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