May 18, 2009 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 filesystems. One of its third level identifiers is ```vfs.generic.maxtypenum`(`VFS_MAXTYPENUM`) that gives the highest valid filesystem type number. Its other third level identifier is ```vfs.generic.conf`(`VFS_CONF`) that returns configuration information about the filesystem type given as a fourth level identifier. The remaining second level identifiers are the filesystem type number returned by a statvfs(2) call or from ```vfs.generic.conf`. The third level identifiers available for each filesystem are given in the header file that defines the mount argument structure for that filesystem.

### 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.acpi.supported_states string no
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.pagesize integer no
hw.physmem integer no
hw.physmem64 quad no
hw.usermem integer no
hw.usermem64 quad no

```hw.acpi.support_states`
  List of possible ACPI sleep states. The list can contain the following values:

  S0
    fully running

  S1
    power on suspend (CPU and hard disks are off)

  S2
    similar to S3, usually not implemented

  S3
    suspend-to-RAM

  S4
    suspend-to-disk (needs BIOS support)

  S5
    power off

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

```hw.byteorder`(`HW_BYTEORDER`
  ) The byteorder (4,321, or 1,234).

```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.

```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

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. The types of data currently available are process information, system vnodes, the open file entries, routing table entries, virtual memory statistics, load average history, and clock rate information.

Second level name Type Changeable
kern.argmax integer no
kern.autonicetime integer yes
kern.autoniceval integer yes
kern.boottime struct timeval no
kern.bufq node not applicable
kern.ccpu integer no
kern.clockrate struct clockinfo no
kern.consdev integer no
kern.cp_id struct no
kern.cp_time uint64_t[] no
kern.defcorename string yes
kern.domainname string yes
kern.drivers struct kinfo_drivers no
kern.file struct file no
kern.forkfsleep integer yes
kern.fscale integer no
kern.fsync integer no
kern.hardclock_ticks integer no
kern.hostid integer yes
kern.hostname string yes
kern.iov_max integer no
kern.job_control integer no
kern.labeloffset integer no
kern.labelsector integer no
kern.login_name_max integer no
kern.logsigexit integer yes
kern.mapped_files integer no
kern.maxfiles integer yes
kern.maxpartitions integer no
kern.maxphys integer no
kern.maxproc integer yes
kern.maxptys integer yes
kern.maxvnodes integer yes
kern.mbuf node not applicable
kern.memlock integer no
kern.memlock_range integer no
kern.memory_protection integer no
kern.monotonic_clock integer no
kern.msgbuf integer no
kern.msgbufsize integer no
kern.ngroups integer no
kern.ntptime struct ntptimeval no
kern.osrelease string no
kern.osrev integer no
kern.ostype string no
kern.pipe node not applicable
kern.posix1 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.prof 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.securelevel integer raise only
kern.synchronized_io integer no
kern.ipc node not applicable
kern.timex struct no
kern.tkstat node not applicable
kern.urandom integer no
kern.version string no
kern.vnode struct vnode no

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

```kern.autonicetime`(`KERN_AUTONICETIME`
  ) The number of seconds of CPU-time a non-root process may accumulate before having its priority lowered from the default to the value of KERN_AUTONICEVAL. If set to 0, automatic lowering of priority is not performed, and if set to -1 all non-root processes are immediately lowered.

```kern.autoniceval`(`KERN_AUTONICEVAL`
  ) The priority assigned for automatically niced processes.

```kern.boottime`(`KERN_BOOTTIME`
  ) A struct timeval structure is returned. This structure contains the time that the system was booted.

```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.

```kern.consdev`(`KERN_CONSDEV`
  ) Console device.

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

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

```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.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 POSIX 1003.1b File Synchronization Option is available on this system, otherwise 0.

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

```kern.hostid`(`KERN_HOSTID`
  ) Get or set the host id.

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

```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.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.mapped_files`(`KERN_MAPPED_FILES`
  ) Returns 1 if the POSIX 1003.1b 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.

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

```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 can only be raised.

```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

  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.memlock`(`KERN_MEMLOCK`
  ) Returns 1 if the POSIX 1003.1b Process Memory Locking Option is available on this system, otherwise 0.

```kern.memlock_range`(`KERN_MEMLOCK_RANGE`
  ) Returns 1 if the POSIX 1003.1b Range Memory Locking Option is available on this system, otherwise 0.

```kern.memory_protection`(`KERN_MEMORY_PROTECTION`
  ) Returns 1 if the POSIX 1003.1b Memory Protection Option is available on this system, otherwise 0.

```kern.monotonic_clock`(`KERN_MONOTONIC_CLOCK`
  ) Returns the standard version the implementation of the POSIX 1003.1b Monotonic Clock Option conforms to, otherwise 0.

```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 string.

```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.posix1version`(`KERN_POSIX1`
  ) The version of ISO/IEC 9945 (POSIX 1003.1) with which the system attempts to comply.

```kern.posix_barriers`(`KERN_POSIX_BARRIERS`
  ) The version of IEEE Std 1003.1 (``POSIX.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 IEEE Std 1003.1 (``POSIX.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 IEEE Std 1003.1 (``POSIX.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 IEEE Std 1003.1 (``POSIX.1'') and its Spin Locks option to which the system attempts to conform, otherwise 0.

```kern.posix_threads`(`KERN_POSIX_THREADS`
  ) The version of IEEE Std 1003.1 (``POSIX.1'') and its Threads option to which the system attempts to conform, otherwise 0.

```kern.posix_timers`(`KERN_POSIX_TIMERS`
  ) The version of IEEE Std 1003.1 (``POSIX.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.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.

```kern.securelevel`(`KERN_SECURELVL`
  ) The system security level. This level may be raised by processes with appropriate privilege. It may only be lowered by process 1.

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

```kern.synchronized_io`(`KERN_SYNCHRONIZED_IO`
  ) Returns 1 if the POSIX 1003.1b Synchronized I/O Option is available on this system, otherwise 0.

```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.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.urandom`(`KERN_URND`
  ) Random integer value.

```kern.veriexec`
  Tunings for Verixec.

  ```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(8) 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.

```kern.coredump.setid`
  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.

  ```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.

### The machdep.* subtree

The set of variables defined is architecture dependent. Most architectures define at least the following variables.

Second level name Type Changeable
```CPU_CONSDEV dev_t no`

### 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 name Variable name Type Changeable
  arp down integer yes
  arp keep integer yes
  arp prune integer yes
  arp refresh 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
  ip allowsrcrt integer yes
  ip anonportmax integer yes
  ip anonportmin integer yes
  ip checkinterface 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 compat_42 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.down`
    Failed ARP entry lifetime.

  ```arp.keep`
    Valid ARP entry lifetime.

  ```arp.prune`
    ARP cache pruning interval.

  ```arp.refresh`
    ARP entry refresh interval.

  ```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.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 ipnat 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.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.

  ```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.compat_42`
    If set to 1, enables work-arounds for bugs in the 4.2BSD TCP implementation. Use of this option is not recommended, although it may be required in order to communicate with extremely old TCP implementations.

  ```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. If this value is 0, an auto-tuning algorithm designed to use an initial window of approximately 4K bytes is in use. Otherwise, this value indicates a fixed number of packets.

  ```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.sendspace`
    The default UDP send buffer size.

  ```udp.recvspace`
    The default UDP receive 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 name Variable name Type Changeable
  icmp6 errppslimit integer yes
  icmp6 mtudisc_hiwat integer yes
  icmp6 mtudisc_lowat integer yes
  icmp6 nd6_debug integer yes
  icmp6 nd6_delay integer yes
  icmp6 nd6_maxnudhint integer yes
  icmp6 nd6_mmaxtries integer yes
  icmp6 nd6_prune integer yes
  icmp6 nd6_umaxtries integer yes
  icmp6 nd6_useloopback integer yes
  icmp6 nodeinfo integer yes
  icmp6 rediraccept integer yes
  icmp6 redirtimeout integer yes
  ip6 accept_rtadv integer yes
  ip6 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 maxflows integer yes
  ip6 maxfragpackets integer yes
  ip6 maxfrags 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.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.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.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`
    IPv6 neighbor discovery permits upper layer protocols to supply reachability hints, to avoid unnecessary neighbor discovery exchanges. The variable defines the number of consecutive hints the neighbor discovery layer will take. For example, by setting the variable to 3, neighbor 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.

  ```udp6.do_loopback_cksum`
    Perform UDP checksum on loopback.

  ```udp6.recvspace`
    Default UDP receive buffer size.

  ```udp6.sendspace`
    Default UDP send buffer size.

  We reuse net.*.tcp for TCP over IPv6, and therefore we do not have variables net.*.tcp6. Variables net.inet6.udp6 have identical meaning to net.inet.udp. 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 name Type Changeable
  debug integer yes
  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

  The variables are as follows:

  ```debug`
    Turn on debugging message from within the kernel. The value is a bitmap, as defined in ```/usr/include/netkey/key_debug.h`.

  ```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.

### 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.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.

  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 is created in the SSTOP state and is never scheduled for running before being stopped. This feature helps attaching a process with a debugger such as gdb(1) before it had the opportunity to actually do anything.

  This value is inherited by the process's children, and it also apply 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 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 helps attaching a process with a debugger such as gdb(1) before it had 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 on 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 a 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.

### 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 POSIX 1003.2, 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 POSIX 1003.2 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.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.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.

### The ddb.* subtree ( CTL_DDB )

The integer 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.radix integer yes
ddb.maxoff integer yes
ddb.lines integer yes
ddb.tabstops integer yes
ddb.onpanic integer yes
ddb.fromconsole integer yes

```ddb.radix`(`DBCTL_RADIX`
  ) The input and output radix.

```ddb.maxoff`(`DBCTL_MAXOFF`
  ) The maximum symbol offset.

```ddb.lines`(`DBCTL_LINES`
  ) Number of display lines.

```ddb.tabstops`(`DBCTL_TABSTOPS`
  ) Tab width.

```ddb.onpanic`(`DBCTL_ONPANIC`
  ) If non-zero, DDB will be entered if the kernel panics.

```ddb.fromconsole`(`DBCTL_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.

These MIB nodes are also available as variables from within the DDB. See ddb(4) for more details.

### The security.* subtree ( CTL_SECURITY )

The ```security` level contains various security-related settings for the system. Available settings are detailed below.

```security.curtain`
  If non-zero, will filter return objects according to the user-id requesting information about them, preventing from users any access to objects they don't 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 an LKM 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(8).

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

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

  ```security.pax.segvguard.max_crashes`
    Max number of segfaults a program can receive before suspension.

### 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(8), sysctl(8)

### HISTORY

The sysctl variables first appeared in 4.4BSD.