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1.1     ! root        1: .\" Copyright (c) 1980,1983,1986 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)intro.2     6.10 (Berkeley) 6/30/90
        !             6: .\"
        !             7: .TH INTRO 2 "June 30, 1990"
        !             8: .UC 4
        !             9: .de en
        !            10: .HP
        !            11: \\$1  \\$2  \\$3
        !            12: .br
        !            13: ..
        !            14: .SH NAME
        !            15: intro \- introduction to system calls and error numbers
        !            16: .SH SYNOPSIS
        !            17: .B #include <sys/errno.h>
        !            18: .SH DESCRIPTION
        !            19: This section provides an overview of the system calls,
        !            20: their error returns, and other common definitions and concepts.
        !            21: .\".LP
        !            22: .\".B "System call restart"
        !            23: .\".PP
        !            24: .\"<more later...>
        !            25: .SH DIAGNOSTICS
        !            26: Most of these calls have one or more error returns.
        !            27: An error condition is indicated by an otherwise impossible return
        !            28: value.  This is almost always \-1; the individual descriptions
        !            29: specify the details.
        !            30: Note that a number of system calls overload the meanings of these
        !            31: error numbers, and that the meanings must be interpreted according
        !            32: to the type and circumstances of the call.
        !            33: .PP
        !            34: As with normal arguments, all return codes and values from
        !            35: functions are of type integer unless otherwise noted.
        !            36: An error number is also made available in the external
        !            37: variable \fIerrno\fP, which is not cleared
        !            38: on successful calls.
        !            39: Thus \fIerrno\fP should be tested only after an error has occurred.
        !            40: .PP
        !            41: The following is a complete list of the errors and their
        !            42: names as given in
        !            43: .RI < sys/errno.h >.
        !            44: .en 0 \h'\w'EIO'u' "Error 0
        !            45: Unused.
        !            46: .en 1 EPERM "Operation not permitted
        !            47: Typically this error indicates
        !            48: an attempt to modify a file in some way forbidden
        !            49: except to its owner or super-user.
        !            50: It is also returned for attempts
        !            51: by ordinary users to do things
        !            52: allowed only to the super-user.
        !            53: .en 2 ENOENT "No such file or directory
        !            54: This error occurs when a file name is specified
        !            55: and the file should exist but doesn't, or when one
        !            56: of the directories in a path name does not exist.
        !            57: .en 3 ESRCH "No such process
        !            58: The process or process group whose number was given
        !            59: does not exist, or any such process is already dead.
        !            60: .en 4 EINTR "Interrupted system call
        !            61: An asynchronous signal (such as interrupt or quit)
        !            62: that the user has elected to catch
        !            63: occurred during a system call.
        !            64: If execution is resumed
        !            65: after processing the signal
        !            66: and the system call is not restarted,
        !            67: it will appear as if the interrupted system call
        !            68: returned this error condition.
        !            69: .en 5 EIO "Input/output error
        !            70: Some physical I/O error occurred during a
        !            71: .I read
        !            72: or
        !            73: .IR write .
        !            74: This error may in some cases occur
        !            75: on a call following the one to which it actually applies.
        !            76: .en 6 ENXIO "Device not configured
        !            77: I/O on a special file refers to a subdevice that does not
        !            78: exist,
        !            79: or beyond the limits of the device.
        !            80: It may also occur when, for example, an illegal tape drive
        !            81: unit number is selected 
        !            82: or a disk pack is not loaded on a drive.
        !            83: .en 7 E2BIG "Argument list too long
        !            84: An argument list longer than 20480 bytes (or the current limit, NCARGS in
        !            85: .IR <sys/param.h> )
        !            86: is presented to
        !            87: .IR execve .
        !            88: .en 8 ENOEXEC "Exec format error
        !            89: A request is made to execute a file
        !            90: that, although it has the appropriate permissions,
        !            91: does not start with a valid magic number, (see
        !            92: .IR a.out (5)).
        !            93: .en 9 EBADF "Bad file descriptor
        !            94: Either a file descriptor refers to no
        !            95: open file,
        !            96: or a read (resp. write) request is made to
        !            97: a file that is open only for writing (resp. reading).
        !            98: .en 10 ECHILD "No child processes
        !            99: .I Wait
        !           100: and the process has no
        !           101: living or unwaited-for children.
        !           102: .en 11 EDEADLK "Resource deadlock avoided
        !           103: An attempt was made to lock a system resource that
        !           104: would have resulted in a deadlock situation.
        !           105: .en 12 ENOMEM "Cannnot allocate memory
        !           106: During an
        !           107: .I execve
        !           108: or
        !           109: .I break,
        !           110: a program asks for more core or swap space than the system is
        !           111: able to supply,
        !           112: or a process size limit would be exceeded.
        !           113: A lack of swap space is normally a temporary condition; however,
        !           114: a lack of core
        !           115: is not a temporary condition; the maximum size
        !           116: of the text, data, and stack segments is a system parameter.
        !           117: Soft limits may be increased to their corresponding hard limits.
        !           118: .en 13 EACCES "Permission denied
        !           119: An attempt was made to access a file in a way forbidden
        !           120: by the protection system.
        !           121: .en 14 EFAULT "Bad address
        !           122: The system encountered a hardware fault in attempting to
        !           123: access the arguments of a system call.
        !           124: .en 15 ENOTBLK "Block device required
        !           125: A plain file was mentioned where a block device was required,
        !           126: e.g., in
        !           127: .IR mount .
        !           128: .en 16 EBUSY "Device busy
        !           129: An attempt to mount a device that was already mounted or
        !           130: an attempt was made to dismount a device
        !           131: on which there is an active file
        !           132: (open file, current directory, mounted-on file, or active text segment).
        !           133: A request was made to an exclusive access device that was already in use.
        !           134: .en 17 EEXIST "File exists
        !           135: An existing file was mentioned in an inappropriate context,
        !           136: e.g.,
        !           137: .IR link .
        !           138: .en 18 EXDEV "Cross-device link
        !           139: A hard link to a file on another device
        !           140: was attempted.
        !           141: .en 19 ENODEV "Operation not supported by device
        !           142: An attempt was made to apply an inappropriate
        !           143: system call to a device,
        !           144: e.g., to read a write-only device,
        !           145: or the device is not configured by the system.
        !           146: .en 20 ENOTDIR "Not a directory
        !           147: A non-directory was specified where a directory
        !           148: is required,
        !           149: for example, in a path name or
        !           150: as an argument to
        !           151: .IR chdir .
        !           152: .en 21 EISDIR "Is a directory
        !           153: An attempt to write on a directory.
        !           154: .en 22 EINVAL "Invalid argument
        !           155: Some invalid argument:
        !           156: dismounting a non-mounted
        !           157: device,
        !           158: mentioning an unknown signal in
        !           159: .I signal,
        !           160: or some other argument inappropriate for the call.
        !           161: Also set by math functions, (see 
        !           162: .IR math (3)).
        !           163: .en 23 ENFILE "Too many open files in system
        !           164: The system's table of open files is full,
        !           165: and temporarily no more
        !           166: .I opens
        !           167: can be accepted.
        !           168: .en 24 EMFILE "Too many open files
        !           169: As released, the limit on the number of
        !           170: open files per process is 64.
        !           171: .IR Getdtablesize (2)
        !           172: will obtain the current limit.
        !           173: Customary configuration limit on most other UNIX systems
        !           174: is 20 per process.
        !           175: .en 25 ENOTTY "Inappropriate ioctl for device
        !           176: The file mentioned in an
        !           177: .I ioctl
        !           178: is not a terminal or one of the
        !           179: devices to which this call applies.
        !           180: .en 26 ETXTBSY "Text file busy
        !           181: An attempt to execute a pure-procedure
        !           182: program that is currently open for writing.
        !           183: Also an attempt to open for writing a pure-procedure
        !           184: program that is being executed.
        !           185: .en 27 EFBIG "File too large
        !           186: The size of a file exceeded the maximum (about
        !           187: .if t 2\u\s-231\s+2\d
        !           188: .if n 2.1E9
        !           189: bytes).
        !           190: .en 28 ENOSPC "No space left on device
        !           191: A
        !           192: .I write
        !           193: to an ordinary file, the creation of a
        !           194: directory or symbolic link, or the creation of a directory
        !           195: entry failed because no more disk blocks are available
        !           196: on the file system, or the allocation of an inode for a newly
        !           197: created file failed because no more inodes are available
        !           198: on the file system.
        !           199: .en 29 ESPIPE "Illegal seek
        !           200: An
        !           201: .I lseek
        !           202: was issued to a socket or pipe.
        !           203: This error may also be issued for
        !           204: other non-seekable devices.
        !           205: .en 30 EROFS "Read-only file system
        !           206: An attempt to modify a file or directory
        !           207: was made
        !           208: on a device mounted read-only.
        !           209: .en 31 EMLINK "Too many links
        !           210: An attempt to make more than 32767 hard links to a file.
        !           211: .en 32 EPIPE "Broken pipe
        !           212: A write on a pipe or socket for which there is no process
        !           213: to read the data.
        !           214: This condition normally generates a signal;
        !           215: the error is returned if the signal is caught or ignored.
        !           216: .en 33 EDOM "Numerical argument out of domain
        !           217: The argument of a function in the math package (3M)
        !           218: is out of the domain of the function.
        !           219: .en 34 ERANGE "Numerical result out of range
        !           220: The value of a function in the math package (3M)
        !           221: is unrepresentable within machine precision.
        !           222: .en 35 EAGAIN "Resource temporarily unavailable
        !           223: This is a temporary condition and later calls to the
        !           224: same routine may complete normally.
        !           225: .en 36 EINPROGRESS "Operation now in progress"
        !           226: An operation that takes a long time to complete (such as
        !           227: a \fIconnect\fP(2)) was attempted on a non-blocking object (see
        !           228: \fIfcntl\fP(2)).
        !           229: .en 37 EALREADY "Operation already in progress"
        !           230: An operation was attempted on a non-blocking object that already
        !           231: had an operation in progress.
        !           232: .en 38 ENOTSOCK "Socket operation on non-socket"
        !           233: Self-explanatory.
        !           234: .en 39 EDESTADDRREQ "Destination address required"
        !           235: A required address was omitted from an operation on a socket.
        !           236: .en 40 EMSGSIZE "Message too long"
        !           237: A message sent on a socket was larger than the internal message buffer
        !           238: or some other network limit.
        !           239: .en 41 EPROTOTYPE "Protocol wrong type for socket"
        !           240: A protocol was specified that does not support the semantics of the
        !           241: socket type requested. For example, you cannot use the ARPA Internet
        !           242: UDP protocol with type SOCK_STREAM.
        !           243: .en 42 ENOPROTOOPT "Protocol not available
        !           244: A bad option or level was specified in a
        !           245: .IR getsockopt (2)
        !           246: or
        !           247: .IR setsockopt (2)
        !           248: call.
        !           249: .en 43 EPROTONOSUPPORT "Protocol not supported"
        !           250: The protocol has not been configured into the
        !           251: system or no implementation for it exists.
        !           252: .en 44 ESOCKTNOSUPPORT "Socket type not supported"
        !           253: The support for the socket type has not been configured into the
        !           254: system or no implementation for it exists.
        !           255: .en 45 EOPNOTSUPP "Operation not supported on socket"
        !           256: For example, trying to \fIaccept\fP a connection on a datagram socket.
        !           257: .en 46 EPFNOSUPPORT "Protocol family not supported"
        !           258: The protocol family has not been configured into the
        !           259: system or no implementation for it exists.
        !           260: .en 47 EAFNOSUPPORT "Address family not supported by protocol family"
        !           261: An address incompatible with the requested protocol was used.
        !           262: For example, you shouldn't necessarily expect to be able to use NS
        !           263: addresses with ARPA Internet protocols.
        !           264: .en 48 EADDRINUSE "Address already in use"
        !           265: Only one usage of each address is normally permitted.
        !           266: .en 49 EADDRNOTAVAIL "Can't assign requested address"
        !           267: Normally results from an attempt to create a socket with an
        !           268: address not on this machine.
        !           269: .en 50 ENETDOWN "Network is down"
        !           270: A socket operation encountered a dead network.
        !           271: .en 51 ENETUNREACH "Network is unreachable"
        !           272: A socket operation was attempted to an unreachable network.
        !           273: .en 52 ENETRESET "Network dropped connection on reset"
        !           274: The host you were connected to crashed and rebooted.
        !           275: .en 53 ECONNABORTED "Software caused connection abort"
        !           276: A connection abort was caused internal to your host machine.
        !           277: .en 54 ECONNRESET "Connection reset by peer"
        !           278: A connection was forcibly closed by a peer.  This normally
        !           279: results from a loss of the connection on the remote socket
        !           280: due to a timeout or a reboot.
        !           281: .en 55 ENOBUFS "No buffer space available"
        !           282: An operation on a socket or pipe was not performed because
        !           283: the system lacked sufficient buffer space or because a queue was full.
        !           284: .en 56 EISCONN "Socket is already connected"
        !           285: A
        !           286: .I connect
        !           287: request was made on an already connected socket; or,
        !           288: a
        !           289: .I sendto
        !           290: or
        !           291: .I sendmsg
        !           292: request on a connected socket specified a destination
        !           293: when already connected.
        !           294: .en 57 ENOTCONN "Socket is not connected"
        !           295: An request to send or receive data was disallowed because
        !           296: the socket is not connected and (when sending on a  datagram socket)
        !           297: no address was supplied.
        !           298: .en 58 ESHUTDOWN "Can't send after socket shutdown"
        !           299: A request to send data was disallowed because the socket
        !           300: had already been shut down with a previous
        !           301: .IR shutdown (2)
        !           302: call.
        !           303: .en 60 ETIMEDOUT "Connection timed out"
        !           304: A
        !           305: .I connect
        !           306: or
        !           307: .I send
        !           308: request failed because the connected party did not
        !           309: properly respond after a period of time.  (The timeout
        !           310: period is dependent on the communication protocol.)
        !           311: .en 61 ECONNREFUSED "Connection refused"
        !           312: No connection could be made because the target machine actively
        !           313: refused it.  This usually results from trying to connect
        !           314: to a service that is inactive on the foreign host.
        !           315: .en 62 ELOOP "Too many levels of symbolic links"
        !           316: A path name lookup involved more than 8 symbolic links.
        !           317: .en 63 ENAMETOOLONG "File name too long"
        !           318: A component of a path name exceeded 255 (MAXNAMELEN) characters, or an entire
        !           319: path name exceeded 1023 (MAXPATHLEN-1) characters.
        !           320: .en 64 EHOSTDOWN "Host is down"
        !           321: A socket operation failed because the destination host was down.
        !           322: .en 65 EHOSTUNREACH "No route to host"
        !           323: A socket operation was attempted to an unreachable host.
        !           324: .en 66 ENOTEMPTY "Directory not empty"
        !           325: A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq
        !           326: was supplied to a remove directory or rename call.
        !           327: .en 67 EPROCLIM "Too many processes"
        !           328: .en 68 EUSERS "Too many users"
        !           329: The quota system ran out of table entries.
        !           330: .en 69 EDQUOT "Disc quota exceeded"
        !           331: A 
        !           332: .I write
        !           333: to an ordinary file, the creation of a
        !           334: directory or symbolic link, or the creation of a directory
        !           335: entry failed because the user's quota of disk blocks was
        !           336: exhausted, or the allocation of an inode for a newly
        !           337: created file failed because the user's quota of inodes
        !           338: was exhausted.
        !           339: .en 70 ESTALE "Stale NFS file handle"
        !           340: An attempt was made to access an open file (on an NFS filesystem)
        !           341: which is now unavailable as referenced by the file descriptor.  
        !           342: This may indicate the file was deleted on the NFS server and some 
        !           343: other catastrophic event occured.
        !           344: .en 72 EBADRPC "RPC struct is bad"
        !           345: Exchange of RPC information was unsuccessful.
        !           346: .en 73 ERPCMISMATCH "RPC version wrong"
        !           347: The version of RPC on the remote peer is not compatible with
        !           348: the local version.
        !           349: .en 74 EPROGUNAVAIL "RPC prog. not avail"
        !           350: The requested program is not registered on the remote host.
        !           351: .en 75 EPROGMISMATCH "Program version wrong"
        !           352: The requested version of the program is not available 
        !           353: on the remote host (RPC).
        !           354: .en 76 EPROCUNAVAIL "Bad procedure for program"
        !           355: An RPC call was attempted for a procedure which doesn't exist
        !           356: in the remote program.
        !           357: .en 77 ENOLCK "No locks available"
        !           358: A system-imposed limit on the number of simultaneous file 
        !           359: locks was reached.
        !           360: .en 78 ENOSYS "Function not implemented"
        !           361: Attempted a system call that is not available on this 
        !           362: system.
        !           363: .SH DEFINITIONS
        !           364: .TP 5
        !           365: Process ID
        !           366: .br
        !           367: Each active process in the system is uniquely identified by a positive
        !           368: integer called a process ID.  The range of this ID is from 0 to 30000.
        !           369: .TP 5
        !           370: Parent process ID
        !           371: .br
        !           372: A new process is created by a currently active process; (see
        !           373: .IR fork (2)).
        !           374: The parent process ID of a process is the process ID of its creator.
        !           375: .TP 5
        !           376: Process Group ID
        !           377: .br
        !           378: Each active process is a member of a process group that is identified by
        !           379: a positive integer called the process group ID.  This is the process
        !           380: ID of the group leader.  This grouping permits the signaling of related
        !           381: processes (see
        !           382: .IR killpg (2))
        !           383: and the job control mechanisms of
        !           384: .IR csh (1).
        !           385: .TP 5
        !           386: Tty Group ID
        !           387: .br
        !           388: Each active process can be a member of a terminal group that is identified
        !           389: by a positive integer called the tty group ID.  This grouping is used
        !           390: to arbitrate between multiple jobs contending for the same terminal;
        !           391: (see
        !           392: .IR csh (1)
        !           393: and
        !           394: .IR tty (4)).
        !           395: .TP 5
        !           396: Real User ID and Real Group ID
        !           397: .br
        !           398: Each user on the system is identified by a positive integer
        !           399: termed the real user ID.
        !           400: .IP
        !           401: Each user is also a member of one or more groups. 
        !           402: One of these groups is distinguished from others and
        !           403: used in implementing accounting facilities.  The positive
        !           404: integer corresponding to this distinguished group is termed 
        !           405: the real group ID.
        !           406: .IP
        !           407: All processes have a real user ID and real group ID.
        !           408: These are initialized from the equivalent attributes
        !           409: of the process that created it.
        !           410: .TP 5
        !           411: Effective User Id, Effective Group Id, and Access Groups
        !           412: .br
        !           413: Access to system resources is governed by three values:
        !           414: the effective user ID, the effective group ID, and the
        !           415: group access list.
        !           416: .IP
        !           417: The effective user ID and effective group ID are initially the
        !           418: process's real user ID and real group ID respectively.  Either
        !           419: may be modified through execution of a set-user-ID or set-group-ID
        !           420: file (possibly by one its ancestors) (see
        !           421: .IR execve (2)).
        !           422: .IP
        !           423: The group access list is an additional set of group ID's
        !           424: used only in determining resource accessibility.  Access checks
        !           425: are performed as described below in ``File Access Permissions''.
        !           426: .TP 5
        !           427: Super-user
        !           428: .br
        !           429: A process is recognized as a
        !           430: .I super-user
        !           431: process and is granted special privileges if its effective user ID is 0.
        !           432: .TP 5
        !           433: Special Processes
        !           434: .br
        !           435: The processes with a process ID's of 0, 1, and 2 are special.
        !           436: Process 0 is the scheduler.  Process 1 is the initialization process
        !           437: .IR init ,
        !           438: and is the ancestor of every other process in the system.
        !           439: It is used to control the process structure.
        !           440: Process 2 is the paging daemon.
        !           441: .TP 5
        !           442: Descriptor
        !           443: .br
        !           444: An integer assigned by the system when a file is referenced
        !           445: by
        !           446: .IR open (2)
        !           447: or
        !           448: .IR dup (2),
        !           449: or when a socket is created by
        !           450: .IR pipe (2),
        !           451: .IR socket (2)
        !           452: or
        !           453: .IR socketpair (2),
        !           454: which uniquely identifies an access path to that file or socket from
        !           455: a given process or any of its children.
        !           456: .TP 5
        !           457: File Name
        !           458: .br
        !           459: Names consisting of up to 255 (MAXNAMELEN) characters may be used to name
        !           460: an ordinary file, special file, or directory.
        !           461: .IP
        !           462: These characters may be selected from the set of all ASCII character
        !           463: excluding 0 (null) and the ASCII code for / (slash).  (The parity bit,
        !           464: bit 8, must be 0.)
        !           465: .IP
        !           466: Note that it is generally unwise to use *, ?, [ or ] as part of
        !           467: file names because of the special meaning attached to these characters
        !           468: by the shell.
        !           469: .TP 5
        !           470: Path Name
        !           471: .br
        !           472: A path name is a null-terminated character string starting with an
        !           473: optional slash (/), followed by zero or more directory names separated
        !           474: by slashes, optionally followed by a file name.
        !           475: The total length of a path name must be less than 1024 (MAXPATHLEN) characters.
        !           476: .IP
        !           477: If a path name begins with a slash, the path search begins at the
        !           478: .I root
        !           479: directory.
        !           480: Otherwise, the search begins from the current working directory.
        !           481: A slash by itself names the root directory.  A null
        !           482: pathname refers to the current directory.
        !           483: .TP 5
        !           484: Directory
        !           485: .br
        !           486: A directory is a special type of file that contains entries
        !           487: that are references to other files.
        !           488: Directory entries are called links.  By convention, a directory
        !           489: contains at least two links, . and .., referred to as
        !           490: .I dot
        !           491: and
        !           492: .I dot-dot
        !           493: respectively.  Dot refers to the directory itself and
        !           494: dot-dot refers to its parent directory.
        !           495: .TP 5
        !           496: Root Directory and Current Working Directory
        !           497: .br
        !           498: Each process has associated with it a concept of a root directory
        !           499: and a current working directory for the purpose of resolving path
        !           500: name searches.  A process's root directory need not be the root
        !           501: directory of the root file system.
        !           502: .TP 5
        !           503: File Access Permissions
        !           504: .br
        !           505: Every file in the file system has a set of access permissions.
        !           506: These permissions are used in determining whether a process
        !           507: may perform a requested operation on the file (such as opening
        !           508: a file for writing).  Access permissions are established at the
        !           509: time a file is created.  They may be changed at some later time
        !           510: through the 
        !           511: .IR chmod (2)
        !           512: call. 
        !           513: .IP
        !           514: File access is broken down according to whether a file may be: read,
        !           515: written, or executed.  Directory files use the execute
        !           516: permission to control if the directory may be searched. 
        !           517: .IP
        !           518: File access permissions are interpreted by the system as
        !           519: they apply to three different classes of users: the owner
        !           520: of the file, those users in the file's group, anyone else.
        !           521: Every file has an independent set of access permissions for
        !           522: each of these classes.  When an access check is made, the system
        !           523: decides if permission should be granted by checking the access
        !           524: information applicable to the caller.
        !           525: .IP
        !           526: Read, write, and execute/search permissions on
        !           527: a file are granted to a process if:
        !           528: .IP
        !           529: The process's effective user ID is that of the super-user.
        !           530: .IP
        !           531: The process's effective user ID matches the user ID of the owner
        !           532: of the file and the owner permissions allow the access.
        !           533: .IP
        !           534: The process's effective user ID does not match the user ID of the
        !           535: owner of the file, and either the process's effective
        !           536: group ID matches the group ID
        !           537: of the file, or the group ID of the file is in
        !           538: the process's group access list,
        !           539: and the group permissions allow the access.
        !           540: .IP
        !           541: Neither the effective user ID nor effective group ID
        !           542: and group access list of the process
        !           543: match the corresponding user ID and group ID of the file,
        !           544: but the permissions for ``other users'' allow access.
        !           545: .IP
        !           546: Otherwise, permission is denied.
        !           547: .TP 5
        !           548: Sockets and Address Families
        !           549: .IP
        !           550: A socket is an endpoint for communication between processes.
        !           551: Each socket has queues for sending and receiving data.
        !           552: .IP
        !           553: Sockets are typed according to their communications properties.
        !           554: These properties include whether messages sent and received
        !           555: at a socket require the name of the partner, whether communication
        !           556: is reliable, the format used in naming message recipients, etc.
        !           557: .IP
        !           558: Each instance of the system supports some
        !           559: collection of socket types; consult
        !           560: .IR socket (2)
        !           561: for more information about the types available and
        !           562: their properties.
        !           563: .IP
        !           564: Each instance of the system supports some number of sets of
        !           565: communications protocols.  Each protocol set supports addresses
        !           566: of a certain format.  An Address Family is the set of addresses
        !           567: for a specific group of protocols.  Each socket has an address
        !           568: chosen from the address family in which the socket was created.
        !           569: .SH SEE ALSO
        !           570: intro(3), perror(3)

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