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[dragonfly.git] / lib / libc / sys / intro.2
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32.\" @(#)intro.2 8.5 (Berkeley) 2/27/95
33.\" $FreeBSD: src/lib/libc/sys/intro.2,v 1.21.2.7 2003/02/24 01:01:48 trhodes Exp $
b564836d 34.\" $DragonFly: src/lib/libc/sys/intro.2,v 1.6 2007/04/11 09:07:33 swildner Exp $
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35.\"
36.Dd February 27, 1995
37.Dt INTRO 2
38.Os
39.Sh NAME
40.Nm intro
41.Nd introduction to system calls and error numbers
42.Sh LIBRARY
43.Lb libc
44.Sh SYNOPSIS
45.In errno.h
46.Sh DESCRIPTION
47This section provides an overview of the system calls,
48their error returns, and other common definitions and concepts.
49.\".Pp
50.\".Sy System call restart
51.\".Pp
52.\"<more later...>
53.Sh RETURN VALUES
54Nearly all of the system calls provide an error number referenced via
834b6336 55the external identifier
f60c028d 56.Va errno .
984263bc 57This identifier is defined in
44cb301e 58.In errno.h
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59as
60.Pp
834b6336
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61.Dl extern __thread int errno;
62.Dl static __inline int * __error(void);
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63.Dl #define errno (* __error())
64.Pp
834b6336
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65This means there exists a thread-local
66.Va errno
67variable, though it is shadowed by the inline
b564836d 68.Fn __error
834b6336
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69function to allow compilation of source code which
70erroneously itself declares
71.Va errno
72as
b564836d 73.Vt extern int errno;
834b6336
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74which collides with the thread-local declaration.
75The
b564836d 76.Fn __error
834b6336 77function returns a pointer the thread specific
984263bc 78.Va errno
834b6336 79variable. As it is defined
b564836d 80.Vt inline ,
834b6336
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81it will compile to a no-op, effectively producing
82the same code as if the define wouldn't exist.
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83.Pp
84When a system call detects an error,
85it returns an integer value
86indicating failure (usually -1)
87and sets the variable
88.Va errno
89accordingly.
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90(This allows interpretation of the failure on receiving
91a -1 and to take action accordingly.)
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92Successful calls never set
93.Va errno ;
94once set, it remains until another error occurs.
95It should only be examined after an error.
96Note that a number of system calls overload the meanings of these
97error numbers, and that the meanings must be interpreted according
98to the type and circumstances of the call.
99.Pp
100The following is a complete list of the errors and their
101names as given in
44cb301e 102.In sys/errno.h .
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103.Bl -hang -width Ds
104.It Er 0 Em "Undefined error: 0" .
105Not used.
106.It Er 1 EPERM Em "Operation not permitted" .
107An attempt was made to perform an operation limited to processes
108with appropriate privileges or to the owner of a file or other
109resources.
110.It Er 2 ENOENT Em "No such file or directory" .
111A component of a specified pathname did not exist, or the
112pathname was an empty string.
113.It Er 3 ESRCH Em "No such process" .
114No process could be found corresponding to that specified by the given
115process ID.
116.It Er 4 EINTR Em "Interrupted system call" .
117An asynchronous signal (such as
118.Dv SIGINT
119or
120.Dv SIGQUIT )
121was caught by the process during the execution of an interruptible
122function.
123If the signal handler performs a normal return, the
124interrupted function call will seem to have returned the error condition.
125.It Er 5 EIO Em "Input/output error" .
126Some physical input or output error occurred.
127This error will not be reported until a subsequent operation on the same file
128descriptor and may be lost (over written) by any subsequent errors.
129.It Er 6 ENXIO Em "Device not configured" .
130Input or output on a special file referred to a device that did not
131exist, or
132made a request beyond the limits of the device.
133This error may also occur when, for example,
134a tape drive is not online or no disk pack is
135loaded on a drive.
136.It Er 7 E2BIG Em "Argument list too long" .
137The number of bytes used for the argument and environment
138list of the new process exceeded the current limit
139of 65536 bytes
140.Pf ( Dv NCARGS
141in
44cb301e 142.In sys/param.h ) .
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143.It Er 8 ENOEXEC Em "Exec format error" .
144A request was made to execute a file
145that, although it has the appropriate permissions,
146was not in the format required for an
147executable file.
148.It Er 9 EBADF Em "Bad file descriptor" .
149A file descriptor argument was out of range, referred to no open file,
150or a read (write) request was made to a file that was only open for
151writing (reading).
152.Pp
153.It Er 10 ECHILD Em "\&No child processes" .
154A
155.Xr wait 2
156or
157.Xr waitpid 2
158function was executed by a process that had no existing or unwaited-for
159child processes.
160.It Er 11 EDEADLK Em "Resource deadlock avoided" .
161An attempt was made to lock a system resource that
162would have resulted in a deadlock situation.
163.It Er 12 ENOMEM Em "Cannot allocate memory" .
164The new process image required more memory than was allowed by the hardware
165or by system-imposed memory management constraints.
166A lack of swap space is normally temporary; however,
167a lack of core is not.
168Soft limits may be increased to their corresponding hard limits.
169.It Er 13 EACCES Em "Permission denied" .
170An attempt was made to access a file in a way forbidden
171by its file access permissions.
172.It Er 14 EFAULT Em "Bad address" .
173The system detected an invalid address in attempting to
174use an argument of a call.
175.It Er 15 ENOTBLK Em "Block device required" .
176A block device operation was attempted on a non-block device or file.
177.It Er 16 EBUSY Em "Device busy" .
178An attempt to use a system resource which was in use at the time
179in a manner which would have conflicted with the request.
180.It Er 17 EEXIST Em "File exists" .
181An existing file was mentioned in an inappropriate context,
182for instance, as the new link name in a
183.Xr link 2
184function.
185.It Er 18 EXDEV Em "Cross-device link" .
186A hard link to a file on another file system
187was attempted.
188.It Er 19 ENODEV Em "Operation not supported by device" .
189An attempt was made to apply an inappropriate
190function to a device,
191for example,
192trying to read a write-only device such as a printer.
193.It Er 20 ENOTDIR Em "Not a directory" .
194A component of the specified pathname existed, but it was
195not a directory, when a directory was expected.
196.It Er 21 EISDIR Em "Is a directory" .
197An attempt was made to open a directory with write mode specified.
198.It Er 22 EINVAL Em "Invalid argument" .
199Some invalid argument was supplied.
200(For example,
201specifying an undefined signal to a
202.Xr signal 3
203or
204.Xr kill 2
205function).
206.It Er 23 ENFILE Em "Too many open files in system" .
207Maximum number of file descriptors allowable on the system
208has been reached and a requests for an open cannot be satisfied
209until at least one has been closed.
210.It Er 24 EMFILE Em "Too many open files" .
211<As released, the limit on the number of
212open files per process is 64.>
213The
214.Xr getdtablesize 2
215function will obtain the current limit.
216.It Er 25 ENOTTY Em "Inappropriate ioctl for device" .
217A control function (see
218.Xr ioctl 2 )
219was attempted for a file or
220special device for which the operation was inappropriate.
221.It Er 26 ETXTBSY Em "Text file busy" .
222The new process was a pure procedure (shared text) file
223which was open for writing by another process, or
224while the pure procedure file was being executed an
225.Xr open 2
226call requested write access.
227.It Er 27 EFBIG Em "File too large" .
228The size of a file exceeded the maximum (about
229.if t 2\u\s-231\s+2\d
230.if n 2.1E9
231bytes).
232.It Er 28 ENOSPC Em "No space left on device" .
233A
234.Xr write 2
235to an ordinary file, the creation of a
236directory or symbolic link, or the creation of a directory
237entry failed because no more disk blocks were available
238on the file system, or the allocation of an inode for a newly
239created file failed because no more inodes were available
240on the file system.
241.It Er 29 ESPIPE Em "Illegal seek" .
242An
243.Xr lseek 2
244function was issued on a socket, pipe or
245.Tn FIFO .
246.It Er 30 EROFS Em "Read-only file system" .
247An attempt was made to modify a file or directory
248on a file system that was read-only at the time.
249.It Er 31 EMLINK Em "Too many links" .
250Maximum allowable hard links to a single file has been exceeded (limit
251of 32767 hard links per file).
252.It Er 32 EPIPE Em "Broken pipe" .
253A write on a pipe, socket or
254.Tn FIFO
255for which there is no process
256to read the data.
257.It Er 33 EDOM Em "Numerical argument out of domain" .
258A numerical input argument was outside the defined domain of the mathematical
259function.
260.It Er 34 ERANGE Em "Result too large" .
261A numerical result of the function was too large to fit in the
262available space (perhaps exceeded precision).
263.It Er 35 EAGAIN Em "Resource temporarily unavailable" .
264This is a temporary condition and later calls to the
265same routine may complete normally.
266.It Er 36 EINPROGRESS Em "Operation now in progress" .
267An operation that takes a long time to complete (such as
268a
269.Xr connect 2 )
270was attempted on a non-blocking object (see
271.Xr fcntl 2 ) .
272.It Er 37 EALREADY Em "Operation already in progress" .
273An operation was attempted on a non-blocking object that already
274had an operation in progress.
275.It Er 38 ENOTSOCK Em "Socket operation on non-socket" .
276Self-explanatory.
277.It Er 39 EDESTADDRREQ Em "Destination address required" .
278A required address was omitted from an operation on a socket.
279.It Er 40 EMSGSIZE Em "Message too long" .
280A message sent on a socket was larger than the internal message buffer
281or some other network limit.
282.It Er 41 EPROTOTYPE Em "Protocol wrong type for socket" .
283A protocol was specified that does not support the semantics of the
284socket type requested.
285For example, you cannot use the
286.Tn ARPA
287Internet
288.Tn UDP
289protocol with type
290.Dv SOCK_STREAM .
291.It Er 42 ENOPROTOOPT Em "Protocol not available" .
292A bad option or level was specified in a
293.Xr getsockopt 2
294or
295.Xr setsockopt 2
296call.
297.It Er 43 EPROTONOSUPPORT Em "Protocol not supported" .
298The protocol has not been configured into the
299system or no implementation for it exists.
300.It Er 44 ESOCKTNOSUPPORT Em "Socket type not supported" .
301The support for the socket type has not been configured into the
302system or no implementation for it exists.
303.It Er 45 EOPNOTSUPP Em "Operation not supported" .
304The attempted operation is not supported for the type of object referenced.
305Usually this occurs when a file descriptor refers to a file or socket
306that cannot support this operation,
307for example, trying to
308.Em accept
309a connection on a datagram socket.
310.It Er 46 EPFNOSUPPORT Em "Protocol family not supported" .
311The protocol family has not been configured into the
312system or no implementation for it exists.
313.It Er 47 EAFNOSUPPORT Em "Address family not supported by protocol family" .
314An address incompatible with the requested protocol was used.
315For example, you shouldn't necessarily expect to be able to use
316.Tn NS
317addresses with
318.Tn ARPA
319Internet protocols.
320.It Er 48 EADDRINUSE Em "Address already in use" .
321Only one usage of each address is normally permitted.
322.Pp
323.It Er 49 EADDRNOTAVAIL Em "Cannot assign requested address" .
324Normally results from an attempt to create a socket with an
325address not on this machine.
326.It Er 50 ENETDOWN Em "Network is down" .
327A socket operation encountered a dead network.
328.It Er 51 ENETUNREACH Em "Network is unreachable" .
329A socket operation was attempted to an unreachable network.
330.It Er 52 ENETRESET Em "Network dropped connection on reset" .
331The host you were connected to crashed and rebooted.
332.It Er 53 ECONNABORTED Em "Software caused connection abort" .
333A connection abort was caused internal to your host machine.
334.It Er 54 ECONNRESET Em "Connection reset by peer" .
335A connection was forcibly closed by a peer. This normally
336results from a loss of the connection on the remote socket
337due to a timeout or a reboot.
338.It Er 55 ENOBUFS Em "\&No buffer space available" .
339An operation on a socket or pipe was not performed because
340the system lacked sufficient buffer space or because a queue was full.
341.It Er 56 EISCONN Em "Socket is already connected" .
342A
343.Xr connect 2
344request was made on an already connected socket; or,
345a
346.Xr sendto 2
347or
348.Xr sendmsg 2
349request on a connected socket specified a destination
350when already connected.
351.It Er 57 ENOTCONN Em "Socket is not connected" .
352An request to send or receive data was disallowed because
353the socket was not connected and (when sending on a datagram socket)
354no address was supplied.
355.It Er 58 ESHUTDOWN Em "Cannot send after socket shutdown" .
356A request to send data was disallowed because the socket
357had already been shut down with a previous
358.Xr shutdown 2
359call.
360.It Er 60 ETIMEDOUT Em "Operation timed out" .
361A
362.Xr connect 2
363or
364.Xr send 2
365request failed because the connected party did not
366properly respond after a period of time. (The timeout
367period is dependent on the communication protocol.)
368.It Er 61 ECONNREFUSED Em "Connection refused" .
369No connection could be made because the target machine actively
370refused it. This usually results from trying to connect
371to a service that is inactive on the foreign host.
372.It Er 62 ELOOP Em "Too many levels of symbolic links" .
373A path name lookup involved more than 32
374.Pq Dv MAXSYMLINKS
375symbolic links.
376.It Er 63 ENAMETOOLONG Em "File name too long" .
377A component of a path name exceeded 255
378.Pq Dv MAXNAMELEN
379characters, or an entire
380path name exceeded 1023
381.Pq Dv MAXPATHLEN Ns -1
382characters.
383.It Er 64 EHOSTDOWN Em "Host is down" .
384A socket operation failed because the destination host was down.
385.It Er 65 EHOSTUNREACH Em "No route to host" .
386A socket operation was attempted to an unreachable host.
387.It Er 66 ENOTEMPTY Em "Directory not empty" .
388A directory with entries other than
389.Ql .\&
390and
391.Ql ..\&
392was supplied to a remove directory or rename call.
393.It Er 67 EPROCLIM Em "Too many processes" .
394.It Er 68 EUSERS Em "Too many users" .
395The quota system ran out of table entries.
396.It Er 69 EDQUOT Em "Disc quota exceeded" .
397A
398.Xr write 2
399to an ordinary file, the creation of a
400directory or symbolic link, or the creation of a directory
401entry failed because the user's quota of disk blocks was
402exhausted, or the allocation of an inode for a newly
403created file failed because the user's quota of inodes
404was exhausted.
405.It Er 70 ESTALE Em "Stale NFS file handle" .
406An attempt was made to access an open file (on an
407.Tn NFS
408filesystem)
409which is now unavailable as referenced by the file descriptor.
410This may indicate the file was deleted on the
411.Tn NFS
412server or some
413other catastrophic event occurred.
414.It Er 72 EBADRPC Em "RPC struct is bad" .
415Exchange of
416.Tn RPC
417information was unsuccessful.
418.It Er 73 ERPCMISMATCH Em "RPC version wrong" .
419The version of
420.Tn RPC
421on the remote peer is not compatible with
422the local version.
423.It Er 74 EPROGUNAVAIL Em "RPC prog. not avail" .
424The requested program is not registered on the remote host.
425.It Er 75 EPROGMISMATCH Em "Program version wrong" .
426The requested version of the program is not available
427on the remote host
428.Pq Tn RPC .
429.It Er 76 EPROCUNAVAIL Em "Bad procedure for program" .
430An
431.Tn RPC
432call was attempted for a procedure which doesn't exist
433in the remote program.
434.It Er 77 ENOLCK Em "No locks available" .
435A system-imposed limit on the number of simultaneous file
436locks was reached.
437.It Er 78 ENOSYS Em "Function not implemented" .
438Attempted a system call that is not available on this
439system.
440.It Er 79 EFTYPE Em "Inappropriate file type or format" .
441The file was the wrong type for the operation, or a data file had
442the wrong format.
443.It Er 80 EAUTH Em "Authentication error" .
444Attempted to use an invalid authentication ticket to mount a
445.Tn NFS
446filesystem.
447.It Er 81 ENEEDAUTH Em "Need authenticator" .
448An authentication ticket must be obtained before the given
449.Tn NFS
450filesystem may be mounted.
451.It Er 82 EIDRM Em "Identifier removed" .
452An IPC identifier was removed while the current process was waiting on it.
453.It Er 83 ENOMSG Em "No message of desired type" .
454An IPC message queue does not contain a message of the desired type, or a
455message catalog does not contain the requested message.
456.It Er 84 EOVERFLOW Em "Value too large to be stored in data type" .
457A numerical result of the function was too large to be stored in the caller
458provided space.
459.It Er 85 ECANCELED Em "Operation canceled" .
460The scheduled operation was canceled.
461.It Er 86 EILSEQ Em "Illegal byte sequence" .
462While decoding a multibyte character the function came along an
463invalid or an incomplete sequence of bytes or the given wide
464character is invalid.
465.El
466.Sh DEFINITIONS
467.Bl -tag -width Ds
468.It Process ID .
469Each active process in the system is uniquely identified by a non-negative
470integer called a process ID. The range of this ID is from 0 to 99999.
471.It Parent process ID
472A new process is created by a currently active process; (see
473.Xr fork 2 ) .
474The parent process ID of a process is initially the process ID of its creator.
475If the creating process exits,
476the parent process ID of each child is set to the ID of a system process,
477.Xr init 8 .
478.It Process Group
479Each active process is a member of a process group that is identified by
480a non-negative integer called the process group ID. This is the process
481ID of the group leader. This grouping permits the signaling of related
482processes (see
483.Xr termios 4 )
484and the job control mechanisms of
485.Xr csh 1 .
486.It Session
487A session is a set of one or more process groups.
488A session is created by a successful call to
489.Xr setsid 2 ,
490which causes the caller to become the only member of the only process
491group in the new session.
492.It Session leader
493A process that has created a new session by a successful call to
494.Xr setsid 2 ,
495is known as a session leader.
496Only a session leader may acquire a terminal as its controlling terminal (see
497.Xr termios 4 ) .
498.It Controlling process
499A session leader with a controlling terminal is a controlling process.
500.It Controlling terminal
501A terminal that is associated with a session is known as the controlling
502terminal for that session and its members.
503.It "Terminal Process Group ID"
504A terminal may be acquired by a session leader as its controlling terminal.
505Once a terminal is associated with a session, any of the process groups
506within the session may be placed into the foreground by setting
507the terminal process group ID to the ID of the process group.
508This facility is used
509to arbitrate between multiple jobs contending for the same terminal;
510(see
511.Xr csh 1
512and
513.Xr tty 4 ) .
514.It "Orphaned Process Group"
515A process group is considered to be
516.Em orphaned
517if it is not under the control of a job control shell.
518More precisely, a process group is orphaned
519when none of its members has a parent process that is in the same session
520as the group,
521but is in a different process group.
522Note that when a process exits, the parent process for its children
523is changed to be
524.Xr init 8 ,
525which is in a separate session.
526Not all members of an orphaned process group are necessarily orphaned
527processes (those whose creating process has exited).
528The process group of a session leader is orphaned by definition.
529.It "Real User ID and Real Group ID"
530Each user on the system is identified by a positive integer
531termed the real user ID.
532.Pp
533Each user is also a member of one or more groups.
534One of these groups is distinguished from others and
535used in implementing accounting facilities. The positive
536integer corresponding to this distinguished group is termed
537the real group ID.
538.Pp
539All processes have a real user ID and real group ID.
540These are initialized from the equivalent attributes
541of the process that created it.
542.It "Effective User Id, Effective Group Id, and Group Access List"
543Access to system resources is governed by two values:
544the effective user ID, and the group access list.
545The first member of the group access list is also known as the
546effective group ID.
547(In POSIX.1, the group access list is known as the set of supplementary
548group IDs, and it is unspecified whether the effective group ID is
549a member of the list.)
550.Pp
551The effective user ID and effective group ID are initially the
552process's real user ID and real group ID respectively. Either
553may be modified through execution of a set-user-ID or set-group-ID
554file (possibly by one its ancestors) (see
555.Xr execve 2 ) .
556By convention, the effective group ID (the first member of the group access
557list) is duplicated, so that the execution of a set-group-ID program
558does not result in the loss of the original (real) group ID.
559.Pp
560The group access list is a set of group IDs
561used only in determining resource accessibility. Access checks
562are performed as described below in ``File Access Permissions''.
563.It "Saved Set User ID and Saved Set Group ID"
564When a process executes a new file, the effective user ID is set
565to the owner of the file if the file is set-user-ID, and the effective
566group ID (first element of the group access list) is set to the group
567of the file if the file is set-group-ID.
568The effective user ID of the process is then recorded as the saved set-user-ID,
569and the effective group ID of the process is recorded as the saved set-group-ID.
570These values may be used to regain those values as the effective user
571or group ID after reverting to the real ID (see
572.Xr setuid 2 ) .
573(In POSIX.1, the saved set-user-ID and saved set-group-ID are optional,
574and are used in setuid and setgid, but this does not work as desired
575for the super-user.)
576.It Super-user
577A process is recognized as a
578.Em super-user
579process and is granted special privileges if its effective user ID is 0.
580.It Special Processes
581The processes with process IDs of 0, 1, and 2 are special.
582Process 0 is the scheduler. Process 1 is the initialization process
583.Xr init 8 ,
584and is the ancestor of every other process in the system.
585It is used to control the process structure.
586Process 2 is the paging daemon.
587.It Descriptor
588An integer assigned by the system when a file is referenced
589by
590.Xr open 2
591or
592.Xr dup 2 ,
593or when a socket is created by
594.Xr pipe 2 ,
595.Xr socket 2
596or
597.Xr socketpair 2 ,
598which uniquely identifies an access path to that file or socket from
599a given process or any of its children.
600.It File Name
601Names consisting of up to 255
602.Pq Dv MAXNAMELEN
603characters may be used to name
604an ordinary file, special file, or directory.
605.Pp
606These characters may be selected from the set of all
607.Tn ASCII
608character
609excluding 0 (NUL) and the
610.Tn ASCII
611code for
612.Ql \&/
613(slash).
614.Pp
615Note that it is generally unwise to use
616.Ql \&* ,
617.Ql \&? ,
618.Ql \&[
619or
620.Ql \&]
621as part of
622file names because of the special meaning attached to these characters
623by the shell.
624.It Path Name
625A path name is a
626.Tn NUL Ns -terminated
627character string starting with an
628optional slash
629.Ql \&/ ,
630followed by zero or more directory names separated
631by slashes, optionally followed by a file name.
632The total length of a path name must be less than 1024
633.Pq Dv MAXPATHLEN
634characters.
635.Pp
636If a path name begins with a slash, the path search begins at the
637.Em root
638directory.
639Otherwise, the search begins from the current working directory.
640A slash by itself names the root directory. An empty
641pathname refers to the current directory.
642.It Directory
643A directory is a special type of file that contains entries
644that are references to other files.
645Directory entries are called links. By convention, a directory
646contains at least two links,
647.Ql .\&
648and
649.Ql \&.. ,
650referred to as
651.Em dot
652and
653.Em dot-dot
654respectively. Dot refers to the directory itself and
655dot-dot refers to its parent directory.
656.It "Root Directory and Current Working Directory"
657Each process has associated with it a concept of a root directory
658and a current working directory for the purpose of resolving path
659name searches. A process's root directory need not be the root
660directory of the root file system.
661.It File Access Permissions
662Every file in the file system has a set of access permissions.
663These permissions are used in determining whether a process
664may perform a requested operation on the file (such as opening
665a file for writing). Access permissions are established at the
666time a file is created. They may be changed at some later time
667through the
668.Xr chmod 2
669call.
670.Pp
671File access is broken down according to whether a file may be: read,
672written, or executed. Directory files use the execute
673permission to control if the directory may be searched.
674.Pp
675File access permissions are interpreted by the system as
676they apply to three different classes of users: the owner
677of the file, those users in the file's group, anyone else.
678Every file has an independent set of access permissions for
679each of these classes. When an access check is made, the system
680decides if permission should be granted by checking the access
681information applicable to the caller.
682.Pp
683Read, write, and execute/search permissions on
684a file are granted to a process if:
685.Pp
686The process's effective user ID is that of the super-user.
687(Note:
688even the super-user cannot execute a non-executable file.)
689.Pp
690The process's effective user ID matches the user ID of the owner
691of the file and the owner permissions allow the access.
692.Pp
693The process's effective user ID does not match the user ID of the
694owner of the file, and either the process's effective
695group ID matches the group ID
696of the file, or the group ID of the file is in
697the process's group access list,
698and the group permissions allow the access.
699.Pp
700Neither the effective user ID nor effective group ID
701and group access list of the process
702match the corresponding user ID and group ID of the file,
703but the permissions for ``other users'' allow access.
704.Pp
705Otherwise, permission is denied.
706.It Sockets and Address Families
707A socket is an endpoint for communication between processes.
708Each socket has queues for sending and receiving data.
709.Pp
710Sockets are typed according to their communications properties.
711These properties include whether messages sent and received
712at a socket require the name of the partner, whether communication
713is reliable, the format used in naming message recipients, etc.
714.Pp
715Each instance of the system supports some
716collection of socket types; consult
717.Xr socket 2
718for more information about the types available and
719their properties.
720.Pp
721Each instance of the system supports some number of sets of
722communications protocols. Each protocol set supports addresses
723of a certain format. An Address Family is the set of addresses
724for a specific group of protocols. Each socket has an address
725chosen from the address family in which the socket was created.
726.El
727.Sh SEE ALSO
728.Xr intro 3 ,
729.Xr perror 3