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SYSCTL(3)              FreeBSD Library Functions Manual              SYSCTL(3)

NAME
     sysctl, sysctlbyname, sysctlnametomib -- get or set system information

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/sysctl.h>

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

     int
     sysctlbyname(const char *name, void *oldp, size_t *oldlenp, void *newp,
         size_t newlen);

     int
     sysctlnametomib(const char *name, int *mibp, size_t *sizep);

DESCRIPTION
     The sysctl() function retrieves system information and allows processes
     with appropriate privileges to set system information.  The information
     available from sysctl() consists of integers, strings, and tables.
     Information may be retrieved and set from the command interface using the
     sysctl(8) utility.

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

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

     The sysctlbyname() function accepts an ASCII representation of the name
     and internally looks up the integer name vector.  Apart from that, it
     behaves the same as the standard sysctl() function.

     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
     and after a call that returns with the error code ENOMEM.  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 sysctlnametomib() function accepts an ASCII representation of the
     name, looks up the integer name vector, and returns the numeric represen-
     tation in the mib array pointed to by mibp.  The number of elements in
     the mib array is given by the location specified by sizep before the
     call, and that location gives the number of entries copied after a suc-
     cessful call.  The resulting mib and size may be used in subsequent
     sysctl() calls to get the data associated with the requested ASCII name.
     This interface is intended for use by applications that want to repeat-
     edly request the same variable (the sysctl() function runs in about a
     third the time as the same request made via the sysctlbyname() function).
     The sysctlnametomib() function is also useful for fetching mib prefixes
     and then adding a final component.  For example, to fetch process infor-
     mation for processes with pid's less than 100:

           int i, mib[4];
           size_t len;
           struct kinfo_proc kp;

           /* Fill out the first three components of the mib */
           len = 4;
           sysctlnametomib("kern.proc.pid", mib, &len);

           /* Fetch and print entries for pid's < 100 */
           for (i = 0; i < 100; i++) {
                   mib[3] = i;
                   len = sizeof(kp);
                   if (sysctl(mib, 4, &kp, &len, NULL, 0) == -1)
                           perror("sysctl");
                   else if (len > 0)
                           printkproc(&kp);
           }

     The top level names are defined with a CTL_ prefix in <sys/sysctl.h>, and
     are as follows.  The next and subsequent levels down are found in the
     include files listed here, and described in separate sections below.

           Name              Next level names          Description
           CTL_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
     allowed in the system:

           int mib[2], maxproc;
           size_t len;

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

     To retrieve the standard search path for the system utilities:

           int mib[2];
           size_t len;
           char *p;

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

   CTL_DEBUG
     The debugging variables vary from system to system.  A debugging variable
     may be added or deleted without need to recompile sysctl() to know about
     it.  Each time it runs, sysctl() gets the list of debugging variables
     from the kernel and displays their current values.  The system defines
     twenty (struct ctldebug) variables named debug0 through debug19.  They
     are declared as separate variables so that they can be individually ini-
     tialized at the location of their associated variable.  The loader pre-
     vents multiple use of the same variable by issuing errors if a variable
     is initialized in more than one place.  For example, to export the vari-
     able 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
     information 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
     detailed below.  The changeable column shows whether a process with
     appropriate 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_FLOATINGPOINT           integer       no
           HW_MACHINE_ARCH            string        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.

     HW_FLOATINGPOINT
             Nonzero if the floating point support is in hardware.

     HW_MACHINE_ARCH
             The machine dependent architecture type.

   CTL_KERN
     The string and integer information available for the CTL_KERN level is
     detailed below.  The changeable column shows whether a process with
     appropriate 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_BOOTFILE              string                 yes
           KERN_BOOTTIME              struct timeval         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_MAXFILES              integer                yes
           KERN_MAXFILESPERPROC       integer                yes
           KERN_MAXPROC               integer                no
           KERN_MAXPROCPERUID         integer                yes
           KERN_MAXVNODES             integer                yes
           KERN_NGROUPS               integer                no
           KERN_NISDOMAINNAME         string                 yes
           KERN_OSRELDATE             integer                no
           KERN_OSRELEASE             string                 no
           KERN_OSREV                 integer                no
           KERN_OSTYPE                string                 no
           KERN_POSIX1                integer                no
           KERN_PROC                  struct proc            no
           KERN_PROF                  node                   not applicable
           KERN_QUANTUM               integer                yes
           KERN_SAVED_IDS             integer                no
           KERN_SECURELVL             integer                raise only
           KERN_UPDATEINTERVAL        integer                no
           KERN_VERSION               string                 no
           KERN_VNODE                 struct vnode           no

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

     KERN_BOOTFILE
             The full pathname of the file from which the kernel was loaded.

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

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

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

     KERN_MAXFILESPERPROC
             The maximum number of files that may be open for a single
             process.  This limit only applies to processes with an effective
             uid of nonzero at the time of the open request.  Files that have
             already been opened are not affected if the limit or the effec-
             tive uid is changed.

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

     KERN_MAXPROCPERUID
             The maximum number of concurrent processes the system will allow
             for a single effective uid.  This limit only applies to processes
             with an effective uid of nonzero at the time of a fork request.
             Processes that have already been started are not affected if the
             limit is changed.

     KERN_MAXVNODES
             The maximum number of vnodes available on the system.

     KERN_NGROUPS
             The maximum number of supplemental groups.

     KERN_NISDOMAINNAME
             The name of the current YP/NIS domain.

     KERN_OSRELDATE
             The system release date in YYYYMM format (January 1996 is encoded
             as 199601).

     KERN_OSRELEASE
             The system release string.

     KERN_OSREV
             The system revision string.

     KERN_OSTYPE
             The system type string.

     KERN_POSIX1
             The version of IEEE Std 1003.1 (``POSIX.1'') with which the sys-
             tem 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 ENOENT.  The third level names
             for the string and integer profiling information is detailed
             below.  The changeable column shows whether a process with appro-
             priate 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_QUANTUM
             The maximum period of time, in microseconds, for which a process
             is allowed to run without being preempted if other processes are
             in the run queue.

     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 not be lowered.

     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
             vnode itself struct vnode.

   CTL_MACHDEP
     The set of variables defined is architecture dependent.  The following
     variables are defined for the i386 architecture.

           Second level name    Type                  Changeable
           CPU_CONSDEV          dev_t                 no
           CPU_ADJKERNTZ        int                   yes
           CPU_DISRTCSET        int                   yes
           CPU_BOOTINFO         struct bootinfo       no
           CPU_WALLCLOCK        int                   yes

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

           Second level name          Type                   Changeable
           PF_ROUTE                   routing messages       no
           PF_INET                    IPv4 values            yes
           PF_INET6                   IPv6 values            yes

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

             The third level name is a protocol number, which is currently
             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

     PF_INET
             Get or set various global information about the IPv4 (Internet
             Protocol version 4).  The third level name is the protocol.  The
             fourth level name is the variable name.  The currently defined
             protocols and names are:

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

             The variables are as follows:

             icmp.bmcastecho
                     Returns 1 if an ICMP echo request to a broadcast or mul-
                     ticast address is to be answered.

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

             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.

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

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

     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.

             For variables net.inet6.* please refer to inet6(4).  For vari-
             ables net.inet6.*.ipsec6, please refer to ipsec(4).

   CTL_USER
     The string and integer information available for the CTL_USER level is
     detailed below.  The changeable column shows whether a process with
     appropriate 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 IEEE Std 1003.2 (``POSIX.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
             Option, 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 IEEE Std 1003.2 (``POSIX.2'') with which the sys-
             tem 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
     detailed below.  The changeable column shows whether a process with
     appropriate privilege may change the value.

           Second level name          Type                 Changeable
           VM_LOADAVG                 struct loadavg       no
           VM_METER                   struct vmtotal       no
           VM_PAGEOUT_ALGORITHM       integer              yes
           VM_SWAPPING_ENABLED        integer              maybe
           VM_V_CACHE_MAX             integer              yes
           VM_V_CACHE_MIN             integer              yes
           VM_V_FREE_MIN              integer              yes
           VM_V_FREE_RESERVED         integer              yes
           VM_V_FREE_TARGET           integer              yes
           VM_V_INACTIVE_TARGET       integer              yes
           VM_V_PAGEOUT_FREE_MIN      integer              yes

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

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

     VM_PAGEOUT_ALGORITHM
             0 if the statistics-based page management algorithm is in use or
             1 if the near-LRU algorithm is in use.

     VM_SWAPPING_ENABLED
             1 if process swapping is enabled or 0 if disabled.  This variable
             is permanently set to 0 if the kernel was built with swapping
             disabled.

     VM_V_CACHE_MAX
             Maximum desired size of the cache queue.

     VM_V_CACHE_MIN
             Minimum desired size of the cache queue.  If the cache queue size
             falls very far below this value, the pageout daemon is awakened.

     VM_V_FREE_MIN
             Minimum amount of memory (cache memory plus free memory) required
             to be available before a process waiting on memory will be awak-
             ened.

     VM_V_FREE_RESERVED
             Processes will awaken the pageout daemon and wait for memory if
             the number of free and cached pages drops below this value.

     VM_V_FREE_TARGET
             The total amount of free memory (including cache memory) that the
             pageout daemon tries to maintain.

     VM_V_INACTIVE_TARGET
             The desired number of inactive pages that the pageout daemon
             should achieve when it runs.  Inactive pages can be quickly
             inserted into process address space when needed.

     VM_V_PAGEOUT_FREE_MIN
             If the amount of free and cache memory falls below this value,
             the pageout daemon will enter "memory conserving mode" to avoid
             deadlock.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     The following errors may be reported:

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

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

     [EINVAL]           A non-null newp 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
                        terminal name.

     [EISDIR]           The name array specifies a terminal name, but the
                        actual name is not terminal.

     [ENOENT]           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 IPv4/IPv6 identifiers
                           and fourth level IPv4/v6 identifiers
     <netinet/icmp_var.h>  definitions for fourth level ICMP identifiers
     <netinet/icmp6.h>     definitions for fourth level ICMPv6 identifiers
     <netinet/udp_var.h>   definitions for fourth level UDP identifiers

SEE ALSO
     sysconf(3), sysctl(8)

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

FreeBSD 4.10                   January 23, 2001                   FreeBSD 4.10

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | FILES | SEE ALSO | HISTORY

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