BSD 4_3_Net_2 release

[unix-history] / usr / src / lib / libc / sys / intro.2

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-.\" Copyright (c) 1980,1983,1986 Regents of the University of California.
-.\" All rights reserved.  The Berkeley software License Agreement
-.\" specifies the terms and conditions for redistribution.
+.\" Copyright (c) 1980,1983,1986,1991 Regents of the University of California.
+.\" All rights reserved.

 .\"
 .\"

-.\"    @(#)intro.2     6.10 (Berkeley) 6/30/90
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"    This product includes software developed by the University of
+.\"    California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.

 .\"
 .\"

-.TH INTRO 2 "June 30, 1990"
-.UC 4
-.de en
-.HP
-\\$1  \\$2  \\$3
-.br
-..
-.SH NAME
-intro \- introduction to system calls and error numbers
-.SH SYNOPSIS
-.B #include <sys/errno.h>
-.SH DESCRIPTION
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)intro.2    6.13 (Berkeley) 7/23/91
+.\"
+.Dd July 23, 1991
+.Dt INTRO 2
+.Os BSD 4
+.Sh NAME
+.Nm intro
+.Nd introduction to system calls and error numbers
+.Sh SYNOPSIS
+.Fd #include <sys/errno.h>
+.Sh DESCRIPTION

 This section provides an overview of the system calls,
 their error returns, and other common definitions and concepts.
 This section provides an overview of the system calls,
 their error returns, and other common definitions and concepts.

-.\".LP
-.\".B "System call restart"
-.\".PP
+.\".Pp
+.\".Sy System call restart
+.\".Pp

 .\"<more later...>
 .\"<more later...>

-.SH DIAGNOSTICS
-Most of these calls have one or more error returns.
-An error condition is indicated by an otherwise impossible return
-value.  This is almost always \-1; the individual descriptions
-specify the details.
+.Sh DIAGNOSTICS
+Nearly all of the system calls provide an error number in the external
+variable
+.Va errno ,
+which is defined as:
+.Pp
+.Dl extern int errno
+.Pp
+When a system call detects an error,
+it returns an integer value
+indicating failure (usually -1)
+and sets the variable
+.Va errno
+accordingly.
+<This allows interpretation of the failure on receiving
+a -1 and to take action accordingly.>
+Successful calls never set
+.Va errno ;
+once set, it remains until another error occurs.
+It should only be examined after an error.

 Note that a number of system calls overload the meanings of these
 error numbers, and that the meanings must be interpreted according
 to the type and circumstances of the call.
 Note that a number of system calls overload the meanings of these
 error numbers, and that the meanings must be interpreted according
 to the type and circumstances of the call.

-.PP
-As with normal arguments, all return codes and values from
-functions are of type integer unless otherwise noted.
-An error number is also made available in the external
-variable \fIerrno\fP, which is not cleared
-on successful calls.
-Thus \fIerrno\fP should be tested only after an error has occurred.
-.PP
+.Pp

 The following is a complete list of the errors and their
 names as given in
 The following is a complete list of the errors and their
 names as given in

-.RI < sys/errno.h >.
-.en 0 \h'\w'EIO'u' "Error 0
-Unused.
-.en 1 EPERM "Operation not permitted
-Typically this error indicates
-an attempt to modify a file in some way forbidden
-except to its owner or super-user.
-It is also returned for attempts
-by ordinary users to do things
-allowed only to the super-user.
-.en 2 ENOENT "No such file or directory
-This error occurs when a file name is specified
-and the file should exist but doesn't, or when one
-of the directories in a path name does not exist.
-.en 3 ESRCH "No such process
-The process or process group whose number was given
-does not exist, or any such process is already dead.
-.en 4 EINTR "Interrupted system call
-An asynchronous signal (such as interrupt or quit)
-that the user has elected to catch
-occurred during a system call.
-If execution is resumed
-after processing the signal
-and the system call is not restarted,
-it will appear as if the interrupted system call
-returned this error condition.
-.en 5 EIO "Input/output error
-Some physical I/O error occurred during a
-.I read
+.Aq Pa sys/errno.h .
+.Bl -hang -width Ds
+.It Er 0 Em "Error 0" .
+Not used.
+.It Er 1 EPERM Em "Operation not permitted .
+An attempt was made to perform an operation limited to processes
+with appropriate privileges or to the owner of a file or other
+resources.
+.It Er 2 ENOENT Em "No such file or directory" .
+A component of a specified pathname did not exist, or the 
+pathname was an empty string.
+.It Er 3 ESRCH Em "No such process" .
+No process could be found corresponding to that specified by the given
+process ID.
+.It Er 4 EINTR Em "Interrupted function call" .
+An asynchronous signal (such as
+.Dv SIGINT

 or
 or

-.IR write .
-This error may in some cases occur
-on a call following the one to which it actually applies.
-.en 6 ENXIO "Device not configured
-I/O on a special file refers to a subdevice that does not
-exist,
-or beyond the limits of the device.
-It may also occur when, for example, an illegal tape drive
-unit number is selected 
-or a disk pack is not loaded on a drive.
-.en 7 E2BIG "Argument list too long
-An argument list longer than 20480 bytes (or the current limit, NCARGS in
-.IR <sys/param.h> )
-is presented to
-.IR execve .
-.en 8 ENOEXEC "Exec format error
-A request is made to execute a file
+.Dv SIGQUIT )
+was caught by the process during the execution of an interruptible
+function. If the signal handler performs a normal return, the
+interupted function call will seem to have returned the error condition.
+.It Er 5 EIO Em "Input/output error" .
+Some physical input or output error occurred.
+This error not be reported until a subsequent operation on the same file
+descriptor and may be lost (over written) by any subsequent errors.
+.It Er 6 ENXIO Em "\&No such device or address" .
+Input or output on a special file referred to a device that did not
+exist, or
+made a request beyond the limits of the device.
+This error may also occur when, for example,
+a tape drive is not online or no disk pack is
+is loaded on a drive.
+.It Er 7 E2BIG Em "Arg list too long" .
+The number of bytes used for the argument and environment
+list of the new process exceeded the current limit
+of 20480 bytes
+.Pf ( Dv NCARGS
+in
+.Aq Pa sys/param.h ) .
+.It Er 8 ENOEXEC Em "Exec format error" .
+A request was made to execute a file

 that, although it has the appropriate permissions,
 that, although it has the appropriate permissions,

-does not start with a valid magic number, (see
-.IR a.out (5)).
-.en 9 EBADF "Bad file descriptor
-Either a file descriptor refers to no
-open file,
-or a read (resp. write) request is made to
-a file that is open only for writing (resp. reading).
-.en 10 ECHILD "No child processes
-.I Wait
-and the process has no
-living or unwaited-for children.
-.en 11 EDEADLK "Resource deadlock avoided
+was not in the format required for an
+executable file.
+.It Er 9 EBADF Em "Bad file descriptor" .
+A file descriptor argument was out of range, referred to no open file,
+or a read (write) request was made to a file that was only open for
+writing (reading).
+.It Er 10 ECHILD Em "\&No child processes" .
+A
+.Xr wait
+or
+.Xr waitpid
+function was executed by a process that had no existing or unwaited-for
+child processes.
+.It Er 11 EDEADLK Em "Resource deadlock avoided" .

 An attempt was made to lock a system resource that
 would have resulted in a deadlock situation.
 An attempt was made to lock a system resource that
 would have resulted in a deadlock situation.

-.en 12 ENOMEM "Cannnot allocate memory
-During an
-.I execve
-or
-.I break,
-a program asks for more core or swap space than the system is
-able to supply,
-or a process size limit would be exceeded.
-A lack of swap space is normally a temporary condition; however,
-a lack of core
-is not a temporary condition; the maximum size
-of the text, data, and stack segments is a system parameter.
+.It Er 12 ENOMEM Em "Cannnot allocate memory" .
+The new process image required more memory than was allowed by the hardware
+or by system-imposed memory management constraints.
+A lack of swap space is normally temporary; however,
+a lack of core is not.

 Soft limits may be increased to their corresponding hard limits.
 Soft limits may be increased to their corresponding hard limits.

-.en 13 EACCES "Permission denied
+.It Er 13 EACCES Em "Permission denied" .

 An attempt was made to access a file in a way forbidden
 An attempt was made to access a file in a way forbidden

-by the protection system.
-.en 14 EFAULT "Bad address
-The system encountered a hardware fault in attempting to
-access the arguments of a system call.
-.en 15 ENOTBLK "Block device required
-A plain file was mentioned where a block device was required,
-e.g., in
-.IR mount .
-.en 16 EBUSY "Device busy
-An attempt to mount a device that was already mounted or
-an attempt was made to dismount a device
-on which there is an active file
-(open file, current directory, mounted-on file, or active text segment).
-A request was made to an exclusive access device that was already in use.
-.en 17 EEXIST "File exists
+by its file access permissions.
+.It Er 14 EFAULT Em "Bad address" .
+The system detected an invalid address in attempting to
+use an argument of a call.
+.It Er 15 ENOTBLK Em "Not a block device" .
+A block device operation was attempted on a non-block device or file.
+.It Er 16 EBUSY Em "Resource busy" .
+An attempt to use a system resource which was in use at the time
+in a manner which would have conflicted with the request.
+.It Er 17 EEXIST Em "File exists" .

 An existing file was mentioned in an inappropriate context,
 An existing file was mentioned in an inappropriate context,

-e.g.,
-.IR link .
-.en 18 EXDEV "Cross-device link
-A hard link to a file on another device
+for instance, as the new link name in a
+.Xr link
+function.
+.It Er 18 EXDEV Em "Improper link" .
+A hard link to a file on another file system

 was attempted.
 was attempted.

-.en 19 ENODEV "Operation not supported by device
+.It Er 19 ENODEV Em "Operation not supported by device" .

 An attempt was made to apply an inappropriate
 An attempt was made to apply an inappropriate

-system call to a device,
-e.g., to read a write-only device,
-or the device is not configured by the system.
-.en 20 ENOTDIR "Not a directory
-A non-directory was specified where a directory
-is required,
-for example, in a path name or
-as an argument to
-.IR chdir .
-.en 21 EISDIR "Is a directory
-An attempt to write on a directory.
-.en 22 EINVAL "Invalid argument
-Some invalid argument:
-dismounting a non-mounted
-device,
-mentioning an unknown signal in
-.I signal,
-or some other argument inappropriate for the call.
-Also set by math functions, (see 
-.IR math (3)).
-.en 23 ENFILE "Too many open files in system
-The system's table of open files is full,
-and temporarily no more
-.I opens
-can be accepted.
-.en 24 EMFILE "Too many open files
-As released, the limit on the number of
-open files per process is 64.
-.IR Getdtablesize (2)
+function to a device,
+for example,
+trying to read a write-only device such as a printer.
+.It Er 20 ENOTDIR Em "Not a directory" .
+A component of the specified pathname existed, but it was
+not a directory, when a directory was expected.
+.It Er 21 EISDIR Em "Is a directory" .
+An attempt was made to open a directory with write mode specified.
+.It Er 22 EINVAL Em "Invalid argument" .
+Some invalid argument was supplied. (For example,
+specifying an undefined signal to a
+.Xr signal
+or
+.Xr kill
+function).
+.It Er 23 ENFILE Em "Too many open files in system" .
+Maximum number of file descriptors allowable on the system
+has been reached and a requests for an open cannot be satisfied
+until at least one has been closed.
+.It Er 24 EMFILE Em "Too many open files" .
+<As released, the limit on the number of
+open files per process is 64.>
+.Xr Getdtablesize 2

 will obtain the current limit.
 will obtain the current limit.

-Customary configuration limit on most other UNIX systems
-is 20 per process.
-.en 25 ENOTTY "Inappropriate ioctl for device
-The file mentioned in an
-.I ioctl
-is not a terminal or one of the
-devices to which this call applies.
-.en 26 ETXTBSY "Text file busy
-An attempt to execute a pure-procedure
-program that is currently open for writing.
-Also an attempt to open for writing a pure-procedure
-program that is being executed.
-.en 27 EFBIG "File too large
+.It Er 25 ENOTTY Em "Inappropriate ioctl for device" .
+A control function (see
+.Xr ioctl 2 )
+was attempted for a file or
+special device for which the operation was inappropriate.
+.It Er 26 ETXTBSY Em "Text file busy" .
+The new process was a pure procedure (shared text) file
+which was open for writing by another process, or
+the pure procedure file was being executed an
+.Xr open
+call requested write access.
+.It Er 27 EFBIG Em "File too large" .

 The size of a file exceeded the maximum (about
 .if t 2\u\s-231\s+2\d
 .if n 2.1E9
 bytes).
 The size of a file exceeded the maximum (about
 .if t 2\u\s-231\s+2\d
 .if n 2.1E9
 bytes).

-.en 28 ENOSPC "No space left on device
+.It Er 28 ENOSPC Em "Device out of space" .

 A
 A

-.I write
+.Xr write

 to an ordinary file, the creation of a
 directory or symbolic link, or the creation of a directory
 entry failed because no more disk blocks are available
 on the file system, or the allocation of an inode for a newly
 created file failed because no more inodes are available
 on the file system.
 to an ordinary file, the creation of a
 directory or symbolic link, or the creation of a directory
 entry failed because no more disk blocks are available
 on the file system, or the allocation of an inode for a newly
 created file failed because no more inodes are available
 on the file system.

-.en 29 ESPIPE "Illegal seek
+.It Er 29 ESPIPE Em "Illegal seek" .

 An
 An

-.I lseek
-was issued to a socket or pipe.
-This error may also be issued for
-other non-seekable devices.
-.en 30 EROFS "Read-only file system
-An attempt to modify a file or directory
+.Xr lseek
+function was issued on a socket, pipe or
+.Tn FIFO .
+.It Er 30 EROFS Em "Read-only file system" .
+An attempt was made to modify a file or directory

 was made
 was made

-on a device mounted read-only.
-.en 31 EMLINK "Too many links
-An attempt to make more than 32767 hard links to a file.
-.en 32 EPIPE "Broken pipe
-A write on a pipe or socket for which there is no process
+on a file system that was read-only at the time.
+.It Er 31 EMLINK Em "Too many links" .
+Maximum allowable hard links to a single file has been exceeded (limit
+of 32767 hard links per file).
+.It Er 32 EPIPE Em "Broken pipe" .
+A write on a pipe, socket or
+.Tn FIFO
+for which there is no process

 to read the data.
 to read the data.

-This condition normally generates a signal;
-the error is returned if the signal is caught or ignored.
-.en 33 EDOM "Numerical argument out of domain
-The argument of a function in the math package (3M)
-is out of the domain of the function.
-.en 34 ERANGE "Numerical result out of range
-The value of a function in the math package (3M)
-is unrepresentable within machine precision.
-.en 35 EAGAIN "Resource temporarily unavailable
+.It Er 33 EDOM Em "Numerical argument out of domain" .
+A numerical input argument was outside the defined domain of the mathematical
+function.
+.It Er 34 ERANGE Em "Numerical result out of range" .
+A numerical result of the function was to large to fit in the
+available space (perhaps exceeded precision).
+.It Er 35 EAGAIN Em "Resource temporarily unavailable" .

 This is a temporary condition and later calls to the
 same routine may complete normally.
 This is a temporary condition and later calls to the
 same routine may complete normally.

-.en 36 EINPROGRESS "Operation now in progress"
+.It Er 36 EINPROGRESS Em "Operation now in progress" .

 An operation that takes a long time to complete (such as
 An operation that takes a long time to complete (such as

-a \fIconnect\fP(2)) was attempted on a non-blocking object (see
-\fIfcntl\fP(2)).
-.en 37 EALREADY "Operation already in progress"
+a
+.Xr connect 2 )
+was attempted on a non-blocking object (see
+.Xr fcntl 2 ) .
+.It Er 37 EALREADY Em "Operation already in progress" .

 An operation was attempted on a non-blocking object that already
 had an operation in progress.
 An operation was attempted on a non-blocking object that already
 had an operation in progress.

-.en 38 ENOTSOCK "Socket operation on non-socket"
+.It Er 38 ENOTSOCK Em "Socket operation on non-socket" .

 Self-explanatory.
 Self-explanatory.

-.en 39 EDESTADDRREQ "Destination address required"
+.It Er 39 EDESTADDRREQ Em "Destination address required" .

 A required address was omitted from an operation on a socket.
 A required address was omitted from an operation on a socket.

-.en 40 EMSGSIZE "Message too long"
+.It Er 40 EMSGSIZE Em "Message too long" .

 A message sent on a socket was larger than the internal message buffer
 or some other network limit.
 A message sent on a socket was larger than the internal message buffer
 or some other network limit.

-.en 41 EPROTOTYPE "Protocol wrong type for socket"
+.It Er 41 EPROTOTYPE Em "Protocol wrong type for socket" .

 A protocol was specified that does not support the semantics of the
 A protocol was specified that does not support the semantics of the

-socket type requested. For example, you cannot use the ARPA Internet
-UDP protocol with type SOCK_STREAM.
-.en 42 ENOPROTOOPT "Protocol not available
+socket type requested. For example, you cannot use the
+.Tn ARPA
+Internet
+.Tn UDP
+protocol with type
+.Dv SOCK_STREAM .
+.It Er 42 ENOPROTOOPT Em "Protocol not available" .

 A bad option or level was specified in a
 A bad option or level was specified in a

-.IR getsockopt (2)
+.Xr getsockopt 2

 or
 or

-.IR setsockopt (2)
+.Xr setsockopt 2

 call.
 call.

-.en 43 EPROTONOSUPPORT "Protocol not supported"
+.It Er 43 EPROTONOSUPPORT Em "Protocol not supported" .

 The protocol has not been configured into the
 system or no implementation for it exists.
 The protocol has not been configured into the
 system or no implementation for it exists.

-.en 44 ESOCKTNOSUPPORT "Socket type not supported"
+.It Er 44 ESOCKTNOSUPPORT Em "Socket type not supported" .

 The support for the socket type has not been configured into the
 system or no implementation for it exists.
 The support for the socket type has not been configured into the
 system or no implementation for it exists.

-.en 45 EOPNOTSUPP "Operation not supported on socket"
-For example, trying to \fIaccept\fP a connection on a datagram socket.
-.en 46 EPFNOSUPPORT "Protocol family not supported"
+.It Er 45 EOPNOTSUPP Em "Operation not supported" .
+The attempted operation is not supported for the type of object referenced.
+Usually this occurs when a file descriptor refers to a file or socket
+that cannot support this operation,
+for example, trying to
+.Em accept
+a connection on a datagram socket.
+.It Er 46 EPFNOSUPPORT Em "Protocol family not supported" .

 The protocol family has not been configured into the
 system or no implementation for it exists.
 The protocol family has not been configured into the
 system or no implementation for it exists.

-.en 47 EAFNOSUPPORT "Address family not supported by protocol family"
+.It Er 47 EAFNOSUPPORT Em "Address family not supported by protocol family" .

 An address incompatible with the requested protocol was used.
 An address incompatible with the requested protocol was used.

-For example, you shouldn't necessarily expect to be able to use NS
-addresses with ARPA Internet protocols.
-.en 48 EADDRINUSE "Address already in use"
+For example, you shouldn't necessarily expect to be able to use
+.Tn NS
+addresses with
+.Tn ARPA
+Internet protocols.
+.It Er 48 EADDRINUSE Em "Address already in use" .

 Only one usage of each address is normally permitted.
 Only one usage of each address is normally permitted.

-.en 49 EADDRNOTAVAIL "Can't assign requested address"
+.It Er 49 EADDRNOTAVAIL Em "Cannot assign requested address" .

 Normally results from an attempt to create a socket with an
 address not on this machine.
 Normally results from an attempt to create a socket with an
 address not on this machine.

-.en 50 ENETDOWN "Network is down"
+.It Er 50 ENETDOWN Em "Network is down" .

 A socket operation encountered a dead network.
 A socket operation encountered a dead network.

-.en 51 ENETUNREACH "Network is unreachable"
+.It Er 51 ENETUNREACH Em "Network is unreachable" .

 A socket operation was attempted to an unreachable network.
 A socket operation was attempted to an unreachable network.

-.en 52 ENETRESET "Network dropped connection on reset"
+.It Er 52 ENETRESET Em "Network dropped connection on reset" .

 The host you were connected to crashed and rebooted.
 The host you were connected to crashed and rebooted.

-.en 53 ECONNABORTED "Software caused connection abort"
+.It Er 53 ECONNABORTED Em "Software caused connection abort" .

 A connection abort was caused internal to your host machine.
 A connection abort was caused internal to your host machine.

-.en 54 ECONNRESET "Connection reset by peer"
+.It Er 54 ECONNRESET Em "Connection reset by peer" .

 A connection was forcibly closed by a peer.  This normally
 results from a loss of the connection on the remote socket
 due to a timeout or a reboot.
 A connection was forcibly closed by a peer.  This normally
 results from a loss of the connection on the remote socket
 due to a timeout or a reboot.

-.en 55 ENOBUFS "No buffer space available"
+.It Er 55 ENOBUFS Em "\&No buffer space available" .

 An operation on a socket or pipe was not performed because
 the system lacked sufficient buffer space or because a queue was full.
 An operation on a socket or pipe was not performed because
 the system lacked sufficient buffer space or because a queue was full.

-.en 56 EISCONN "Socket is already connected"
+.It Er 56 EISCONN Em "Socket is already connected" .

 A
 A

-.I connect
+.Xr connect

 request was made on an already connected socket; or,
 a
 request was made on an already connected socket; or,
 a

-.I sendto
+.Xr sendto

 or
 or

-.I sendmsg
+.Xr sendmsg

 request on a connected socket specified a destination
 when already connected.
 request on a connected socket specified a destination
 when already connected.

-.en 57 ENOTCONN "Socket is not connected"
+.It Er 57 ENOTCONN Em "Socket is not connected" .

 An request to send or receive data was disallowed because
 the socket is not connected and (when sending on a  datagram socket)
 no address was supplied.
 An request to send or receive data was disallowed because
 the socket is not connected and (when sending on a  datagram socket)
 no address was supplied.

-.en 58 ESHUTDOWN "Can't send after socket shutdown"
+.It Er 58 ESHUTDOWN Em "Cannot send after socket shutdown" .

 A request to send data was disallowed because the socket
 had already been shut down with a previous
 A request to send data was disallowed because the socket
 had already been shut down with a previous

-.IR shutdown (2)
+.Xr shutdown 2

 call.
 call.

-.en 60 ETIMEDOUT "Connection timed out"
+.It Er 60 ETIMEDOUT Em "Connection timed out" .

 A
 A

-.I connect
+.Xr connect

 or
 or

-.I send
+.Xr send

 request failed because the connected party did not
 properly respond after a period of time.  (The timeout
 period is dependent on the communication protocol.)
 request failed because the connected party did not
 properly respond after a period of time.  (The timeout
 period is dependent on the communication protocol.)

-.en 61 ECONNREFUSED "Connection refused"
+.It Er 61 ECONNREFUSED Em "Connection refused" .

 No connection could be made because the target machine actively
 refused it.  This usually results from trying to connect
 to a service that is inactive on the foreign host.
 No connection could be made because the target machine actively
 refused it.  This usually results from trying to connect
 to a service that is inactive on the foreign host.

-.en 62 ELOOP "Too many levels of symbolic links"
+.It Er 62 ELOOP Em "Too many levels of symbolic links" .

 A path name lookup involved more than 8 symbolic links.
 A path name lookup involved more than 8 symbolic links.

-.en 63 ENAMETOOLONG "File name too long"
-A component of a path name exceeded 255 (MAXNAMELEN) characters, or an entire
-path name exceeded 1023 (MAXPATHLEN-1) characters.
-.en 64 EHOSTDOWN "Host is down"
+.It Er 63 ENAMETOOLONG Em "File name too long" .
+A component of a path name exceeded 255
+.Pq Dv MAXNAMELEN
+characters, or an entire
+path name exceeded 1023
+.Pq Dv MAXPATHLEN Ns -1
+characters.
+.It Er 64 EHOSTDOWN Em "Host is down" .

 A socket operation failed because the destination host was down.
 A socket operation failed because the destination host was down.

-.en 65 EHOSTUNREACH "No route to host"
+.It Er 65 EHOSTUNREACH Em "No route to host" .

 A socket operation was attempted to an unreachable host.
 A socket operation was attempted to an unreachable host.

-.en 66 ENOTEMPTY "Directory not empty"
-A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq
+.It Er 66 ENOTEMPTY Em "Directory not empty" .
+A directory with entries other than
+.Ql \&.
+and
+.Ql \&..

 was supplied to a remove directory or rename call.
 was supplied to a remove directory or rename call.

-.en 67 EPROCLIM "Too many processes"
-.en 68 EUSERS "Too many users"
+.It Er 67 EPROCLIM Em "Too many processes" .
+.It Er 68 EUSERS Em "Too many users" .

 The quota system ran out of table entries.
 The quota system ran out of table entries.

-.en 69 EDQUOT "Disc quota exceeded"
+.It Er 69 EDQUOT Em "Disc quota exceeded" .

 A 
 A 

-.I write
+.Xr write

 to an ordinary file, the creation of a
 directory or symbolic link, or the creation of a directory
 entry failed because the user's quota of disk blocks was
 exhausted, or the allocation of an inode for a newly
 created file failed because the user's quota of inodes
 was exhausted.
 to an ordinary file, the creation of a
 directory or symbolic link, or the creation of a directory
 entry failed because the user's quota of disk blocks was
 exhausted, or the allocation of an inode for a newly
 created file failed because the user's quota of inodes
 was exhausted.

-.en 70 ESTALE "Stale NFS file handle"
-An attempt was made to access an open file (on an NFS filesystem)
+.It Er 70 ESTALE Em "Stale NFS file handle" .
+An attempt was made to access an open file (on an
+.Tn NFS
+filesystem)

 which is now unavailable as referenced by the file descriptor.  
 which is now unavailable as referenced by the file descriptor.  

-This may indicate the file was deleted on the NFS server and some 
+This may indicate the file was deleted on the
+.Tn NFS 
+server or some 

 other catastrophic event occured.
 other catastrophic event occured.

-.en 72 EBADRPC "RPC struct is bad"
-Exchange of RPC information was unsuccessful.
-.en 73 ERPCMISMATCH "RPC version wrong"
-The version of RPC on the remote peer is not compatible with
+.It Er 72 EBADRPC Em "RPC struct is bad" .
+Exchange of
+.Tn RPC
+information was unsuccessful.
+.It Er 73 ERPCMISMATCH Em "RPC version wrong" .
+The version of
+.Tn RPC
+on the remote peer is not compatible with

 the local version.
 the local version.

-.en 74 EPROGUNAVAIL "RPC prog. not avail"
+.It Er 74 EPROGUNAVAIL Em "RPC prog. not avail" .

 The requested program is not registered on the remote host.
 The requested program is not registered on the remote host.

-.en 75 EPROGMISMATCH "Program version wrong"
+.It Er 75 EPROGMISMATCH Em "Program version wrong" .

 The requested version of the program is not available 
 The requested version of the program is not available 

-on the remote host (RPC).
-.en 76 EPROCUNAVAIL "Bad procedure for program"
-An RPC call was attempted for a procedure which doesn't exist
+on the remote host
+.Pq Tn RPC .
+.It Er 76 EPROCUNAVAIL Em "Bad procedure for program" .
+An
+.Tn RPC
+call was attempted for a procedure which doesn't exist

 in the remote program.
 in the remote program.

-.en 77 ENOLCK "No locks available"
+.It Er 77 ENOLCK Em "No locks available" .

 A system-imposed limit on the number of simultaneous file 
 locks was reached.
 A system-imposed limit on the number of simultaneous file 
 locks was reached.

-.en 78 ENOSYS "Function not implemented"
+.It Er 78 ENOSYS Em "Function not implemented" .

 Attempted a system call that is not available on this 
 system.
 Attempted a system call that is not available on this 
 system.

-.SH DEFINITIONS
-.TP 5
-Process ID
-.br
-Each active process in the system is uniquely identified by a positive
+.Sh DEFINITIONS
+.Bl -tag -width Ds
+.It  Process ID .
+Each active process in the system is uniquely identified by a non-negative

 integer called a process ID.  The range of this ID is from 0 to 30000.
 integer called a process ID.  The range of this ID is from 0 to 30000.

-.TP 5
-Parent process ID
-.br
+.It  Parent process ID

 A new process is created by a currently active process; (see
 A new process is created by a currently active process; (see

-.IR fork (2)).
+.Xr fork 2 ) .

 The parent process ID of a process is the process ID of its creator.
 The parent process ID of a process is the process ID of its creator.

-.TP 5
-Process Group ID
-.br
+.It  Process Group ID

 Each active process is a member of a process group that is identified by
 Each active process is a member of a process group that is identified by

-a positive integer called the process group ID.  This is the process
+a non-negative integer called the process group ID.  This is the process

 ID of the group leader.  This grouping permits the signaling of related
 processes (see
 ID of the group leader.  This grouping permits the signaling of related
 processes (see

-.IR killpg (2))
+.Xr killpg 2 )

 and the job control mechanisms of
 and the job control mechanisms of

-.IR csh (1).
-.TP 5
-Tty Group ID
-.br
+.Xr csh 1 .
+.It  Tty Group ID

 Each active process can be a member of a terminal group that is identified
 Each active process can be a member of a terminal group that is identified

-by a positive integer called the tty group ID.  This grouping is used
+by a non-negative integer called the tty group ID.  This grouping is used

 to arbitrate between multiple jobs contending for the same terminal;
 (see
 to arbitrate between multiple jobs contending for the same terminal;
 (see

-.IR csh (1)
+.Xr csh 1

 and
 and

-.IR tty (4)).
-.TP 5
-Real User ID and Real Group ID
-.br
+.Xr tty 4 ) .
+.It "Real User ID and Real Group ID"

 Each user on the system is identified by a positive integer
 termed the real user ID.
 Each user on the system is identified by a positive integer
 termed the real user ID.

-.IP
+.Pp

 Each user is also a member of one or more groups. 
 One of these groups is distinguished from others and
 used in implementing accounting facilities.  The positive
 integer corresponding to this distinguished group is termed 
 the real group ID.
 Each user is also a member of one or more groups. 
 One of these groups is distinguished from others and
 used in implementing accounting facilities.  The positive
 integer corresponding to this distinguished group is termed 
 the real group ID.

-.IP
+.Pp

 All processes have a real user ID and real group ID.
 These are initialized from the equivalent attributes
 of the process that created it.
 All processes have a real user ID and real group ID.
 These are initialized from the equivalent attributes
 of the process that created it.

-.TP 5
-Effective User Id, Effective Group Id, and Access Groups
-.br
+.It "Effective User Id, Effective Group Id, and Access Groups"

 Access to system resources is governed by three values:
 the effective user ID, the effective group ID, and the
 group access list.
 Access to system resources is governed by three values:
 the effective user ID, the effective group ID, and the
 group access list.

-.IP
+.Pp

 The effective user ID and effective group ID are initially the
 process's real user ID and real group ID respectively.  Either
 may be modified through execution of a set-user-ID or set-group-ID
 file (possibly by one its ancestors) (see
 The effective user ID and effective group ID are initially the
 process's real user ID and real group ID respectively.  Either
 may be modified through execution of a set-user-ID or set-group-ID
 file (possibly by one its ancestors) (see

-.IR execve (2)).
-.IP
+.Xr execve 2 ) .
+.Pp

 The group access list is an additional set of group ID's
 used only in determining resource accessibility.  Access checks
 are performed as described below in ``File Access Permissions''.
 The group access list is an additional set of group ID's
 used only in determining resource accessibility.  Access checks
 are performed as described below in ``File Access Permissions''.

-.TP 5
-Super-user
-.br
+.It  Super-user

 A process is recognized as a
 A process is recognized as a

-.I super-user
+.Em super-user

 process and is granted special privileges if its effective user ID is 0.
 process and is granted special privileges if its effective user ID is 0.

-.TP 5
-Special Processes
-.br
+.It  Special Processes

 The processes with a process ID's of 0, 1, and 2 are special.
 Process 0 is the scheduler.  Process 1 is the initialization process
 The processes with a process ID's of 0, 1, and 2 are special.
 Process 0 is the scheduler.  Process 1 is the initialization process

-.IR init ,
+.Xr init ,

 and is the ancestor of every other process in the system.
 It is used to control the process structure.
 Process 2 is the paging daemon.
 and is the ancestor of every other process in the system.
 It is used to control the process structure.
 Process 2 is the paging daemon.

-.TP 5
-Descriptor
-.br
+.It  Descriptor

 An integer assigned by the system when a file is referenced
 by
 An integer assigned by the system when a file is referenced
 by

-.IR open (2)
+.Xr open 2

 or
 or

-.IR dup (2),
+.Xr dup 2 ,

 or when a socket is created by
 or when a socket is created by

-.IR pipe (2),
-.IR socket (2)
+.Xr pipe 2 ,
+.Xr socket 2

 or
 or

-.IR socketpair (2),
+.Xr socketpair 2 ,

 which uniquely identifies an access path to that file or socket from
 a given process or any of its children.
 which uniquely identifies an access path to that file or socket from
 a given process or any of its children.

-.TP 5
-File Name
-.br
-Names consisting of up to 255 (MAXNAMELEN) characters may be used to name
+.It  File Name
+Names consisting of up to 255
+.Pq Dv MAXNAMELEN
+characters may be used to name

 an ordinary file, special file, or directory.
 an ordinary file, special file, or directory.

-.IP
-These characters may be selected from the set of all ASCII character
-excluding 0 (null) and the ASCII code for / (slash).  (The parity bit,
-bit 8, must be 0.)
-.IP
-Note that it is generally unwise to use *, ?, [ or ] as part of
+.Pp
+These characters may be selected from the set of all
+.Tn ASCII
+character
+excluding 0 (NUL) and the
+.Tn ASCII
+code for
+.Ql \&/
+(slash).  (The parity bit,
+bit 7, must be 0.)
+.Pp
+Note that it is generally unwise to use
+.Ql \&* ,
+.Ql \&? ,
+.Ql \&[
+or
+.Ql \&]
+as part of

 file names because of the special meaning attached to these characters
 by the shell.
 file names because of the special meaning attached to these characters
 by the shell.

-.TP 5
-Path Name
-.br
-A path name is a null-terminated character string starting with an
-optional slash (/), followed by zero or more directory names separated
+.It  Path Name
+A path name is a
+.Tn NUL Ns -terminated
+character string starting with an
+optional slash
+.Ql \&/ ,
+followed by zero or more directory names separated

 by slashes, optionally followed by a file name.
 by slashes, optionally followed by a file name.

-The total length of a path name must be less than 1024 (MAXPATHLEN) characters.
-.IP
+The total length of a path name must be less than 1024
+.Pq Dv MAXPATHLEN
+characters.
+.Pp

 If a path name begins with a slash, the path search begins at the
 If a path name begins with a slash, the path search begins at the

-.I root
+.Em root

 directory.
 Otherwise, the search begins from the current working directory.
 directory.
 Otherwise, the search begins from the current working directory.

-A slash by itself names the root directory.  A null
+A slash by itself names the root directory.  An empty

 pathname refers to the current directory.
 pathname refers to the current directory.

-.TP 5
-Directory
-.br
+.It  Directory

 A directory is a special type of file that contains entries
 that are references to other files.
 Directory entries are called links.  By convention, a directory
 A directory is a special type of file that contains entries
 that are references to other files.
 Directory entries are called links.  By convention, a directory

-contains at least two links, . and .., referred to as
-.I dot
+contains at least two links,
+.Ql \&.
+and
+.Ql \&.. ,
+referred to as
+.Em dot

 and
 and

-.I dot-dot
+.Em dot-dot

 respectively.  Dot refers to the directory itself and
 dot-dot refers to its parent directory.
 respectively.  Dot refers to the directory itself and
 dot-dot refers to its parent directory.

-.TP 5
-Root Directory and Current Working Directory
-.br
+.It "Root Directory and Current Working Directory"

 Each process has associated with it a concept of a root directory
 and a current working directory for the purpose of resolving path
 name searches.  A process's root directory need not be the root
 directory of the root file system.
 Each process has associated with it a concept of a root directory
 and a current working directory for the purpose of resolving path
 name searches.  A process's root directory need not be the root
 directory of the root file system.

-.TP 5
-File Access Permissions
-.br
+.It  File Access Permissions

 Every file in the file system has a set of access permissions.
 These permissions are used in determining whether a process
 may perform a requested operation on the file (such as opening
 a file for writing).  Access permissions are established at the
 time a file is created.  They may be changed at some later time
 through the 
 Every file in the file system has a set of access permissions.
 These permissions are used in determining whether a process
 may perform a requested operation on the file (such as opening
 a file for writing).  Access permissions are established at the
 time a file is created.  They may be changed at some later time
 through the 

-.IR chmod (2)
+.Xr chmod 2

 call. 
 call. 

-.IP
+.Pp

 File access is broken down according to whether a file may be: read,
 written, or executed.  Directory files use the execute
 permission to control if the directory may be searched. 
 File access is broken down according to whether a file may be: read,
 written, or executed.  Directory files use the execute
 permission to control if the directory may be searched. 

-.IP
+.Pp

 File access permissions are interpreted by the system as
 they apply to three different classes of users: the owner
 of the file, those users in the file's group, anyone else.
 File access permissions are interpreted by the system as
 they apply to three different classes of users: the owner
 of the file, those users in the file's group, anyone else.


@@ -522,49 +562,54 @@ Every file has an independent set of access permissions for
 each of these classes.  When an access check is made, the system
 decides if permission should be granted by checking the access
 information applicable to the caller.
 each of these classes.  When an access check is made, the system
 decides if permission should be granted by checking the access
 information applicable to the caller.

-.IP
+.Pp

 Read, write, and execute/search permissions on
 a file are granted to a process if:
 Read, write, and execute/search permissions on
 a file are granted to a process if:

-.IP
-The process's effective user ID is that of the super-user.
-.IP
+.Pp
+The process's effective user ID is that of the super-user. (Note:
+even the super-user cannot execute a non-executable file.)
+.Pp

 The process's effective user ID matches the user ID of the owner
 of the file and the owner permissions allow the access.
 The process's effective user ID matches the user ID of the owner
 of the file and the owner permissions allow the access.

-.IP
+.Pp

 The process's effective user ID does not match the user ID of the
 owner of the file, and either the process's effective
 group ID matches the group ID
 of the file, or the group ID of the file is in
 the process's group access list,
 and the group permissions allow the access.
 The process's effective user ID does not match the user ID of the
 owner of the file, and either the process's effective
 group ID matches the group ID
 of the file, or the group ID of the file is in
 the process's group access list,
 and the group permissions allow the access.

-.IP
+.Pp

 Neither the effective user ID nor effective group ID
 and group access list of the process
 match the corresponding user ID and group ID of the file,
 but the permissions for ``other users'' allow access.
 Neither the effective user ID nor effective group ID
 and group access list of the process
 match the corresponding user ID and group ID of the file,
 but the permissions for ``other users'' allow access.

-.IP
+.Pp

 Otherwise, permission is denied.
 Otherwise, permission is denied.

-.TP 5
-Sockets and Address Families
-.IP
+.It  Sockets and Address Families
+.Pp

 A socket is an endpoint for communication between processes.
 Each socket has queues for sending and receiving data.
 A socket is an endpoint for communication between processes.
 Each socket has queues for sending and receiving data.

-.IP
+.Pp

 Sockets are typed according to their communications properties.
 These properties include whether messages sent and received
 at a socket require the name of the partner, whether communication
 is reliable, the format used in naming message recipients, etc.
 Sockets are typed according to their communications properties.
 These properties include whether messages sent and received
 at a socket require the name of the partner, whether communication
 is reliable, the format used in naming message recipients, etc.

-.IP
+.Pp

 Each instance of the system supports some
 collection of socket types; consult
 Each instance of the system supports some
 collection of socket types; consult

-.IR socket (2)
+.Xr socket 2

 for more information about the types available and
 their properties.
 for more information about the types available and
 their properties.

-.IP
+.Pp

 Each instance of the system supports some number of sets of
 communications protocols.  Each protocol set supports addresses
 of a certain format.  An Address Family is the set of addresses
 for a specific group of protocols.  Each socket has an address
 chosen from the address family in which the socket was created.
 Each instance of the system supports some number of sets of
 communications protocols.  Each protocol set supports addresses
 of a certain format.  An Address Family is the set of addresses
 for a specific group of protocols.  Each socket has an address
 chosen from the address family in which the socket was created.

-.SH SEE ALSO
+.Sh SEE ALSO

 intro(3), perror(3)
 intro(3), perror(3)

+.Sh HISTORY
+An
+.Nm intro
+appeared in
+.At v6 .