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1.1 root 1: .\" Copyright (c) 1980,1983,1986 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)intro.2 6.7 (Berkeley) 5/23/86
6: .\"
7: .TH INTRO 2 "May 23, 1986"
8: .UC 4
9: .de en
10: .HP
11: \\$1 \\$2 \\$3
12: .br
13: ..
14: .SH NAME
15: intro \- introduction to system calls and error numbers
16: .SH SYNOPSIS
17: .B #include <sys/errno.h>
18: .SH DESCRIPTION
19: This section describes all of the system calls. Most
20: of these calls have one or more error returns.
21: An error condition is indicated by an otherwise impossible return
22: value. This is almost always \-1; the individual descriptions
23: specify the details.
24: Note that a number of system calls overload the meanings of these
25: error numbers, and that the meanings must be interpreted according
26: to the type and circumstances of the call.
27: .PP
28: As with normal arguments, all return codes and values from
29: functions are of type integer unless otherwise noted.
30: An error number is also made available in the external
31: variable \fIerrno\fP, which is not cleared
32: on successful calls.
33: Thus \fIerrno\fP should be tested only after an error has occurred.
34: .PP
35: The following is a complete list of the errors and their
36: names as given in
37: .RI < sys/errno.h >.
38: .en 0 \h'\w'EIO'u' "Error 0
39: Unused.
40: .en 1 EPERM "Not owner
41: Typically this error indicates
42: an attempt to modify a file in some way forbidden
43: except to its owner or super-user.
44: It is also returned for attempts
45: by ordinary users to do things
46: allowed only to the super-user.
47: .en 2 ENOENT "No such file or directory
48: This error occurs when a file name is specified
49: and the file should exist but doesn't, or when one
50: of the directories in a path name does not exist.
51: .en 3 ESRCH "No such process
52: The process or process group whose number was given
53: does not exist, or any such process is already dead.
54: .en 4 EINTR "Interrupted system call
55: An asynchronous signal (such as interrupt or quit)
56: that the user has elected to catch
57: occurred during a system call.
58: If execution is resumed
59: after processing the signal
60: and the system call is not restarted,
61: it will appear as if the interrupted system call
62: returned this error condition.
63: .en 5 EIO "I/O error
64: Some physical I/O error occurred during a
65: .I read
66: or
67: .IR write .
68: This error may in some cases occur
69: on a call following the one to which it actually applies.
70: .en 6 ENXIO "No such device or address
71: I/O on a special file refers to a subdevice that does not
72: exist,
73: or beyond the limits of the device.
74: It may also occur when, for example, an illegal tape drive
75: unit number is selected
76: or a disk pack is not loaded on a drive.
77: .en 7 E2BIG "Arg list too long
78: An argument list longer than 20480 bytes (or the current limit, NCARGS in
79: .IR <sys/param.h> )
80: is presented to
81: .IR execve .
82: .en 8 ENOEXEC "Exec format error
83: A request is made to execute a file
84: that, although it has the appropriate permissions,
85: does not start with a valid magic number, (see
86: .IR a.out (5)).
87: .en 9 EBADF "Bad file number
88: Either a file descriptor refers to no
89: open file,
90: or a read (resp. write) request is made to
91: a file that is open only for writing (resp. reading).
92: .en 10 ECHILD "No children
93: .I Wait
94: and the process has no
95: living or unwaited-for children.
96: .en 11 EAGAIN "No more processes
97: In a
98: .I fork,
99: the system's process table is full
100: or the user is not allowed to create any more
101: processes.
102: .en 12 ENOMEM "Not enough memory
103: During an
104: .I execve
105: or
106: .I break,
107: a program asks for more core or swap space than the system is
108: able to supply,
109: or a process size limit would be exceeded.
110: A lack of swap space is normally a temporary condition; however,
111: a lack of core
112: is not a temporary condition; the maximum size
113: of the text, data, and stack segments is a system parameter.
114: Soft limits may be increased to their corresponding hard limits.
115: .en 13 EACCES "Permission denied
116: An attempt was made to access a file in a way forbidden
117: by the protection system.
118: .en 14 EFAULT "Bad address
119: The system encountered a hardware fault in attempting to
120: access the arguments of a system call.
121: .en 15 ENOTBLK "Block device required
122: A plain file was mentioned where a block device was required,
123: e.g., in
124: .IR mount .
125: .en 16 EBUSY "Device busy
126: An attempt to mount a device that was already mounted or
127: an attempt was made to dismount a device
128: on which there is an active file
129: (open file, current directory, mounted-on file, or active text segment).
130: A request was made to an exclusive access device that was already in use.
131: .en 17 EEXIST "File exists
132: An existing file was mentioned in an inappropriate context,
133: e.g.,
134: .IR link .
135: .en 18 EXDEV "Cross-device link
136: A hard link to a file on another device
137: was attempted.
138: .en 19 ENODEV "No such device
139: An attempt was made to apply an inappropriate
140: system call to a device,
141: e.g., to read a write-only device,
142: or the device is not configured by the system.
143: .en 20 ENOTDIR "Not a directory
144: A non-directory was specified where a directory
145: is required,
146: for example, in a path name or
147: as an argument to
148: .IR chdir .
149: .en 21 EISDIR "Is a directory
150: An attempt to write on a directory.
151: .en 22 EINVAL "Invalid argument
152: Some invalid argument:
153: dismounting a non-mounted
154: device,
155: mentioning an unknown signal in
156: .I signal,
157: or some other argument inappropriate for the call.
158: Also set by math functions, (see
159: .IR math (3)).
160: .en 23 ENFILE "File table overflow
161: The system's table of open files is full,
162: and temporarily no more
163: .I opens
164: can be accepted.
165: .en 24 EMFILE "Too many open files
166: As released, the limit on the number of
167: open files per process is 64.
168: .IR Getdtablesize (2)
169: will obtain the current limit.
170: Customary configuration limit on most other UNIX systems
171: is 20 per process.
172: .en 25 ENOTTY "Inappropriate ioctl for device
173: The file mentioned in an
174: .I ioctl
175: is not a terminal or one of the
176: devices to which this call applies.
177: .en 26 ETXTBSY "Text file busy
178: An attempt to execute a pure-procedure
179: program that is currently open for writing.
180: Also an attempt to open for writing a pure-procedure
181: program that is being executed.
182: .en 27 EFBIG "File too large
183: The size of a file exceeded the maximum (about
184: .if t 2\u\s-231\s+2\d
185: .if n 2.1E9
186: bytes).
187: .en 28 ENOSPC "No space left on device
188: A
189: .I write
190: to an ordinary file, the creation of a
191: directory or symbolic link, or the creation of a directory
192: entry failed because no more disk blocks are available
193: on the file system, or the allocation of an inode for a newly
194: created file failed because no more inodes are available
195: on the file system.
196: .en 29 ESPIPE "Illegal seek
197: An
198: .I lseek
199: was issued to a socket or pipe.
200: This error may also be issued for
201: other non-seekable devices.
202: .en 30 EROFS "Read-only file system
203: An attempt to modify a file or directory
204: was made
205: on a device mounted read-only.
206: .en 31 EMLINK "Too many links
207: An attempt to make more than 32767 hard links to a file.
208: .en 32 EPIPE "Broken pipe
209: A write on a pipe or socket for which there is no process
210: to read the data.
211: This condition normally generates a signal;
212: the error is returned if the signal is caught or ignored.
213: .en 33 EDOM "Argument too large
214: The argument of a function in the math package (3M)
215: is out of the domain of the function.
216: .en 34 ERANGE "Result too large
217: The value of a function in the math package (3M)
218: is unrepresentable within machine precision.
219: .en 35 EWOULDBLOCK "Operation would block"
220: An operation that would cause a process to block was attempted
221: on an object in non-blocking mode (see \fIfcntl\fP(2)).
222: .en 36 EINPROGRESS "Operation now in progress"
223: An operation that takes a long time to complete (such as
224: a \fIconnect\fP(2)) was attempted on a non-blocking object (see
225: \fIfcntl\fP(2)).
226: .en 37 EALREADY "Operation already in progress"
227: An operation was attempted on a non-blocking object that already
228: had an operation in progress.
229: .en 38 ENOTSOCK "Socket operation on non-socket"
230: Self-explanatory.
231: .en 39 EDESTADDRREQ "Destination address required"
232: A required address was omitted from an operation on a socket.
233: .en 40 EMSGSIZE "Message too long"
234: A message sent on a socket was larger than the internal message buffer
235: or some other network limit.
236: .en 41 EPROTOTYPE "Protocol wrong type for socket"
237: A protocol was specified that does not support the semantics of the
238: socket type requested. For example, you cannot use the ARPA Internet
239: UDP protocol with type SOCK_STREAM.
240: .en 42 ENOPROTOOPT "Option not supported by protocol
241: A bad option or level was specified in a
242: .IR getsockopt (2)
243: or
244: .IR setsockopt (2)
245: call.
246: .en 43 EPROTONOSUPPORT "Protocol not supported"
247: The protocol has not been configured into the
248: system or no implementation for it exists.
249: .en 44 ESOCKTNOSUPPORT "Socket type not supported"
250: The support for the socket type has not been configured into the
251: system or no implementation for it exists.
252: .en 45 EOPNOTSUPP "Operation not supported on socket"
253: For example, trying to \fIaccept\fP a connection on a datagram socket.
254: .en 46 EPFNOSUPPORT "Protocol family not supported"
255: The protocol family has not been configured into the
256: system or no implementation for it exists.
257: .en 47 EAFNOSUPPORT "Address family not supported by protocol family"
258: An address incompatible with the requested protocol was used.
259: For example, you shouldn't necessarily expect to be able to use NS
260: addresses with ARPA Internet protocols.
261: .en 48 EADDRINUSE "Address already in use"
262: Only one usage of each address is normally permitted.
263: .en 49 EADDRNOTAVAIL "Can't assign requested address"
264: Normally results from an attempt to create a socket with an
265: address not on this machine.
266: .en 50 ENETDOWN "Network is down"
267: A socket operation encountered a dead network.
268: .en 51 ENETUNREACH "Network is unreachable"
269: A socket operation was attempted to an unreachable network.
270: .en 52 ENETRESET "Network dropped connection on reset"
271: The host you were connected to crashed and rebooted.
272: .en 53 ECONNABORTED "Software caused connection abort"
273: A connection abort was caused internal to your host machine.
274: .en 54 ECONNRESET "Connection reset by peer"
275: A connection was forcibly closed by a peer. This normally
276: results from a loss of the connection on the remote socket
277: due to a timeout or a reboot.
278: .en 55 ENOBUFS "No buffer space available"
279: An operation on a socket or pipe was not performed because
280: the system lacked sufficient buffer space or because a queue was full.
281: .en 56 EISCONN "Socket is already connected"
282: A
283: .I connect
284: request was made on an already connected socket; or,
285: a
286: .I sendto
287: or
288: .I sendmsg
289: request on a connected socket specified a destination
290: when already connected.
291: .en 57 ENOTCONN "Socket is not connected"
292: An request to send or receive data was disallowed because
293: the socket is not connected and (when sending on a datagram socket)
294: no address was supplied.
295: .en 58 ESHUTDOWN "Can't send after socket shutdown"
296: A request to send data was disallowed because the socket
297: had already been shut down with a previous
298: .IR shutdown (2)
299: call.
300: .en 59 \fIunused\fP
301: .en 60 ETIMEDOUT "Connection timed out"
302: A
303: .I connect
304: or
305: .I send
306: request failed because the connected party did not
307: properly respond after a period of time. (The timeout
308: period is dependent on the communication protocol.)
309: .en 61 ECONNREFUSED "Connection refused"
310: No connection could be made because the target machine actively
311: refused it. This usually results from trying to connect
312: to a service that is inactive on the foreign host.
313: .en 62 ELOOP "Too many levels of symbolic links"
314: A path name lookup involved more than 8 symbolic links.
315: .en 63 ENAMETOOLONG "File name too long"
316: A component of a path name exceeded 255 (MAXNAMELEN) characters, or an entire
317: path name exceeded 1023 (MAXPATHLEN-1) characters.
318: .en 64 EHOSTDOWN "Host is down"
319: A socket operation failed because the destination host was down.
320: .en 65 EHOSTUNREACH "Host is unreachable"
321: A socket operation was attempted to an unreachable host.
322: .en 66 ENOTEMPTY "Directory not empty"
323: A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq
324: was supplied to a remove directory or rename call.
325: ...en 67 EPROCLIM "Too many processes"
326: ...en 68 EUSERS "Too many users"
327: .en 69 EDQUOT "Disc quota exceeded"
328: A
329: .I write
330: to an ordinary file, the creation of a
331: directory or symbolic link, or the creation of a directory
332: entry failed because the user's quota of disk blocks was
333: exhausted, or the allocation of an inode for a newly
334: created file failed because the user's quota of inodes
335: was exhausted.
336: .SH DEFINITIONS
337: .TP 5
338: Process ID
339: .br
340: Each active process in the system is uniquely identified by a positive
341: integer called a process ID. The range of this ID is from 0 to 30000.
342: .TP 5
343: Parent process ID
344: .br
345: A new process is created by a currently active process; (see
346: .IR fork (2)).
347: The parent process ID of a process is the process ID of its creator.
348: .TP 5
349: Process Group ID
350: .br
351: Each active process is a member of a process group that is identified by
352: a positive integer called the process group ID. This is the process
353: ID of the group leader. This grouping permits the signaling of related
354: processes (see
355: .IR killpg (2))
356: and the job control mechanisms of
357: .IR csh (1).
358: .TP 5
359: Tty Group ID
360: .br
361: Each active process can be a member of a terminal group that is identified
362: by a positive integer called the tty group ID. This grouping is used
363: to arbitrate between multiple jobs contending for the same terminal;
364: (see
365: .IR csh (1)
366: and
367: .IR tty (4)).
368: .TP 5
369: Real User ID and Real Group ID
370: .br
371: Each user on the system is identified by a positive integer
372: termed the real user ID.
373: .IP
374: Each user is also a member of one or more groups.
375: One of these groups is distinguished from others and
376: used in implementing accounting facilities. The positive
377: integer corresponding to this distinguished group is termed
378: the real group ID.
379: .IP
380: All processes have a real user ID and real group ID.
381: These are initialized from the equivalent attributes
382: of the process that created it.
383: .TP 5
384: Effective User Id, Effective Group Id, and Access Groups
385: .br
386: Access to system resources is governed by three values:
387: the effective user ID, the effective group ID, and the
388: group access list.
389: .IP
390: The effective user ID and effective group ID are initially the
391: process's real user ID and real group ID respectively. Either
392: may be modified through execution of a set-user-ID or set-group-ID
393: file (possibly by one its ancestors) (see
394: .IR execve (2)).
395: .IP
396: The group access list is an additional set of group ID's
397: used only in determining resource accessibility. Access checks
398: are performed as described below in ``File Access Permissions''.
399: .TP 5
400: Super-user
401: .br
402: A process is recognized as a
403: .I super-user
404: process and is granted special privileges if its effective user ID is 0.
405: .TP 5
406: Special Processes
407: .br
408: The processes with a process ID's of 0, 1, and 2 are special.
409: Process 0 is the scheduler. Process 1 is the initialization process
410: .IR init ,
411: and is the ancestor of every other process in the system.
412: It is used to control the process structure.
413: Process 2 is the paging daemon.
414: .TP 5
415: Descriptor
416: .br
417: An integer assigned by the system when a file is referenced
418: by
419: .IR open (2)
420: or
421: .IR dup (2),
422: or when a socket is created by
423: .IR pipe (2),
424: .IR socket (2)
425: or
426: .IR socketpair (2),
427: which uniquely identifies an access path to that file or socket from
428: a given process or any of its children.
429: .TP 5
430: File Name
431: .br
432: Names consisting of up to 255 (MAXNAMELEN) characters may be used to name
433: an ordinary file, special file, or directory.
434: .IP
435: These characters may be selected from the set of all ASCII character
436: excluding 0 (null) and the ASCII code for / (slash). (The parity bit,
437: bit 8, must be 0.)
438: .IP
439: Note that it is generally unwise to use *, ?, [ or ] as part of
440: file names because of the special meaning attached to these characters
441: by the shell.
442: .TP 5
443: Path Name
444: .br
445: A path name is a null-terminated character string starting with an
446: optional slash (/), followed by zero or more directory names separated
447: by slashes, optionally followed by a file name.
448: The total length of a path name must be less than 1024 (MAXPATHLEN) characters.
449: .IP
450: If a path name begins with a slash, the path search begins at the
451: .I root
452: directory.
453: Otherwise, the search begins from the current working directory.
454: A slash by itself names the root directory. A null
455: pathname refers to the current directory.
456: .TP 5
457: Directory
458: .br
459: A directory is a special type of file that contains entries
460: that are references to other files.
461: Directory entries are called links. By convention, a directory
462: contains at least two links, . and .., referred to as
463: .I dot
464: and
465: .I dot-dot
466: respectively. Dot refers to the directory itself and
467: dot-dot refers to its parent directory.
468: .TP 5
469: Root Directory and Current Working Directory
470: .br
471: Each process has associated with it a concept of a root directory
472: and a current working directory for the purpose of resolving path
473: name searches. A process's root directory need not be the root
474: directory of the root file system.
475: .TP 5
476: File Access Permissions
477: .br
478: Every file in the file system has a set of access permissions.
479: These permissions are used in determining whether a process
480: may perform a requested operation on the file (such as opening
481: a file for writing). Access permissions are established at the
482: time a file is created. They may be changed at some later time
483: through the
484: .IR chmod (2)
485: call.
486: .IP
487: File access is broken down according to whether a file may be: read,
488: written, or executed. Directory files use the execute
489: permission to control if the directory may be searched.
490: .IP
491: File access permissions are interpreted by the system as
492: they apply to three different classes of users: the owner
493: of the file, those users in the file's group, anyone else.
494: Every file has an independent set of access permissions for
495: each of these classes. When an access check is made, the system
496: decides if permission should be granted by checking the access
497: information applicable to the caller.
498: .IP
499: Read, write, and execute/search permissions on
500: a file are granted to a process if:
501: .IP
502: The process's effective user ID is that of the super-user.
503: .IP
504: The process's effective user ID matches the user ID of the owner
505: of the file and the owner permissions allow the access.
506: .IP
507: The process's effective user ID does not match the user ID of the
508: owner of the file, and either the process's effective
509: group ID matches the group ID
510: of the file, or the group ID of the file is in
511: the process's group access list,
512: and the group permissions allow the access.
513: .IP
514: Neither the effective user ID nor effective group ID
515: and group access list of the process
516: match the corresponding user ID and group ID of the file,
517: but the permissions for ``other users'' allow access.
518: .IP
519: Otherwise, permission is denied.
520: .TP 5
521: Sockets and Address Families
522: .IP
523: A socket is an endpoint for communication between processes.
524: Each socket has queues for sending and receiving data.
525: .IP
526: Sockets are typed according to their communications properties.
527: These properties include whether messages sent and received
528: at a socket require the name of the partner, whether communication
529: is reliable, the format used in naming message recipients, etc.
530: .IP
531: Each instance of the system supports some
532: collection of socket types; consult
533: .IR socket (2)
534: for more information about the types available and
535: their properties.
536: .IP
537: Each instance of the system supports some number of sets of
538: communications protocols. Each protocol set supports addresses
539: of a certain format. An Address Family is the set of addresses
540: for a specific group of protocols. Each socket has an address
541: chosen from the address family in which the socket was created.
542: .SH SEE ALSO
543: intro(3), perror(3)
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