200 lines
5.5 KiB
Groff
200 lines
5.5 KiB
Groff
'\"macro stdmacro
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.\" Copyright (c) 1983 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)socket.2 6.5 (Berkeley) 5/23/86
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.\"
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.if n .pH man2.socket @(#)socket 30.3 of 2/1/86
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.TH SOCKET 2
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.UC 5
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.SH NAME
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socket \- create an endpoint for communication
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.Op c p a
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.SH C SYNOPSIS
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.B #include <sys/types.h>
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.br
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.B #include <sys/socket.h>
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.sp .5
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.br
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.B "int socket\|(int domain, int type, int protocol);"
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.Op
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.Op f
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.SH FORTRAN SYNOPSIS
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.B "integer *4 function socket (domain, type, protocol)"
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.br
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.B "integer *4 domain, type, protocol"
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.Op
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.SH DESCRIPTION
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.I Socket
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creates an endpoint for communication and returns a descriptor.
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.PP
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The
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.I domain
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parameter specifies a communications domain within which
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communication will take place; this selects the protocol family
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which should be used.
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The protocol family generally is the same as the address family
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for the addresses supplied in later operations on the socket.
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These families are defined in the include file
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.IR <sys/socket.h> .
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The currently understood formats are:
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.PP
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.RS
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.nf
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.ta 1.25i 1.75i
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PF_INET (DARPA Internet protocols)
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PF_RAW (Link-level protocols)
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PF_UNIX (4.3BSD UNIX internal protocols)
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.fi
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.RE
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.sp .5v
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The formats
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PF_NS (Xerox Network Systems protocols) and
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PF_IMPLINK (IMP link layer) are not implemented.
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.PP
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The socket has the indicated
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.I type,
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which specifies the semantics of communication. Currently
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implemented types are:
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.PP
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.RS
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.nf
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SOCK_STREAM
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SOCK_DGRAM
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SOCK_RAW
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.fi
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.RE
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.PP
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A SOCK_STREAM type provides sequenced, reliable,
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two-way connection based byte streams.
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An out-of-band data transmission mechanism may be supported.
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A SOCK_DGRAM socket supports
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datagrams (connectionless, unreliable messages of
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a fixed (typically small) maximum length).
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SOCK_RAW sockets, which are available only to the super-user,
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provide access to internal network protocols and interfaces.
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The types
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SOCK_SEQPACKET and SOCK_RDM are currently unimplemented.
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.PP
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The
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.I protocol
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specifies a particular protocol to be used with the socket.
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Normally only a single protocol exists to support a particular
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socket type within a given protocol family. However, it is possible
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that many protocols may exist, in which case a particular protocol
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must be specified in this manner. The protocol number to use is
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particular to the \*(lqcommunication domain\*(rq in which communication
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is to take place; see
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.IR getprotoent (3N).
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.PP
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Sockets of type SOCK_STREAM
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are full-duplex byte streams, similar
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to pipes. A stream socket must be in a
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.I connected
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state before any data may be sent or received
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on it. A connection to another socket is created with a
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.IR connect (2)
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call. Once connected, data may be transferred using
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.IR read (2)
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and
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.IR write (2)
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calls or some variant of the
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.IR send (2)
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and
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.IR recv (2)
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calls.
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Note that for the
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.I read
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and
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.IR recv -style
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calls,
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the number of bytes actually read may be less than the number requested.
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When a session has been completed a
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.IR close (2)
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may be performed.
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Out-of-band data may also be transmitted as described in
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.IR send (2)
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and received as described in
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.IR recv (2).
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.PP
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The communications protocols used to implement a
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SOCK_STREAM insure that data
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is not lost or duplicated. If a piece of data for which the
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peer protocol has buffer space cannot be successfully transmitted
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within a reasonable length of time, then
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the connection is considered broken and calls
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will indicate an error with
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\-1 returns and with ETIMEDOUT as the specific code
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in the global variable errno.
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The protocols optionally keep sockets \*(lqwarm\*(rq by
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forcing transmissions
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roughly every minute in the absence of other activity.
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An error is then indicated if no response can be
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elicited on an otherwise
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idle connection for a extended period (e.g. 5 minutes).
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A SIGPIPE signal is raised if a process sends
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on a broken stream; this causes naive processes,
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which do not handle the signal, to exit.
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.PP
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SOCK_DGRAM and SOCK_RAW
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sockets allow sending of datagrams to correspondents
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named in
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.IR send (2)
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calls. Datagrams are generally received with
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.IR recvfrom (2),
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which returns the next datagram with its return address.
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.PP
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An
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.IR fcntl (2)
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call can be used to specify a process group to receive
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a SIGURG signal when the out-of-band data arrives.
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The FIONBIO i/o control (see
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.IR ioctl (2))
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or the
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FNDELAY fcntl (see
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.IR fcntl (2))
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enable non-blocking I/O and asynchronous notification of I/O events
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via SIGIO.
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.PP
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The operation of sockets is controlled by socket level
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.IR options .
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These options are defined in the file
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.RI < sys/socket.h >.
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.IR setsockopt (2)
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and
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.IR getsockopt (2)
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are used to set and get options, respectively.
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.SH "RETURN VALUE
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A \-1 is returned if an error occurs, otherwise the return
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value is a descriptor referencing the socket.
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.ne 5
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.SH "ERRORS
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The \f2socket\fP call fails if:
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.TP 25
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[EPROTONOSUPPORT]
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The protocol type or the specified protocol is not supported
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within this domain.
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.TP 25
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[EMFILE]
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The per-process descriptor table is full.
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.TP 25
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[ENFILE]
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The system file table is full.
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.TP 25
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[EACCESS]
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Permission to create a socket of the specified type and/or protocol
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is denied.
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.TP 25
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[ENOBUFS]
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Insufficient buffer space is available.
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The socket cannot be created until sufficient resources are freed.
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.SH SEE ALSO
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accept(2), bind(2), connect(2), fcntl(2), getsockname(2), getsockopt(2),
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ioctl(2), listen(2), read(2), recv(2), select(2), send(2), socketpair(2),
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write(2), inet(7F), raw(7F), unix(7F)
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.SH NOTE
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ABI-compliant versions of the above calls can be obtained from
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.IR libsocket.so .
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'\".so /pubs/tools/origin.bsd
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