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33 .Nd introduction to system calls and error numbers
39 This section provides an overview of the system calls,
40 their error returns, and other common definitions and concepts.
42 .\".Sy System call restart
46 Nearly all of the system calls provide an error number referenced via
47 the external identifier errno.
48 This identifier is defined in
52 .Dl extern int * __error();
53 .Dl #define errno (* __error())
57 function returns a pointer to a field in the thread specific structure for
58 threads other than the initial thread.
59 For the initial thread and
60 non-threaded processes,
62 returns a pointer to a global
64 variable that is compatible with the previous definition.
66 When a system call detects an error,
67 it returns an integer value
68 indicating failure (usually -1)
72 (This allows interpretation of the failure on receiving
73 a -1 and to take action accordingly.)
74 Successful calls never set
76 once set, it remains until another error occurs.
77 It should only be examined after an error.
78 Note that a number of system calls overload the meanings of these
79 error numbers, and that the meanings must be interpreted according
80 to the type and circumstances of the call.
82 The following is a complete list of the errors and their
86 .It Er 0 Em "Undefined error: 0" .
88 .It Er 1 EPERM Em "Operation not permitted" .
89 An attempt was made to perform an operation limited to processes
90 with appropriate privileges or to the owner of a file or other
92 .It Er 2 ENOENT Em "No such file or directory" .
93 A component of a specified pathname did not exist, or the
94 pathname was an empty string.
95 .It Er 3 ESRCH Em "No such process" .
96 No process could be found corresponding to that specified by the given
98 .It Er 4 EINTR Em "Interrupted system call" .
99 An asynchronous signal (such as
103 was caught by the process during the execution of an interruptible
105 If the signal handler performs a normal return, the
106 interrupted system call will seem to have returned the error condition.
107 .It Er 5 EIO Em "Input/output error" .
108 Some physical input or output error occurred.
109 This error will not be reported until a subsequent operation on the same file
110 descriptor and may be lost (over written) by any subsequent errors.
111 .It Er 6 ENXIO Em "Device not configured" .
112 Input or output on a special file referred to a device that did not
114 made a request beyond the limits of the device.
115 This error may also occur when, for example,
116 a tape drive is not online or no disk pack is
118 .It Er 7 E2BIG Em "Argument list too long" .
119 The number of bytes used for the argument and environment
120 list of the new process exceeded the current limit
124 .It Er 8 ENOEXEC Em "Exec format error" .
125 A request was made to execute a file
126 that, although it has the appropriate permissions,
127 was not in the format required for an
129 .It Er 9 EBADF Em "Bad file descriptor" .
130 A file descriptor argument was out of range, referred to no open file,
131 or a read (write) request was made to a file that was only open for
133 .It Er 10 ECHILD Em "\&No child processes" .
138 function was executed by a process that had no existing or unwaited-for
140 .It Er 11 EDEADLK Em "Resource deadlock avoided" .
141 An attempt was made to lock a system resource that
142 would have resulted in a deadlock situation.
143 .It Er 12 ENOMEM Em "Cannot allocate memory" .
144 The new process image required more memory than was allowed by the hardware
145 or by system-imposed memory management constraints.
146 A lack of swap space is normally temporary; however,
147 a lack of core is not.
148 Soft limits may be increased to their corresponding hard limits.
149 .It Er 13 EACCES Em "Permission denied" .
150 An attempt was made to access a file in a way forbidden
151 by its file access permissions.
152 .It Er 14 EFAULT Em "Bad address" .
153 The system detected an invalid address in attempting to
154 use an argument of a call.
155 .It Er 15 ENOTBLK Em "Block device required" .
156 A block device operation was attempted on a non-block device or file.
157 .It Er 16 EBUSY Em "Device busy" .
158 An attempt to use a system resource which was in use at the time
159 in a manner which would have conflicted with the request.
160 .It Er 17 EEXIST Em "File exists" .
161 An existing file was mentioned in an inappropriate context,
162 for instance, as the new link name in a
165 .It Er 18 EXDEV Em "Cross-device link" .
166 A hard link to a file on another file system
168 .It Er 19 ENODEV Em "Operation not supported by device" .
169 An attempt was made to apply an inappropriate
170 function to a device,
172 trying to read a write-only device such as a printer.
173 .It Er 20 ENOTDIR Em "Not a directory" .
174 A component of the specified pathname existed, but it was
175 not a directory, when a directory was expected.
176 .It Er 21 EISDIR Em "Is a directory" .
177 An attempt was made to open a directory with write mode specified.
178 .It Er 22 EINVAL Em "Invalid argument" .
179 Some invalid argument was supplied.
181 specifying an undefined signal to a
187 .It Er 23 ENFILE Em "Too many open files in system" .
188 Maximum number of open files allowable on the system
189 has been reached and requests for an open cannot be satisfied
190 until at least one has been closed.
191 .It Er 24 EMFILE Em "Too many open files" .
192 Maximum number of file descriptors allowable in the process
193 has been reached and requests for an open cannot be satisfied
194 until at least one has been closed.
197 system call will obtain the current limit.
198 .It Er 25 ENOTTY Em "Inappropriate ioctl for device" .
199 A control function (see
201 was attempted for a file or
202 special device for which the operation was inappropriate.
203 .It Er 26 ETXTBSY Em "Text file busy" .
204 The new process was a pure procedure (shared text) file
205 which was open for writing by another process, or
206 while the pure procedure file was being executed an
208 call requested write access.
209 .It Er 27 EFBIG Em "File too large" .
210 The size of a file exceeded the maximum.
211 .It Er 28 ENOSPC Em "No space left on device" .
214 to an ordinary file, the creation of a
215 directory or symbolic link, or the creation of a directory
216 entry failed because no more disk blocks were available
217 on the file system, or the allocation of an inode for a newly
218 created file failed because no more inodes were available
220 .It Er 29 ESPIPE Em "Illegal seek" .
223 system call was issued on a socket, pipe or
225 .It Er 30 EROFS Em "Read-only file system" .
226 An attempt was made to modify a file or directory
227 on a file system that was read-only at the time.
228 .It Er 31 EMLINK Em "Too many links" .
229 Maximum allowable hard links to a single file has been exceeded (limit
230 of 32767 hard links per file).
231 .It Er 32 EPIPE Em "Broken pipe" .
232 A write on a pipe, socket or
234 for which there is no process
236 .It Er 33 EDOM Em "Numerical argument out of domain" .
237 A numerical input argument was outside the defined domain of the mathematical
239 .It Er 34 ERANGE Em "Result too large" .
240 A numerical result of the function was too large to fit in the
241 available space (perhaps exceeded precision).
242 .It Er 35 EAGAIN Em "Resource temporarily unavailable" .
243 This is a temporary condition and later calls to the
244 same routine may complete normally.
245 .It Er 36 EINPROGRESS Em "Operation now in progress" .
246 An operation that takes a long time to complete (such as
249 was attempted on a non-blocking object (see
251 .It Er 37 EALREADY Em "Operation already in progress" .
252 An operation was attempted on a non-blocking object that already
253 had an operation in progress.
254 .It Er 38 ENOTSOCK Em "Socket operation on non-socket" .
256 .It Er 39 EDESTADDRREQ Em "Destination address required" .
257 A required address was omitted from an operation on a socket.
258 .It Er 40 EMSGSIZE Em "Message too long" .
259 A message sent on a socket was larger than the internal message buffer
260 or some other network limit.
261 .It Er 41 EPROTOTYPE Em "Protocol wrong type for socket" .
262 A protocol was specified that does not support the semantics of the
263 socket type requested.
264 For example, you cannot use the
270 .It Er 42 ENOPROTOOPT Em "Protocol not available" .
271 A bad option or level was specified in a
276 .It Er 43 EPROTONOSUPPORT Em "Protocol not supported" .
277 The protocol has not been configured into the
278 system or no implementation for it exists.
279 .It Er 44 ESOCKTNOSUPPORT Em "Socket type not supported" .
280 The support for the socket type has not been configured into the
281 system or no implementation for it exists.
282 .It Er 45 EOPNOTSUPP Em "Operation not supported" .
283 The attempted operation is not supported for the type of object referenced.
284 Usually this occurs when a file descriptor refers to a file or socket
285 that cannot support this operation,
286 for example, trying to
288 a connection on a datagram socket.
289 .It Er 46 EPFNOSUPPORT Em "Protocol family not supported" .
290 The protocol family has not been configured into the
291 system or no implementation for it exists.
292 .It Er 47 EAFNOSUPPORT Em "Address family not supported by protocol family" .
293 An address incompatible with the requested protocol was used.
294 For example, you should not necessarily expect to be able to use
299 .It Er 48 EADDRINUSE Em "Address already in use" .
300 Only one usage of each address is normally permitted.
301 .It Er 49 EADDRNOTAVAIL Em "Can't assign requested address" .
302 Normally results from an attempt to create a socket with an
303 address not on this machine.
304 .It Er 50 ENETDOWN Em "Network is down" .
305 A socket operation encountered a dead network.
306 .It Er 51 ENETUNREACH Em "Network is unreachable" .
307 A socket operation was attempted to an unreachable network.
308 .It Er 52 ENETRESET Em "Network dropped connection on reset" .
309 The host you were connected to crashed and rebooted.
310 .It Er 53 ECONNABORTED Em "Software caused connection abort" .
311 A connection abort was caused internal to your host machine.
312 .It Er 54 ECONNRESET Em "Connection reset by peer" .
313 A connection was forcibly closed by a peer.
315 results from a loss of the connection on the remote socket
316 due to a timeout or a reboot.
317 .It Er 55 ENOBUFS Em "\&No buffer space available" .
318 An operation on a socket or pipe was not performed because
319 the system lacked sufficient buffer space or because a queue was full.
320 .It Er 56 EISCONN Em "Socket is already connected" .
323 request was made on an already connected socket; or,
328 request on a connected socket specified a destination
329 when already connected.
330 .It Er 57 ENOTCONN Em "Socket is not connected" .
331 An request to send or receive data was disallowed because
332 the socket was not connected and (when sending on a datagram socket)
333 no address was supplied.
334 .It Er 58 ESHUTDOWN Em "Can't send after socket shutdown" .
335 A request to send data was disallowed because the socket
336 had already been shut down with a previous
339 .It Er 60 ETIMEDOUT Em "Operation timed out" .
344 request failed because the connected party did not
345 properly respond after a period of time.
347 period is dependent on the communication protocol.)
348 .It Er 61 ECONNREFUSED Em "Connection refused" .
349 No connection could be made because the target machine actively
351 This usually results from trying to connect
352 to a service that is inactive on the foreign host.
353 .It Er 62 ELOOP Em "Too many levels of symbolic links" .
354 A path name lookup involved more than 32
357 .It Er 63 ENAMETOOLONG Em "File name too long" .
358 A component of a path name exceeded
360 characters, or an entire
364 (See also the description of
368 .It Er 64 EHOSTDOWN Em "Host is down" .
369 A socket operation failed because the destination host was down.
370 .It Er 65 EHOSTUNREACH Em "No route to host" .
371 A socket operation was attempted to an unreachable host.
372 .It Er 66 ENOTEMPTY Em "Directory not empty" .
373 A directory with entries other than
377 was supplied to a remove directory or rename call.
378 .It Er 67 EPROCLIM Em "Too many processes" .
379 .It Er 68 EUSERS Em "Too many users" .
380 The quota system ran out of table entries.
381 .It Er 69 EDQUOT Em "Disc quota exceeded" .
384 to an ordinary file, the creation of a
385 directory or symbolic link, or the creation of a directory
386 entry failed because the user's quota of disk blocks was
387 exhausted, or the allocation of an inode for a newly
388 created file failed because the user's quota of inodes
390 .It Er 70 ESTALE Em "Stale NFS file handle" .
391 An attempt was made to access an open file (on an
394 which is now unavailable as referenced by the file descriptor.
395 This may indicate the file was deleted on the
398 other catastrophic event occurred.
399 .It Er 72 EBADRPC Em "RPC struct is bad" .
402 information was unsuccessful.
403 .It Er 73 ERPCMISMATCH Em "RPC version wrong" .
406 on the remote peer is not compatible with
408 .It Er 74 EPROGUNAVAIL Em "RPC prog. not avail" .
409 The requested program is not registered on the remote host.
410 .It Er 75 EPROGMISMATCH Em "Program version wrong" .
411 The requested version of the program is not available
414 .It Er 76 EPROCUNAVAIL Em "Bad procedure for program" .
417 call was attempted for a procedure which does not exist
418 in the remote program.
419 .It Er 77 ENOLCK Em "No locks available" .
420 A system-imposed limit on the number of simultaneous file
422 .It Er 78 ENOSYS Em "Function not implemented" .
423 Attempted a system call that is not available on this
425 .It Er 79 EFTYPE Em "Inappropriate file type or format" .
426 The file was the wrong type for the operation, or a data file had
428 .It Er 80 EAUTH Em "Authentication error" .
429 Attempted to use an invalid authentication ticket to mount a
432 .It Er 81 ENEEDAUTH Em "Need authenticator" .
433 An authentication ticket must be obtained before the given
435 file system may be mounted.
436 .It Er 82 EIDRM Em "Identifier removed" .
437 An IPC identifier was removed while the current process was waiting on it.
438 .It Er 83 ENOMSG Em "No message of desired type" .
439 An IPC message queue does not contain a message of the desired type, or a
440 message catalog does not contain the requested message.
441 .It Er 84 EOVERFLOW Em "Value too large to be stored in data type" .
442 A numerical result of the function was too large to be stored in the caller
444 .It Er 85 ECANCELED Em "Operation canceled" .
445 The scheduled operation was canceled.
446 .It Er 86 EILSEQ Em "Illegal byte sequence" .
447 While decoding a multibyte character the function came along an
448 invalid or an incomplete sequence of bytes or the given wide
449 character is invalid.
450 .It Er 87 ENOATTR Em "Attribute not found" .
451 The specified extended attribute does not exist.
452 .It Er 88 EDOOFUS Em "Programming error" .
453 A function or API is being abused in a way which could only be detected
455 .It Er 89 EBADMSG Em "Bad message" .
456 A corrupted message was detected.
457 .It Er 90 EMULTIHOP Em "Multihop attempted" .
458 This error code is unused, but present for compatibility with other systems.
459 .It Er 91 ENOLINK Em "Link has been severed" .
460 This error code is unused, but present for compatibility with other systems.
461 .It Er 92 EPROTO Em "Protocol error" .
462 A device or socket encountered an unrecoverable protocol error.
463 .It Er 93 ENOTCAPABLE Em "Capabilities insufficient" .
464 An operation on a capability file descriptor requires greater privilege than
465 the capability allows.
466 .It Er 94 ECAPMODE Em "Not permitted in capability mode" .
467 The system call or operation is not permitted for capability mode processes.
468 .It Er 95 ENOTRECOVERABLE Em "State not recoverable" .
469 The state protected by a robust mutex is not recoverable.
470 .It Er 96 EOWNERDEAD Em "Previous owner died" .
471 The owner of a robust mutex terminated while holding the mutex lock.
472 .It Er 97 EINTEGRITY Em "Integrity check failed" .
473 An integrity check such as a check-hash or a cross-correlation failed.
474 The integrity error falls in the kernel I/O stack between
476 that identifies errors in parameters to a system call and
478 that identifies errors with the underlying storage media.
479 It is typically raised by intermediate kernel layers such as a
480 filesystem or an in-kernel GEOM subsystem when they detect inconsistencies.
481 Uses include allowing the
483 command to return a different exit value to automate the running of
485 during a system boot.
490 Each active process in the system is uniquely identified by a non-negative
491 integer called a process ID.
492 The range of this ID is from 0 to 99999.
493 .It Parent process ID
494 A new process is created by a currently active process (see
496 The parent process ID of a process is initially the process ID of its creator.
497 If the creating process exits,
498 the parent process ID of each child is set to the ID of the calling process's
504 Each active process is a member of a process group that is identified by
505 a non-negative integer called the process group ID.
507 ID of the group leader.
508 This grouping permits the signaling of related
511 and the job control mechanisms of
514 A session is a set of one or more process groups.
515 A session is created by a successful call to
517 which causes the caller to become the only member of the only process
518 group in the new session.
520 A process that has created a new session by a successful call to
522 is known as a session leader.
523 Only a session leader may acquire a terminal as its controlling terminal (see
525 .It Controlling process
526 A session leader with a controlling terminal is a controlling process.
527 .It Controlling terminal
528 A terminal that is associated with a session is known as the controlling
529 terminal for that session and its members.
530 .It "Terminal Process Group ID"
531 A terminal may be acquired by a session leader as its controlling terminal.
532 Once a terminal is associated with a session, any of the process groups
533 within the session may be placed into the foreground by setting
534 the terminal process group ID to the ID of the process group.
535 This facility is used
536 to arbitrate between multiple jobs contending for the same terminal;
541 .It "Orphaned Process Group"
542 A process group is considered to be
544 if it is not under the control of a job control shell.
545 More precisely, a process group is orphaned
546 when none of its members has a parent process that is in the same session
548 but is in a different process group.
549 Note that when a process exits, the parent process for its children
550 is normally changed to be
552 which is in a separate session.
553 Not all members of an orphaned process group are necessarily orphaned
554 processes (those whose creating process has exited).
555 The process group of a session leader is orphaned by definition.
556 .It "Real User ID and Real Group ID"
557 Each user on the system is identified by a positive integer
558 termed the real user ID.
560 Each user is also a member of one or more groups.
561 One of these groups is distinguished from others and
562 used in implementing accounting facilities.
564 integer corresponding to this distinguished group is termed
567 All processes have a real user ID and real group ID.
568 These are initialized from the equivalent attributes
569 of the process that created it.
570 .It "Effective User Id, Effective Group Id, and Group Access List"
571 Access to system resources is governed by two values:
572 the effective user ID, and the group access list.
573 The first member of the group access list is also known as the
575 (In POSIX.1, the group access list is known as the set of supplementary
576 group IDs, and it is unspecified whether the effective group ID is
577 a member of the list.)
579 The effective user ID and effective group ID are initially the
580 process's real user ID and real group ID respectively.
582 may be modified through execution of a set-user-ID or set-group-ID
583 file (possibly by one its ancestors) (see
585 By convention, the effective group ID (the first member of the group access
586 list) is duplicated, so that the execution of a set-group-ID program
587 does not result in the loss of the original (real) group ID.
589 The group access list is a set of group IDs
590 used only in determining resource accessibility.
592 are performed as described below in ``File Access Permissions''.
593 .It "Saved Set User ID and Saved Set Group ID"
594 When a process executes a new file, the effective user ID is set
595 to the owner of the file if the file is set-user-ID, and the effective
596 group ID (first element of the group access list) is set to the group
597 of the file if the file is set-group-ID.
598 The effective user ID of the process is then recorded as the saved set-user-ID,
599 and the effective group ID of the process is recorded as the saved set-group-ID.
600 These values may be used to regain those values as the effective user
601 or group ID after reverting to the real ID (see
603 (In POSIX.1, the saved set-user-ID and saved set-group-ID are optional,
604 and are used in setuid and setgid, but this does not work as desired
607 A process is recognized as a
609 process and is granted special privileges if its effective user ID is 0.
611 An integer assigned by the system when a file is referenced
616 or when a socket is created by
621 which uniquely identifies an access path to that file or socket from
622 a given process or any of its children.
624 Names consisting of up to
626 characters may be used to name
627 an ordinary file, special file, or directory.
629 These characters may be arbitrary eight-bit values,
639 Note that it is generally unwise to use
646 file names because of the special meaning attached to these characters
650 .Dv NUL Ns -terminated
651 character string starting with an
654 followed by zero or more directory names separated
655 by slashes, optionally followed by a file name.
656 The total length of a path name must be less than
659 (On some systems, this limit may be infinite.)
661 If a path name begins with a slash, the path search begins at the
664 Otherwise, the search begins from the current working directory.
665 A slash by itself names the root directory.
667 pathname refers to the current directory.
669 A directory is a special type of file that contains entries
670 that are references to other files.
671 Directory entries are called links.
672 By convention, a directory
673 contains at least two links,
682 Dot refers to the directory itself and
683 dot-dot refers to its parent directory.
684 .It "Root Directory and Current Working Directory"
685 Each process has associated with it a concept of a root directory
686 and a current working directory for the purpose of resolving path
688 A process's root directory need not be the root
689 directory of the root file system.
690 .It File Access Permissions
691 Every file in the file system has a set of access permissions.
692 These permissions are used in determining whether a process
693 may perform a requested operation on the file (such as opening
695 Access permissions are established at the
696 time a file is created.
697 They may be changed at some later time
702 File access is broken down according to whether a file may be: read,
703 written, or executed.
704 Directory files use the execute
705 permission to control if the directory may be searched.
707 File access permissions are interpreted by the system as
708 they apply to three different classes of users: the owner
709 of the file, those users in the file's group, anyone else.
710 Every file has an independent set of access permissions for
711 each of these classes.
712 When an access check is made, the system
713 decides if permission should be granted by checking the access
714 information applicable to the caller.
716 Read, write, and execute/search permissions on
717 a file are granted to a process if:
719 The process's effective user ID is that of the super-user.
721 even the super-user cannot execute a non-executable file.)
723 The process's effective user ID matches the user ID of the owner
724 of the file and the owner permissions allow the access.
726 The process's effective user ID does not match the user ID of the
727 owner of the file, and either the process's effective
728 group ID matches the group ID
729 of the file, or the group ID of the file is in
730 the process's group access list,
731 and the group permissions allow the access.
733 Neither the effective user ID nor effective group ID
734 and group access list of the process
735 match the corresponding user ID and group ID of the file,
736 but the permissions for ``other users'' allow access.
738 Otherwise, permission is denied.
739 .It Sockets and Address Families
740 A socket is an endpoint for communication between processes.
741 Each socket has queues for sending and receiving data.
743 Sockets are typed according to their communications properties.
744 These properties include whether messages sent and received
745 at a socket require the name of the partner, whether communication
746 is reliable, the format used in naming message recipients, etc.
748 Each instance of the system supports some
749 collection of socket types; consult
751 for more information about the types available and
754 Each instance of the system supports some number of sets of
755 communications protocols.
756 Each protocol set supports addresses
758 An Address Family is the set of addresses
759 for a specific group of protocols.
760 Each socket has an address
761 chosen from the address family in which the socket was created.