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SYSCTL(3)                   BSD Programmer's Manual                  SYSCTL(3)

NAME
     sysctl - get or set system information

SYNOPSIS
     #include <&lt;sys/sysctl.h>&gt;

     int
     sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp, void *newp,
             size_t newlen);

DESCRIPTION
     The sysctl function retrieves system information and allows processes
     with appropriate privileges to set system information.  The information
     available from sysctl consists of integers, strings, and tables.  Infor-
     mation may be retrieved and set from the command interface using the
     sysctl(1) utility.

     Unless explicitly noted below, sysctl returns a consistent snapshot of
     the data requested.  Consistency is obtained by locking the destination
     buffer into memory so that the data may be copied out without blocking.
     Calls to sysctl are serialized to avoid deadlock.

     The state is described using a ``Management Information Base'' (MIB)
     style name, listed in name, which is a namelen length array of integers.

     The information is copied into the buffer specified by oldp. The size of
     the buffer is given by the location specified by oldlenp before the call,
     and that location gives the amount of data copied after a successful
     call.  If the amount of data available is greater than the size of the
     buffer supplied, the call supplies as much data as fits in the buffer
     provided and returns with the error code ENOMEM.  If the old value is not
     desired, oldp and oldlenp should be set to NULL.

     The size of the available data can be determined by calling sysctl with a
     NULL parameter for oldp. The size of the available data will be returned
     in the location pointed to by oldlenp. For some operations, the amount of
     space may change often.  For these operations, the system attempts to
     round up so that the returned size is large enough for a call to return
     the data shortly thereafter.

     To set a new value, newp is set to point to a buffer of length newlen
     from which the requested value is to be taken.  If a new value is not to
     be set, newp should be set to NULL and newlen set to 0.

     The top level names are defined with a CTL_ prefix in &lt;sys/sysctl.h&gt;, and
     are as follows.  The next and subsequent levels down are found in the in-
     clude files listed here, and described in separate sections below.

           Name              Next level names          Description
           CTL_DEBUG         sys/sysctl.h              Debugging
           CTL_VFS           sys/mount.h               Filesystem
           CTL_HW            sys/sysctl.h              Generic CPU, I/O
           CTL_KERN          sys/sysctl.h              High kernel limits
           CTL_MACHDEP       sys/sysctl.h              Machine dependent
           CTL_NET           sys/socket.h              Networking
           CTL_USER          sys/sysctl.h              User-level
           CTL_VM            vm/vm_param.h             Virtual memory

     For example, the following retrieves the maximum number of processes al-
     lowed in the system:
           int mib[2], maxproc;
           size_t len;

           mib[0] = CTL_KERN;
           mib[1] = KERN_MAXPROC;
           len = sizeof(maxproc);
           sysctl(mib, 2, &maxproc, &len, NULL, 0);

     To retrieve the standard search path for the system utilities:
           int mib[2];
           size_t len;
           char *p;

           mib[0] = CTL_USER;
           mib[1] = USER_CS_PATH;
           sysctl(mib, 2, NULL, &len, NULL, 0);
           p = malloc(len);
           sysctl(mib, 2, p, &len, NULL, 0);

CTL_DEBUG
     The debugging variables vary from system to system.  A debugging variable
     may be added or deleted without need to recompile sysctl to know about
     it.  Each time it runs, sysctl gets the list of debugging variables from
     the kernel and displays their current values.  The system defines twenty
     (struct ctldebug) variables named debug0 through debug19. They are de-
     clared as separate variables so that they can be individually initialized
     at the location of their associated variable.  The loader prevents multi-
     ple use of the same variable by issuing errors if a variable is initial-
     ized in more than one place.  For example, to export the variable
     dospecialcheck as a debugging variable, the following declaration would
     be used:
           int dospecialcheck = 1;
           struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };

CTL_VFS
     A distinguished second level name, VFS_GENERIC, is used to get general
     information about all filesystems.  One of its third level identifiers is
     VFS_MAXTYPENUM that gives the highest valid filesystem type number.  Its
     other third level identifier is VFS_CONF that returns configuration in-
     formation about the filesystem type given as a fourth level identifier
     (see getvfsbyname(3) as an example of its use).  The remaining second
     level identifiers are the filesystem type number returned by a statfs(2)
     call or from VFS_CONF.  The third level identifiers available for each
     filesystem are given in the header file that defines the mount argument
     structure for that filesystem.

CTL_HW
     The string and integer information available for the CTL_HW level is de-
     tailed below.  The changeable column shows whether a process with appro-
     priate privilege may change the value.

           Second level name          Type          Changeable
           HW_MACHINE                 string        no
           HW_MODEL                   string        no
           HW_NCPU                    integer       no
           HW_BYTEORDER               integer       no
           HW_PHYSMEM                 integer       no
           HW_USERMEM                 integer       no
           HW_PAGESIZE                integer       no

     HW_MACHINE
             The machine class.

     HW_MODEL
             The machine model

     HW_NCPU



             The number of cpus.

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

     HW_PHYSMEM
             The bytes of physical memory.

     HW_USERMEM
             The bytes of non-kernel memory.

     HW_PAGESIZE
             The software page size.

CTL_KERN
     The string and integer information available for the CTL_KERN level is
     detailed below.  The changeable column shows whether a process with ap-
     propriate 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_BOOTTIME               struct timeval         no
           KERN_CHOWN_RESTRICTED       integer                no
           KERN_CLOCKRATE              struct clockinfo       no
           KERN_FILE                   struct file            no
           KERN_HOSTID                 integer                yes
           KERN_HOSTNAME               string                 yes
           KERN_JOB_CONTROL            integer                no
           KERN_LINK_MAX               integer                no
           KERN_MAXFILES               integer                yes
           KERN_MAXPROC                integer                yes
           KERN_MAXVNODES              integer                yes
           KERN_MAX_CANON              integer                no
           KERN_MAX_INPUT              integer                no
           KERN_NAME_MAX               integer                no
           KERN_NGROUPS                integer                no
           KERN_NO_TRUNC               integer                no
           KERN_OSRELEASE              string                 no
           KERN_OSREV                  integer                no
           KERN_OSTYPE                 string                 no
           KERN_PATH_MAX               integer                no
           KERN_PIPE_BUF               integer                no
           KERN_POSIX1                 integer                no
           KERN_PROC                   struct proc            no
           KERN_PROF                   node                   not applicable
           KERN_SAVED_IDS              integer                no
           KERN_SECURELVL              integer                raise only
           KERN_VDISABLE               integer                no
           KERN_VERSION                string                 no
           KERN_VNODE                  struct vnode           no

     KERN_ARGMAX
             The maximum bytes of argument to exec(2).

     KERN_BOOTTIME
             A struct timeval structure is returned.  This structure contains
             the time that the system was booted.

     KERN_CHOWN_RESTRICTED
             Return 1 if appropriate privileges are required for the chown(2)


             system call, otherwise 0.

     KERN_CLOCKRATE
             A struct clockinfo structure is returned.  This structure con-
             tains the clock, statistics clock and profiling clock frequen-
             cies, and the number of micro-seconds per hz tick.

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

     KERN_HOSTID
             Get or set the host id.

     KERN_HOSTNAME
             Get or set the hostname.

     KERN_JOB_CONTROL
             Return 1 if job control is available on this system, otherwise 0.

     KERN_LINK_MAX
             The maximum file link count.

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

     KERN_MAXPROC
             The maximum number of simultaneous processes the system will al-
             low.

     KERN_MAXVNODES
             The maximum number of vnodes available on the system.

     KERN_MAX_CANON
             The maximum number of bytes in terminal canonical input line.

     KERN_MAX_INPUT
             The minimum maximum number of bytes for which space is available
             in a terminal input queue.

     KERN_NAME_MAX
             The maximum number of bytes in a file name.

     KERN_NGROUPS
             The maximum number of supplemental groups.

     KERN_NO_TRUNC
             Return 1 if file names longer than KERN_NAME_MAX are truncated.

     KERN_OSRELEASE
             The system release string.

     KERN_OSREV
             The system revision string.

     KERN_OSTYPE
             The system type string.

     KERN_PATH_MAX
             The maximum number of bytes in a pathname.

     KERN_PIPE_BUF
             The maximum number of bytes which will be written atomically to a


             pipe.

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

     KERN_PROC
             Return the entire process table, or a subset of it.  An array of
             struct kinfo_proc structures is returned, whose size depends on
             the current number of such objects in the system.  The third and
             fourth level names are as follows:

                   Third level name          Fourth level is:
                   KERN_PROC_ALL             None
                   KERN_PROC_PID             A process ID
                   KERN_PROC_PGRP            A process group
                   KERN_PROC_TTY             A tty device
                   KERN_PROC_UID             A user ID
                   KERN_PROC_RUID            A real user ID

     KERN_PROF
             Return profiling information about the kernel.  If the kernel is
             not compiled for profiling, attempts to retrieve any of the
             KERN_PROF values will fail with EOPNOTSUPP.  The third level
             names for the string and integer profiling information is de-
             tailed below.  The changeable column shows whether a process with
             appropriate privilege may change the value.

                   Third level name      Type                   Changeable
                   GPROF_STATE           integer                yes
                   GPROF_COUNT           u_short[]              yes
                   GPROF_FROMS           u_short[]              yes
                   GPROF_TOS             struct tostruct        yes
                   GPROF_GMONPARAM       struct gmonparam       no

             The variables are as follows:

             GPROF_STATE
                     Returns GMON_PROF_ON or GMON_PROF_OFF to show that pro-
                     filing is running or stopped.

             GPROF_COUNT
                     Array of statistical program counter counts.

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

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

             GPROF_GMONPARAM
                     Structure giving the sizes of the above arrays.

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

     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_VDISABLE
             Returns the terminal character disabling value.

     KERN_VERSION

             The system version string.

     KERN_VNODE
             Return the entire vnode table.  Note, the vnode table is not nec-
             essarily a consistent snapshot of the system.  The returned data
             consists of an array whose size depends on the current number of
             such objects in the system.  Each element of the array contains
             the kernel address of a vnode struct vnode * followed by the vn-
             ode itself struct vnode.

CTL_MACHDEP
     The set of variables defined is architecture dependent.  Most architec-
     tures define at least the following variables.

           Second level name    Type          Changeable
           CPU_CONSDEV          dev_t         no

CTL_NET
     The string and integer information available for the CTL_NET level is de-
     tailed below.  The changeable column shows whether a process with appro-
     priate privilege may change the value.

           Second level name          Type                   Changeable
           PF_ROUTE                   routing messages       no
           PF_INET                    internet values        yes

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

             The third level name is a protocol number, which is currently al-
             ways 0.  The fourth level name is an address family, which may be
             set to 0 to select all address families.  The fifth and sixth
             level names are as follows:

                   Fifth level name          Sixth level is:
                   NET_RT_FLAGS              rtflags
                   NET_RT_DUMP               None
                   NET_RT_IFLIST             None

     PF_INET
             Get or set various global information about the internet proto-
             cols.  The third level name is the protocol.  The fourth level
             name is the variable name.  The currently defined protocols and
             names are:

                   Protocol name          Variable
                                                                            name       Type          Changeable
                   ip                     forwarding          integer       yes
                   ip                     redirect            integer       yes
                   ip                     ttl                 integer       yes
                   icmp                   maskrepl            integer       yes
                   udp                    checksum            integer       yes

             The variables are as follows:

             ip.forwarding
                     Returns 1 when IP forwarding is enabled for the host,
                     meaning that the host is acting as a router.

             ip.redirect
                     Returns 1 when ICMP redirects may be sent by the host.
                     This option is ignored unless the host is routing IP

                     packets, and should normally be enabled on all systems.

             ip.ttl  The maximum time-to-live (hop count) value for an IP
                     packet sourced by the system.  This value applies to nor-
                     mal transport protocols, not to ICMP.

             icmp.maskrepl
                     Returns 1 if ICMP network mask requests are to be an-
                     swered.

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

CTL_USER
     The string and integer information available for the CTL_USER level is
     detailed below.  The changeable column shows whether a process with ap-
     propriate privilege may change the value.

           Second level name           Type          Changeable
           USER_BC_BASE_MAX            integer       no
           USER_BC_DIM_MAX             integer       no
           USER_BC_SCALE_MAX           integer       no
           USER_BC_STRING_MAX          integer       no
           USER_COLL_WEIGHTS_MAX       integer       no
           USER_CS_PATH                string        no
           USER_EXPR_NEST_MAX          integer       no
           USER_LINE_MAX               integer       no
           USER_POSIX2_CHAR_TERM       integer       no
           USER_POSIX2_C_BIND          integer       no
           USER_POSIX2_C_DEV           integer       no
           USER_POSIX2_FORT_DEV        integer       no
           USER_POSIX2_FORT_RUN        integer       no
           USER_POSIX2_LOCALEDEF       integer       no
           USER_POSIX2_SW_DEV          integer       no
           USER_POSIX2_UPE             integer       no
           USER_POSIX2_VERSION         integer       no
           USER_RE_DUP_MAX             integer       no
           USER_STREAM_MAX             integer       no
           USER_TZNAME_MAX             integer       no

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

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

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

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

     USER_COLL_WEIGHTS_MAX
             The maximum number of weights that can be assigned to any entry
             of the LC_COLLATE order keyword in the locale definition file.

     USER_CS_PATH
             Return a value for the PATH environment variable that finds all
             the standard utilities.

     USER_EXPR_NEST_MAX
             The maximum number of expressions that can be nested within


             parenthesis by the expr(1) utility.

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

     USER_POSIX2_CHAR_TERM
             Return 1 if the system supports at least one terminal type capa-
             ble of all operations described in POSIX 1003.2, otherwise 0.

     USER_POSIX2_C_BIND
             Return 1 if the system's C-language development facilities sup-
             port the C-Language Bindings Option, otherwise 0.

     USER_POSIX2_C_DEV
             Return 1 if the system supports the C-Language Development Utili-
             ties Option, otherwise 0.

     USER_POSIX2_FORT_DEV
             Return 1 if the system supports the FORTRAN Development Utilities
             Option, otherwise 0.

     USER_POSIX2_FORT_RUN
             Return 1 if the system supports the FORTRAN Runtime Utilities Op-
             tion, otherwise 0.

     USER_POSIX2_LOCALEDEF
             Return 1 if the system supports the creation of locales, other-
             wise 0.

     USER_POSIX2_SW_DEV
             Return 1 if the system supports the Software Development Utili-
             ties Option, otherwise 0.

     USER_POSIX2_UPE
             Return 1 if the system supports the User Portability Utilities
             Option, otherwise 0.

     USER_POSIX2_VERSION
             The version of POSIX 1003.2 with which the system attempts to
             comply.

     USER_RE_DUP_MAX
             The maximum number of repeated occurrences of a regular expres-
             sion permitted when using interval notation.

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

     USER_TZNAME_MAX
             The minimum maximum number of types supported for the name of a
             timezone.

CTL_VM
     The string and integer information available for the CTL_VM level is de-
     tailed below.  The changeable column shows whether a process with appro-
     priate privilege may change the value.

           Second level name          Type                 Changeable
           VM_LOADAVG                 struct loadavg       no
           VM_METER                   struct vmtotal       no

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

             struct loadavg.

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

RETURN VALUES
     If the call to sysctl is successful, the number of bytes copied out is
     returned.  Otherwise -1 is returned and errno is set appropriately.

ERRORS
     The following errors may be reported:

     [EFAULT]      The buffer name, oldp, newp, or length pointer oldlenp con-
                   tains an invalid address.

     [EINVAL]      The name array is less than two or greater than
                   CTL_MAXNAME.

     [EINVAL]      A non-null newp is given and its specified length in newlen
                   is too large or too small.

     [ENOMEM]      The length pointed to by oldlenp is too short to hold the
                   requested value.

     [ENOTDIR]     The name array specifies an intermediate rather than termi-
                   nal name.

     [EOPNOTSUPP]  The name array specifies a value that is unknown.

     [EPERM]       An attempt is made to set a read-only value.

     [EPERM]       A process without appropriate privilege attempts to set a
                   value.

FILES
     <sys/sysctl.h>        definitions for top level identifiers, second level
                           kernel and hardware identifiers, and user level
                           identifiers
     <sys/socket.h>        definitions for second level network identifiers
     <sys/gmon.h>          definitions for third level profiling identifiers
     <vm/vm_param.h>       definitions for second level virtual memory identi-
                           fiers
     <netinet/in.h>        definitions for third level Internet identifiers
                           and fourth level IP identifiers
     <netinet/icmp_var.h>  definitions for fourth level ICMP identifiers
     <netinet/udp_var.h>   definitions for fourth level UDP identifiers

SEE ALSO
     sysctl(8)

HISTORY
     The sysctl function first appeared in 4.4BSD.

4.4BSD                            May 9, 1995                                9