bsd/man/man2/socket.2

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  34 .\"     @(#)socket.2    8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd March 18, 2015
  37 .Dt SOCKET 2
  38 .Os
  39 .Sh NAME
  40 .Nm socket
  41 .Nd create an endpoint for communication
  42 .Sh SYNOPSIS
  43 .Fd #include <sys/socket.h>
  44 .Ft int
  45 .Fo socket
  46 .Fa "int domain"
  47 .Fa "int type"
  48 .Fa "int protocol"
  49 .Fc
  50 .Sh DESCRIPTION
  51 .Fn socket
  52 creates an endpoint for communication and returns a descriptor.
  53 .Pp
  54 The
  55 .Fa domain
  56 parameter specifies a communications domain within which
  57 communication will take place; this selects the protocol family
  58 which should be used.
  59 These families are defined in the include file
  60 .Ao Pa sys/socket.h Ac .
  61 The currently understood formats are
  62 .Pp
  63 .Bd -literal -offset indent -compact
  64 PF_LOCAL        Host-internal protocols, formerly called PF_UNIX,
  65 PF_UNIX         Host-internal protocols, deprecated, use PF_LOCAL,
  66 PF_INET         Internet version 4 protocols,
  67 PF_ROUTE        Internal Routing protocol,
  68 PF_KEY          Internal key-management function,
  69 PF_INET6        Internet version 6 protocols,
  70 PF_SYSTEM       System domain,
  71 PF_NDRV         Raw access to network device
  72 .Ed
  73 .Pp
  74 The socket has the indicated
  75 .Fa type ,
  76 which specifies the semantics of communication.  Currently
  77 defined types are:
  78 .Pp
  79 .Bd -literal -offset indent -compact
  80 SOCK_STREAM
  81 SOCK_DGRAM
  82 SOCK_RAW
  83 .\"SOCK_SEQPACKET
  84 .\"SOCK_RDM
  85 .Ed
  86 .Pp
  87 A
  88 .Dv SOCK_STREAM
  89 type provides sequenced, reliable,
  90 two-way connection based byte streams.
  91 An out-of-band data transmission mechanism may be supported.
  92 A
  93 .Dv SOCK_DGRAM
  94 socket supports
  95 datagrams (connectionless, unreliable messages of
  96 a fixed (typically small) maximum length).
  97 .\"A
  98 .\".Dv SOCK_SEQPACKET
  99 .\"socket may provide a sequenced, reliable,
 100 .\"two-way connection-based data transmission path for datagrams
 101 .\"of fixed maximum length; a consumer may be required to read
 102 .\"an entire packet with each read system call.
 103 .\"This facility is protocol specific, and presently implemented
 104 .\"only for
 105 .\".Dv PF_NS .
 106 .Dv SOCK_RAW
 107 sockets provide access to internal network protocols and interfaces.
 108 The type
 109 .Dv SOCK_RAW ,
 110 which is available only to the super-user.
 111 .\" , and
 112 .\" .Dv SOCK_RDM ,
 113 .\" which is planned,
 114 .\" but not yet implemented, are not described here.
 115 .Pp
 116 The
 117 .Fa protocol
 118 specifies a particular protocol to be used with the socket.
 119 Normally only a single protocol exists to support a particular
 120 socket type within a given protocol family.  However, it is possible
 121 that many protocols may exist, in which case a particular protocol
 122 must be specified in this manner.  The protocol number to use is
 123 particular to the \*(lqcommunication domain\*(rq in which communication
 124 is to take place; see
 125 .Xr protocols 5 .
 126 .Pp
 127 Sockets of type
 128 .Dv SOCK_STREAM
 129 are full-duplex byte streams, similar
 130 to pipes.  A stream socket must be in a
 131 .Em connected
 132 state before any data may be sent or received
 133 on it.  A connection to another socket is created with a
 134 .Xr connect 2
 135 or
 136 .Xr connectx 2
 137 call.  Once connected, data may be transferred using
 138 .Xr read 2
 139 and
 140 .Xr write 2
 141 calls or some variant of the
 142 .Xr send 2
 143 and
 144 .Xr recv 2
 145 calls.  When a session has been completed a
 146 .Xr close 2
 147 may be performed.
 148 Out-of-band data may also be transmitted as described in
 149 .Xr send 2
 150 and received as described in
 151 .Xr recv 2 .
 152 .Pp
 153 The communications protocols used to implement a
 154 .Dv SOCK_STREAM
 155 insure that data
 156 is not lost or duplicated.  If a piece of data for which the
 157 peer protocol has buffer space cannot be successfully transmitted
 158 within a reasonable length of time, then
 159 the connection is considered broken and calls
 160 will indicate an error with
 161 -1 returns and with
 162 .Dv ETIMEDOUT
 163 as the specific code
 164 in the global variable
 165 .Va errno .
 166 The protocols optionally keep sockets
 167 .Dq warm
 168 by forcing transmissions
 169 roughly every minute in the absence of other activity.
 170 An error is then indicated if no response can be
 171 elicited on an otherwise
 172 idle connection for a extended period (e.g. 5 minutes).
 173 A
 174 .Dv SIGPIPE
 175 signal is raised if a process sends
 176 on a broken stream; this causes naive processes,
 177 which do not handle the signal, to exit.
 178 .\" .Pp
 179 .\" .Dv SOCK_SEQPACKET
 180 .\" sockets employ the same system calls
 181 .\" as
 182 .\" .Dv SOCK_STREAM
 183 .\" sockets.  The only difference
 184 .\" is that
 185 .\" .Xr read 2
 186 .\" calls will return only the amount of data requested,
 187 .\" and any remaining in the arriving packet will be discarded.
 188 .Pp
 189 .Dv SOCK_DGRAM
 190 and
 191 .Dv SOCK_RAW
 192 sockets allow sending of datagrams to correspondents
 193 named in
 194 .Xr send 2
 195 calls.  Datagrams are generally received with
 196 .Xr recvfrom 2 ,
 197 which returns the next datagram with its return address.
 198 .Pp
 199 An
 200 .Xr fcntl 2
 201 call can be used to specify a process group to receive
 202 a
 203 .Dv SIGURG
 204 signal when the out-of-band data arrives.
 205 It may also enable non-blocking I/O
 206 and asynchronous notification of I/O events
 207 via
 208 .Dv SIGIO .
 209 .Pp
 210 The operation of sockets is controlled by socket level
 211 .Em options .
 212 These options are defined in the file
 213 .Ao Pa sys/socket.h Ac .
 214 .Xr Setsockopt 2
 215 and
 216 .Xr getsockopt 2
 217 are used to set and get options, respectively.
 218 .Sh RETURN VALUES
 219 A -1 is returned if an error occurs, otherwise the return
 220 value is a descriptor referencing the socket.
 221 .Sh ERRORS
 222 The
 223 .Fn socket
 224 system call fails if:
 225 .Bl -tag -width Er
 226 .\" ===========
 227 .It Bq Er EACCES
 228 Permission to create a socket of the specified type and/or protocol
 229 is denied.
 230 .\" ===========
 231 .It Bq Er EAFNOSUPPORT
 232 The specified address family is not supported.
 233 .\" ===========
 234 .It Bq Er EMFILE
 235 The per-process descriptor table is full.
 236 .\" ===========
 237 .It Bq Er ENFILE
 238 The system file table is full.
 239 .\" ===========
 240 .It Bq Er ENOBUFS
 241 Insufficient buffer space is available.
 242 The socket cannot be created until sufficient resources are freed.
 243 .\" ===========
 244 .It Bq Er ENOMEM
 245 Insufficient memory was available to fulfill the request.
 246 .\" ===========
 247 .It Bq Er EPROTONOSUPPORT
 248 The protocol type or the specified protocol is not supported
 249 within this domain.
 250 .\" ===========
 251 .It Bq Er EPROTOTYPE
 252 The socket type is not supported by the protocol.
 253 .El
 254 .Pp
 255 If a new protocol family is defined,
 256 the socreate process is free to return any desired error code.
 257 The
 258 .Fn socket
 259 system call will pass this error code along
 260 (even if it is undefined).
 261 .Sh LEGACY SYNOPSIS
 262 .Fd #include <sys/types.h>
 263 .Fd #include <sys/socket.h>
 264 .Pp
 265 The include file
 266 .In sys/types.h
 267 is necessary.
 268 .Sh SEE ALSO
 269 .Xr accept 2 ,
 270 .Xr bind 2 ,
 271 .Xr connect 2 ,
 272 .Xr connectx 2 ,
 273 .Xr disconnectx 2 ,
 274 .Xr getsockname 2 ,
 275 .Xr getsockopt 2 ,
 276 .Xr ioctl 2 ,
 277 .Xr listen 2 ,
 278 .Xr read 2 ,
 279 .Xr recv 2 ,
 280 .Xr select 2 ,
 281 .Xr send 2 ,
 282 .Xr shutdown 2 ,
 283 .Xr socketpair 2 ,
 284 .Xr write 2 ,
 285 .Xr getprotoent 3 ,
 286 .Xr inet 4 ,
 287 .Xr inet6 4 ,
 288 .Xr unix 4 ,
 289 .Xr compat 5
 290 .Rs
 291 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
 292 .%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
 293 .Re
 294 .Rs
 295 .%T "BSD Interprocess Communication Tutorial"
 296 .%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
 297 .Re
 298 .Sh HISTORY
 299 The
 300 .Fn socket
 301 function call appeared in
 302 .Bx 4.2 .