SYSCTL(3) NetBSD Programmer's Manual SYSCTL(3)
NAME
sysctl - get or set system information
LIBRARY
Standard C Library (libc, -lc)
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. Infor- mation 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 returned in the location pointed to by oldlenp. For some operations, the amount of space may change often. For these operations, the system attempts to round up so that the returned size is large enough for a call to return the data shortly thereafter. To set a new value, newp is set to point to a buffer of length newlen from which the requested value is to be taken. If a new value is not to be set, newp should be set to NULL and newlen set to 0. The top level names are defined with a CTL_ prefix in <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_VFS sys/mount.h Filesystem CTL_HW sys/sysctl.h Generic CPU, I/O CTL_KERN sys/sysctl.h High kernel limits CTL_MACHDEP sys/sysctl.h Machine dependent CTL_NET sys/socket.h Networking CTL_USER sys/sysctl.h User-level CTL_VM vm/vm_param.h Virtual memory For example, the following retrieves the maximum number of processes al- lowed in the system: int mib[2], maxproc; size_t len; mib[0] = CTL_KERN; mib[1] = KERN_MAXPROC; len = sizeof(maxproc); sysctl(mib, 2, &maxproc, &len, NULL, 0); To retrieve the standard search path for the system utilities: int mib[2]; size_t len; char *p; mib[0] = CTL_USER; mib[1] = USER_CS_PATH; sysctl(mib, 2, NULL, &len, NULL, 0); p = malloc(len); sysctl(mib, 2, p, &len, NULL, 0);
CTL_DEBUG
The debugging variables vary from system to system. A debugging variable may be added or deleted without need to recompile sysctl to know about it. Each time it runs, sysctl gets the list of debugging variables from the kernel and displays their current values. The system defines twenty (struct ctldebug) variables named debug0 through debug19. They are de- clared as separate variables so that they can be individually initialized at the location of their associated variable. The loader prevents multi- ple use of the same variable by issuing errors if a variable is initial- ized in more than one place. For example, to export the variable dospecialcheck as a debugging variable, the following declaration would be used: int dospecialcheck = 1; struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
CTL_VFS
A distinguished second level name, VFS_GENERIC, is used to get general information about all filesystems. One of its third level identifiers is VFS_MAXTYPENUM that gives the highest valid filesystem type number. Its other third level identifier is VFS_CONF that returns configuration in- formation about the filesystem type given as a fourth level identifier (see getvfsbyname(3) as an example of its use). The remaining second level identifiers are the filesystem type number returned by a statfs(2) call or from VFS_CONF. The third level identifiers available for each filesystem are given in the header file that defines the mount argument structure for that filesystem.
CTL_HW
The string and integer information available for the CTL_HW level is de- tailed below. The changeable column shows whether a process with appro- priate privilege may change the value. Second level name Type Changeable HW_MACHINE string no HW_MODEL string no HW_NCPU integer no HW_BYTEORDER integer no HW_PHYSMEM integer no HW_USERMEM integer no HW_PAGESIZE integer no HW_MACHINE_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_MACHINE_ARCH The machine cpu class.
CTL_KERN
The string and integer information available for the CTL_KERN level is detailed below. The changeable column shows whether a process with ap- propriate privilege may change the value. The types of data currently available are process information, system vnodes, the open file entries, routing table entries, virtual memory statistics, load average history, and clock rate information. Second level name Type Changeable KERN_ARGMAX integer no KERN_AUTONICETIME integer yes KERN_AUTONICEVAL integer yes 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_IOV_MAX integer no 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_MSGBUFSIZE integer no KERN_NAME_MAX integer no KERN_NGROUPS integer no KERN_NO_TRUNC integer no KERN_OSRELEASE string no KERN_OSREV integer no KERN_OSTYPE string no KERN_PATH_MAX integer no KERN_PIPE_BUF integer no KERN_POSIX1 integer no KERN_PROC struct proc no KERN_PROF node not applicable KERN_RAWPARTITION integer no KERN_SAVED_IDS integer no KERN_SECURELVL integer raise only KERN_SHORTCORENAME integer yes KERN_SYNCHRONIZED_IO integer no 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 execve(2). KERN_AUTONICETIME The number of seconds of cpu-time a non-root process may accumu- late before having its priority lowered from the default to the value of KERN_AUTONICEVAL. If set to 0, automatic lowering of priority is not performed, and if set to -1 all non-root process- es are immediately lowered. KERN_AUTONICEVAL The priority assigned for automatically niced processes. 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 POSIX 1003.1b File Synchronization Option is available on this system, otherwise 0. KERN_HOSTID Get or set the host id. KERN_HOSTNAME Get or set the hostname. KERN_IOV_MAX Return the maximum number of iovec structures that a process has available for use with preadv(2), pwritev(2), readv(2), recvmsg(2), sendmsg(2) and writev(2). 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_MSGBUFSIZE The maximum number of characters that the kernel message buffer can hold. KERN_NAME_MAX The maximum number of bytes in a file name. KERN_NGROUPS The maximum number of supplemental groups. KERN_NO_TRUNC Return 1 if file names longer than KERN_NAME_MAX are truncated. KERN_OSRELEASE The system release string. KERN_OSREV The system revision string. KERN_OSTYPE The system type string. KERN_PATH_MAX The maximum number of bytes in a pathname. KERN_PIPE_BUF The maximum number of bytes which will be written atomically to a pipe. KERN_POSIX1 The version of ISO/IEC 9945 (POSIX 1003.1) with which the system attempts to comply. KERN_PROC Return the entire process table, or a subset of it. An array of struct kinfo_proc structures is returned, whose size depends on the current number of such objects in the system. The third and fourth level names are as follows: Third level name Fourth level is: KERN_PROC_ALL None KERN_PROC_PID A process ID KERN_PROC_PGRP A process group KERN_PROC_TTY A tty device KERN_PROC_UID A user ID KERN_PROC_RUID A real user ID KERN_PROF Return profiling information about the kernel. If the kernel is not compiled for profiling, attempts to retrieve any of the KERN_PROF values will fail with EOPNOTSUPP. The third level names for the string and integer profiling information is de- tailed below. The changeable column shows whether a process with appropriate privilege may change the value. Third level name Type Changeable GPROF_STATE integer yes GPROF_COUNT u_short[] yes GPROF_FROMS u_short[] yes GPROF_TOS struct tostruct yes GPROF_GMONPARAM struct gmonparam no The variables are as follows: GPROF_STATE Returns GMON_PROF_ON or GMON_PROF_OFF to show that pro- filing is running or stopped. GPROF_COUNT Array of statistical program counter counts. GPROF_FROMS Array indexed by program counter of call-from points. GPROF_TOS Array of struct tostruct describing destination of calls and their counts. GPROF_GMONPARAM Structure giving the sizes of the above arrays. KERN_RAWPARTITION The raw partition of a disk (a == 0). 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_SHORTCORENAME Whether core dumps are named programname.core (default, value 0) or core (value 1). The default value can be changed to 1 with the kernel configuration option options SHORTCORENAME (see options(4), core(5)). KERN_SYNCHRONIZED_IO Returns 1 if the POSIX 1003.1b Synchronized I/O Option is avail- able on this system, otherwise 0. 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 privilege may change the value. Second level name Type Changeable PF_ROUTE routing messages no PF_INET internet values yes PF_ROUTE Return the entire routing table or a subset of it. The data is returned as a sequence of routing messages (see route(4) for the header file, format and meaning). The length of each message is contained in the message header. The third level name is a protocol number, which is currently al- ways 0. The fourth level name is an address family, which may be set to 0 to select all address families. The fifth and sixth level names are as follows: Fifth level name Sixth level is: NET_RT_FLAGS rtflags NET_RT_DUMP None NET_RT_IFLIST None PF_INET Get or set various global information about the internet proto- cols. The third level name is the protocol. The fourth level name is the variable name. The currently defined protocols and names are: Protocol name Variable name Type Changeable ip forwarding integer yes ip redirect integer yes ip ttl integer yes ip forwsrcrt integer yes ip directed-broadcast integer yes ip allowsrcrt integer yes ip subnetsarelocal integer yes ip mtudisc integer yes ip anonportmin integer yes ip anonportmax integer yes ip mtudisctimeout integer yes icmp maskrepl integer yes tcp rfc1323 integer yes tcp sendspace integer yes tcp recvspace integer yes tcp mssdflt integer yes tcp syn_cache_limit integer yes tcp syn_bucket_limit integer yes tcp syn_cache_interval integer yes tcp init_win integer yes tcp mss_ifmtu integer yes tcp sack integer yes tcp win_scale integer yes tcp timestamps integer yes tcp compat_42 integer yes tcp cwm integer yes tcp cwm_burstsize integer yes tcp ack_on_push integer yes tcp keepidle integer yes tcp keepintvl integer yes tcp keepcnt integer yes tcp slowhz integer no tcp newreno integer yes udp checksum integer yes udp sendspace integer yes udp recvspace integer yes The variables are as follows: ip.forwarding Returns 1 when IP forwarding is enabled for the host, meaning that the host is acting as a router. ip.redirect Returns 1 when ICMP redirects may be sent by the host. This option is ignored unless the host is routing IP packets, and should normally be enabled on all systems. ip.ttl The maximum time-to-live (hop count) value for an IP packet sourced by the system. This value applies to nor- mal transport protocols, not to ICMP. ip.forwsrcrt Returns 1 when forwarding of source-routed packets is en- abled for the host. This value may only be changed if the kernel security level is less than 1. ip.directed-broadcast Returns 1 if directed broadcast behavior is enabled for the host. ip.allowsrcrt Returns 1 if the host accepts source routed packets. ip.subnetsarelocal Returns 1 if subnets are to be considered local address- es. ip.mtudisc Returns 1 if Path MTU Discovery is enabled. ip.anonportmin The lowest port number to use for TCP and UDP ephemeral port allocation. This cannot be set to less that 1024 or greater than 65535. ip.anonportmax The highest port number to use for TCP and UDP ephemeral port allocation. This cannot be set to less that 1024 or greater than 65535, and must be greater than ip.anonportmin. ip.mtudisctimeout Returns the number of seconds in which a route added by the Path MTU Discovery engine will time out. When the route times out, the Path MTU Discovery engine will at- tempt to probe a larger path MTU. 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.sendspace Returns the default TCP send buffer size. tcp.recvspace Returns the default TCP receive buffer size. tcp.mssdflt Returns the default maximum segment size both advertsized to the peer and to use when the peer does not advertize a maximum segment size to us during connection setup. Do not change this value unless you really know what you are doing. tcp.syn_cache_limit Returns the maximum number of entries allowed in the TCP compressed state engine. tcp.syn_bucket_limit Returns the maximum number of entries allowed per hash bucket in the TCP compressed state engine. tcp.syn_cache_interval Returns the TCP compressed state engine's timer interval. tcp.init_win Returns a value indicating the TCP initial congestion window. If this value is 0, an auto-tuning algorithm de- signed to use an initial window of approximately 4K bytes is in use. Otherwise, this value indicates a fixed num- ber of packets. tcp.mss_ifmtu Returns 1 if TCP calculates the outgoing maximum segment size based on the MTU of the appropriate interface. Oth- erwise, it is calculated based on the greater of the MTU of the interface, and the largest (non-loopback) inter- face MTU on the system. tcp.sack Returns a value which determines the level of Selective Acknowledgement supported by TCP. If 2, we will transmit and receive SACK options. If 1, we will transmit SACK options, but ignore any SACK options received. If 0, SACK is disabled. tcp.win_scale If rfc1323 is enabled, a value of 1 indicates RFC1323 window scale options, for increasing the TCP window size, are enabled. tcp.timestamps If rfc1323 is enabled, a value of 1 indicates RFC1323 time stamp options, used for measuring TCP round trip times, are enabled. tcp.compat_42 Returns 1 if work-arounds for bugs in the 4.2BSD TCP im- plementation are enabled. Use of this option is not rec- ommended, although it may be required in order to commu- nicate with extremely old TCP implementations. tcp.cwm Returns 1 if use of the Hughes/Touch/Heidemann Congestion Window Monitoring algorithm is enabled. This algorithm prevents line-rate bursts of packets that could otherwise occur when data begins flowing on an idle TCP connection. These line-rate bursts can contribute to network and router congestion. This can be particularly useful on World Wide Web servers which support HTTP/1.1, which has lingering connections. tcp.cwm_burstsize Returns the Congestion Window Monitoring allowed burst size, in terms of packet count. tcp.ack_on_push Returns 1 if TCP is to immediately transmit an ACK upon reception of a packet with PUSH set. This can avoid los- ing a round trip time in some rare situations, but has the caveat of potentially defeating TCP's delayed ACK al- gorithm. Use of this option is generally not recommend- ed, but the variable exists in case your configuration really needs it. tcp.keepidle Time a connection must be idle before keepalives are sent (if keepalives are enabled for the connection). 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.keepcnt Number of keepalive probes sent before declaring a con- nection dead. If set to zero, there is no limit; keepalives will be sent until some kind of response is received from the peer. 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.newreno Returns 1 if the use of J. Hoe's NewReno congestion con- trol algorithm is enabled. This algorithm improves the start-up behavior of TCP connections. udp.checksum Returns 1 when UDP checksums are being computed and checked. Disabling UDP checksums is strongly discour- aged. udp.sendspace Returns the default UDP send buffer size. udp.recvspace Returns the default UDP receive buffer size.
CTL_USER
The string and integer information available for the CTL_USER level is detailed below. The changeable column shows whether a process with ap- propriate privilege may change the value. Second level name Type Changeable USER_BC_BASE_MAX integer no USER_BC_DIM_MAX integer no USER_BC_SCALE_MAX integer no USER_BC_STRING_MAX integer no USER_COLL_WEIGHTS_MAX integer no USER_CS_PATH string no USER_EXPR_NEST_MAX integer no USER_LINE_MAX integer no USER_POSIX2_CHAR_TERM integer no USER_POSIX2_C_BIND integer no USER_POSIX2_C_DEV integer no USER_POSIX2_FORT_DEV integer no USER_POSIX2_FORT_RUN integer no USER_POSIX2_LOCALEDEF integer no USER_POSIX2_SW_DEV integer no USER_POSIX2_UPE integer no USER_POSIX2_VERSION integer no USER_RE_DUP_MAX integer no USER_STREAM_MAX integer no USER_TZNAME_MAX integer no USER_BC_BASE_MAX The maximum ibase/obase values in the bc(1) utility. USER_BC_DIM_MAX The maximum array size in the bc(1) utility. USER_BC_SCALE_MAX The maximum scale value in the bc(1) utility. USER_BC_STRING_MAX The maximum string length in the bc(1) utility. USER_COLL_WEIGHTS_MAX The maximum number of weights that can be assigned to any entry of the LC_COLLATE order keyword in the locale definition file. USER_CS_PATH Return a value for the PATH environment variable that finds all the standard utilities. USER_EXPR_NEST_MAX The maximum number of expressions that can be nested within parenthesis by the expr(1) utility. USER_LINE_MAX The maximum length in bytes of a text-processing utility's input line. USER_POSIX2_CHAR_TERM Return 1 if the system supports at least one terminal type capa- ble of all operations described in POSIX 1003.2, otherwise 0. USER_POSIX2_C_BIND Return 1 if the system's C-language development facilities sup- port the C-Language Bindings Option, otherwise 0. USER_POSIX2_C_DEV Return 1 if the system supports the C-Language Development Utili- ties Option, otherwise 0. USER_POSIX2_FORT_DEV Return 1 if the system supports the FORTRAN Development Utilities Option, otherwise 0. USER_POSIX2_FORT_RUN Return 1 if the system supports the FORTRAN Runtime Utilities Op- tion, otherwise 0. USER_POSIX2_LOCALEDEF Return 1 if the system supports the creation of locales, other- wise 0. USER_POSIX2_SW_DEV Return 1 if the system supports the Software Development Utili- ties Option, otherwise 0. USER_POSIX2_UPE Return 1 if the system supports the User Portability Utilities Option, otherwise 0. USER_POSIX2_VERSION The version of POSIX 1003.2 with which the system attempts to comply. USER_RE_DUP_MAX The maximum number of repeated occurrences of a regular expres- sion permitted when using interval notation. USER_STREAM_MAX The minimum maximum number of streams that a process may have open at any one time. USER_TZNAME_MAX The minimum maximum number of types supported for the name of a timezone.
CTL_VM
The string and integer information available for the CTL_VM level is de- tailed below. The changeable column shows whether a process with appro- priate privilege may change the value. Second level name Type Changeable VM_LOADAVG struct loadavg no VM_METER struct vmtotal no VM_LOADAVG Return the load average history. The returned data consists of a struct loadavg. VM_METER Return the system wide virtual memory statistics. The returned data consists of a struct vmtotal.
CTL_DDB
The integer information available for the CTL_DDB level is detailed be- low. The changeable column shows whether a process with appropriate privilege may change the value. Second level name Type Changeable DBCTL_RADIX integer yes DBCTL_MAXOFF integer yes DBCTL_LINES integer yes DBCTL_TABSTOPS integer yes DBCTL_ONPANIC integer yes DBCTL_RADIX The input and output radix. DBCTL_MAXOFF The maximum symbol offset. DBCTL_LINES Number of display lines. DBCTL_TABSTOPS Tab width. DBCTL_ONPANIC If non-zero, DDB will be entered when the kernel panics. These MIB nodes are also available as variables from within the DDB. See ddb(4) for more details.
RETURN VALUES
If the call to sysctl is successful, the number of bytes copied out is returned. Otherwise -1 is returned and errno is set appropriately.
ERRORS
The following errors may be reported: [EFAULT] The buffer name, oldp, newp, or length pointer oldlenp con- tains an invalid address. [EINVAL] The name array is less than two or greater than CTL_MAX- NAME. [EINVAL] A non-null newp is given and its specified length in newlen is too large or too small. [ENOMEM] The length pointed to by oldlenp is too short to hold the requested value. [ENOTDIR] The name array specifies an intermediate rather than termi- nal name. [EOPNOTSUPP] The name array specifies a value that is unknown. [EPERM] An attempt is made to set a read-only value. [EPERM] A process without appropriate privilege attempts to set a value. [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. NetBSD 1.4 May 9, 1995 14
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