The error code macros are defined in the header file errno.h. All of them expand into integer constant values. Some of these error codes can't occur on GNU systems, but they can occur using the GNU C Library on other systems.
Operation not permitted; only the owner of the file (or other resource) or processes with special privileges can perform the operation.
No such file or directory. This is a “file doesn't exist” error for ordinary files that are referenced in contexts where they are expected to already exist.
Interrupted function call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.
You can choose to have functions resume after a signal that is handled, rather than failing with
EINTR; see Interrupted Primitives.
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.
Argument list too long; used when the arguments passed to a new program being executed with one of the
execfunctions (see Executing a File) occupy too much memory space. This condition never arises on GNU/Hurd systems.
Invalid executable file format. This condition is detected by the
execfunctions; see Executing a File.
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.
No memory available. The system cannot allocate more virtual memory because its capacity is full.
Bad address; an invalid pointer was detected. On GNU/Hurd systems, this error never happens; you get a signal instead.
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.
File exists; an existing file was specified in a context where it only makes sense to specify a new file.
The wrong type of device was given to a function that expects a particular sort of device.
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.
In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the
RLIMIT_NOFILElimit or make it unlimited; see Limits on Resources.
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs on GNU/Hurd systems.
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for “text file busy”.) This is not an error on GNU/Hurd systems; the text is copied as necessary.
No space left on device; write operation on a file failed because the disk is full.
Too many links; the link count of a single file would become too large.
renamecan cause this error if the file being renamed already has as many links as it can take (see Renaming Files).
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a
SIGPIPEsignal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see
EPIPEunless it has handled or blocked
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.
Resource temporarily unavailable; the call might work if you try again later. The macro
EWOULDBLOCKis another name for
EAGAIN; they are always the same in the GNU C Library.
This error can happen in a few different situations:
- An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use
selectto find out when the operation will be possible; see Waiting for I/O.
Portability Note: In many older Unix systems, this condition was indicated by
EWOULDBLOCK, which was a distinct error code different from
EAGAIN. To make your program portable, you should check for both codes and treat them the same.
- A temporary resource shortage made an operation impossible.
forkcan return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.
In the GNU C Library, this is another name for
EAGAIN(above). The values are always the same, on every operating system.
C libraries in many older Unix systems have
EWOULDBLOCKas a separate error code.
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as
connect; see Connecting) never return
EAGAIN. Instead, they return
EINPROGRESSto indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return
EALREADY. You can use the
selectfunction to find out when the pending operation has completed; see Waiting for I/O.
An operation is already in progress on an object that has non-blocking mode selected.
The size of a message sent on a socket was larger than the supported maximum size.
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. On GNU/Hurd systems, this error can happen for many calls when the object does not support the particular operation; it is a generic indication that the server knows nothing to do for that call.
The address family specified for a socket is not supported; it is inconsistent with the protocol being used on the socket. See Sockets.
The requested socket address is already in use. See Socket Addresses.
The requested socket address is not available; for example, you tried to give a socket a name that doesn't match the local host name. See Socket Addresses.
A socket operation failed because the subnet containing the remote host was unreachable.
A network connection was closed for reasons outside the control of the local host, such as by the remote machine rebooting or an unrecoverable protocol violation.
The kernel's buffers for I/O operations are all in use. In GNU, this error is always synonymous with
ENOMEM; you may get one or the other from network operations.
You tried to connect a socket that is already connected. See Connecting.
The socket is not connected to anything. You get this error when you try to transmit data over a socket, without first specifying a destination for the data. For a connectionless socket (for datagram protocols, such as UDP), you get
No default destination address was set for the socket. You get this error when you try to transmit data over a connectionless socket, without first specifying a destination for the data with
A socket operation with a specified timeout received no response during the timeout period.
A remote host refused to allow the network connection (typically because it is not running the requested service).
Too many levels of symbolic links were encountered in looking up a file name. This often indicates a cycle of symbolic links.
Directory not empty, where an empty directory was expected. Typically, this error occurs when you are trying to delete a directory.
This means that the per-user limit on new process would be exceeded by an attempted
fork. See Limits on Resources, for details on the
Stale file handle. This indicates an internal confusion in the file system which is due to file system rearrangements on the server host for NFS file systems or corruption in other file systems. Repairing this condition usually requires unmounting, possibly repairing and remounting the file system.
An attempt was made to NFS-mount a remote file system with a file name that already specifies an NFS-mounted file. (This is an error on some operating systems, but we expect it to work properly on GNU/Hurd systems, making this error code impossible.)
No locks available. This is used by the file locking facilities; see File Locks. This error is never generated by GNU/Hurd systems, but it can result from an operation to an NFS server running another operating system.
Inappropriate file type or format. The file was the wrong type for the operation, or a data file had the wrong format.
On some systems
chmodreturns this error if you try to set the sticky bit on a non-directory file; see Setting Permissions.
Function not implemented. This indicates that the function called is not implemented at all, either in the C library itself or in the operating system. When you get this error, you can be sure that this particular function will always fail with
ENOSYSunless you install a new version of the C library or the operating system.
Not supported. A function returns this error when certain parameter values are valid, but the functionality they request is not available. This can mean that the function does not implement a particular command or option value or flag bit at all. For functions that operate on some object given in a parameter, such as a file descriptor or a port, it might instead mean that only that specific object (file descriptor, port, etc.) is unable to support the other parameters given; different file descriptors might support different ranges of parameter values.
If the entire function is not available at all in the implementation, it returns
While decoding a multibyte character the function came along an invalid or an incomplete sequence of bytes or the given wide character is invalid.
On GNU/Hurd systems, servers supporting the
termprotocol return this error for certain operations when the caller is not in the foreground process group of the terminal. Users do not usually see this error because functions such as
writetranslate it into a
SIGTTOUsignal. See Job Control, for information on process groups and these signals.
On GNU/Hurd systems, opening a file returns this error when the file is translated by a program and the translator program dies while starting up, before it has connected to the file.
Operation canceled; an asynchronous operation was canceled before it completed. See Asynchronous I/O. When you call
aio_cancel, the normal result is for the operations affected to complete with this error; see Cancel AIO Operations.
The following error codes are defined by the Linux/i386 kernel. They are not yet documented.