range (KERN_MEMLOCK_RANGE)
    Returns 1 if the p1003.1b-93 Range Memory Locking Option is available on this system, otherwise 0.

kern.memory_protection (KERN_MEMORY_PROTECTION)
    Returns 1 if the p1003.1b-93 Memory Protection Option is available on this system, otherwise 0.

kern.messages
    Kernel console message verbosity. See <sys/reboot.h>
    Value | Verbosity | sys/reboot.h equivalent
    0 | Silent | AB_SILENT
    1 | Quiet | AB_QUIET
    2 | Normal | AB_NORMAL
    3 | Verbose | AB_VERBOSE
    4 | Debug | AB_DEBUG

kern.module
    Settings related to kernel modules. The third level names for the settings are described below.
    Third level name | Type | Changeable
    kern.module.autoload integer yes
    kern.module.autounload_unsafe integer yes
    kern.module.autotime integer yes
    kern.module.verbose boolean yes

    The variables are as follows:

    kern.module.autoload
        A boolean that controls whether kernel modules are loaded automatically. See module(7) for details.

    kern.module.autounload_unsafe
        A boolean that controls whether the kernel will autounload modules that were automatically loaded and have not been audited for autounload.

        By default, only modules that have been audited will be autounloaded, and only if they were autoloaded to begin with.

    kern.module.autotime
        An integer that controls the delay before an attempt is made to automatically unload a module that was auto-loaded. Setting this value to zero disables the auto-unload function.

    kern.module.verbose
        A boolean that enables or disables verbose debug messages related to kernel modules.

kern.monotonic_clock (KERN_MONOTONIC_CLOCK)
    Returns the standard version the implementation of the p1003.1b-93 Monotonic Clock Option conforms to, otherwise 0.

kern.mqueue
    Settings related to POSIX message queues; see mqueue(3). This node is created dynamically when the corresponding kernel module is loaded. The third level names for the settings are described below.
    Third level name | Type | Changeable
    kern.mqueue.mq_open_max integer yes
    kern.mqueue.mq_prio_max integer yes
    kern.mqueue.mq_max_msgsize integer yes
    kern.mqueue.mq_def_maxmsg integer yes
    kern.mqueue.mq_max_maxmsg integer yes

    The variables are:

    kern.mqueue.mq_open_max
        The maximum number of message queue descriptors any single process can open.

    kern.mqueue.mq_prio_max
        The maximum priority of a message.

    kern.mqueue.mq_max_msgsize
        The maximum size of a message in a message queue.

    kern.mqueue.mq_def_maxmsg
        The default maximum message count.

    kern.mqueue.mq_max_maxmsg
        The maximum number of messages in a message queue.

kern.msgbuf (KERN_MSGBUF)
    The kernel message buffer, rotated so that the head of the circular kernel message buffer is at the start of the returned data. The returned data may contain NUL bytes.

kern.msgbufsize (KERN_MSGBUFSIZE)
    The maximum number of characters that the kernel message buffer can hold.

kern.ngroups (KERN_NGROUPS)
    The maximum number of supplemental groups.

kern.ntptime (KERN_NTPTIME)
    A struct ntptimeval structure is returned. This structure contains data used by the ntpd(8) program.

kern.osrelease (KERN_OSRELEASE)
    The system release string.

kern.osrevision (KERN_OSREV)
    The system revision, expressed as an integer.

kern.ostype (KERN_OSTYPE)
    The system type string.

kern.pipe (KERN_PIPE)
    Pipe settings. The third level names for the integer pipe settings is detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
    Third level name | Type | Changeable
    kern.pipe.kvasiz integer yes
    kern.pipe.maxbigpipes integer yes
    kern.pipe.maxkvasz integer yes
    kern.pipe.limitkva integer yes
    kern.pipe.nbigpipes integer yes

    The variables are as follows:

    kern.pipe.kvasiz (KERN_PIPE_KVASIZ)
        Amount of kernel memory consumed by pipe buffers.

    kern.pipe.maxbigpipes (KERN_PIPE_MAXBIGPIPES)
        Maximum number of “big” pipes.

    kern.pipe.maxkvasz (KERN_PIPE_MAXKVASZ)
        Maximum amount of kernel memory to be used for pipes.

    kern.pipe.limitkva (KERN_PIPE_LIMITKVA)
        Limit for direct transfers via page loan.

    kern.pipe.nbigpipes (KERN_PIPE_NBIGPIPES)
        Number of “big” pipes.

kern.pool
    Provides statistics about the pool(9) and pool_cache(9) subsystems.

kern.posix1version (KERN_POSIX1)
    The version of ISO/IEC 9945 (p1003.1) with which the system attempts to comply.

kern.posix_aio
    The version of p1003.1 and its Asynchronous I/O option to which the system attempts to conform.

kern.posix_barriers (KERN_POSIX_BARRIERS)
    The version of p1003.1 and its Barriers option to which the system attempts to conform, otherwise 0.

kern.posix_reader_writer_locks (KERN_POSIX_READER_WRITER_LOCKS)
    The version of p1003.1 and its Read-Write Locks option to which the system attempts to conform, otherwise 0.

kern.posix_semaphores (KERN_POSIX_SEMAPHORES)
    The version of p1003.1 and its Semaphores option to which the system attempts to conform, otherwise 0.

kern.posix_spin_locks (KERN_POSIX_SPIN_LOCKS)
    The version of p1003.1 and its Spin Locks option to which the system attempts to conform, otherwise 0.

kern.posix_threads (KERN_POSIX_THREADS)
    The version of p1003.1 and its Threads option to which the system attempts to conform, otherwise 0.

kern.posix_timers (KERN_POSIX_TIMERS)
    The version of p1003.1 and its Timers option to which the system attempts to conform, otherwise 0.

kern.proc (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 numeric names are as follows:
    Third level name | Fourth level is:
    KERN_PROC_ALL None
    KERN_PROC_GID A group ID
    KERN_PROC_PID A process ID
    KERN_PROC_PGRP A process group
    KERN_PROC_RGID A real group ID
    KERN_PROC_RUID A real user ID
    KERN_PROC_SESSION A session ID
    KERN_PROC_TTY A tty device
    KERN_PROC_UID A user ID

kern.proc2 (KERN_PROC2)
    As for KERN_PROC, but an array of struct kinfo_proc2 structures are returned. The fifth level name is the size of the struct kinfo_proc2 and the sixth level name is the number of structures to return.

kern.proc_args (KERN_PROC_ARGS)
    Return the argv or environment strings (or the number thereof) of a process. Multiple strings are returned separated by NUL characters. The third level name is the process ID. The fourth level name is as follows:
    KERN_PROC_ARGV The argv strings
    KERN_PROC_ENV The environ strings
    KERN_PROC_NARGV The number of argv strings
    KERN_PROC_NENV The number of environ strings
    KERN_PROC_PATHNAME The full pathname of the executable
    KERN_PROC_CWD The current working directory

kern.profiling (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 below. The changeable column shows whether a process with appropriate privilege may change the value.
    Third level name | Type | Changeable
    kern.profiling.count u_short[] yes
    kern.profiling.froms u_short[] yes
    kern.profiling.gmonparam struct gmonparam no
    kern.profiling.state integer yes
    kern.profiling.tos struct tostruct yes

    The variables are as follows:

    kern.profiling.count (GPROF_COUNT)
        Array of statistical program counter counts.

    kern.profiling.froms (GPROF_FROMS)
        Array indexed by program counter of call-from points.

    kern.profiling.gmonparams (GPROF_GMONPARAM)
        Structure giving the sizes of the above arrays.

    kern.profiling.state (GPROF_STATE)
        Profiling state. If set to GMON_PROF_ON, starts profiling. If set to GMON_PROF_OFF, stops profiling.

    kern.profiling.tos (GPROF_TOS)
        Array of struct tostruct describing destination of calls and their counts.

kern.rawpartition (KERN_RAWPARTITION)
    The raw partition of a disk (a == 0).

kern.root_device (KERN_ROOT_DEVICE)
    The name of the root device (e.g., “wd0”).

kern.root_partition (KERN_ROOT_PARTITION)
    The root partition on the root device (a == 0).

kern.rtc_offset (KERN_RTC_OFFSET)
    Return the offset of real time clock from UTC in minutes.

kern.saved_ids (KERN_SAVED_IDS)
    Returns 1 if saved set-group and saved set-user ID is available.

kern.sbmax (KERN_SBMAX)
    Maximum socket buffer size in bytes.

kern.securelevel (KERN_SECURELVL)
    See secmodel_securelevel(9).

kern.sched (dynamic)
    Influence the scheduling of LWPs, their priorisation and how they are distributed on and moved between CPUs.
    Third level name Type Changeable
    kern.sched.cacheht_time integer yes
    kern.sched.balance_period integer yes
    kern.sched.average_weight integer yes
    kern.sched.min_catch integer yes
    kern.sched.timesoftints integer yes
    kern.sched.kpreempt_pri integer yes
    kern.sched.upreempt_pri integer yes
    kern.sched.maxts integer yes
    kern.sched.mints integer yes
    kern.sched.name string no
    kern.sched.rtts integer no
    kern.sched.pri_min integer no
    kern.sched.pri_max integer no

    The variables are as follows:

    kern.sched.cacheht_time (dynamic)
        Cache hotness time in which a LWP is kept on one particular CPU and not moved to another CPU. This reduces the overhead of flushing and reloading caches. Defaults to 3ms. Needs to be given in “hz” units, see mstohz(9).

    kern.sched.balance_period (dynamic)
        Interval at which the CPU queues are checked for re-balancing. Defaults to 300ms. Needs to be given in “hz” units, see mstohz(9).

    kern.sched.average_weight (dynamic)
        Can be used to influence how likely LWPs are to be migrated from one CPU's queue of LWPs that are ready to run to a different, idle CPU. The value gives the percentage for weighting the average count of migratable threads from the past against the current number of migratable threads. A small value gives more weight to the past, a larger values more weight on the current situation. Defaults to 50 and must be between 0 and 100.

    kern.sched.min_catch (dynamic)
        Minimum count of migratable (runnable) threads for catching (stealing) from another CPU. Defaults to 1 but can be increased to decrease chance of thread migration between CPUs.

    kern.sched.timesoftints (dynamic)
        Enable tracking of CPU time for soft interrupts as part of a LWP's real execution time. Set to a non-zero value to enable, and see ps(1) for printing CPU times.

    kern.sched.kpreempt_pri (dynamic)
        Minimum priority to trigger kernel preemption.

    kern.sched.upreempt_pri (dynamic)
        Minimum priority to trigger user preemption.

    kern.sched.maxts (dynamic)
        Scheduler specific maximal time quantum (in milliseconds). Must be set to a value larger than “mints” and between 10 and “hz” as given by the kern.clockrate sysctl. Provided by the M2 scheduler.

    kern.sched.mints (dynamic)
        Scheduler specific minimal time quantum (in milliseconds). Must be set to a value smaller than “maxts” and between 1 and “hz” as given by the “kern.clockrate” sysctl. Provided by the M2 scheduler.

    kern.sched.name (dynamic)
        Scheduler name. Provided both by the M2 and the 4BSD scheduler.

    kern.sched.rtts (dynamic)
        Fixed scheduler specific round-robin time quantum in milliseconds. Provided both by the M2 and the 4BSD scheduler.

    kern.sched.pri_min (dynamic)
        Minimal POSIX real-time priority. See sched(3).

    kern.sched.pri_max (dynamic)
        Maximal POSIX real-time priority. See sched(3).

kern.sofixedbuf (KERN_SOFIXEDBUF)
    Prevent socket buffer autoscaling when a size is set with SO_SNDBUF or SO_RCVBUF.

kern.somaxkva (KERN_SOMAXKVA)
    Maximum amount of kernel memory to be used for socket buffers in bytes.

kern.sooptions
    Set the default socket option flags for socket(2) creation. See setsockopt(2) for a list of supported flags.

kern.synchronized_io (KERN_SYNCHRONIZED_IO)
    Returns 1 if the p1003.1b-93 Synchronized I/O Option is available on this system, otherwise 0.

kern.timecounter (dynamic)
    Display and control the timecounter source of the system.
    Third level name | Type | Changeable
    kern.timecounter.choice string no
    kern.timecounter.hardware string yes
    kern.timecounter.timestepwarnings integer yes

    The variables are as follows:

    kern.timecounter.choice (dynamic)
        The list of available timecounters with their quality and frequency.

    kern.timecounter.hardware (dynamic)
        The currently selected timecounter source.

    kern.timecounter.timestepwarnings (dynamic)
        If non-zero display a message each time the time is stepped.

kern.timex (KERN_TIMEX)
    Not available.

kern.tkstat (KERN_TKSTAT)
    Return information about the number of characters sent and received on ttys. The third level names for the tty statistic variables are detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
    Third level name | Type | Changeable
    kern.tkstat.cancc quad no
    kern.tkstat.nin quad no
    kern.tkstat.nout quad no
    kern.tkstat.rawcc quad no

    The variables are as follows:

    kern.tkstat.cancc (KERN_TKSTAT_CANCC)
        The number of canonical input characters.

    kern.tkstat.nin (KERN_TKSTAT_NIN)
        The total number of input characters.

    kern.tkstat.nout (KERN_TKSTAT_NOUT)
        The total number of output characters.

    kern.tkstat.rawcc (KERN_TKSTAT_RAWCC)
        The number of raw input characters.

kern.tty
    The third level names for the tty setup variables are detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
    Third level name | Type | Changeable
    kern.tty.qsize int yes

    The variables are as follows:

    kern.tty.qsize
        Control/display the size of the default input and output queues selected during tty creation. Is converted to a power of two and its range is between 1024 and 65536.

kern.uidinfo
    Resource usage for the current user.
    Third level name | Type | Changeable
    kern.uidinfo.proccnt integer no
    kern.uidinfo.lwpcnt integer no
    kern.uidinfo.lockcnt integer no
    kern.uidinfo.semcnt integer no
    kern.uidinfo.sbsize integer no

    kern.uidinfo.proccnt
        Returns the number of active processes for the current user.

    kern.uidinfo.lwpcnt
        Returns the number of active threads for the current user; the first thread of each process is not counted.

    kern.uidinfo.lockcnt
        Number of locks held by the current user.

    kern.uidinfo.semcnt
        Number of semaphores held by the current user.

    kern.uidinfo.sbsize
        Number of bytes in socket buffers allocated to the current user.

kern.urandom (KERN_URND)
    Random integer value.

kern.usercrypto
    When enabled, allows userland to open(2) the /dev/crypto special device, used by the crypto(4) system.

kern.userasymcrypto
    Enables or disables the use of software asymmetric crypto support in the crypto(4) system.

kern.veriexec
    Runtime information for veriexec(8).
    Third level name | Type | Changeable
    kern.veriexec.algorithms string no
    kern.veriexec.count node not applicable
    kern.veriexec.strict integer yes
    kern.veriexec.verbose integer yes

    kern.veriexec.algorithms
        Returns a string with the supported algorithms in Veriexec.

    kern.veriexec.count
        Sub-nodes are added to this node as new mounts are monitored by Veriexec. Each mount will be under its own tableN node. Under each node there will be three variables, indicating the mount point, the file system type, and the number of entries.

    kern.veriexec.strict
        Controls the strict level of Veriexec. See security(7) for more information on each level's implications.

    kern.veriexec.verbose
        Controls the verbosity level of Veriexec. If 0, only the minimal indication required will be given about what's happening - fingerprint mismatches, removal of entries from the tables, modification of a fingerprinted file. If 1, more messages will be printed (ie., when a file with a valid fingerprint is accessed). Verbose level 2 is debug mode.

kern.version (KERN_VERSION)
    The system version string.

kern.vnode (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.

  The machdep.* subtree
The set of variables defined is architecture dependent. Most architectures define at least the following variables.
Second level name | Type | Changeable
machdep.booted_kernel string no

  The net.* subtree
The string and integer information available for the net level is detailed below. The changeable column shows whether a process with appropriate privilege may change the value. The second and third levels are typically the protocol family and protocol number, though this is not always the case.
Second level name | Type | Changeable
net.route routing messages no
net.inet IPv4 values yes
net.inet6 IPv6 values yes
net.key IPsec key management values yes

net.route (PF_ROUTE)
    Return the entire routing table or a subset of it. The data is returned as a sequence of routing messages (see route(4) for the header file, format and meaning). The length of each message is contained in the message header.

    The third level name is a protocol number, which is currently always 0. The fourth level name is an address family, which may be set to 0 to select all address families. The fifth and sixth level names are as follows:
    Fifth level name | Sixth level is:
    NET_RT_FLAGS rtflags
    NET_RT_DUMP None
    NET_RT_IFLIST None

net.inet (PF_INET)
    Get or set various global information about the IPv4 (Internet Protocol version 4). The third level name is the protocol. The fourth level name is the variable name. The currently defined protocols and names are:
    Protocol Variable | Type | Changeable
    arp nd_delay integer yes
    arp nd_bmaxtries integer yes
    arp nd_umaxtries integer yes
    arp nd_basereachable integer yes
    arp nd_retrans integer yes
    arp nd_nud integer yes
    arp nd_maxnudhint integer yes
    arp log_movements integer yes
    arp log_permanent_modify integer yes
    arp log_unknown_network integer yes
    arp log_wrong_iface integer yes
    carp allow integer yes
    carp preempt integer yes
    carp log integer yes
    carp arpbalance integer yes
    icmp errppslimit integer yes
    icmp maskrepl integer yes
    icmp rediraccept integer yes
    icmp redirtimeout integer yes
    icmp bmcastecho integer yes
    icmp dynamic_rt_msg boolean yes
    ip allowsrcrt integer yes
    ip anonportalgo.selected string yes
    ip anonportalgo.available string yes
    ip anonportalgo.reserve struct yes
    ip anonportmax integer yes
    ip anonportmin integer yes
    ip checkinterface integer yes
    ip dad_count integer yes
    ip directed-broadcast integer yes
    ip do_loopback_cksum integer yes
    ip forwarding integer yes
    ip forwsrcrt integer yes
    ip gifttl integer yes
    ip grettl integer yes
    ip hashsize integer yes
    ip hostzerobroadcast integer yes
    ip lowportmin integer yes
    ip lowportmax integer yes
    ip maxflows integer yes
    ip maxfragpackets integer yes
    ip mtudisc integer yes
    ip mtudisctimeout integer yes
    ip random_id integer yes
    ip redirect integer yes
    ip subnetsarelocal integer yes
    ip ttl integer yes
    tcp rfc1323 integer yes
    tcp sendspace integer yes
    tcp recvspace integer yes
    tcp mssdflt integer yes
    tcp syn_cache_limit integer yes
    tcp syn_bucket_limit integer yes
    tcp syn_cache_interval integer yes
    tcp init_win integer yes
    tcp init_win_local integer yes
    tcp mss_ifmtu integer yes
    tcp win_scale integer yes
    tcp timestamps integer yes
    tcp cwm integer yes
    tcp cwm_burstsize integer yes
    tcp ack_on_push integer yes
    tcp keepidle integer yes
    tcp keepintvl integer yes
    tcp keepcnt integer yes
    tcp slowhz integer no
    tcp keepinit integer yes
    tcp log_refused integer yes
    tcp rstppslimit integer yes
    tcp ident struct no
    tcp drop struct no
    tcp sack.enable integer yes
    tcp sack.globalholes integer no
    tcp sack.globalmaxholes integer yes
    tcp sack.maxholes integer yes
    tcp ecn.enable integer yes
    tcp ecn.maxretries integer yes
    tcp congctl.selected string yes
    tcp congctl.available string yes
    tcp abc.enable integer yes
    tcp abc.aggressive integer yes
    udp checksum integer yes
    udp do_loopback_cksum integer yes
    udp recvspace integer yes
    udp sendspace integer yes

    The variables are as follows:

    arp.nd_delay
        The delay in seconds before sending the first probe, after it has been decided that the entry is stale.

    arp.nd_bmaxtries
        The maximum number of broadcasts send to discover the hardware address claiming an IP address.

    arp.nd_umaxtries
        The maximum number of unicasts send to the hardware address to ensure it still claims an IP address.

    arp.nd_basereachable
        The number of milliseconds the ARP entry is considered reachable before probing reachability.

    arp.nd_retrans
        The number of milliseconds between ARP probes.

    arp.nd_nud
        If set to non-zero, perform Neighor Unreachability Detection.

    arp.nd_maxnudhint
        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 discovery layer will take 3 consecutive hints in maximum. After receiving 3 hints, neighbor discovery layer will perform normal neighbor discovery process.

    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.arpbalance
        If set to any value other than 0, the ARP balancing functionality of carp(4) is enabled. When ARP requests are received for an IP address which is part of any virtual host, carp will hash the source IP in the ARP request to select one of the virtual hosts from the set of all the virtual hosts which have that IP address. The master of that host will respond with the correct virtual MAC address. Disabled by default.

    carp.log
        If set to any value other than 0, carp(4) will log errors. Disabled by default.

    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.

    ip.allowsrcrt
        If set to 1, the host accepts source routed packets.

    ip.anonportalgo.available
        The available RFC 6056 port randomization algorithms.

    ip.anonportalgo.reserve
        A bitmask of ports that will not be used during anonymous or privileged port selection.

    ip.anonportalgo.selected
        The currently selected RFC 6056 port randomization algorithm; see rfc6056(7) for details.

    ip.anonportmax
        The highest port number to use for TCP and UDP ephemeral port allocation. This cannot be set to less than 1024 or greater than 65535, and must be greater than ip.anonportmin.

    ip.anonportmin
        The lowest port number to use for TCP and UDP ephemeral port allocation. This cannot be set to less than 1024 or greater than 65535.

    ip.checkinterface
        If set to non-zero, the host will reject packets addressed to it that arrive on an interface not bound to that address. Currently, this must be disabled if NAT is used to translate the destination address to another local interface, or if addresses are added to the loopback interface instead of the interface where the packets for those packets are received.

    ip.dad_count
        The number of arp(4) probes sent for Address Conflict Detection. Set to 0 to disable this.

    ip.directed-broadcast
        If set to 1, enables directed broadcast behavior for the host.

    ip.do_loopback_cksum
        Perform IP checksum on loopback.

    ip.forwarding
        If set to 1, enables IP forwarding for the host, meaning that the host is acting as a router.

    ip.forwsrcrt
        If set to 1, enables forwarding of source-routed packets for the host. This value may only be changed if the kernel security level is less than 1.

    ip.gifttl
        The maximum time-to-live (hop count) value for an IPv4 packet generated by gif(4) tunnel interface.

    ip.grettl
        The maximum time-to-live (hop count) value for an IPv4 packet generated by gre(4) tunnel interface.

    ip.hashsize
        The size of IPv4 Fast Forward hash table. This value must be a power of 2 (64, 256...). A larger hash table size results in fewer collisions. Also see ip.maxflows.

    ip.hostzerobroadcast
        All zeroes address is broadcast address.

    ip.lowportmax
        The highest port number to use for TCP and UDP reserved port allocation. This cannot be set to less than 0 or greater than 1024, and must be greater than ip.lowportmin.

    ip.lowportmin
        The lowest port number to use for TCP and UDP reserved port allocation. This cannot be set to less than 0 or greater than 1024, and must be smaller than ip.lowportmax.

    ip.maxflows
        IPv4 Fast Forwarding is enabled by default. If set to 0, IPv4 Fast Forwarding is disabled. ip.maxflows controls the maximum amount of flows which can be created. The default value is 256.

    ip.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.

    ip.mtudisc
        If set to 1, enables Path MTU Discovery (RFC 1191). When Path MTU Discovery is enabled, the transmitted TCP segment size will be determined by the advertised maximum segment size (MSS) from the remote end, as constrained by the path MTU. If MTU Discovery is disabled, the transmitted segment size will never be greater than tcp.mssdflt (the local maximum segment size).

    ip.mtudisctimeout
        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.random_id
        Assign random ip_id values.

    ip.redirect
        If set to 1, 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.subnetsarelocal
        If set to 1, subnets are to be considered local addresses.

    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.

    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.maskrepl
        If set to 1, 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
        The variable specifies lifetime of routing entries generated by incoming ICMP redirect. This defaults to 600 seconds.

    icmp.returndatabytes
        Number of bytes to return in an ICMP error message.

    icmp.bmcastecho
        If set to 1, enables responding to ICMP echo or timestamp request to the broadcast address.

    icmp.dynamic_rt_msg
        A boolean that the kernel sends routing message for RTM_DYNAMIC or not. If set to true, sends such routing message.

    tcp.ack_on_push
        If set to 1, TCP is to immediately transmit an ACK upon reception of a packet with PUSH set. This can avoid losing a round trip time in some rare situations, but has the caveat of potentially defeating TCP's delayed ACK algorithm. Use of this option is generally not recommended, but the variable exists in case your configuration really needs it.

    tcp.cwm
        If set to 1, enables use of the Hughes/Touch/Heidemann Congestion Window Monitoring algorithm. This algorithm prevents line-rate bursts of packets that could otherwise occur when data begins flowing on an idle TCP connection. These line-rate bursts can contribute to network and router congestion. This can be particularly useful on World Wide Web servers which support HTTP/1.1, which has lingering connections.

    tcp.cwm_burstsize
        The Congestion Window Monitoring allowed burst size, in terms of packet count.

    tcp.delack_ticks
        Number of ticks to delay sending an ACK.

    tcp.do_loopback_cksum
        Perform TCP checksum on loopback.

    tcp.init_win
        A value indicating the TCP initial congestion window. The valid range is 0 to 10 (maximum specified by RFC6928), with a default of 4 (approximately 4K per RFC3390).

    tcp.init_win_local
        Like tcp.init_win, but used when communicating with hosts on a local network.

    tcp.keepcnt
        Number of keepalive probes sent before declaring a connection dead. If set to zero, there is no limit; keepalives will be sent until some kind of response is received from the peer.

    tcp.keepidle
        Time a connection must be idle before keepalives are sent (if keepalives are enabled for the connection). See also tcp.slowhz.

    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.log_refused
        If set to 1, refused TCP connections to the host will be logged.

    tcp.keepinit
        Timeout in seconds during connection establishment.

    tcp.mss_ifmtu
        If set to 1, TCP calculates the outgoing maximum segment size based on the MTU of the appropriate interface. If set to 0, it is calculated based on the greater of the MTU of the interface, and the largest (non-loopback) interface MTU on the system.

    tcp.mssdflt
        The default maximum segment size both advertised to the peer and to use when either the peer does not advertise a maximum segment size to us during connection setup or Path MTU Discovery (ip.mtudisc) is disabled. Do not change this value unless you really know what you are doing.

    tcp.recvspace
        The default TCP receive buffer size.

    tcp.rfc1323
        If set to 1, enables RFC 1323 extensions to TCP.

    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.ident
        Return the user ID of a connected socket pair. (RFC1413 Identification Protocol lookups.)

    tcp.drop
        Drop a TCP socket pair connection.

    tcp.sack.enable
        If set to 1, enables RFC 2018 Selective ACKnowledgement.

    tcp.sack.globalholes
        Global number of TCP SACK holes.

    tcp.sack.globalmaxholes
        Global maximum number of TCP SACK holes.

    tcp.sack.maxholes
        Maximum number of TCP SACK holes allowed per connection.

    tcp.ecn.enable
        If set to 1, enables RFC 3168 Explicit Congestion Notification.

    tcp.ecn.maxretries
        Number of times to retry sending the ECN-setup packet.

    tcp.sendspace
        The default TCP send buffer size.

    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.syn_bucket_limit
        The maximum number of entries allowed per hash bucket in the TCP compressed state engine.

    tcp.syn_cache_limit
        The maximum number of entries allowed in the TCP compressed state engine.

    tcp.timestamps
        If rfc1323 is enabled, a value of 1 indicates RFC 1323 time stamp options, used for measuring TCP round trip times, are enabled.

    tcp.win_scale
        If rfc1323 is enabled, a value of 1 indicates RFC 1323 window scale options, for increasing the TCP window size, are enabled.

    tcp.congctl.available
        The available TCP congestion control algorithms.

    tcp.congctl.selected
        The currently selected TCP congestion control algorithm.

    tcp.abc.enable
        If set to 1, use RFC 3465 Appropriate Byte Counting (ABC). If set to 0, use traditional Packet Counting.

    tcp.abc.aggressive
        Choose the L parameter found in RFC 3465. L is the maximum cwnd increase for an ack during slow start. If set to 1, use L=2*SMSS. If set to 0, use L=1*SMSS. It has no effect unless tcp.abc.enable is set to 1.

    udp.checksum
        If set to 1, UDP checksums are being computed. Received non-zero UDP checksums are always checked. Disabling UDP checksums is strongly discouraged.

    udp.recvspace
        The default UDP receive buffer size.

    udp.sendspace
        The default UDP send buffer size.

    For variables net.*.ipsec, please refer to ipsec(4).

net.inet6 (PF_INET6)
    Get or set various global information about the IPv6 (Internet Protocol version 6). The third level name is the protocol. The fourth level name is the variable name. The currently defined protocols and names are:
    Protocol Variable | 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
    icmp6 reflect_pmtu boolean yes
    icmp6 dynamic_rt_msg boolean yes
    ip6 accept_rtadv integer yes
    ip6 addctlpolicy struct in6_addrpolicy no
    ip6 anonportalgo.selected string yes
    ip6 anonportalgo.available string yes
    ip6 anonportalgo.reserve struct yes
    ip6 anonportmax integer yes
    ip6 anonportmin integer yes
    ip6 auto_flowlabel integer yes
    ip6 dad_count integer yes
    ip6 defmcasthlim integer yes
    ip6 forwarding integer yes
    ip6 gifhlim integer yes
    ip6 hashsize integer yes
    ip6 hlim integer yes
    ip6 hdrnestlimit integer yes
    ip6 kame_version string no
    ip6 keepfaith integer yes
    ip6 log_interval integer yes
    ip6 lowportmax integer yes
    ip6 lowportmin integer yes
    ip6 maxdynroutes integer yes
    ip6 maxifprefixes integer yes
    ip6 maxifdefrouters integer yes
    ip6 maxflows integer yes
    ip6 maxfragpackets integer yes
    ip6 maxfrags integer yes
    ip6 neighborgcthresh integer yes
    ip6 param_rt_msg integer yes
    ip6 redirect integer yes
    ip6 rr_prune integer yes
    ip6 use_deprecated integer yes
    ip6 v6only integer yes
    udp6 do_loopback_cksum integer yes
    udp6 recvspace integer yes
    udp6 sendspace integer yes

    The variables are as follows:

    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.

    ip6.anonportalgo.available
        The available RFC 6056 port randomization algorithms.

    ip6.anonportalgo.reserve
        A bitmask of ports that will not be used during anonymous or privileged port selection.

    ip6.anonportalgo.selected
        The currently selected RFC 6056 port randomization algorithm; see rfc6056(7) for details.

    ip6.anonportmax
        The highest port number to use for TCP and UDP ephemeral port allocation. This cannot be set to less than 1024 or greater than 65535, and must be greater than ip6.anonportmin.

    ip6.anonportmin
        The lowest port number to use for TCP and UDP ephemeral port allocation. This cannot be set to less than 1024 or greater than 65535.

    ip6.auto_flowlabel
        On connected transport protocol packets, fill IPv6 flowlabel field to help intermediate routers to identify packet flows.

    ip6.dad_count
        The variable configures number of IPv6 DAD (duplicated address detection) probe packets. The packets will be generated when IPv6 interface addresses are configured.

    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. There are APIs to override the value, as documented in ip6(4).

    ip6.forwarding
        If set to 1, enables IPv6 forwarding for the node, meaning that the node is acting as a router. If set to 0, disables IPv6 forwarding for the node, meaning that the node is acting as a host. IPv6 specification defines node behavior for “router” case and “host” case quite differently, and changing this variable during operation may cause serious trouble. It is recommended to configure the variable at bootstrap time, and bootstrap time only.

    ip6.gifhlim
        The maximum hop limit value for an IPv6 packet generated by gif(4) tunnel interface.

    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.hashsize
        The size of IPv6 Fast Forward hash table. This value must be a power of 2 (64, 256, ...). A larger hash table size results in fewer collisions. Also see ip6.maxflows.

    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. There are APIs to override the value, as documented in ip6(4).

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

    ip6.keepfaith
        If set to non-zero, it enables “FAITH” TCP relay IPv6-to-IPv4 translator code in the kernel. Refer faith(4) and faithd(8) for detail.

    ip6.log_interval
        The variable controls amount of logs generated by IPv6 packet forwarding engine, by setting interval between log output (in seconds).

    ip6.lowportmax
        The highest port number to use for TCP and UDP reserved port allocation. This cannot be set to less than 0 or greater than 1024, and must be greater than ip6.lowportmin.

    ip6.lowportmin
        The lowest port number to use for TCP and UDP reserved port allocation. This cannot be set to less than 0 or greater than 1024, and must be smaller than ip6.lowportmax.

    ip6.maxdynroutes
        Maximum number of routes created by redirect. Set it to negative to disable. The default value is 4096.

    ip6.maxifprefixes
        Maximum number of prefixes created by route advertisements per interface. Set it to negative to disable. The default value is 16.

    ip6.maxifdefrouters 16
        Maximum number of default routers created by route advertisements per interface. Set it to negative to disable. The default value is 16.

    ip6.maxflows
        IPv6 Fast Forwarding is enabled by default. If set to 0, IPv6 Fast Forwarding is disabled. ip6.maxflows controls the maximum amount of flows which can be created. The default value is 256.

    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.neighborgcthresh
        Maximum number of entries in neighbor cache per interface. Set to negative to disable. The default value is 2048.

    ip6.param_rt_msg
        If set to 0, parameter changing routing message is suppressed. If set to 1, parameter changing routing message is sent by RTM_NEWADDR. Other values are undefined yet.

    ip6.redirect
        If set to 1, 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
        The variable specifies interval between IPv6 router renumbering prefix babysitting, in seconds.

    ip6.use_deprecated
        The variable controls use of deprecated address, specified in RFC 2462 5.5.4.

    ip6.v6only
        The variable specifies initial value for IPV6_V6ONLY socket option for AF_INET6 socket. Please refer to ip6(4) for detail.

    icmp6.errppslimit
        The variable specifies the maximum number of outgoing ICMPv6 error messages, per second. ICMPv6 error messages that exceeded the value are subject to rate limitation and will not go out from the node. Negative value disables rate limitation.

    icmp6.mtudisc_hiwat

    icmp6.mtudisc_lowat
        The variables define the maximum number of routing table entries, created due to path MTU discovery (prevents denial-of-service attacks with ICMPv6 too big messages). When IPv6 path MTU discovery happens, we keep path MTU information into 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, kernel IPv6 neighbor discovery code will generate debugging messages. The debug outputs are useful to diagnose IPv6 interoperability issues. The flag must be set to 0 for normal operation.

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

    icmp6.nd6_maxnudhint
        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 discovery layer will take 3 consecutive hints in maximum. After receiving 3 hints, neighbor discovery layer will perform normal neighbor discovery process.

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

    icmp6.nd6_prune
        The variable specifies interval between IPv6 neighbor cache babysitting, in seconds.

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

    icmp6.nd6_useloopback
        If set to non-zero, kernel IPv6 stack will use 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 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, and the variable is meaningful on IPv6 hosts (non-router) only.

    icmp6.redirtimeout
        The variable specifies lifetime of routing entries generated by incoming ICMPv6 redirect.

    icmp6.reflect_pmtu
        A boolean that icmpv6 reflecting uses path MTU discovery or not. When not, icmpv6 reflecting uses IPV6_MINMTU.

    icmp6.dynamic_rt_msg
        A boolean that the kernel sends routing message for RTM_DYNAMIC or not. If set to true, sends such routing message.

    udp6.do_loopback_cksum
        Perform UDP checksum on loopback.

    udp6.recvspace
        Default UDP receive buffer size.

    udp6.sendspace
        Default UDP send buffer size.

    Variables net.inet6.tcp6.* and net.inet6.udp6.* have identical meanings to net.inet.tcp.* and net.inet.udp.*, respectively. Please refer to PF_INET section above. For variables net.*.ipsec6, please refer to ipsec(4).

net.key (PF_KEY)
    Get or set various global information about the IPsec key management. The third level name is the variable name. The currently defined variable and names are:
    Variable Type | Changeable
    debug integer yes
    enabled integer yes
    used integer no
    spi_try integer yes
    spi_min_value integer yes
    spi_max_value integer yes
    larval_lifetime integer yes
    blockacq_count integer yes
    blockacq_lifetime integer yes
    esp_keymin integer yes
    esp_auth integer yes
    ah_keymin integer yes
    allow_different_idtype boolean yes
    The variables are as follows:

    debug
        Turn on debugging message from within the kernel. The value is a bitmap, as defined in <netipsec/key_debug.h>.

    enabled
        Control processing of IPsec control messages.

        0   Never allow IPsec processing

        1   Allow IPsec processing when SPD policies are present.

        2   Force IPsec processing even when SPD policies are not present.

    used
        Based on if IPsec is enabled, and SPD rule existence, show if IPsec is being used. Note that currently once IPsec is being used, it cannot be disabled.

    spi_try
        The number of times the kernel will try to obtain an unique SPI when it generates it from random number generator.

    spi_min_value
        Minimum SPI value when generating it within the kernel.

    spi_max_value
        Maximum SPI value when generating it within the kernel.

    larval_lifetime
        Lifetime for LARVAL SAD entries, in seconds.

    blockacq_count
        Number of ACQUIRE PF_KEY messages to be blocked after an ACQUIRE message. It avoids flood of ACQUIRE PF_KEY from being sent from the kernel to the key management daemon.

    blockacq_lifetime
        Lifetime of ACQUIRE PF_KEY message.

    esp_keymin
        Minimum ESP key length, in bits. The value is used when the kernel creates proposal payload on ACQUIRE PF_KEY message.

    esp_auth
        Whether ESP authentication should be used or not. Non-zero value indicates that ESP authentication should be used. The value is used when the kernel creates proposal payload on ACQUIRE PF_KEY message.

    ah_keymin
        Minimum AH key length, in bits, The value is used when the kernel creates proposal payload on ACQUIRE PF_KEY message.

    allow_different_idtype
        A boolean that allow or disallow different identifier types on IDii and IDir. Allowing that can improve interconnectivity to some VPN appliances.

net.local (PF_LOCAL)
    Get or set various global information about AF_LOCAL type sockets. For some variables, the third level name is the variable name:
    Variable Type | Changeable
    inflight integer no
    deferred integer no
    The variables are as follows:

    inflight
        The number of file descriptors currently passed between processes, "in flight".

    deferred
        The number of file descriptors passed between processes that have been deferred for cleanup by a kernel task.

    Other variables are specific to a socket type:
    Socket Type Variable Type | Changeable
    dgram pcblist struct no
    dgram recvspace integer yes
    dgram sendspace integer yes
    seqpacket pcblist struct no
    stream pcblist struct no
    stream recvspace integer yes
    stream sendspace integer yes
    The variables are as follows:

    dgram.pcblist
        The Protocol Control Block list structure for datagram sockets. Parsed by netstat(1) or sockstat(1).

    dgram.recvspace
        The default datagram receive buffer size.

    dgram.sendspace
        The default datagram send buffer size.

    seqpacket.pcblist
        The Protocol Control Block list structure for Sequential Packet sockets. Parsed by netstat(1) or sockstat(1).

    stream.pcblist
        The Protocol Control Block list structure for stream sockets. Parsed by netstat(1) or sockstat(1).

    stream.recvspace
        The default stream receive buffer size.

    stream.sendspace
        The default stream send buffer size.

  The proc.* subtree
The string and integer information available for the proc level is detailed below. The changeable column shows whether a process with appropriate privilege may change the value. These values are per-process, and as such may change from one process to another. When a process is created, the default values are inherited from its parent. When a set-user-ID or set-group-ID binary is executed, the value of PROC_PID_CORENAME is reset to the system default value. The second level name is either the magic value PROC_CURPROC, which points to the current process, or the PID of the target process.
Third level name | Type | Changeable
proc.pid.corename string yes
proc.pid.rlimit node not applicable
proc.pid.stopfork int yes
proc.pid.stopexec int yes
proc.pid.stopexit int yes
proc.pid.paxflags int no

proc.pid.corename (PROC_PID_CORENAME)
    The template used for the core dump file name (see core(5) for details). The base name must either be core or end with the suffix .core (the super-user may set arbitrary names). By default it points to KERN_DEFCORENAME.

proc.pid.rlimit (PROC_PID_LIMIT)
    Return resources limits, as defined for the getrlimit(2) and setrlimit(2) system calls. The fourth level name is one of:

    proc.pid.rlimit.cputime (PROC_PID_LIMIT_CPU)
        The maximum amount of CPU time (in seconds) to be used by each process.

    proc.pid.rlimit.filesize (PROC_PID_LIMIT_FSIZE)
        The largest size (in bytes) file that may be created.

    proc.pid.rlimit.datasize (PROC_PID_LIMIT_DATA)
        The maximum size (in bytes) of the data segment for a process; this defines how far a program may extend its break with the sbrk(2) system call.

    proc.pid.rlimit.stacksize (PROC_PID_LIMIT_STACK)
        The maximum size (in bytes) of the stack segment for a process; this defines how far a program's stack segment may be extended. Stack extension is performed automatically by the system.

    proc.pid.rlimit.coredumpsize (PROC_PID_LIMIT_CORE)
        The largest size (in bytes) core file that may be created.

    proc.pid.rlimit.memoryuse (PROC_PID_LIMIT_RSS)
        The maximum size (in bytes) to which a process's resident set size may grow. This imposes a limit on the amount of physical memory to be given to a process; if memory is tight, the system will prefer to take memory from processes that are exceeding their declared resident set size.

    proc.pid.rlimit.memorylocked (PROC_PID_LIMIT_MEMLOCK)
        The maximum size (in bytes) which a process may lock into memory using the mlock(2) function.

    proc.pid.rlimit.maxproc (PROC_PID_LIMIT_NPROC)
        The maximum number of simultaneous processes for this user id.

    proc.pid.rlimit.descriptors (PROC_PID_LIMIT_NOFILE)
        The maximum number of open files for this process.

    proc.pid.rlimit.sbsize (PROC_PID_LIMIT_SBSIZE)
        The maximum size (in bytes) of the socket buffers set by the setsockopt(2) SO_RCVBUF and SO_SNDBUF options.

    proc.pid.rlimit.vmemoryuse (PROC_PID_LIMIT_AS)
        The maximum size (in bytes) which a process can obtain.

    proc.pid.rlimit.maxlwp (PROC_PID_LIMIT_NTHR)
        The maximum number of threads that cen be created and running at one time in the process. The first thread of each process is not counted against this.

    The fifth level name is one of soft (PROC_PID_LIMIT_TYPE_SOFT) or hard (PROC_PID_LIMIT_TYPE_HARD), to select respectively the soft or hard limit. Both are of type integer.

proc.pid.stopfork (PROC_PID_STOPFORK)
    If non zero, the process' children will be stopped after fork(2) calls. The children are created in the SSTOP state and are never scheduled for running before being stopped. This feature enables attaching to a process with a debugger such as gdb(1) before the process has the opportunity to actually do anything.

    This value is inherited by the process's children, and it also applies to emulation specific system calls that fork a new process, such as sproc() or clone().

proc.pid.stopexec (PROC_PID_STOPEXEC)
    If non zero, the process will be stopped on the next exec(3) call. The process created by exec(3) is created in the SSTOP state and is never scheduled for running before being stopped. This feature enables attaching to a process with a debugger such as gdb(1) before the process has the opportunity to actually do anything.

    This value is inherited by the process's children.

proc.pid.stopexit (PROC_PID_STOPEXIT)
    If non zero, the process will be stopped when it has cause to exit, either by way of calling exit(3), _exit(2), or by the receipt of a specific signal. The process is stopped before any of its resources or vm space is released allowing examination of the termination state of the process before it disappears. This feature can be used to examine the final conditions of the process's vmspace via pmap(1) or its resource settings with sysctl(8) before it disappears.

    This value is also inherited by the process's children.

proc.pid.paxflags (PROC_PID_PAXFLAGS)
    This read-only variable returns the current value of the process's pax flags (see paxctl(8)).

  The user.* subtree ( CTL_USER )
The string and integer information available for the user level is detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
Second level name | Type | Changeable
user.atexit_max integer no
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.stream_max integer no
user.tzname_max integer no

user.atexit_max (USER_ATEXIT_MAX)
    The maximum number of functions that may be registered with atexit(3).

user.bc_base_max (USER_BC_BASE_MAX)
    The maximum ibase/obase values in the bc(1) utility.

user.bc_dim_max (USER_BC_DIM_MAX)
    The maximum array size in the bc(1) utility.

user.bc_scale_max (USER_BC_SCALE_MAX)
    The maximum scale value in the bc(1) utility.

user.bc_string_max (USER_BC_STRING_MAX)
    The maximum string length in the bc(1) utility.

user.coll_weights_max (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 (USER_CS_PATH)
    Return a value for the PATH environment variable that finds all the standard utilities.

user.expr_nest_max (USER_EXPR_NEST_MAX)
    The maximum number of expressions that can be nested within parenthesis by the expr(1) utility.

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

user.posix2_char_term (USER_POSIX2_CHAR_TERM)
    Return 1 if the system supports at least one terminal type capable of all operations described in p1003.2, otherwise 0.

user.posix2_c_bind (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 (USER_POSIX2_C_DEV)
    Return 1 if the system supports the C-Language Development Utilities Option, otherwise 0.

user.posix2_fort_dev (USER_POSIX2_FORT_DEV)
    Return 1 if the system supports the FORTRAN Development Utilities Option, otherwise 0.

user.posix2_fort_run (USER_POSIX2_FORT_RUN)
    Return 1 if the system supports the FORTRAN Runtime Utilities Option, otherwise 0.

user.posix2_localedef (USER_POSIX2_LOCALEDEF)
    Return 1 if the system supports the creation of locales, otherwise 0.

user.posix2_sw_dev (USER_POSIX2_SW_DEV)
    Return 1 if the system supports the Software Development Utilities Option, otherwise 0.

user.posix2_upe (USER_POSIX2_UPE)
    Return 1 if the system supports the User Portability Utilities Option, otherwise 0.

user.posix2_version (USER_POSIX2_VERSION)
    The version of p1003.2 with which the system attempts to comply.

user.re_dup_max (USER_RE_DUP_MAX)
    The maximum number of repeated occurrences of a regular expression permitted when using interval notation.

user.stream_max (USER_STREAM_MAX)
    The minimum maximum number of streams that a process may have open at any one time.

user.tzname_max (USER_TZNAME_MAX)
    The minimum maximum number of types supported for the name of a timezone.

  The vm.* subtree ( CTL_VM )
The string and integer information available for the vm level is detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
Second level name | Type | Changeable
vm.anonmax int yes
vm.anonmin int yes
vm.bufcache int yes
vm.bufmem int no
vm.bufmem_hiwater int yes
vm.bufmem_lowater int yes
vm.execmax int yes
vm.execmin int yes
vm.filemax int yes
vm.filemin int yes
vm.loadavg struct loadavg no
vm.maxslp int no
vm.nkmempages int no
vm.uspace int no
vm.uvmexp struct uvmexp no
vm.uvmexp2 struct uvmexp_sysctl no
vm.vmmeter struct vmtotal no
vm.proc.map struct kinfo_vmentry no
vm.guard_size unsigned int no
vm.thread_guard_size unsigned int yes
vm.swap_encrypt bool yes

vm.anonmax (VM_ANONMAX)
    The percentage of physical memory which will be reclaimed from other types of memory usage to store anonymous application data.

vm.anonmin (VM_ANONMIN)
    The percentage of physical memory which will be always be available for anonymous application data.

vm.bufcache (VM_BUFCACHE)
    The percentage of physical memory which will be available for the buffer cache.

vm.bufmem (VM_BUFMEM)
    The amount of kernel memory that is being used by the buffer cache.

vm.bufmem_lowater (VM_BUFMEM_LOWATER)
    The minimum amount of kernel memory to reserve for the buffer cache.

vm.bufmem_hiwater (VM_BUFMEM_HIWATER)
    The maximum amount of kernel memory to be used for the buffer cache.

vm.execmax (VM_EXECMAX)
    The percentage of physical memory which will be reclaimed from other types of memory usage to store cached executable data.

vm.execmin (VM_EXECMIN)
    The percentage of physical memory which will be always be available for cached executable data.

vm.filemax (VM_FILEMAX)
    The percentage of physical memory which will be reclaimed from other types of memory usage to store cached file data.

vm.filemin (VM_FILEMIN)
    The percentage of physical memory which will be always be available for cached file data.

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

vm.maxslp (VM_MAXSLP)
    The value of the maxslp kernel global variable.

vm.vmmeter (VM_METER)
    Return system wide virtual memory statistics. The returned data consists of a struct vmtotal.

vm.user_va0_disable
    A flag which controls whether user processes can map virtual address 0.

vm.proc.map (VM_PROC)
    The third level is VM_PROC_MAP, the fourth is the pid of the process to display the vm object entries for, and the fifth is the size of struct kinfo_vmentry. Returns an array of struct kinfo_vmentry objects.

vm.ubc_direct [EXPERIMENTAL, default off]
    Use direct map for UBC I/O, avoiding need to map and unmap buffer memory. Speeds up operation for fast I/O devices like NVMe, especially on multi-CPU systems. Only available on some architectures.

vm.uspace (VM_USPACE)
    The number of bytes allocated for each kernel stack.

vm.uvmexp (VM_UVMEXP)
    Return system wide virtual memory statistics. The returned data consists of a struct uvmexp.

vm.uvmexp2 (VM_UVMEXP2)
    Return system wide virtual memory statistics. The returned data consists of a struct uvmexp_sysctl.

vm.guard_size
    Return system wide guard size for the main thread of a program.

vm.thread_guard_size
    Return system wide default size for the guard area of all other threads of a program.

vm.swap_encrypt
    If true, encrypt data while swapped out to disk.

    Each swap device maintains an independent AES-256 key, generated when the first page is swapped to that device. Each page is swapped independently using AES-CBC, with an initialization vector chosen by the encryption under the AES-256 key of the little-endian swap slot number padded to 128 bits with zeros. (This is essentially the cgd(4) ‘encblkno1’ method.)

    Changes to vm.swap_encrypt only affect pages of swap newly written out. To force encrypting or decrypting all existing swap, or to rekey previously encrypted swap, you can remove the swap devices and re-add them with swapctl(8), with the caveat that whatever pages were already written to disk unencrypted or encrypted with a compromised key may still be written to disk afterward.

  The ddb.* subtree ( CTL_DDB )
The information available for the ddb level is detailed below. The changeable column shows whether a process with appropriate privilege may change the value.
Second level name | Type | Changeable
ddb.commandonenter string yes
ddb.dumpstack integer yes
ddb.fromconsole integer yes
ddb.lines integer yes
ddb.maxoff integer yes
ddb.maxwidth integer yes
ddb.onpanic integer yes
ddb.panicstackframes integer yes
ddb.radix integer yes
ddb.tabstops integer yes
ddb.tee_msgbuf integer yes

ddb.commandonenter
    If not empty, the string is used as the DDB command to be executed each time DDB is entered.

ddb.dumpstack
    A value of 1 causes a stack trace to be printed on entering ddb from a panic. A value of 0 disables this behaviour. The default value is 1.

ddb.fromconsole (DDBCTL_FROMCONSOLE)
    If not zero, DDB may be entered by sending a break on a serial console or by a special key sequence on a graphics console.

ddb.lines (DDBCTL_LINES)
    Number of display lines.

ddb.maxoff (DDBCTL_MAXOFF)
    The maximum symbol offset.

ddb.maxwidth (DDBCTL_MAXWIDTH)
    The maximum output line width.

ddb.onpanic (DDBCTL_ONPANIC)
    If greater than zero, DDB will be entered if the kernel panics. A value of 1 causes the system to enter DDB on panic. A value of 0 causes the kernel to attempt to print a stack trace, then reboot, while a value of -1 means neither a stack trace will be printed nor DDB entered.

ddb.panicstackframes
    Number of stack frames to display on panic. Useful to avoid scrolling away the interesting frames on a glass tty. Default value is 65535 (all frames), useful value around 10.

ddb.radix (DDBCTL_RADIX)
    The input and output radix.

ddb.tabstops (DDBCTL_TABSTOPS)
    Tab width.

ddb.tee_msgbuf
    If not zero, DDB will output also to the kernel message buffer.

Some of these MIB nodes are also available as variables from within the debugger. See ddb(4) for more details.

  The security.* subtree ( CTL_SECURITY )
The security level contains various security-related settings for the system. The available second level names are:
Second level name | Type | Changeable
security.curtain integer yes
security.models node not applicable
security.pax node not applicable

Available settings are detailed below.

security.curtain
    If non-zero, will filter return objects according to the user ID requesting information about them, preventing users from accessing any objects they do not own.

    At the moment, it affects ps(1), netstat(1) (for PF_INET, PF_INET6, and PF_UNIX PCBs), and w(1).

security.models
    NetBSD supports pluggable security models. Every security model used, whether if loaded as a module or built with the system, is required to add an entry to this node with at least one element, “name”, indicating the name of the security model.

    In addition to the name, any settings and other information private to the security model will be available under this node. See secmodel(9) for more information.

security.pax
    Settings for PaX — exploit mitigation features. For more information on any of the PaX features, please see paxctl(8) and security(7). The available third and fourth level names are:
    Third and fourth level names | Type | Changeable
    security.pax.aslr.enabled integer yes
    security.pax.aslr.global integer yes
    security.pax.mprotect.enabled integer yes
    security.pax.mprotect.global integer yes
    security.pax.mprotect.ptrace integer yes
    security.pax.segvguard.enabled integer yes
    security.pax.segvguard.expiry_timeout integer yes
    security.pax.segvguard.global integer yes
    security.pax.segvguard.max_crashes integer yes
    security.pax.segvguard.suspend_timeout integer yes

    security.pax.aslr.enabled
        Enable PaX ASLR (Address Space Layout Randomization).

        The value of this knob must be non-zero for PaX ASLR to be enabled, even if a program is set to explicit enable.

    security.pax.aslr.global
        Specifies the default global policy for programs without an explicit enable/disable flag.

        When non-zero, all programs will get PaX ASLR, except those exempted with paxctl(8). Otherwise, all programs will not get PaX ASLR, except those specifically marked as such with paxctl(8).

    security.pax.mprotect.enabled
        Enable PaX MPROTECT restrictions.

        These are mprotect(2) restrictions to better enforce a W^X policy. The value of this knob must be non-zero for PaX MPROTECT to be enabled, even if a program is set to explicit enable.

    security.pax.mprotect.global
        Specifies the default global policy for programs without an explicit enable/disable flag.

        When non-zero, all programs will get the PaX MPROTECT restrictions, except those exempted with paxctl(8). Otherwise, all programs will not get the PaX MPROTECT restrictions, except those specifically marked as such with paxctl(8).

    security.pax.mprotect.ptrace
        This variable allows ptrace(2) to override PaX MPROTECT permissions. It can have the following values:
        0   Does not let override any permissions.
        1   Disables PaX MPROTECT from processes that start executing while traced (default).
        2   Bypasses PaX MPROTECT for all processes being traced.

    security.pax.segvguard.enabled
        Enable PaX Segvguard.

        PaX Segvguard can detect and prevent certain exploitation attempts, where an attacker may try for example to brute-force function return addresses of respawning daemons.

        Note: The NetBSD interface and implementation of the Segvguard is still experimental, and may change in future releases.

    security.pax.segvguard.expiry_timeout
        If the max number was not reached within this timeout (in seconds), the entry will expire.

    security.pax.segvguard.global
        Specifies the default global policy for programs without an explicit enable/disable flag.

        When non-zero, all programs will get the PaX Segvguard, except those exempted with paxctl(8). Otherwise, no program will get the PaX Segvguard restrictions, except those specifically marked as such with paxctl(8).

    security.pax.segvguard.max_crashes
        The maximum number of segfaults a program can receive before suspension.

    security.pax.segvguard.suspend_timeout
        Number of seconds to suspend a user from running a faulting program when the limit was exceeded.

  The vendor.* subtree ( CTL_VENDOR )
The vendor toplevel name is reserved to be used by vendors who wish to have their own private MIB tree. Intended use is to store values under “vendor.<yourname>.*”.

SEE ALSO
sysctl(3), ipsec(4), tcp(4), security(7), sysctl(8)

HISTORY
The sysctl variables first appeared in 4.4BSD.