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91409caa | 1 | .\" Copyright (c) 1980,1983,1986 Regents of the University of California. |
5822f3c2 KM |
2 | .\" All rights reserved. The Berkeley software License Agreement |
3 | .\" specifies the terms and conditions for redistribution. | |
4 | .\" | |
c8051adb | 5 | .\" @(#)intro.2 6.10 (Berkeley) %G% |
5822f3c2 | 6 | .\" |
8af6b0db | 7 | .TH INTRO 2 "" |
5822f3c2 KM |
8 | .UC 4 |
9 | .de en | |
10 | .HP | |
11 | \\$1 \\$2 \\$3 | |
12 | .br | |
13 | .. | |
14 | .SH NAME | |
5e1f9d48 | 15 | intro \- introduction to system calls and error numbers |
5822f3c2 | 16 | .SH SYNOPSIS |
91409caa | 17 | .B #include <sys/errno.h> |
5822f3c2 | 18 | .SH DESCRIPTION |
f9238312 MK |
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. | |
5e1f9d48 KM |
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. | |
91409caa MK |
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. | |
5822f3c2 | 33 | .PP |
5e1f9d48 KM |
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. | |
5822f3c2 | 40 | .PP |
5e1f9d48 KM |
41 | The following is a complete list of the errors and their |
42 | names as given in | |
91409caa | 43 | .RI < sys/errno.h >. |
5822f3c2 KM |
44 | .en 0 \h'\w'EIO'u' "Error 0 |
45 | Unused. | |
c8051adb | 46 | .en 1 EPERM "Operation not permitted |
5822f3c2 KM |
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 | |
91409caa MK |
58 | The process or process group whose number was given |
59 | does not exist, or any such process is already dead. | |
5822f3c2 | 60 | .en 4 EINTR "Interrupted system call |
750588ad SS |
61 | An asynchronous signal (such as interrupt or quit) |
62 | that the user has elected to catch | |
5822f3c2 KM |
63 | occurred during a system call. |
64 | If execution is resumed | |
91409caa MK |
65 | after processing the signal |
66 | and the system call is not restarted, | |
5822f3c2 KM |
67 | it will appear as if the interrupted system call |
68 | returned this error condition. | |
c8051adb | 69 | .en 5 EIO "Input/output error |
5822f3c2 KM |
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. | |
c8051adb | 76 | .en 6 ENXIO "Device not configured |
750588ad | 77 | I/O on a special file refers to a subdevice that does not |
5822f3c2 KM |
78 | exist, |
79 | or beyond the limits of the device. | |
5e1f9d48 KM |
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. | |
c8051adb | 83 | .en 7 E2BIG "Argument list too long |
91409caa MK |
84 | An argument list longer than 20480 bytes (or the current limit, NCARGS in |
85 | .IR <sys/param.h> ) | |
5822f3c2 | 86 | is presented to |
5e1f9d48 | 87 | .IR execve . |
5822f3c2 KM |
88 | .en 8 ENOEXEC "Exec format error |
89 | A request is made to execute a file | |
750588ad | 90 | that, although it has the appropriate permissions, |
9b718484 KD |
91 | does not start with a valid magic number, (see |
92 | .IR a.out (5)). | |
c8051adb | 93 | .en 9 EBADF "Bad file descriptor |
5822f3c2 KM |
94 | Either a file descriptor refers to no |
95 | open file, | |
96 | or a read (resp. write) request is made to | |
750588ad | 97 | a file that is open only for writing (resp. reading). |
c8051adb | 98 | .en 10 ECHILD "No child processes |
5822f3c2 KM |
99 | .I Wait |
100 | and the process has no | |
101 | living or unwaited-for children. | |
c8051adb TH |
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 | |
5822f3c2 | 106 | During an |
5e1f9d48 | 107 | .I execve |
5822f3c2 KM |
108 | or |
109 | .I break, | |
5e1f9d48 | 110 | a program asks for more core or swap space than the system is |
91409caa MK |
111 | able to supply, |
112 | or a process size limit would be exceeded. | |
9b718484 | 113 | A lack of swap space is normally a temporary condition; however, |
5e1f9d48 KM |
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. | |
91409caa | 117 | Soft limits may be increased to their corresponding hard limits. |
5822f3c2 KM |
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, | |
9b718484 | 126 | e.g., in |
5822f3c2 | 127 | .IR mount . |
b5984ffe | 128 | .en 16 EBUSY "Device busy |
5822f3c2 KM |
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 | |
91409caa | 132 | (open file, current directory, mounted-on file, or active text segment). |
b5984ffe | 133 | A request was made to an exclusive access device that was already in use. |
5822f3c2 KM |
134 | .en 17 EEXIST "File exists |
135 | An existing file was mentioned in an inappropriate context, | |
9b718484 | 136 | e.g., |
5822f3c2 KM |
137 | .IR link . |
138 | .en 18 EXDEV "Cross-device link | |
5e1f9d48 | 139 | A hard link to a file on another device |
5822f3c2 | 140 | was attempted. |
c8051adb | 141 | .en 19 ENODEV "Operation not supported by device |
5822f3c2 | 142 | An attempt was made to apply an inappropriate |
91409caa | 143 | system call to a device, |
9b718484 | 144 | e.g., to read a write-only device, |
91409caa | 145 | or the device is not configured by the system. |
5822f3c2 KM |
146 | .en 20 ENOTDIR "Not a directory |
147 | A non-directory was specified where a directory | |
148 | is required, | |
9b718484 | 149 | for example, in a path name or |
5822f3c2 KM |
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, | |
91409caa | 160 | or some other argument inappropriate for the call. |
9b718484 KD |
161 | Also set by math functions, (see |
162 | .IR math (3)). | |
c8051adb | 163 | .en 23 ENFILE "Too many open files in system |
5822f3c2 KM |
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 | |
339207b0 KM |
169 | As released, the limit on the number of |
170 | open files per process is 64. | |
91409caa MK |
171 | .IR Getdtablesize (2) |
172 | will obtain the current limit. | |
339207b0 KM |
173 | Customary configuration limit on most other UNIX systems |
174 | is 20 per process. | |
175 | .en 25 ENOTTY "Inappropriate ioctl for device | |
5e1f9d48 KM |
176 | The file mentioned in an |
177 | .I ioctl | |
91409caa | 178 | is not a terminal or one of the |
8af6b0db | 179 | devices to which this call applies. |
5822f3c2 KM |
180 | .en 26 ETXTBSY "Text file busy |
181 | An attempt to execute a pure-procedure | |
750588ad | 182 | program that is currently open for writing. |
5822f3c2 KM |
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 | |
91409caa MK |
187 | .if t 2\u\s-231\s+2\d |
188 | .if n 2.1E9 | |
5822f3c2 KM |
189 | bytes). |
190 | .en 28 ENOSPC "No space left on device | |
fd690c8b | 191 | A |
5822f3c2 | 192 | .I write |
fd690c8b KM |
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. | |
5822f3c2 KM |
199 | .en 29 ESPIPE "Illegal seek |
200 | An | |
201 | .I lseek | |
91409caa | 202 | was issued to a socket or pipe. |
5e1f9d48 | 203 | This error may also be issued for |
5822f3c2 KM |
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 | |
5e1f9d48 | 210 | An attempt to make more than 32767 hard links to a file. |
5822f3c2 | 211 | .en 32 EPIPE "Broken pipe |
5e1f9d48 | 212 | A write on a pipe or socket for which there is no process |
5822f3c2 KM |
213 | to read the data. |
214 | This condition normally generates a signal; | |
91409caa | 215 | the error is returned if the signal is caught or ignored. |
c8051adb | 216 | .en 33 EDOM "Numerical argument out of domain |
5822f3c2 KM |
217 | The argument of a function in the math package (3M) |
218 | is out of the domain of the function. | |
c8051adb | 219 | .en 34 ERANGE "Numerical result out of range |
5822f3c2 KM |
220 | The value of a function in the math package (3M) |
221 | is unrepresentable within machine precision. | |
c8051adb TH |
222 | .en 35 EAGAIN "Resource temporarily unavailable |
223 | This is a temporary condition and later calls to the | |
224 | same routine may complete normally. | |
5e1f9d48 | 225 | .en 36 EINPROGRESS "Operation now in progress" |
750588ad | 226 | An operation that takes a long time to complete (such as |
91409caa MK |
227 | a \fIconnect\fP(2)) was attempted on a non-blocking object (see |
228 | \fIfcntl\fP(2)). | |
5e1f9d48 | 229 | .en 37 EALREADY "Operation already in progress" |
750588ad | 230 | An operation was attempted on a non-blocking object that already |
5e1f9d48 KM |
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" | |
91409caa MK |
237 | A message sent on a socket was larger than the internal message buffer |
238 | or some other network limit. | |
5e1f9d48 | 239 | .en 41 EPROTOTYPE "Protocol wrong type for socket" |
750588ad | 240 | A protocol was specified that does not support the semantics of the |
9b718484 | 241 | socket type requested. For example, you cannot use the ARPA Internet |
5e1f9d48 | 242 | UDP protocol with type SOCK_STREAM. |
c8051adb | 243 | .en 42 ENOPROTOOPT "Protocol not available |
91409caa | 244 | A bad option or level was specified in a |
5e1f9d48 KM |
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. | |
91409caa MK |
262 | For example, you shouldn't necessarily expect to be able to use NS |
263 | addresses with ARPA Internet protocols. | |
5e1f9d48 KM |
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 | |
91409caa MK |
279 | results from a loss of the connection on the remote socket |
280 | due to a timeout or a reboot. | |
5e1f9d48 KM |
281 | .en 55 ENOBUFS "No buffer space available" |
282 | An operation on a socket or pipe was not performed because | |
91409caa | 283 | the system lacked sufficient buffer space or because a queue was full. |
5e1f9d48 KM |
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 | |
91409caa | 293 | when already connected. |
5e1f9d48 KM |
294 | .en 57 ENOTCONN "Socket is not connected" |
295 | An request to send or receive data was disallowed because | |
91409caa MK |
296 | the socket is not connected and (when sending on a datagram socket) |
297 | no address was supplied. | |
5e1f9d48 KM |
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. | |
5e1f9d48 KM |
303 | .en 60 ETIMEDOUT "Connection timed out" |
304 | A | |
305 | .I connect | |
91409caa MK |
306 | or |
307 | .I send | |
5e1f9d48 KM |
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 | |
750588ad | 314 | to a service that is inactive on the foreign host. |
5e1f9d48 KM |
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" | |
91409caa MK |
318 | A component of a path name exceeded 255 (MAXNAMELEN) characters, or an entire |
319 | path name exceeded 1023 (MAXPATHLEN-1) characters. | |
8af6b0db KM |
320 | .en 64 EHOSTDOWN "Host is down" |
321 | A socket operation failed because the destination host was down. | |
c8051adb | 322 | .en 65 EHOSTUNREACH "No route to host" |
8af6b0db KM |
323 | A socket operation was attempted to an unreachable host. |
324 | .en 66 ENOTEMPTY "Directory not empty" | |
5e1f9d48 KM |
325 | A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq |
326 | was supplied to a remove directory or rename call. | |
c8051adb | 327 | .en 67 EPROCLIM "Too many processes" |
a0f47338 KB |
328 | .en 68 EUSERS "Too many users" |
329 | The quota system ran out of table entries. | |
8af6b0db | 330 | .en 69 EDQUOT "Disc quota exceeded" |
fd690c8b | 331 | A |
91409caa | 332 | .I write |
fd690c8b KM |
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. | |
c8051adb TH |
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. | |
5e1f9d48 KM |
363 | .SH DEFINITIONS |
364 | .TP 5 | |
365 | Process ID | |
366 | .br | |
367 | Each active process in the system is uniquely identified by a positive | |
91409caa | 368 | integer called a process ID. The range of this ID is from 0 to 30000. |
5e1f9d48 KM |
369 | .TP 5 |
370 | Parent process ID | |
371 | .br | |
9b718484 KD |
372 | A new process is created by a currently active process; (see |
373 | .IR fork (2)). | |
5e1f9d48 KM |
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 | |
91409caa | 380 | ID of the group leader. This grouping permits the signaling of related |
5e1f9d48 KM |
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; | |
9b718484 KD |
391 | (see |
392 | .IR csh (1) | |
5822f3c2 | 393 | and |
9b718484 | 394 | .IR tty (4)). |
5e1f9d48 KM |
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. | |
5822f3c2 | 400 | .IP |
5e1f9d48 KM |
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 | |
750588ad | 409 | of the process that created it. |
5e1f9d48 KM |
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 | |
9b718484 KD |
420 | file (possibly by one its ancestors) (see |
421 | .IR execve (2)). | |
5e1f9d48 KM |
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 | |
91409caa MK |
446 | .IR open (2) |
447 | or | |
5e1f9d48 | 448 | .IR dup (2), |
91409caa MK |
449 | or when a socket is created by |
450 | .IR pipe (2), | |
5e1f9d48 KM |
451 | .IR socket (2) |
452 | or | |
750588ad | 453 | .IR socketpair (2), |
5e1f9d48 KM |
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 | |
91409caa | 459 | Names consisting of up to 255 (MAXNAMELEN) characters may be used to name |
5e1f9d48 KM |
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. | |
91409caa | 475 | The total length of a path name must be less than 1024 (MAXPATHLEN) characters. |
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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 | |
750588ad SS |
486 | A directory is a special type of file that contains entries |
487 | that are references to other files. | |
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488 | Directory entries are called links. By convention, a directory |
489 | contains at least two links, . and .., referred to as | |
490 | .I dot | |
5822f3c2 | 491 | and |
5e1f9d48 KM |
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) |