INTRO(2)
NAME
intro − introduction to system calls and error numbers
USAGE
#include <errno.h>
DESCRIPTION
This section describes all of the system calls. This page describes the errors that these calls may return. Most of these calls have one or more error returns. An error condition is indicated by an otherwise impossible return value (usually −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 <errno.h>.
Kernel Errors
0 unused
1 EPERM Not owner
Typically this error indicates an attempt to modify a file in some way that is forbidden to anyone but the file’s owner or the super-user. It also may indicate an attempt by an ordinary user to do something permitted only to the super-user.
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 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. Occasionally, this error occurs 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 attempts to read/write beyond the limits of the device. It may also occur when, for example, an illegal tape drive unit number is selected.
7 E2BIG Arg list too long
An argument list longer than 10240 bytes is presented to execve.
8 ENOEXEC Exec format error
A request is made to execute a file which, although it has the appropriate permissions, is not of the correct type.
9 EBADF Bad file number
A file descriptor refers to no open file, or a read (write) request is made to a file which is open only for writing (reading).
10 ECHILD No children
A wait was executed by a process with no living or unwaited-for children.
11 EAGAIN No more processes
A fork was attempted when the system’s process table was full.
12 ENOMEM Not enough memory
During an exec, break, or sbrk, a program asks for more memory than the system is able to supply.
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 system encountered a hardware fault in attempting to access the arguments of a system call.
15 ENOTBLK Block device required
A non-block file was mentioned where a block device was required.
16 EBUSY Device busy
An attempt was made to acquire a device that is already acquired or an release a device on which there is an active file directory.
17 EEXIST File exists
An existing file was mentioned in an inappropriate context, e.g. link.
18 EXDEV Cross-device link
An attempt was made to create a hard link to a file on another device.
19 ENODEV No such device
An attempt was made to apply an inappropriate system call to a device; e.g. read a write-only device.
20 ENOTDIR Not a directory
Something that is not a 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 was made to 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 seek 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. No more opens can succeed unless a currently-open file is first closed.
24 EMFILE Too many open files
A process is limited to 20 open file descriptors.
25 ENOTTY Not a character device
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 was made to execute a shell script that is currently open for writing, or to write to a shell script that is being executed.
27 EFBIG File too large
The size of a file exceeded the maximum file size set by ulimit(2).
28 ENOSPC No space left on device
A write was attempted to an ordinary file when there was no free space left on the device.
29 ESPIPE Illegal seek
An lseek was issued to a pipe.
30 EROFS Read-only file system
An attempt was made to modify a file or directory resident on a device mounted read-only.
31 EMLINK Too many links
An attempt was made to establish more than 1000 links to a file.
32 EPIPE Broken pipe
A write was attempted on a pipe for which there is no process to read the data. This condition normally generates a SIGPIPE signal. This error is returned only if that if the signal is ignored.
Math Library Errors
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.
Interprocess Communication Errors
35 EWOULDBLOCK Operation would block
An operation that 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 that 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 which already had an operation in progress.
38 ENOTSOCK Socket operation on non-socket
A socket operation was attempted on something that is not a socket.
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 protocol with type SOCK_STREAM.
42 ENOPROTOOPT Bad protocol option
A bad option was specified in a getsockopt(2) or setsockopt(2) call.
43 EPROTONOSUPPORT Protocol not supported
The requested protocol is not supported on the system.
44 ESOCKTNOSUPPORT Socket type not supported
The support for the socket type has not been configured into the system or no implementation for it exists.
45 EOPNOTSUPP Operation not supported on socket
An operation was attempted on a socket type that does not support it (e.g., trying to accept a connection on a datagram socket.)
46 EPFNOSUPPORT Protocol family not supported
The protocol family has not been configured into the system or no implementation for it exists.
47 EAFNOSUPPORT Address family not supported by protocol family
Th specified address was incompatible with the requested protocol. 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 attempted to reach a socket on 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 by 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
An operation on a socket or pipe failed because the system lacked sufficient buffer space.
56 EISCONN Socket is already connected
A connect was requested to a socket that is already connected, or a sendto or sendmsg request on a connected socket specified a destination other than the connected party.
57 ENOTCONN Socket is not connected
An request to send or receive data failed because the specified socket is not connected.
58 ESHUTDOWN Can’t send after socket shutdown
A request to send data failed because the socket had already been shut down (see shutdown(2)).
59 unused
60 ETIMEDOUT Connection timed out
A connect request failed because the connected party did not properly respond after a period of time. (The timeout period is dependent on the communication protocol.)
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.
75 EHOSTUNREACH Host is unreachable
An attempt was made to reach an unreachable host.
76 ENOTEMPTY Directory not empty
An attempt was made to remove a directory that had more entries than “.” and “..”.
DEFINITIONS
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 the process ID of the group leader. This grouping permits the signalling of related processes (see killpg(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), and tty(4).
User ID and Group ID
Each user on the system is identified by a positive integer termed the user ID.
Each user is also a member of one or more groups. One of these groups is distinguished from others and used in implementing accounting facilities. The positive integer corresponding to this distinguished group is termed the real group ID.
All processes have a user ID and group ID. These are initialized from the equivalent attributes of the process which created it.
Effective User Id, Effective Group Id, and Access Groups
Access to system resources is governed by three values: the effective user ID, the effective group ID, and the group access list.
The effective user ID and effective group ID are initially the process’s real user ID and real group ID respectively. Either may be modified through execution of a set-user-ID or set-group-ID file (possibly by one its ancestors); see execve(2).
The group access list is an additional set of group ID’s used only in determining resource accessibility. Access checks are performed as described below in “File Access Permissions”.
Super-user
A process is recognized as a uper-user process and is granted special privileges if its user ID is 0.
Special Processes
The processes with process ID’s 1-11 are special. Process 1 is normally Display Manager (DM) on DOMAIN nodes and the Server Process Manager (SPM) on DOMAIN Server Processors. It is the ancestor of every other process in the system. It is used to control the process structure. Other special processes include the Null Process (usually process 2), the Clock, the Page Purifier, and the network service processes.
Descriptor
This is an integer assigned by the system when a file is referenced by open(2), dup(2), or pipe(2) or a socket is referenced by socket(2) or socketpair(2) which uniquely identifies an access path to that file or socket from a given process or any of its children.
Filename
Names consisting of up to 32 characters may be used to name an ordinary file, special file, or directory.
These characters may be selected from the set of all ASCII character excluding 0 (null) and the ASCII code for / (slash).
Note that it is generally unwise to use *, ?, [ or ] in filenames. These characters have special meaning to the shell.
Pathname
A pathname is a null-terminated character string that includes 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 node’s entry (root) directory. If a path name begins with a double slash, the path search begins at the network root, a list of all nodes on the network. Otherwise, the search begins from the current working directory. A slash by itself names the node’s entry directory. A null pathname refers to the current directory.
Directory
A directory is a special type of file which contains entries that are references to other files. 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.
File Access Permissions
Every file in the file system has a set of access permissions. These permissions are used in determining whether a process may perform a requested operation on the file (such as opening a file for writing). Access permissions are established at the time a file is created. They may be changed at some later time through the chmod(2) call.
File access is broken down according to whether a file may be: read, written, or executed. Directory files use the execute permission to control if the directory may be searched.
File access permissions are interpreted by the system as they apply to three different classes of users: the owner of the file, those users in the file’s group, anyone else. Every file has an independent set of access permissions for each of these classes. When an access check is made, the system decides if permission should be granted by checking the access information applicable to the caller.
Read, write, and execute/search permissions on a file are granted to a process if:
The process’s effective user ID is that of the super-user.
The process’s effective user ID matches the user ID of the owner of the file and the owner permissions allow the access.
The process’s effective user ID does not match the user ID of the owner of the file, and either the process’s effective group ID matches the group ID of the file, or the group ID of the file is in the process’s group access list, and the group permissions allow the access.
Neither the effective user ID nor effective group ID and group access list of the process match the corresponding user ID and group ID of the file, but the permissions for “other users” allow access.
Otherwise, permission is denied.
Sockets and Address Families
A socket is an endpoint for communication between processes. Each socket has queues for sending and receiving data.
Sockets are typed according to their communications properties. These properties include whether messages sent and received at a socket require the name of the partner, whether communication is reliable, the format used in naming message recipients, etc.
Each instance of the system supports some collection of socket types; consult socket(2) for more information about the types available and their properties.
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.