xref: /netbsd-src/lib/libc/sys/intro.2 (revision 2a399c6883d870daece976daec6ffa7bb7f934ce)
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34.\"     @(#)intro.2	8.3 (Berkeley) 12/11/93
35.\"
36.Dd December 11, 1993
37.Dt INTRO 2
38.Os BSD 4
39.Sh NAME
40.Nm intro ,
41.Nm errno
42.Nd introduction to system calls and error numbers
43.Sh SYNOPSIS
44.Fd #include <sys/errno.h>
45.Sh DESCRIPTION
46This section provides an overview of the system calls,
47their error returns, and other common definitions and concepts.
48.\".Pp
49.\".Sy System call restart
50.\".Pp
51.\"<more later...>
52.Sh DIAGNOSTICS
53Nearly all of the system calls provide an error number in the external
54variable
55.Va errno ,
56which is defined as:
57.Pp
58.Dl extern int errno
59.Pp
60When a system call detects an error,
61it returns an integer value
62indicating failure (usually -1)
63and sets the variable
64.Va errno
65accordingly.
66<This allows interpretation of the failure on receiving
67a -1 and to take action accordingly.>
68Successful calls never set
69.Va errno ;
70once set, it remains until another error occurs.
71It should only be examined after an error.
72Note that a number of system calls overload the meanings of these
73error numbers, and that the meanings must be interpreted according
74to the type and circumstances of the call.
75.Pp
76The following is a complete list of the errors and their
77names as given in
78.Aq Pa sys/errno.h .
79.Bl -hang -width Ds
80.It Er 0 Em "Error 0" .
81Not used.
82.It Er 1 EPERM Em "Operation not permitted" .
83An attempt was made to perform an operation limited to processes
84with appropriate privileges or to the owner of a file or other
85resources.
86.It Er 2 ENOENT Em "No such file or directory" .
87A component of a specified pathname did not exist, or the
88pathname was an empty string.
89.It Er 3 ESRCH Em "No such process" .
90No process could be found corresponding to that specified by the given
91process ID.
92.It Er 4 EINTR Em "Interrupted function call" .
93An asynchronous signal (such as
94.Dv SIGINT
95or
96.Dv SIGQUIT )
97was caught by the process during the execution of an interruptible
98function. If the signal handler performs a normal return, the
99interrupted function call will seem to have returned the error condition.
100.It Er 5 EIO Em "Input/output error" .
101Some physical input or output error occurred.
102This error will not be reported until a subsequent operation on the same file
103descriptor and may be lost (over written) by any subsequent errors.
104.It Er 6 ENXIO Em "\&No such device or address" .
105Input or output on a special file referred to a device that did not
106exist, or
107made a request beyond the limits of the device.
108This error may also occur when, for example,
109a tape drive is not online or no disk pack is
110loaded on a drive.
111.It Er 7 E2BIG Em "Arg list too long" .
112The number of bytes used for the argument and environment
113list of the new process exceeded the current limit
114of 20480 bytes
115.Pf ( Dv NCARGS
116in
117.Aq Pa sys/param.h ) .
118.It Er 8 ENOEXEC Em "Exec format error" .
119A request was made to execute a file
120that, although it has the appropriate permissions,
121was not in the format required for an
122executable file.
123.It Er 9 EBADF Em "Bad file descriptor" .
124A file descriptor argument was out of range, referred to no open file,
125or a read (write) request was made to a file that was only open for
126writing (reading).
127.It Er 10 ECHILD Em "\&No child processes" .
128A
129.Xr wait 2
130or
131.Xr waitpid 2
132function was executed by a process that had no existing or unwaited-for
133child processes.
134.It Er 11 EDEADLK Em "Resource deadlock avoided" .
135An attempt was made to lock a system resource that
136would have resulted in a deadlock situation.
137.It Er 12 ENOMEM Em "Cannot allocate memory" .
138The new process image required more memory than was allowed by the hardware
139or by system-imposed memory management constraints.
140A lack of swap space is normally temporary; however,
141a lack of core is not.
142Soft limits may be increased to their corresponding hard limits.
143.It Er 13 EACCES Em "Permission denied" .
144An attempt was made to access a file in a way forbidden
145by its file access permissions.
146.It Er 14 EFAULT Em "Bad address" .
147The system detected an invalid address in attempting to
148use an argument of a call.
149.It Er 15 ENOTBLK Em "Not a block device" .
150A block device operation was attempted on a non-block device or file.
151.It Er 16 EBUSY Em "Resource busy" .
152An attempt to use a system resource which was in use at the time
153in a manner which would have conflicted with the request.
154.It Er 17 EEXIST Em "File exists" .
155An existing file was mentioned in an inappropriate context,
156for instance, as the new link name in a
157.Xr link 2
158function.
159.It Er 18 EXDEV Em "Improper link" .
160A hard link to a file on another file system
161was attempted.
162.It Er 19 ENODEV Em "Operation not supported by device" .
163An attempt was made to apply an inappropriate
164function to a device,
165for example,
166trying to read a write-only device such as a printer.
167.It Er 20 ENOTDIR Em "Not a directory" .
168A component of the specified pathname existed, but it was
169not a directory, when a directory was expected.
170.It Er 21 EISDIR Em "Is a directory" .
171An attempt was made to open a directory with write mode specified.
172.It Er 22 EINVAL Em "Invalid argument" .
173Some invalid argument was supplied. (For example,
174specifying an undefined signal to a
175.Xr signal 3
176or
177.Xr kill 2
178function).
179.It Er 23 ENFILE Em "Too many open files in system" .
180Maximum number of file descriptors allowable on the system
181has been reached and a requests for an open cannot be satisfied
182until at least one has been closed.
183.It Er 24 EMFILE Em "Too many open files" .
184<As released, the limit on the number of
185open files per process is 64.>
186.Xr Getdtablesize 3
187will obtain the current limit.
188.It Er 25 ENOTTY Em "Inappropriate ioctl for device" .
189A control function (see
190.Xr ioctl 2 )
191was attempted for a file or
192special device for which the operation was inappropriate.
193.It Er 26 ETXTBSY Em "Text file busy" .
194The new process was a pure procedure (shared text) file
195which was open for writing by another process, or
196while the pure procedure file was being executed an
197.Xr open 2
198call requested write access.
199.It Er 27 EFBIG Em "File too large" .
200The size of a file exceeded the maximum (about
201.if t 2\u\s-231\s+2\d
202.if n 2.1E9
203bytes).
204.It Er 28 ENOSPC Em "Device out of space" .
205A
206.Xr write 2
207to an ordinary file, the creation of a
208directory or symbolic link, or the creation of a directory
209entry failed because no more disk blocks were available
210on the file system, or the allocation of an inode for a newly
211created file failed because no more inodes were available
212on the file system.
213.It Er 29 ESPIPE Em "Illegal seek" .
214An
215.Xr lseek 2
216function was issued on a socket, pipe or
217.Tn FIFO .
218.It Er 30 EROFS Em "Read-only file system" .
219An attempt was made to modify a file or directory
220was made
221on a file system that was read-only at the time.
222.It Er 31 EMLINK Em "Too many links" .
223Maximum allowable hard links to a single file has been exceeded (limit
224of 32767 hard links per file).
225.It Er 32 EPIPE Em "Broken pipe" .
226A write on a pipe, socket or
227.Tn FIFO
228for which there is no process
229to read the data.
230.It Er 33 EDOM Em "Numerical argument out of domain" .
231A numerical input argument was outside the defined domain of the mathematical
232function.
233.It Er 34 ERANGE Em "Numerical result out of range" .
234A numerical result of the function was too large to fit in the
235available space (perhaps exceeded precision).
236.It Er 35 EAGAIN Em "Resource temporarily unavailable" .
237This is a temporary condition and later calls to the
238same routine may complete normally.
239.It Er 36 EINPROGRESS Em "Operation now in progress" .
240An operation that takes a long time to complete (such as
241a
242.Xr connect 2 )
243was attempted on a non-blocking object (see
244.Xr fcntl 2 ) .
245.It Er 37 EALREADY Em "Operation already in progress" .
246An operation was attempted on a non-blocking object that already
247had an operation in progress.
248.It Er 38 ENOTSOCK Em "Socket operation on non-socket" .
249Self-explanatory.
250.It Er 39 EDESTADDRREQ Em "Destination address required" .
251A required address was omitted from an operation on a socket.
252.It Er 40 EMSGSIZE Em "Message too long" .
253A message sent on a socket was larger than the internal message buffer
254or some other network limit.
255.It Er 41 EPROTOTYPE Em "Protocol wrong type for socket" .
256A protocol was specified that does not support the semantics of the
257socket type requested. For example, you cannot use the
258.Tn ARPA
259Internet
260.Tn UDP
261protocol with type
262.Dv SOCK_STREAM .
263.It Er 42 ENOPROTOOPT Em "Protocol not available" .
264A bad option or level was specified in a
265.Xr getsockopt 2
266or
267.Xr setsockopt 2
268call.
269.It Er 43 EPROTONOSUPPORT Em "Protocol not supported" .
270The protocol has not been configured into the
271system or no implementation for it exists.
272.It Er 44 ESOCKTNOSUPPORT Em "Socket type not supported" .
273The support for the socket type has not been configured into the
274system or no implementation for it exists.
275.It Er 45 EOPNOTSUPP Em "Operation not supported" .
276The attempted operation is not supported for the type of object referenced.
277Usually this occurs when a file descriptor refers to a file or socket
278that cannot support this operation,
279for example, trying to
280.Em accept
281a connection on a datagram socket.
282.It Er 46 EPFNOSUPPORT Em "Protocol family not supported" .
283The protocol family has not been configured into the
284system or no implementation for it exists.
285.It Er 47 EAFNOSUPPORT Em "Address family not supported by protocol family" .
286An address incompatible with the requested protocol was used.
287For example, you shouldn't necessarily expect to be able to use
288.Tn NS
289addresses with
290.Tn ARPA
291Internet protocols.
292.It Er 48 EADDRINUSE Em "Address already in use" .
293Only one usage of each address is normally permitted.
294.It Er 49 EADDRNOTAVAIL Em "Cannot assign requested address" .
295Normally results from an attempt to create a socket with an
296address not on this machine.
297.It Er 50 ENETDOWN Em "Network is down" .
298A socket operation encountered a dead network.
299.It Er 51 ENETUNREACH Em "Network is unreachable" .
300A socket operation was attempted to an unreachable network.
301.It Er 52 ENETRESET Em "Network dropped connection on reset" .
302The host you were connected to crashed and rebooted.
303.It Er 53 ECONNABORTED Em "Software caused connection abort" .
304A connection abort was caused internal to your host machine.
305.It Er 54 ECONNRESET Em "Connection reset by peer" .
306A connection was forcibly closed by a peer.  This normally
307results from a loss of the connection on the remote socket
308due to a timeout or a reboot.
309.It Er 55 ENOBUFS Em "\&No buffer space available" .
310An operation on a socket or pipe was not performed because
311the system lacked sufficient buffer space or because a queue was full.
312.It Er 56 EISCONN Em "Socket is already connected" .
313A
314.Xr connect 2
315request was made on an already connected socket; or,
316a
317.Xr sendto 2
318or
319.Xr sendmsg 2
320request on a connected socket specified a destination
321when already connected.
322.It Er 57 ENOTCONN Em "Socket is not connected" .
323An request to send or receive data was disallowed because
324the socket was not connected and (when sending on a datagram socket)
325no address was supplied.
326.It Er 58 ESHUTDOWN Em "Cannot send after socket shutdown" .
327A request to send data was disallowed because the socket
328had already been shut down with a previous
329.Xr shutdown 2
330call.
331.It Er 60 ETIMEDOUT Em "Operation timed out" .
332A
333.Xr connect 2
334or
335.Xr send 2
336request failed because the connected party did not
337properly respond after a period of time.  (The timeout
338period is dependent on the communication protocol.)
339.It Er 61 ECONNREFUSED Em "Connection refused" .
340No connection could be made because the target machine actively
341refused it.  This usually results from trying to connect
342to a service that is inactive on the foreign host.
343.It Er 62 ELOOP Em "Too many levels of symbolic links" .
344A path name lookup involved more than 8 symbolic links.
345.It Er 63 ENAMETOOLONG Em "File name too long" .
346A component of a path name exceeded 255
347.Pq Dv MAXNAMELEN
348characters, or an entire
349path name exceeded 1023
350.Pq Dv MAXPATHLEN Ns -1
351characters.
352.It Er 64 EHOSTDOWN Em "Host is down" .
353A socket operation failed because the destination host was down.
354.It Er 65 EHOSTUNREACH Em "No route to host" .
355A socket operation was attempted to an unreachable host.
356.It Er 66 ENOTEMPTY Em "Directory not empty" .
357A directory with entries other than
358.Ql \&.
359and
360.Ql \&..
361was supplied to a remove directory or rename call.
362.It Er 67 EPROCLIM Em "Too many processes" .
363.It Er 68 EUSERS Em "Too many users" .
364The quota system ran out of table entries.
365.It Er 69 EDQUOT Em "Disc quota exceeded" .
366A
367.Xr write 2
368to an ordinary file, the creation of a
369directory or symbolic link, or the creation of a directory
370entry failed because the user's quota of disk blocks was
371exhausted, or the allocation of an inode for a newly
372created file failed because the user's quota of inodes
373was exhausted.
374.It Er 70 ESTALE Em "Stale NFS file handle" .
375An attempt was made to access an open file (on an
376.Tn NFS
377filesystem)
378which is now unavailable as referenced by the file descriptor.
379This may indicate the file was deleted on the
380.Tn NFS
381server or some
382other catastrophic event occurred.
383.It Er 72 EBADRPC Em "RPC struct is bad" .
384Exchange of
385.Tn RPC
386information was unsuccessful.
387.It Er 73 ERPCMISMATCH Em "RPC version wrong" .
388The version of
389.Tn RPC
390on the remote peer is not compatible with
391the local version.
392.It Er 74 EPROGUNAVAIL Em "RPC prog. not avail" .
393The requested program is not registered on the remote host.
394.It Er 75 EPROGMISMATCH Em "Program version wrong" .
395The requested version of the program is not available
396on the remote host
397.Pq Tn RPC .
398.It Er 76 EPROCUNAVAIL Em "Bad procedure for program" .
399An
400.Tn RPC
401call was attempted for a procedure which doesn't exist
402in the remote program.
403.It Er 77 ENOLCK Em "No locks available" .
404A system-imposed limit on the number of simultaneous file
405locks was reached.
406.It Er 78 ENOSYS Em "Function not implemented" .
407Attempted a system call that is not available on this
408system.
409.Sh DEFINITIONS
410.Bl -tag -width Ds
411.It  Process ID .
412Each active process in the system is uniquely identified by a non-negative
413integer called a process ID.  The range of this ID is from 0 to 30000.
414.It  Parent process ID
415A new process is created by a currently active process; (see
416.Xr fork 2 ) .
417The parent process ID of a process is initially the process ID of its creator.
418If the creating process exits,
419the parent process ID of each child is set to the ID of a system process,
420.Xr init 8 .
421.It  Process Group
422Each active process is a member of a process group that is identified by
423a non-negative integer called the process group ID.  This is the process
424ID of the group leader.  This grouping permits the signaling of related
425processes (see
426.Xr termios 4 )
427and the job control mechanisms of
428.Xr csh 1 .
429.It Session
430A session is a set of one or more process groups.
431A session is created by a successful call to
432.Xr setsid 2 ,
433which causes the caller to become the only member of the only process
434group in the new session.
435.It Session leader
436A process that has created a new session by a successful call to
437.Xr setsid 2 ,
438is known as a session leader.
439Only a session leader may acquire a terminal as its controlling terminal (see
440.Xr termios 4 ) .
441.It Controlling process
442A session leader with a controlling terminal is a controlling process.
443.It Controlling terminal
444A terminal that is associated with a session is known as the controlling
445terminal for that session and its members.
446.It  "Terminal Process Group ID"
447A terminal may be acquired by a session leader as its controlling terminal.
448Once a terminal is associated with a session, any of the process groups
449within the session may be placed into the foreground by setting
450the terminal process group ID to the ID of the process group.
451This facility is used
452to arbitrate between multiple jobs contending for the same terminal;
453(see
454.Xr csh 1
455and
456.Xr tty 4 ) .
457.It  "Orphaned Process Group"
458A process group is considered to be
459.Em orphaned
460if it is not under the control of a job control shell.
461More precisely, a process group is orphaned
462when none of its members has a parent process that is in the same session
463as the group,
464but is in a different process group.
465Note that when a process exits, the parent process for its children
466is changed to be
467.Xr init 8 ,
468which is in a separate session.
469Not all members of an orphaned process group are necessarily orphaned
470processes (those whose creating process has exited).
471The process group of a session leader is orphaned by definition.
472.It "Real User ID and Real Group ID"
473Each user on the system is identified by a positive integer
474termed the real user ID.
475.Pp
476Each user is also a member of one or more groups.
477One of these groups is distinguished from others and
478used in implementing accounting facilities.  The positive
479integer corresponding to this distinguished group is termed
480the real group ID.
481.Pp
482All processes have a real user ID and real group ID.
483These are initialized from the equivalent attributes
484of the process that created it.
485.It "Effective User Id, Effective Group Id, and Group Access List"
486Access to system resources is governed by two values:
487the effective user ID, and the group access list.
488The first member of the group access list is also known as the
489effective group ID.
490(In POSIX.1, the group access list is known as the set of supplementary
491group IDs, and it is unspecified whether the effective group ID is
492a member of the list.)
493.Pp
494The effective user ID and effective group ID are initially the
495process's real user ID and real group ID respectively.  Either
496may be modified through execution of a set-user-ID or set-group-ID
497file (possibly by one its ancestors) (see
498.Xr execve 2 ) .
499By convention, the effective group ID (the first member of the group access
500list) is duplicated, so that the execution of a set-group-ID program
501does not result in the loss of the original (real) group ID.
502.Pp
503The group access list is a set of group IDs
504used only in determining resource accessibility.  Access checks
505are performed as described below in ``File Access Permissions''.
506.It  "Saved Set User ID and Saved Set Group ID"
507When a process executes a new file, the effective user ID is set
508to the owner of the file if the file is set-user-ID, and the effective
509group ID (first element of the group access list) is set to the group
510of the file if the file is set-group-ID.
511The effective user ID of the process is then recorded as the saved set-user-ID,
512and the effective group ID of the process is recorded as the saved set-group-ID.
513These values may be used to regain those values as the effective user
514or group ID after reverting to the real ID (see
515.Xr setuid 2 ) .
516(In POSIX.1, the saved set-user-ID and saved set-group-ID are optional,
517and are used in setuid and setgid, but this does not work as desired
518for the super-user.)
519.It  Super-user
520A process is recognized as a
521.Em super-user
522process and is granted special privileges if its effective user ID is 0.
523.It  Special Processes
524The processes with process IDs of 0, 1, and 2 are special.
525Process 0 is the scheduler.  Process 1 is the initialization process
526.Xr init 8 ,
527and is the ancestor of every other process in the system.
528It is used to control the process structure.
529Process 2 is the paging daemon.
530.It  Descriptor
531An integer assigned by the system when a file is referenced
532by
533.Xr open 2
534or
535.Xr dup 2 ,
536or when a socket is created by
537.Xr pipe 2 ,
538.Xr socket 2 ,
539or
540.Xr socketpair 2 ,
541which uniquely identifies an access path to that file or socket from
542a given process or any of its children.
543.It  File Name
544Names consisting of up to 255
545.Pq Dv MAXNAMELEN
546characters may be used to name
547an ordinary file, special file, or directory.
548.Pp
549These characters may be selected from the set of all
550.Tn ASCII
551character
552excluding 0 (NUL) and the
553.Tn ASCII
554code for
555.Ql \&/
556(slash).  (The parity bit,
557bit 7, must be 0.)
558.Pp
559Note that it is generally unwise to use
560.Ql \&* ,
561.Ql \&? ,
562.Ql \&[
563or
564.Ql \&]
565as part of
566file names because of the special meaning attached to these characters
567by the shell.
568.It  Path Name
569A path name is a
570.Tn NUL Ns -terminated
571character string starting with an
572optional slash
573.Ql \&/ ,
574followed by zero or more directory names separated
575by slashes, optionally followed by a file name.
576The total length of a path name must be less than 1024
577.Pq Dv MAXPATHLEN
578characters.
579.Pp
580If a path name begins with a slash, the path search begins at the
581.Em root
582directory.
583Otherwise, the search begins from the current working directory.
584A slash by itself names the root directory.  An empty
585pathname refers to the current directory.
586.It  Directory
587A directory is a special type of file that contains entries
588that are references to other files.
589Directory entries are called links.  By convention, a directory
590contains at least two links,
591.Ql \&.
592and
593.Ql \&.. ,
594referred to as
595.Em dot
596and
597.Em dot-dot
598respectively.  Dot refers to the directory itself and
599dot-dot refers to its parent directory.
600.It "Root Directory and Current Working Directory"
601Each process has associated with it a concept of a root directory
602and a current working directory for the purpose of resolving path
603name searches.  A process's root directory need not be the root
604directory of the root file system.
605.It  File Access Permissions
606Every file in the file system has a set of access permissions.
607These permissions are used in determining whether a process
608may perform a requested operation on the file (such as opening
609a file for writing).  Access permissions are established at the
610time a file is created.  They may be changed at some later time
611through the
612.Xr chmod 2
613call.
614.Pp
615File access is broken down according to whether a file may be: read,
616written, or executed.  Directory files use the execute
617permission to control if the directory may be searched.
618.Pp
619File access permissions are interpreted by the system as
620they apply to three different classes of users: the owner
621of the file, those users in the file's group, anyone else.
622Every file has an independent set of access permissions for
623each of these classes.  When an access check is made, the system
624decides if permission should be granted by checking the access
625information applicable to the caller.
626.Pp
627Read, write, and execute/search permissions on
628a file are granted to a process if:
629.Pp
630The process's effective user ID is that of the super-user. (Note:
631even the super-user cannot execute a non-executable file.)
632.Pp
633The process's effective user ID matches the user ID of the owner
634of the file and the owner permissions allow the access.
635.Pp
636The process's effective user ID does not match the user ID of the
637owner of the file, and either the process's effective
638group ID matches the group ID
639of the file, or the group ID of the file is in
640the process's group access list,
641and the group permissions allow the access.
642.Pp
643Neither the effective user ID nor effective group ID
644and group access list of the process
645match the corresponding user ID and group ID of the file,
646but the permissions for ``other users'' allow access.
647.Pp
648Otherwise, permission is denied.
649.It  Sockets and Address Families
650.Pp
651A socket is an endpoint for communication between processes.
652Each socket has queues for sending and receiving data.
653.Pp
654Sockets are typed according to their communications properties.
655These properties include whether messages sent and received
656at a socket require the name of the partner, whether communication
657is reliable, the format used in naming message recipients, etc.
658.Pp
659Each instance of the system supports some
660collection of socket types; consult
661.Xr socket 2
662for more information about the types available and
663their properties.
664.Pp
665Each instance of the system supports some number of sets of
666communications protocols.  Each protocol set supports addresses
667of a certain format.  An Address Family is the set of addresses
668for a specific group of protocols.  Each socket has an address
669chosen from the address family in which the socket was created.
670.Sh SEE ALSO
671.Xr intro 3 ,
672.Xr perror 3
673.Sh HISTORY
674An
675.Nm intro
676manual page appeared in
677.At v6 .
678