Provided by: freebsd-manpages_12.2-1_all bug

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

     int
     sysctlbyname(const char *name, void *oldp, size_t *oldlenp, const 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 the NULL argument
     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 representation 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 successful
     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 repeatedly 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 information 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>             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 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 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 };

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

   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_FLOATINGPT        integer       no
           HW_MACHINE_ARCH      string        no
           HW_REALMEM           integer       no
           HW_AVAILPAGES        integer       no

     HW_MACHINE
             The machine class.

     HW_MODEL
             The machine model

     HW_NCPU
             The number of cpus.

     HW_BYTEORDER
             The byteorder (4321 or 1234).

     HW_PHYSMEM
             Amount of physical memory (in bytes), minus the amount used by the kernel, pre-
             loaded modules, and (on x86) the dcons buffer.

     HW_USERMEM
             Amount of memory (in bytes) which is not wired.

     HW_PAGESIZE
             The software page size.

     HW_FLOATINGPT
             Nonzero if the floating point support is in hardware.

     HW_MACHINE_ARCH
             The machine dependent architecture type.

     HW_REALMEM
             Amount of memory (in bytes) reported by the firmware.  That value is sometimes not
             sane; in that case, the kernel reports the max memory address instead.

     HW_AVAILPAGES
             The same value as HW_PHYSMEM, measured in pages rather than bytes.

   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 xfile           no
           KERN_HOSTID                integer                yes
           KERN_HOSTUUID              string                 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                  node                   not applicable
           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 xvnode          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 contains the clock,
             statistics clock and profiling clock frequencies, the number of micro-seconds per hz
             tick and the skew rate.

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

     KERN_HOSTID
             Get or set the host ID.

     KERN_HOSTUUID
             Get or set the host's universally unique identifier (UUID).

     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
             effective 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 kernel release version in the format MmmRxx, where M is the major version, mm is
             the two digit minor version, R is 0 if release branch, otherwise 1, and xx is
             updated when the available APIs change.

             The userland release version is available from <osreldate.h>; parse this file if you
             need to get the release version of the currently installed userland.

     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 system attempts to comply.

     KERN_PROC
             Return selected information about specific running processes.

             For the following names, an array of struct kinfo_proc structures is returned, whose
             size depends on the current number of such objects in the system.

                   Third Level Name          Fourth Level
                   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

             If the third level name is KERN_PROC_ARGS then the command line argument array is
             returned in a flattened form, i.e., zero-terminated arguments follow each other.
             The total size of array is returned.  It is also possible for a process to set its
             own process title this way.  If the third level name is KERN_PROC_PATHNAME, the path
             of the process' text file is stored.  For KERN_PROC_PATHNAME, a process ID of -1
             implies the current process.

                   Third Level Name          Fourth Level
                   KERN_PROC_ARGS            A process ID
                   KERN_PROC_PATHNAME        A process 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 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 profiling 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 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 consists of a struct xvnode.

   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, sixth, and seventh level names are as follows:

                   Fifth level    Sixth Level    Seventh Level
                   NET_RT_FLAGS   rtflags        None
                   NET_RT_DUMP    None           None or fib number
                   NET_RT_IFLIST  0 or if_index  None
                   NET_RT_IFMALIST               0 or if_index    None
                   NET_RT_IFLISTL 0 or if_index  None

             The NET_RT_IFMALIST name returns information about multicast group memberships on
             all interfaces if 0 is specified, or for the interface specified by if_index.

             The NET_RT_IFLISTL is like NET_RT_IFLIST, just returning message header structs with
             additional fields allowing the interface to be extended without breaking binary
             compatibility.  The NET_RT_IFLISTL uses 'l' versions of the message header
             structures: struct if_msghdrl and struct ifa_msghdrl.

     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 multicast 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 normal transport protocols, not to ICMP.

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

                     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 variables
             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 capable 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 support the C-Language
             Bindings Option, otherwise 0.

     USER_POSIX2_C_DEV
             Return 1 if the system supports the C-Language Development Utilities 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, otherwise 0.

     USER_POSIX2_SW_DEV
             Return 1 if the system supports the Software Development Utilities 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 system attempts to comply.

     USER_RE_DUP_MAX
             The maximum number of repeated occurrences of a regular expression 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_TOTAL                   struct vmtotal       no
           VM_SWAPPING_ENABLED        integer              maybe
           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_OVERCOMMIT              integer              yes

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

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

     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_FREE_MIN
             Minimum amount of memory (cache memory plus free memory) required to be available
             before a process waiting on memory will be awakened.

     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.

     VM_OVERCOMMIT
             Overcommit behaviour, as described in tuning(7).

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.

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 identifiers
     <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

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.

     [ENOMEM]           The smaller of either the length pointed to by oldlenp or the estimated
                        size of the returned data exceeds the system limit on locked memory.

     [ENOMEM]           Locking the buffer oldp, or a portion of the buffer if the estimated size
                        of the data to be returned is smaller, would cause the process to exceed
                        its per-process locked memory limit.

     [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.

SEE ALSO

     confstr(3), kvm(3), sysconf(3), sysctl(8)

HISTORY

     The sysctl() function first appeared in 4.4BSD.