INTRO(2) — System Interface Manual — System Calls
NAME
intro − introduction to system calls and error numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
This section describes all of the system calls. Most of these calls have one or more error returns. An error condition is indicated by an otherwise impossible return value. This is almost always −1; the individual descriptions specify the details.
As with normal arguments, all return codes and values from functions are of type integer unless otherwise noted. An error number is also made available in the external variable errno, which is not cleared on successful calls. Thus errno should be tested only after an error has occurred.
The following is a complete list of the errors and their names as given in <error.h>.
0 Error 0
Unused.
1 EPERM Not owner
Typically this error indicates an attempt to modify a file in some way forbidden except to its owner or super-user. It is also returned for attempts by ordinary users to do things allowed only to the super-user. It also means that a pathname contained a byte with the high-order bit set and the request made against the file was something other than an attempt to delete the file.
2 ENOENT No such file or directory
This error occurs when a file name is specified and the file should exist but doesn’t, or when one of the directories in a path name does not exist.
3 ESRCH No such process
The process whose number was given to kill and ptrace does not exist, or is already dead.
4 EINTR Interrupted system call
An asynchronous signal (such as interrupt or quit), which the user has elected to catch, occurred during a system call. If execution is resumed after processing the signal, it will appear as if the interrupted system call returned this error condition.
5 EIO I/O error
Some physical I/O error occurred during a read or write. This error may in some cases occur on a call following the one to which it actually applies.
6 ENXIO No such device or address
I/O on a special file refers to a subdevice which does not exist, or beyond the limits of the device. It may also occur when, for example, an illegal tape drive unit number is selected or a disk pack is not loaded on a drive.
7 E2BIG Arg list too long
An argument list longer than 10240 bytes is presented to exec.
8 ENOEXEC Exec format error
A request is made to execute a file which, although it has the appropriate permissions, does not start with a valid magic number, see a.out(5).
9 EBADF Bad file number
Either a file descriptor refers to no open file, or a read (resp. write) request is made to a file which is open only for writing (resp. reading).
10 ECHILD No children
Wait and the process has no living or unwaited-for children.
11 EAGAIN No more processes
In a fork, the system’s process table is full or the user is not allowed to create any more processes.
12 ENOMEM Not enough core
During an exec or break, a program asks for more core or swap space than the system is able to supply. A lack of swap space is normally a temporary condition, however a lack of core is not a temporary condition; the maximum size of the text, data, and stack segments is a system parameter.
13 EACCES Permission denied
An attempt was made to access a file in a way forbidden by the protection system.
14 EFAULT Bad address
The arguments or results of a system call were at an invalid or protected address.
15 ENOTBLK Block device required
A plain file was mentioned where a block device was required, for example, in mount.
16 EBUSY Mount device busy
An attempt to mount a device that was already mounted or an attempt was made to dismount a device on which there is an active file directory (open file, current directory, mounted-on file, active text segment).
17 EEXIST File exists
An existing file was mentioned in an inappropriate context, for example, link.
18 EXDEV Cross-device link
A link between file systems was attempted.
19 ENODEV No such device
An attempt was made to apply an inappropriate system call to a device; for example, read a write-only device.
20 ENOTDIR Not a directory
A non-directory was specified where a directory is required, for example in a path name or as an argument to chdir.
21 EISDIR Is a directory
An attempt to write on a directory.
22 EINVAL Invalid argument
Some invalid argument: dismounting a non-mounted device, mentioning an unknown signal in signal, reading or writing a file for which lseek has generated a negative pointer. Also set by math functions, see intro(3).
23 ENFILE File table overflow
The system’s table of open files is full, and temporarily no more opens can be accepted.
24 EMFILE Too many open files
Customary configuration limit is 20 per process.
25 ENOTTY Not a typewriter
The file mentioned in an ioctl is not a terminal or one of the other devices to which these calls apply.
26 ETXTBSY Text file busy
An attempt to execute a pure-procedure program which is currently open for writing (or reading!). Also an attempt to open for writing a pure-procedure program that is being executed.
27 EFBIG File too large
The size of a file exceeded the maximum (about 109 bytes).
28 ENOSPC No space left on device
During a write to an ordinary file, there is no free space left on the device.
29 ESPIPE Illegal seek
An lseek was issued to a pipe. This error may also be issued for other non-seekable devices.
30 EROFS Read-only file system
An attempt to modify a file or directory was made on a device mounted read-only.
31 EMLINK Too many links
An attempt to make more than 32767 hard links to a file.
32 EPIPE Broken pipe
A write on a pipe or socket for which there is no process to read the data. This condition normally generates a signal; the error is returned if the signal is ignored.
33 EDOM Math argument
The argument of a function in the math package (3M) is out of the domain of the function.
34 ERANGE Result too large
The value of a function in the math package (3M) is unrepresentable within machine precision.
35 EWOULDBLOCK Operation would block
An operation which would cause a process to block was attempted on a object in non-blocking mode (see ioctl (2)).
36 EINPROGRESS Operation now in progress
An operation which takes a long time to complete (such as a connect (2)) was attempted on a non-blocking object (see ioctl (2)).
37 EALREADY Operation already in progress
An operation was attempted on a non-blocking object while there is another operation in progress. For example, attempting a connect while a connect was already in progress.
38 ENOTSOCK Socket operation on non-socket
Self-explanatory.
39 EDESTADDRREQ Destination address required
A required address was omitted from an operation on a socket.
40 EMSGSIZE Message too long
A message sent on a socket was larger than the internal message buffer.
41 EPROTOTYPE Protocol wrong type for socket
A protocol was specified which does not support the semantics of the socket type requested. For example you cannot use the ARPA Internet UDP datagram protocol with type SOCK_STREAM.
42 ENOPROTOOPT Protocol not available
In this incarnation of the system.
43 EPROTONOSUPPORT Protocol not supported
In this incarnation of the system.
44 ESOCKTNOSUPPORT Socket type not supported
In this incarnation of the system.
45 EOPNOTSUPP Operation not supported on socket
For example, trying to accept a connection on a datagram socket.
46 EPFNOSUPPORT Protocol family not supported
In this incarnation of the system.
47 EAFNOSUPPORT Address family not supported by protocol family
An address incompatible with the requested protocol was used. For example, you shouldn’t necessarily expect to be able to use PUP Internet addresses with ARPA Internet protocols.
48 EADDRINUSE Address already in use
Only one usage of each address is normally permitted.
49 EADDRNOTAVAIL Can’t assign requested address
Normally results from an attempt to create a socket with an address not on this machine.
50 ENETDOWN Network is down
A socket operation encountered a dead network.
51 ENETUNREACH Network is unreachable
A socket operation was attempted to an unreachable network.
52 ENETRESET Network dropped connection on reset
The host you were connected to crashed and rebooted.
53 ECONNABORTED Software caused connection abort
A connection abort was caused internal to your host machine.
54 ECONNRESET Connection reset by peer
A connection was forcibly closed by a peer. This normally results from the peer executing a shutdown (2) call.
55 ENOBUFS No buffer space available
For a socket or a pipe in the buffer pool.
56 EISCONN Socket is already connected
57 ENOTCONN Socket is not connected
58 ESHUTDOWN Can’t send after socket shutdown
59 unused
60 ETIMEDOUT Connection timed out
Due to failure to initiate properly or because keep-alives failed.
61 ECONNREFUSED Connection refused
No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service which is inactive on the foreign host.
62 ELOOP Too many levels of symbolic links
A path name lookup involved more than 8 symbolic links.
63 ENAMETOOLONG File name too long
A component of a path name exceeded 255 characters, or an entire path name exceeded 1023 characters.
64 ENOTEMPTY Directory not empty
A directory with entries other than . and .. was supplied to a remove directory or rename call.
DEFINITIONS
The notation {something} means ‘the value of something’ defined by a symbolic constant in a specific header file. This notation comes from the UniForum (formerly /usr/group) standard. In general, the synopsis on a given manual page names the header files which must be included for a given function.
Process ID
Each active process in the system is uniquely identified by a positive integer called a process ID. The range of this ID is from 0 to {PROC_MAX}.
Parent process ID
A new process is created by a currently active process; see fork(2). The parent process ID of a process is the process ID of its creator.
Process Group ID
Each active process is a member of a process group that is identified by a positive integer called the process group ID. This is is the process ID of the group leader. This grouping permits the signalling of related processes (see kill(2)) and the job control mechanisms of csh(1).
Tty Group ID
Each active process can be a member of a terminal group that is identified by a positive integer called the tty group ID. This grouping is used to arbitrate between multiple jobs contending for the same terminal; see csh(1), jobs(3) and tty(4).
Real User ID, Real Group ID, and Access Groups
Each user allowed on the system is identified by a positive integer called a real user ID.
Each user is also a member of a group. The group is identified by a positive integer called the real group ID and is used to implement accounting.
Each user is also the member of a number of access groups. The access groups allow the user additional access to files.
An active process has a real user ID and real group ID and an access group set. These are initialized from the equivalent attributes of the process which created it.
Effective User Id and Effective Group Id
An active process has an effective user ID and an effective group ID that are used to determine file access permissions (see below). The effective user ID and effective group ID are equal to the process’s real user ID and real group ID respectively, unless the process or one of its ancestors evolved from a file that had the set-user-ID flag or set-group ID flag set; see exec(2).
Super-user
A process is recognized as a super-user process and is granted special privileges if its effective user ID is 0.
Special Processes
The processes with a process ID’s of 0, 1, and 2 are special. Proc0 is the scheduler. Proc1 is the initialization process init, and is the ancestor of every other process in the system. It is used to control the process structure. Proc2 is the paging daemon.
Descriptor
An integer assigned by the system when a file is referenced by open(2), creat(2), dup(2), fcntl(2), or pipe(2) or a socket is referenced by socket(2) or socketpair(2) which uniquely identifies an access path into that file or socket from a given process or any of its children.
File Name
Names consisting of up to {NAME_MAX} characters may be used to name an ordinary file, special file, or directory. These characters may be selected from the set of all seven-bit ASCII characters excluding 0 (null) and the ASCII code for / (slash). ASCII characters with the high-order bit set are invalid characters for filenames.
Note that it is generally unwise to use ∗, ?, [ or ] as part of file names because of the special meaning attached to these characters by the shell.
Path Name
A path name is a null-terminated character string starting with an optional slash (/), followed by zero or more directory names separated by slashes, optionally followed by a file name. The total length of a path name must be less than {PATHNAME_MAX} characters.
If a path name begins with a slash, the path search begins at the root directory. Otherwise, the search begins from the current working directory. A slash by itself names the root directory. A null pathname refers to the current directory.
Directory
Directory entries are called links. By convention, a directory contains at least two links, . and .., referred to as dot and dot-dot respectively. Dot refers to the directory itself and dot-dot refers to its parent directory.
Root Directory and Current Working Directory
Each process has associated with it a concept of a root directory and a current working directory for the purpose of resolving path name searches. A process’s root directory need not be the root directory of the root file system.
File Access Permissions
Read, write, and execute/search permissions on a file are granted to a process if:
The process’s effective user ID is super-user.
The process’s effective user ID matches the user ID of the owner of the file and the appropriate access bit of the owner portion of the file mode is set.
The process’s effective user ID does not match the user ID of the owner of the file, and either the process’s group ID matches the group of the file, or the group of the file is the process’s access group set, and the appropriate access bit of the group portion of the file name is set.
The process is neither the same user ID as the file nor is it the same group as the file, but the appropriate access bit of the other bit of the file mode is set.
Otherwise, the corresponding permissions are denied.
Sockets and Address Families
An endpoint for messages or stream communications. Each socket has queues for sending and receiving data.
Each instance of the system supports some number of sets of communications protocols. Each protocol set supports addresses of a certain format. An Address Family is the set of addresses for a specific group of protocols. Each socket has an address chosen from the address family in which the socket was created.
SEE ALSO
Sun System Release 0.3 — 25 April 1983