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1.1 root 1: .TH INTRO 2
2: .de {n
3: .HP
4: \\$1 \\$2 \\$3
5: .br
6: ..
7: .SH NAME
8: intro \- introduction to system calls and error numbers
9: .SH SYNOPSIS
10: .B #include \|<errno.h>
11: .SH DESCRIPTION
12: This section
13: describes all of the system calls.
14: Most of these calls have one or more error returns.
15: An error condition is indicated by an otherwise
16: impossible returned value.
17: This is almost always \-1;
18: the individual descriptions specify the details.
19: An error number is also made available
20: in the external variable
21: .IR errno .
22: .I Errno\^
23: is not cleared on successful calls, so it should be tested only
24: after an error has been indicated.
25: .PP
26: Each system call description attempts to
27: list all possible error numbers.
28: The following is a complete list of the error numbers and
29: their names as defined in
30: .BR <errno.h> .
31: .{n 1 \s-1EPERM\s+1 "Not owner"
32: Typically this error indicates
33: an attempt to modify a file in some way forbidden
34: except to its owner or super-user.
35: It is also returned for attempts
36: by ordinary users to do things
37: allowed only to the super-user.
38: .{n 2 \s-1ENOENT\s+1 "No such file or directory"
39: This error occurs when a file name is specified
40: and the file should exist but doesn't, or when one
41: of the directories in a path name does not exist.
42: .{n 3 \s-1ESRCH\s+1 "No such process"
43: No process can be found corresponding to that specified by
44: .I pid\^
45: in
46: .I kill\^
47: or
48: .IR ptrace .
49: .{n 4 \s-1EINTR\s+1 "Interrupted system call"
50: An asynchronous signal (such as interrupt or quit),
51: which the user has elected to catch,
52: occurred during a system call.
53: If execution is resumed
54: after processing the signal,
55: it will appear as if the interrupted system call
56: returned this error condition.
57: .{n 5 \s-1EIO\s+1 "I/O error"
58: Some physical I/O error has occurred.
59: This error may in some cases occur
60: on a call following the one to which it actually applies.
61: .{n 6 \s-1ENXIO\s+1 "No such device or address"
62: I/O on a special file refers to a subdevice which does not
63: exist,
64: or beyond the limits of the device.
65: It may also occur when, for example, a tape drive
66: is not on-line or no disk pack is loaded on a drive.
67: .{n 7 \s-1E2BIG\s+1 "Arg list too long"
68: An argument list longer than 5,120 bytes
69: is presented to a member of the
70: .I exec\^
71: family.
72: .{n 8 \s-1ENOEXEC\s+1 "Exec format error"
73: A request is made to execute a file
74: which, although it has the appropriate permissions,
75: does not start with a valid magic number (see
76: .IR a.out (4)).
77: .{n 9 \s-1EBADF\s+1 "Bad file number"
78: Either a file descriptor refers to no
79: open file,
80: or a read (respectively, write) request is made to
81: a file which is open only for writing (respectively, reading).
82: .{n 10 \s-1ECHILD\s+1 "No child processes"
83: A
84: .I wait
85: was executed by a process that had no existing or unwaited-for child processes.
86: .{n 11 \s-1EAGAIN\s+1 "No more processes"
87: A
88: .I fork
89: failed because the system's process table is full
90: or the user is not allowed to create any more
91: processes.
92: .{n 12 \s-1ENOMEM\s+1 "Not enough space"
93: During an
94: .IR exec ,
95: .IR brk ,
96: or
97: .IR sbrk ,
98: a program asks for more space than the system is able to supply.
99: This is not a temporary condition; the maximum space size
100: is a system parameter.
101: The error may also occur if the arrangement
102: of text, data, and stack segments
103: requires too many segmentation registers, or
104: if there is not enough swap space during a
105: .IR fork .
106: .{n 13 \s-1EACCES\s+1 "Permission denied"
107: An attempt was made to access a file in a way forbidden
108: by the protection system.
109: .{n 14 \s-1EFAULT\s+1 "Bad address"
110: The system encountered a hardware fault in attempting to
111: use an argument of a system call.
112: .{n 15 \s-1ENOTBLK\s+1 "Block device required"
113: A non-block file was mentioned where a block device was required,
114: e.g., in
115: .IR mount .
116: .{n 16 \s-1EBUSY\s+1 "Device or resource busy"
117: An attempt was made to mount a device that was already mounted or
118: an attempt was made to dismount a device
119: on which there is an active file
120: (open file, current directory, mounted-on file, active text segment).
121: It will also occur if an attempt is made to enable accounting when it is
122: already enabled.
123: The device or resource is currently unavailable.
124: .{n 17 \s-1EEXIST\s+1 "File exists"
125: An existing file was mentioned in an inappropriate context,
126: e.g.,
127: .IR link .
128: .{n 18 \s-1EXDEV\s+1 "Cross-device link"
129: A link to a file on another device
130: was attempted.
131: .{n 19 \s-1ENODEV\s+1 "No such device"
132: An attempt was made to apply an inappropriate
133: system call to a device;
134: e.g., read a write-only device.
135: .{n 20 \s-1ENOTDIR\s+1 "Not a directory"
136: A non-directory was specified where a directory
137: is required,
138: for example in a path prefix or
139: as an argument to
140: .IR chdir (2).
141: .{n 21 \s-1EISDIR\s+1 "Is a directory"
142: An attempt was made to write on a directory.
143: .{n 22 \s-1EINVAL\s+1 "Invalid argument"
144: Some invalid argument (e.g., dismounting a non-mounted device;
145: mentioning an undefined signal in
146: .IR signal ,
147: or
148: .IR kill ;
149: reading or writing a file for which
150: .I lseek\^
151: has generated a negative pointer).
152: Also set by the math functions described in the (3M) entries
153: of this manual.
154: .{n 23 \s-1ENFILE\s+1 "File table overflow"
155: The system file table is full,
156: and temporarily no more
157: .I opens\^
158: can be accepted.
159: .{n 24 \s-1EMFILE\s+1 "Too many open files"
160: No process may have more than 20 file descriptors open at a time.
161: .{n 25 \s-1ENOTTY\s+1 "Not a character device"
162: An attempt was made to \f2ioctl\fR(2) a file that
163: is not a special character device.
164: .{n 26 \s-1ETXTBSY\s+1 "Text file busy"
165: An attempt was made to execute a pure-procedure
166: program that is currently open for writing.
167: Also an attempt to open for writing a pure-procedure
168: program that is being executed.
169: .{n 27 \s-1EFBIG\s+1 "File too large"
170: The size of a file exceeded the maximum
171: file size (1,082,201,088 bytes) or
172: .SM ULIMIT\*S;
173: see
174: .IR ulimit (2).
175: .{n 28 \s-1ENOSPC\s+1 "No space left on device"
176: During a
177: .I write\^
178: to an ordinary file,
179: there is no free space left on the device.
180: .{n 29 \s-1ESPIPE\s+1 "Illegal seek"
181: An
182: .I lseek\^
183: was issued to a pipe.
184: .{n 30 \s-1EROFS\s+1 "Read-only file system"
185: An attempt to modify a file or directory
186: was made
187: on a device mounted read-only.
188: .{n 31 \s-1EMLINK\s+1 "Too many links"
189: An attempt to make more than the maximum number of links (1000) to a file.
190: .{n 32 \s-1EPIPE\s+1 "Broken pipe"
191: A write on a pipe for which there is no process
192: to read the data.
193: This condition normally generates a signal;
194: the error is returned if the signal is ignored.
195: .{n 33 \s-1EDOM\s+1 "Math argument"
196: The argument of a function in the math package (3M)
197: is out of the domain of the function.
198: .{n 34 \s-1ERANGE\s+1 "Result too large"
199: The value of a function in the math package (3M)
200: is not representable within machine precision.
201: .{n 35 \s-1EWOULDBLOCK\s+1 "Operation would block"
202: An operation which would cause a process to block was attempted
203: on a object in non-blocking mode (see \fIioctl\fP (2)).
204: .{n 36 \s-1EINPROGRESS\s+1 "Operation now in progress"
205: An operation which takes a long time to complete (such as
206: a \fIconnect\fP (2)) was attempted on a non-blocking object (see
207: \fIioctl\fP (2)).
208: .{n 37 \s-1EALREADY\s+1 "Operation already in progress"
209: An operation was attempted on a non-blocking object which already
210: had an operation in progress.
211: .{n 38 \s-1ENOTSOCK\s+1 "Socket operation on non-socket"
212: Self-explanatory.
213: .{n 39 \s-1EDESTADDRREQ\s+1 "Destination address required"
214: A required address was omitted from an operation on a socket.
215: .{n 40 \s-1EMSGSIZE\s+1 "Message too long"
216: A message sent on a socket was larger than the internal message buffer.
217: .{n 41 \s-1EPROTOTYPE\s+1 "Protocol wrong type for socket"
218: A protocol was specified which does not support the semantics of the
219: socket type requested. For example you cannot use the ARPA Internet
220: UDP protocol with type SOCK_STREAM.
221: .{n 42 \s-1ENOPROTOOPT\s+1 "Bad protocol option"
222: A bad option was specified in a
223: .IR getsockopt (2)
224: or
225: .IR setsockopt (2)
226: call.
227: .{n 43 \s-1EPROTONOSUPPORT\s+1 "Protocol not supported"
228: The protocol has not been configured into the
229: system or no implementation for it exists.
230: .{n 44 \s-1ESOCKTNOSUPPORT\s+1 "Socket type not supported"
231: The support for the socket type has not been configured into the
232: system or no implementation for it exists.
233: .{n 45 \s-1EOPNOTSUPP\s+1 "Operation not supported on socket"
234: For example, trying to \fIaccept\fP a connection on a datagram socket.
235: .{n 46 \s-1EPFNOSUPPORT\s+1 "Protocol family not supported"
236: The protocol family has not been configured into the
237: system or no implementation for it exists.
238: .{n 47 \s-1EAFNOSUPPORT\s+1 "Address family not supported by protocol family"
239: An address incompatible with the requested protocol was used.
240: For example, you shouldn't necessarily expect to be able to use PUP
241: Internet addresses with ARPA Internet protocols.
242: .{n 48 \s-1EADDRINUSE\s+1 "Address already in use"
243: Only one usage of each address is normally permitted.
244: .{n 49 \s-1EADDRNOTAVAIL\s+1 "Can't assign requested address"
245: Normally results from an attempt to create a socket with an
246: address not on this machine.
247: .{n 50 \s-1ENETDOWN\s+1 "Network is down"
248: A socket operation encountered a dead network.
249: .{n 51 \s-1ENETUNREACH\s+1 "Network is unreachable"
250: A socket operation was attempted to an unreachable network.
251: .{n 52 \s-1ENETRESET\s+1 "Network dropped connection on reset"
252: The host you were connected to crashed and rebooted.
253: .{n 53 \s-1ECONNABORTED\s+1 "Software caused connection abort"
254: A connection abort was caused internal to your host machine.
255: .{n 54 \s-1ECONNRESET\s+1 "Connection reset by peer"
256: A connection was forcibly closed by a peer. This normally
257: results from the peer executing a \fIshutdown\fP (2) call.
258: .{n 55 \s-1ENOBUFS\s+1 "No buffer space available"
259: An operation on a socket or pipe was not performed because
260: the system lacked sufficient buffer space.
261: .{n 56 \s-1EISCONN\s+1 "Socket is already connected"
262: A
263: .I connect
264: request was made on an already connected socket; or,
265: a
266: .I sendto
267: or
268: .I sendmsg
269: request on a connected socket specified a destination
270: other than the connected party.
271: .{n 57 \s-1ENOTCONN\s+1 "Socket is not connected"
272: An request to send or receive data was disallowed because
273: the socket is not connected.
274: .{n 58 \s-1ESHUTDOWN\s+1 "Can't send after socket shutdown"
275: A request to send data was disallowed because the socket
276: had already been shut down with a previous
277: .IR shutdown (2)
278: call.
279: .{n 59 \fIunused\fP
280: .{n 60 \s-1ETIMEDOUT\s+1 "Connection timed out"
281: A
282: .I connect
283: request failed because the connected party did not
284: properly respond after a period of time. (The timeout
285: period is dependent on the communication protocol.)
286: .{n 61 \s-1ECONNREFUSED\s+1 "Connection refused"
287: No connection could be made because the target machine actively
288: refused it. This usually results from trying to connect
289: to a service which is inactive on the foreign host.
290: .{n 62 \s-1ELOOP\s+1 "Too many levels of symbolic links"
291: A path name lookup involved more than 8 symbolic links.
292: .{n 63 \s-1ENAMETOOLONG\s+1 "File name too long"
293: A component of a path name exceeded 255 characters, or an entire
294: path name exceeded 1023 characters.
295: .{n 64 \s-1EHOSTDOWN\s+1 "Host is down"
296: The host machine is not up.
297: .{n 65 \s-1EHOSTUNREACH\s+1 "No route to host"
298: The host machine cannot be reached.
299: .{n 66 \s-1ENOTEMPTY\s+1 "Directory not empty"
300: A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq
301: was supplied to a remove directory or rename call.
302: .{n 67 \fIunused\fP
303: .{n 68 \s-1EUSERS\s+1 "Too many users"
304: The quota table is full.
305: .{n 69 \s-1EDQUOT\s+1 "Disc quota exceeded"
306: A process has exceeded its disk quota.
307: .{n 70 \s-1ENOMSG\s+1 "No message of desired type"
308: An attempt was made to receive a message of a type
309: that does not exist on the specified message queue; see
310: .IR msgop (2).
311: .{n 71 \s-1EIDRM\s+1 "Identifier Removed"
312: This error is returned to processes that resume execution due to the removal
313: of an identifier from the file system's name space (see
314: .IR msgctl "(2), " semctl "(2), and " shmctl (2)).
315: .SH "DEFINITIONS"
316: .SS "Process \s-1ID\s+1"
317: Each active process in the system is uniquely identified by a
318: positive integer called a process
319: .SM ID\*S.
320: The range of this
321: .SM ID
322: is from 1 to 30,000.
323: .SS "Parent Process \s-1ID\s+1"
324: A new process is created by a currently active
325: process; see
326: .IR fork (2).
327: The parent process
328: .SM ID
329: of a process is the process
330: .SM ID
331: of its creator.
332: .SS "Process Group \s-1ID\s+1"
333: Each active process is a member of a process group that is
334: identified by a positive integer called the process group
335: .SM ID\*S.
336: This
337: .SM ID
338: is the process
339: .SM ID
340: of the group leader.
341: This grouping permits the signaling of related processes; see
342: .IR kill (2).
343: .SS "Tty Group \s-1ID\s+1"
344: Each active process can be a member of a terminal group that
345: is identified by a positive integer called the tty group
346: .SM ID\*S.
347: This grouping is used to terminate a group of related processes upon termination
348: of one of the processes in the group; see
349: .IR exit (2)
350: and
351: .IR signal (2).
352: .SS "Real User \s-1ID\s+1 and Real Group \s-1ID\s+1"
353: Each user allowed on the system is
354: identified by a positive integer called a real user
355: .SM ID\*S.
356: .PP
357: Each user is also a member of a group.
358: The group is identified by a positive integer called the real group
359: .SM ID\*S.
360: .PP
361: An active process has a real user
362: .SM ID
363: and real group
364: .SM ID
365: that are set to the real user
366: .SM ID
367: and real group
368: .SM ID\*S,
369: respectively, of the user responsible for the creation of the process.
370: .SS "Effective User \s-1ID\s+1 and Effective Group \s-1ID\s+1"
371: An active process has an effective user
372: .SM ID
373: and an effective group
374: .SM ID
375: that are used to determine file access permissions (see below).
376: The effective
377: user
378: .SM ID
379: and effective group
380: .SM ID
381: are equal to the process's real user
382: .SM ID
383: and real group
384: .SM ID
385: respectively, unless the process
386: or one of its ancestors evolved from a file that had the set-user-\s-1ID\s+1
387: bit or set-group
388: .SM ID
389: bit set; see
390: .IR exec (2).
391: .SS Super-user
392: A process is recognized as a
393: .I super-user\^
394: process and is granted special privileges if its effective user
395: .SM ID
396: is 0.
397: .SS "Special Processes"
398: The processes with a process
399: .SM ID
400: of 0 and a process
401: .SM ID
402: of 1 are special processes and are referred to as
403: .IR proc0 " and " proc1.
404: .PP
405: .I Proc0\^
406: is the scheduler.
407: .I Proc1\^
408: is the initialization process
409: .RI ( init ).
410: Proc1 is the ancestor of every other
411: process in the system and is used to control the process structure.
412: .SS File Descriptor
413: A file descriptor is a small integer used
414: to do \s-1I/O\s+1 on a file.
415: The value of a file descriptor is from
416: 0 to 19.
417: A process may have no more than 20 file descriptors (0-19)
418: open simultaneously.
419: A file descriptor is returned by system calls such as
420: \f2open\fR(2),
421: or \f2pipe\fR(2).
422: The file descriptor is used as an
423: argument by calls such as
424: \f2read\fR(2),
425: \f2write\fR(2),
426: \f2ioctl\fR(2),
427: and
428: \f2close\fR(2).
429: .SS "File Name"
430: Names consisting of 1 to 14 characters may be used to name an ordinary file,
431: special file or directory.
432: .PP
433: These characters may be selected from the set of all character values
434: excluding \e0 (null) and the
435: .SM ASCII
436: code for
437: .B /
438: (slash).
439: .PP
440: Note that it is generally unwise to use
441: .BR "*" ,
442: .BR "?" ,
443: .BR "[" ,
444: or
445: .B "]"
446: as part of file names because of the special meaning attached to these
447: characters by the shell.
448: See
449: .IR sh (1).
450: Although permitted, it is advisable to avoid the use of unprintable
451: characters in file names.
452: .SS "Path Name and Path Prefix"
453: A path name is a null-terminated character string
454: starting with an optional slash
455: .RB ( / ),
456: followed by
457: zero or more directory names separated by slashes, optionally followed
458: by a file name.
459: .PP
460: More precisely, a path name is a null-terminated character string
461: constructed as follows:
462: .PP
463: .RS
464: <path-name>::=<file-name>\(bv<path-prefix><file-name>|/
465: .br
466: <path-prefix>::=<rtprefix>\(bv/<rtprefix>
467: .br
468: <rtprefix>::=<dirname>/\(bv<rtprefix><dirname>/
469: .RE
470: .PP
471: where <file-name> is a string of 1 to 14
472: characters other than the
473: .SM ASCII
474: slash and null, and
475: <dirname> is a string of 1 to 14 characters
476: (other than the
477: .SM ASCII
478: slash and null)
479: that names a directory.
480: .PP
481: If a path name begins with a slash, the path search begins at the
482: .I root\^
483: directory.
484: Otherwise, the search begins from the current working directory.
485: .PP
486: A slash by itself names the root directory.
487: .PP
488: Unless specifically stated otherwise,
489: the null path name is treated as if it named
490: a non-existent file.
491: .SS Directory
492: .PP
493: Directory entries are called links.
494: By convention, a directory contains at least two links,
495: .B .
496: and
497: .BR .. ,
498: referred to as
499: .I dot\^
500: and
501: .I dot-dot\^
502: respectively.
503: Dot refers to the directory itself and dot-dot refers to its parent
504: directory.
505: .SS "Root Directory and Current Working Directory"
506: Each process has associated with it a concept of a root directory and
507: a current working directory for the purpose of resolving path name searches.
508: The root directory of a process need not be the root directory of the root
509: file system.
510: .SS "File Access Permissions"
511: .PP
512: Read, write, and execute/search permissions on a file are
513: granted to a process if one or more of the following are true:
514: .IP
515: The effective user
516: .SM ID
517: of the process
518: is super-user.
519: .IP
520: The effective user
521: .SM ID
522: of the process
523: matches the user
524: .SM ID
525: of the owner of the file
526: and the appropriate access bit of the
527: ``owner'' portion (0700) of the file mode is set.
528: .IP
529: The effective user
530: .SM ID
531: of the process
532: does not match the user
533: .SM ID
534: of the owner of the file,
535: and the effective group
536: .SM ID
537: of the process
538: matches the group of the file and
539: the appropriate access bit of the ``group'' portion
540: (070) of the file mode is set.
541: .IP
542: The effective user
543: .SM ID
544: of the process
545: does not match the user
546: .SM ID
547: of the owner of the file,
548: and the effective group
549: .SM ID
550: of the process
551: does not match the group
552: .SM ID
553: of the file,
554: and the appropriate access bit of the ``other'' portion (07) of the
555: file mode is set.
556: .PP
557: Otherwise, the corresponding permissions are denied.
558: .SS "Message Queue Identifier"
559: A message queue identifier (msqid) is a unique positive integer created by a
560: .IR msgget (2)
561: system call.
562: Each msqid has a message queue and a data structure associated with it.
563: The data structure is referred to as
564: .I msqid_ds
565: and contains the following members:
566: .PP
567: .RS
568: .ta 8n 28n
569: .nf
570: struct ipc_perm msg_perm; /\(** operation permission struct \(**/
571: ushort msg_cbytes; /\(** current number of bytes on q \(**/
572: ushort msg_qnum; /\(** number of msgs on q \(**/
573: ushort msg_qbytes; /\(** max number of bytes on q \(**/
574: ushort msg_lspid; /\(** pid of last msgsnd operation \(**/
575: ushort msg_lrpid; /\(** pid of last msgrcv operation \(**/
576: time_t msg_stime; /\(** last msgsnd time \(**/
577: time_t msg_rtime; /\(** last msgrcv time \(**/
578: time_t msg_ctime; /\(** last change time \(**/
579: /\(** Times measured in secs since \(**/
580: /\(** 00:00:00 \s-1GMT\s+1, Jan. 1, 1970 \(**/
581: .fi
582: .RE
583: .PP
584: .B Msg_perm
585: is an ipc_perm structure that
586: specifies the message operation permission (see below).
587: This structure includes the following members:
588: .PP
589: .RS
590: .ta 8n 20n
591: .nf
592: ushort cuid; /\(** creator user id \(**/
593: ushort cgid; /\(** creator group id \(**/
594: ushort uid; /\(** user id \(**/
595: ushort gid; /\(** group id \(**/
596: ushort mode; /\(** r/w permission \(**/
597: .PP
598: .fi
599: .RE
600: .B Msg_cbytes
601: is the current number of bytes on the queue.
602: .B Msg_qnum
603: is the number of messages currently on the queue.
604: .B Msg_qbytes
605: is the maximum number of bytes allowed on the queue.
606: .B Msg_lspid
607: is the process id of the last process that performed a
608: .IR msgsnd " operation."
609: .B Msg_lrpid
610: is the process id of the last process that performed a
611: .IR msgrcv " operation."
612: .B Msg_stime
613: is the time of the last
614: .I msgsnd
615: operation,
616: .B msg_rtime
617: is the time of the last
618: .I msgrcv
619: operation, and
620: .B msg_ctime
621: is the time of the last
622: .IR msgctl (2)
623: operation that changed a member of the above structure.
624: .SS "Message Operation Permissions"
625: In the
626: .IR msgop "(2) and " msgctl (2)
627: system call descriptions, the permission required
628: for an operation is given as "{token}", where "token" is the type
629: of permission needed interpreted as follows:
630: .PP
631: .RS 0.75i
632: .PD 0
633: .TP 1.50i
634: 00400
635: Read by user
636: .TP
637: 00200
638: Write by user
639: .TP
640: 00060
641: Read, Write by group
642: .TP
643: 00006
644: Read, Write by others
645: .RE
646: .PD
647: .PP
648: Read and Write permissions on a msqid are
649: granted to a process if one or more of the following are true:
650: .IP
651: The effective user
652: .SM ID
653: of the process
654: is super-user.
655: .IP
656: The effective user
657: .SM ID
658: of the process
659: matches
660: .B msg_perm.[c]uid
661: in the data structure associated with
662: .I msqid
663: and the appropriate bit of the
664: ``user'' portion (0600) of
665: .B msg_perm.mode
666: is set.
667: .IP
668: The effective user
669: .SM ID
670: of the process
671: does not match
672: .B msg_perm.[c]uid
673: and the effective group
674: .SM ID
675: of the process
676: matches
677: .B msg_perm.[c]gid
678: and the appropriate bit of the ``group'' portion
679: (060) of
680: .B msg_perm.mode
681: is set.
682: .IP
683: The effective user
684: .SM ID
685: of the process
686: does not match
687: .B msg_perm.[c]uid
688: and the effective group
689: .SM ID
690: of the process
691: does not match
692: .B msg_perm.[c]gid
693: and the appropriate bit of the ``other'' portion (06) of
694: .B msg_perm.mode
695: is set.
696: .PP
697: Otherwise, the corresponding permissions are denied.
698: .SS "Semaphore Identifier"
699: A semaphore identifier (semid) is a unique positive integer created by a
700: .IR semget (2)
701: system call.
702: Each semid has a set of semaphores and a data structure associated with it.
703: The data structure is referred to as
704: .I semid_ds
705: and contains the following members:
706: .PP
707: .RS
708: .ta 8n 28n
709: .nf
710: struct ipc_perm sem_perm; /\(** operation permission struct \(**/
711: ushort sem_nsems; /\(** number of sems in set \(**/
712: time_t sem_otime; /\(** last operation time \(**/
713: time_t sem_ctime; /\(** last change time \(**/
714: /\(** Times measured in secs since \(**/
715: /\(** 00:00:00 \s-1GMT\s+1, Jan. 1, 1970 \(**/
716: .fi
717: .RE
718: .PP
719: .B Sem_perm
720: is an ipc_perm structure that
721: specifies the semaphore operation permission (see below).
722: This structure includes the following members:
723: .PP
724: .RS
725: .ta 8n 20n
726: .nf
727: ushort cuid; /\(** creator user id \(**/
728: ushort cgid; /\(** creator group id \(**/
729: ushort uid; /\(** user id \(**/
730: ushort gid; /\(** group id \(**/
731: ushort mode; /\(** r/a permission \(**/
732: .PP
733: .fi
734: .RE
735: The value of
736: .B sem_nsems
737: is equal to the number of semaphores in the set.
738: Each semaphore in the set is referenced by a positive integer
739: referred to as a
740: .IR sem_num .
741: Sem_num values run sequentially from 0 to the value of sem_nsems minus 1.
742: .B Sem_otime
743: is the time of the last
744: .IR semop (2)
745: operation, and
746: .B sem_ctime
747: is the time of the last
748: .IR semctl (2)
749: operation that changed a member of the above structure.
750: .PP
751: A semaphore is a data structure that contains the following members:
752: .PP
753: .RS
754: .ta 8n 20n
755: .nf
756: ushort semval; /\(** semaphore value \(**/
757: short sempid; /\(** pid of last operation \(**/
758: ushort semncnt; /\(** # awaiting semval > cval \(**/
759: ushort semzcnt; /\(** # awaiting semval = 0 \(**/
760: .fi
761: .RE
762: .PP
763: .B Semval
764: is a non-negative integer.
765: .B Sempid
766: is equal to the process
767: .SM ID
768: of the last process that performed a semaphore operation on this semaphore.
769: .B Semncnt
770: is a count of the number of processes that are currently suspended
771: awaiting this semaphore's semval to become greater than its current value.
772: .B Semzcnt
773: is a count of the number of processes that are currently suspended
774: awaiting this semaphore's semval to become zero.
775: .SS "Semaphore Operation Permissions"
776: In the
777: .IR semop "(2) and " semctl (2)
778: system call descriptions, the permission required
779: for an operation is given as "{token}", where "token" is the type
780: of permission needed interpreted as follows:
781: .PP
782: .RS 0.75i
783: .PD 0
784: .TP 1.50i
785: 00400
786: Read by user
787: .TP
788: 00200
789: Alter by user
790: .TP
791: 00060
792: Read, Alter by group
793: .TP
794: 00006
795: Read, Alter by others
796: .RE
797: .PD
798: .PP
799: Read and Alter permissions on a semid are
800: granted to a process if one or more of the following are true:
801: .IP
802: The effective user
803: .SM ID
804: of the process
805: is super-user.
806: .IP
807: The effective user
808: .SM ID
809: of the process
810: matches
811: .B sem_perm.[c]uid
812: in the data structure associated with
813: .I semid
814: and the appropriate bit of the
815: ``user'' portion (0600) of
816: .B sem_perm.mode
817: is set.
818: .IP
819: The effective user
820: .SM ID
821: of the process
822: does not match
823: .B sem_perm.[c]uid
824: and the effective group
825: .SM ID
826: of the process
827: matches
828: .B sem_perm.[c]gid
829: and the appropriate bit of the ``group'' portion
830: (060) of
831: .B sem_perm.mode
832: is set.
833: .IP
834: The effective user
835: .SM ID
836: of the process
837: does not match
838: .B sem_perm.[c]uid
839: and the effective group
840: .SM ID
841: of the process
842: does not match
843: .B sem_perm.[c]gid
844: and the appropriate bit of the ``other'' portion (06) of
845: .B sem_perm.mode
846: is set.
847: .PP
848: Otherwise, the corresponding permissions are denied.
849: .SS "Shared Memory Identifier"
850: A shared memory identifier (shmid) is a unique positive integer created by a
851: .IR shmget (2)
852: system call.
853: Each shmid has a segment of memory (referred to as a shared memory segment)
854: and a data structure associated with it.
855: The data structure is referred to as
856: .I shmid_ds
857: and contains the following members:
858: .PP
859: .RS
860: .ta 8n 28n
861: .nf
862: struct ipc_perm shm_perm; /\(** operation permission struct \(**/
863: int shm_segsz; /\(** size of segment \(**/
864: struct proc *shm_perm; /\(** address of linked proc \(**/
865: short shm_pidx; /\(** index of this segment \(**/
866: ushort shm_cpid; /\(** creator pid \(**/
867: ushort shm_lpid; /\(** pid of last operation \(**/
868: short shm_cnattch; /\(** number of loaded attaches \(**/
869: short shm_nattch; /\(** number of current attaches \(**/
870: time_t shm_atime; /\(** last attach time \(**/
871: time_t shm_dtime; /\(** last detach time \(**/
872: time_t shm_ctime; /\(** last change time \(**/
873: /\(** Times measured in secs since \(**/
874: /\(** 00:00:00 \s-1GMT\s+1, Jan. 1, 1970 \(**/
875: .fi
876: .RE
877: .PP
878: .B Shm_perm
879: is an ipc_perm structure that
880: specifies the shared memory operation permission (see below).
881: This structure includes the following members:
882: .PP
883: .RS
884: .ta 8n 20n
885: .nf
886: ushort cuid; /\(** creator user id \(**/
887: ushort cgid; /\(** creator group id \(**/
888: ushort uid; /\(** user id \(**/
889: ushort gid; /\(** group id \(**/
890: ushort mode; /\(** r/w permission \(**/
891: .PP
892: .fi
893: .RE
894: .B Shm_segsz
895: specifies the size of the shared memory segment.
896: .B Shm_proc
897: is the address of the first process linked to this segment.
898: .B Shm_pidx
899: is the index of this shared memory segment in the shared memory table belonging
900: to that process.
901: .B Shm_cpid
902: is the process id of the process that created the shared memory identifier.
903: .B Shm_lpid
904: is the process id of the last process that performed a
905: .IR shmop "(2) operation."
906: .B Shm_cnattch
907: is the number of in-core processes attached to this segment.
908: .B Shm_nattch
909: is the number of processes that currently have this segment attached.
910: .B Shm_atime
911: is the time of the last
912: .I shmat
913: operation,
914: .B shm_dtime
915: is the time of the last
916: .I shmdt
917: operation,
918: and
919: .B shm_ctime
920: is the time of the last
921: .IR shmctl (2)
922: operation that changed one of the members of the above structure.
923: .SS "Shared Memory Operation Permissions"
924: In the
925: .IR shmop "(2) and " shmctl (2)
926: system call descriptions, the permission required
927: for an operation is given as "{token}", where "token" is the type
928: of permission needed interpreted as follows:
929: .PP
930: .RS 0.75i
931: .PD 0
932: .TP 1.50i
933: 00400
934: Read by user
935: .TP
936: 00200
937: Write by user
938: .TP
939: 00060
940: Read, Write by group
941: .TP
942: 00006
943: Read, Write by others
944: .RE
945: .PD
946: .PP
947: Read and Write permissions on a shmid are
948: granted to a process if one or more of the following are true:
949: .IP
950: The effective user
951: .SM ID
952: of the process
953: is super-user.
954: .IP
955: The effective user
956: .SM ID
957: of the process
958: matches
959: .B shm_perm.[c]uid
960: in the data structure associated with
961: .I shmid
962: and the appropriate bit of the
963: ``user'' portion (0600) of
964: .B shm_perm.mode
965: is set.
966: .IP
967: The effective user
968: .SM ID
969: of the process
970: does not match
971: .B shm_perm.[c]uid
972: and the effective group
973: .SM ID
974: of the process
975: matches
976: .B shm_perm.[c]gid
977: and the appropriate bit of the ``group'' portion
978: (060) of
979: .B shm_perm.mode
980: is set.
981: .IP
982: The effective user
983: .SM ID
984: of the process
985: does not match
986: .B shm_perm.[c]uid
987: and the effective group
988: .SM ID
989: of the process
990: does not match
991: .B shm_perm.[c]gid
992: and the appropriate bit of the ``other'' portion (06) of
993: .B shm_perm.mode
994: is set.
995: .PP
996: Otherwise, the corresponding permissions are denied.
997: .SS "System Five Interfaces Library"
998: The following system calls constitute the system 5 interfaces library:
999: .PP
1000: .RS
1001: .IR msgctl ,
1002: .br
1003: .IR msgget ,
1004: .br
1005: .IR msgrcv ,
1006: .br
1007: .IR msgsnd ,
1008: .br
1009: .IR plock ,
1010: .br
1011: .IR semctl ,
1012: .br
1013: .IR semget ,
1014: .br
1015: .IR semop ,
1016: .br
1017: .IR shmat ,
1018: .br
1019: .IR shmctl ,
1020: .br
1021: .IR shmdt ,
1022: .br
1023: .IR shmget ,
1024: .br
1025: .IR ulimit ,
1026: .br
1027: .IR uname ,
1028: .br
1029: .IR ustat ,
1030: .RE
1031: .SH NOTES
1032: This manual page replaces the 4.2BSD manual page.
1033: .SH FILES
1034: .nf
1035: /usr/lib/libsys5.a System Five Interfaces Library
1036: .fi
1037: .SH SEE ALSO
1038: close(2),
1039: ioctl(2),
1040: open(2),
1041: pipe(2),
1042: read(2),
1043: write(2),
1044: intro(3).
1045: .\" @(#)intro.2 6.2 of 9/6/83
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