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SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) NAME sysctl - get or set system information SYNOPSIS #include <sys/sysctl.h> int sysctl(name, namelen, oldp, *oldlenp, *newp, newlen) 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 informa- tion. The information available from sysctl consists of integers, strings, and tables. Information may be retrieved and set from the command interface using the sysctl(1) util- ity. Unless explicitly noted below, sysctl returns a consistent snapshot of the data requested. Calls to sysctl are serial- ized 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 Printed 11/26/99 January 13, 1995 1 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) 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 include 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 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 ini- tialized in more than one place. For example, to export the Printed 11/26/99 January 13, 1995 2 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) variable dospecialcheck as a debugging variable, the follow- ing declaration would be used: int dospecialcheck = 1; struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck }; CTL_FS There are currently no second level names for the file sys- tem. 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_MACHINE The machine class. HW_MODEL The machine model HW_NCPU The number of cpus. HW_BYTEORDER The byteorder (3412, 4321, or 1234). 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 appropriate privilege may change the value. The types of data currently available are Printed 11/26/99 January 13, 1995 3 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) process information, system inodes, the open file entries, routing table entries, virtual memory statistics, load aver- age 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 long yes KERN_HOSTNAME string yes KERN_JOB_CONTROL integer no KERN_MAXFILES integer no KERN_MAXPROC integer no KERN_MAXINODES integer no KERN_MAXTEXTS integer no KERN_NGROUPS 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_SAVED_IDS integer no KERN_SECURELVL integer raise only KERN_TEXT struct text no KERN_VERSION string no KERN_INODE struct inode 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_CLOCKRATE A struct clockinfo structure is returned. This struc- ture contains the clock, statistics clock and profiling clock frequencies, and the number of micro-seconds per hz tick. KERN_FILE Return the entire file table as an array of extended file structures. Each element of the array contains the kernel address of a file struct inode * followed by the file itself struct file. There can never be more than KERN_MAXFILES inodes returned. KERN_HOSTID Printed 11/26/99 January 13, 1995 4 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) 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 open files that may be open in the system. KERN_MAXPROC The maximum number of simultaneous processes the system will allow. KERN_MAXINODES The maximum number of inodes available on the system. KERN_MAXTEXTS The maximum number of text structures available on the system. KERN_NGROUPS The maximum number of supplemental groups. KERN_OSRELEASE The system release string. KERN_OSREV The system revision string. KERN_OSTYPE The system type string. 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 Printed 11/26/99 January 13, 1995 5 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) KERN_PROC_TTY A tty device KERN_PROC_UID A user ID KERN_PROC_RUID A real user ID KERN_PROF Return kernel profiling information. 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 infor- mation 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 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_VERSION The system version string. KERN_INODE Return the entire inode table. Note, the inode table is not Printed 11/26/99 January 13, 1995 6 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) necessarily a consistent snapshot of the system. The returned data consists of an array whose size depends on the current number of such objects in the system. Each element of the array contains the kernel address of a inode struct inode * followed by the inode itself struct inode. There can never be more than KERN_MAXINODES inodes returned. KERN_TEXT Return the entire text table. The returned data consists of an array whose size depends on the current number of such objects active in the system. Each element of the array con- tains the kernel address of a text struct text * followed by the text structure itself struct text. There can never be more structures than returned by KERN_MAXTEXTS. CTL_MACHDEP The set of variables defined is architecture dependent. Most architectures define at least the following variables. Second level name Type Changeable CPU_CONSDEV dev_t no 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 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 always 0. The fourth level name is an address family, which may be set to 0 to select all address fami- lies. 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 inter- net protocols. The third level name is the protocol. Printed 11/26/99 January 13, 1995 7 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) 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 normal transport protocols, not to ICMP. icmp.maskrepl Returns 1 if ICMP network mask requests are to be answered. udp.checksum Returns 1 when UDP checksums are being computed and checked. Disabling UDP checksums is strongly discouraged. 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 Printed 11/26/99 January 13, 1995 8 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) 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 POSIX 1003.2, otherwise 0. USER_POSIX2_C_BIND Return 1 if the system's C-language development facili- ties support the C-Language Bindings Option, otherwise 0. USER_POSIX2_C_DEV Printed 11/26/99 January 13, 1995 9 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) Return 1 if the system supports the C-Language Develop- ment 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 Develop- ment 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 POSIX 1003.2 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_METER struct vmtotal no VM_SWAPMAP struct map no VM_COREMAP struct map no Printed 11/26/99 January 13, 1995 10 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) 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_SWAPMAP Return the swapmap. The size of this structure is fixed and may be determined by specifying a oldlenp initialized to zero, the kernel will fill in the size of the swapmap. VM_COREMAP Same as for swapmap above except that the core alloca- tion map is returned. RETURN VALUES If the call to sysctl is successful, 0 is returned. Other- wise -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 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. EOPNOTSUPP The name array specifies a value that is unk- nown. 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 Printed 11/26/99 January 13, 1995 11 SYSCTL(3) UNIX Programmer's Manual SYSCTL(3) <sys/socket.h> definitions for second level network identif- iers <sys/gmon.h> definitions for third level profiling iden- tifiers <sys/vmparam.h> definitions for second level virtual memory identifiers <netinet/in.h> definitions for third level Internet identif- iers 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. The KERN_TEXT, KERN_MAXTEXTS, VM_SWAPMAP, VM_COREMAP options are 2.11BSD specific extensions to the 4.4BSD sysctl impl- mentation. Having KERN_FILE return the address of the file structure before the actual struct file is a 2.11BSD enhancement. The inode (vnode under 4.4) table was handled this way. Printed 11/26/99 January 13, 1995 12
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