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RocketLink!--> Man page versions: OpenBSD FreeBSD Others



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

NAME
     sysctl - get or set system information



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

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

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

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

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

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

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

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

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

           Name              Next level names          Description
           CTL_DEBUG         sys/sysctl.h              Debugging
           CTL_FS            sys/sysctl.h              File system
           CTL_HW            sys/sysctl.h              Generic CPU, I/O
           CTL_KERN          sys/sysctl.h              High kernel limits
           CTL_MACHDEP       sys/sysctl.h              Machine dependent
           CTL_NET           sys/socket.h              Networking
           CTL_USER          sys/sysctl.h              User-level
           CTL_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
     declared as separate variables so that they can be individually initial-
     ized at the location of their associated variable.  The loader prevents
     multiple use of the same variable by issuing errors if a variable is ini-
     tialized in more than one place.  For example, to export the variable
     dospecialcheck as a debugging variable, the following declaration would
     be used:

           int dospecialcheck = 1;
           struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };

   CTL_FS
     There are currently no second level names for the file system.

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

           Second level name           Type                   Changeable
           KERN_ARGMAX                 integer                no
           KERN_ARND                   integer                no
           KERN_BOOTTIME               struct timeval         no
           KERN_CHOWN_RESTRICTED       integer                no
           KERN_CLOCKRATE              struct clockinfo       no
           KERN_DOMAINNAME             string                 yes
           KERN_FILE                   struct file            no
           KERN_FSYNC                  integer                no
           KERN_HOSTID                 integer                yes
           KERN_HOSTNAME               string                 yes
           KERN_JOB_CONTROL            integer                no
           KERN_LINK_MAX               integer                no
           KERN_MAXFILES               integer                yes
           KERN_MAXPARTITIONS          integer                no
           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_NOSUIDCOREDUMP         integer yes
           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_RAWPARTITION           integer                no
           KERN_RND                    struct rndstats        no
           KERN_SAVED_IDS              integer                no
           KERN_SECURELVL              integer                raise only
           KERN_SYSVMSG                integer                no
           KERN_SYSVSEM                integer                no
           KERN_SYSVSHM                integer                no
           KERN_VDISABLE               integer                no
           KERN_VERSION                string                 no
           KERN_VNODE                  struct vnode           no

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

     KERN_ARND
             Returns a random integer from the kernel arc4random() function.
             This can be useful if /dev/arandom is not available (see


             random(4)).

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

     KERN_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, the number of micro-seconds per hz tick, and the clock skew
             rate.

     KERN_DOMAINNAME
             Get or set the YP domain name.

     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_FSYNC
             Return 1 if the File Synchronisation Option is available on this
             system, otherwise 0.

     KERN_HOSTID
             Get or set the host ID.

     KERN_HOSTNAME
             Get or set the hostname.

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

     KERN_LINK_MAX
             The maximum file link count.

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

     KERN_MAXPARTITIONS
             The maximum number of partitions allowed per disk.

     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_NOSUIDCOREDUMP
             Programs with their set-user-ID bit set will not dump core when
             this is set.

     KERN_OSRELEASE
             The system release string.

     KERN_OSREV
             The system revision number.

     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 detailed be-
             low.  The changeable column shows whether a process with appro-
             priate privileges 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_RAWPARTITION
             The raw partition of a disk (a == 0).

     KERN_RND
             Returns statistics about the /dev/random device in a struct
             rndstats structure.

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

     KERN_SECURELVL
             The system security level.  This level may be raised by processes
             with appropriate privileges.  It may only be lowered by process
             1.

     KERN_SYSVMSG
             Returns 1 if System V style message queue functionality is avail-
             able on this system, otherwise 0.

     KERN_SYSVSEM
             Returns 1 if System V style semaphore functionality is available
             on this system, otherwise 0.

     KERN_SYSVSHM
             Returns 1 if System V style share memory functionality is avail-
             able on this system, otherwise 0.

     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 privileges may change the value.


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

     PF_ENCAP
             Get or set various global information about the IP security pro-
             tocols.  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
                   encap            encdebug         integer    yes

             The variables are as follows:

             encap.encdebug
                     Returns 1 when error message reporting is enabled for the
                     host.  If the kernel has been compiled with the ENCDEBUG
                     option, then debugging information will also be reported
                     when this variable is set.

     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
                   tcp              rfc1323          integer    yes
                   tcp              baddynamic       array      yes
                   tcp              ident            structure  no
                   tcp              keepidle         integer    yes
                   tcp              keepintvl        integer    yes
                   tcp              slowhz           integer    yes
                   tcp              sack             integer    yes
                   tcp              mssdflt          integer    yes
                   udp              checksum         integer    yes
                   udp              baddynamic       array      yes

             The variables are as follows:

             ip.forwarding
                     Returns 1 when IP forwarding is enabled for the host, in-

                     dicating 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.

             tcp.rfc1323
                     Returns 1 if RFC1323 extensions to TCP are enabled.

             tcp.baddynamic
                     An array of in_port_t is returned specifying the bitmask
                     of TCP ports between 512 and 1023 inclusive that should
                     not be allocated dynamically by the kernel (i.e., they
                     must be bound specifically by port number).

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

             tcp.keepidle
                     If the socket option SO_KEEPALIVE has been set, time a
                     connection needs to be idle before keepalives are sent.
                     See also tcp.slowhz.

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

             tcp.slowhz
                     The units for tcp.keepidle and tcp.keepintvl; those vari-
                     ables 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.sack
                     Returns 1 if RFC2018 Selective Acknowledgements are en-
                     abled.

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

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

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

   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 privileges may change the value.

           Second level name           Type          Changeable
           USER_BC_BASE_MAX            integer       no
           USER_BC_DIM_MAX             integer       no
           USER_BC_SCALE_MAX           integer       no
           USER_BC_STRING_MAX          integer       no
           USER_COLL_WEIGHTS_MAX       integer       no
           USER_CS_PATH                string        no
           USER_EXPR_NEST_MAX          integer       no
           USER_LINE_MAX               integer       no
           USER_POSIX2_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 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 privileges 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 unsuccessful, -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 pointer is given and its specified length

                   in newlen is too large or too small.

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

     [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 privileges attempts to set a
                   value.

     [EPERM]       An attempt to change a value protected by the current ker-
                   nel security level is made.

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/tcp_var.h>   definitions for fourth level TCP identifiers
     <netinet/udp_var.h>   definitions for fourth level UDP identifiers

SEE ALSO
     sysctl(8)

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

OpenBSD 2.6                      June 4, 1993                               11

Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.



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