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Error Codes

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 the GNU system, but they can occur using the GNU library on other systems.

Macro: int EPERM

Operation not permitted; only the owner of the file (or other resource) or processes with special privileges can perform the operation.

Macro: int ENOENT

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.

Macro: int ESRCH

No process matches the specified process ID.

Macro: int EINTR

Interrupted function call; an asynchronous signal occured 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 section Primitives Interrupted by Signals.

Macro: int EIO

Input/output error; usually used for physical read or write errors.

Macro: int ENXIO

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.

Macro: int E2BIG

Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see section Executing a File) occupy too much memory space. This condition never arises in the GNU system.

Macro: int ENOEXEC

Invalid executable file format. This condition is detected by the exec functions; see section Executing a File.

Macro: int EBADF

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).

Macro: int ECHILD

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.

Macro: int EDEADLK

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 section File Locks, for an example.

Macro: int ENOMEM

No memory available. The system cannot allocate more virtual memory because its capacity is full.

Macro: int EACCES

Permission denied; the file permissions do not allow the attempted operation.

Macro: int EFAULT

Bad address; an invalid pointer was detected.

Macro: int ENOTBLK

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.

Macro: int EBUSY

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.

Macro: int EEXIST

File exists; an existing file was specified in a context where it only makes sense to specify a new file.

Macro: int EXDEV

An attempt to make an improper link across file systems was detected. This happens not only when you use link (see section Hard Links) but also when you rename a file with rename (see section Renaming Files).

Macro: int ENODEV

The wrong type of device was given to a function that expects a particular sort of device.

Macro: int ENOTDIR

A file that isn't a directory was specified when a directory is required.

Macro: int EISDIR

File is a directory; attempting to open a directory for writing gives this error.

Macro: int EINVAL

Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

Macro: int EMFILE

The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

Macro: int ENFILE

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 section Linked Channels. This error never occurs in the GNU system.

Macro: int ENOTTY

Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

Macro: int ETXTBSY

An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

Macro: int EFBIG

File too big; the size of a file would be larger than allowed by the system.

Macro: int ENOSPC

No space left on device; write operation on a file failed because the disk is full.

Macro: int ESPIPE

Invalid seek operation (such as on a pipe).

Macro: int EROFS

An attempt was made to modify something on a read-only file system.

Macro: int EMLINK

Too many links; the link count of a single file is too large. rename can cause this error if the file being renamed already has as many links as it can take (see section Renaming Files).

Macro: int EPIPE

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 SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

Macro: int EDOM

Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

Macro: int ERANGE

Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

Macro: int EAGAIN

Resource temporarily unavailable; the call might work if you try again later. Only fork returns error code EAGAIN for such a reason.


An operation that would block was attempted on an object that has non-blocking mode selected.

Portability Note: In 4.4BSD and GNU, EWOULDBLOCK and EAGAIN are the same. Earlier versions of BSD (see section Berkeley Unix) have two distinct codes, and use EWOULDBLOCK to indicate an I/O operation that would block on an object with non-blocking mode set, and EAGAIN for other kinds of errors.


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 section Making a Connection) never return EWOULDBLOCK. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY.

Macro: int EALREADY

An operation is already in progress on an object that has non-blocking mode selected.

Macro: int ENOTSOCK

A file that isn't a socket was specified when a socket is required.


No destination address was supplied on a socket operation that needed one.

Macro: int EMSGSIZE

The size of a message sent on a socket was larger than the supported maximum size.


The socket type does not support the requested communications protocol.


You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See section Socket Options.


The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid.) See section Creating a Socket.


The socket type is not supported.


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.


The socket communications protocol family you requested is not supported.


The address family specified for a socket is not supported; it is inconsistent with the protocol being used on the socket. See section Sockets.


The requested socket address is already in use. See section 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 section Socket Addresses.

Macro: int ENETDOWN

A socket operation failed because the network was down.


A socket operation failed because the subnet containing the remost host was unreachable.

Macro: int ENETRESET

A network connection was reset because the remote host crashed.


A network connection was aborted locally.


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.

Macro: int ENOBUFS

The kernel's buffers for I/O operations are all in use.

Macro: int EISCONN

You tried to connect a socket that is already connected. See section Making a Connection.

Macro: int ENOTCONN

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.

Macro: int ESHUTDOWN

The socket has already been shut down.

Macro: int ETIMEDOUT

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).

Macro: int ELOOP

Too many levels of symbolic links were encountered in looking up a file name. This often indicates a cycle of symbolic links.


Filename too long (longer than PATH_MAX; see section Limits on File System Capacity) or host name too long (in gethostname or sethostname; see section Host Identification).

Macro: int EHOSTDOWN

The remote host for a requested network connection is down.


The remote host for a requested network connection is not reachable.

Macro: int ENOTEMPTY

Directory not empty, where an empty directory was expected. Typically, this error occurs when you are trying to delete a directory.

Macro: int EUSERS

The file quota system is confused because there are too many users.

Macro: int EDQUOT

The user's disk quota was exceeded.

Macro: int ESTALE

Stale NFS file handle. This indicates an internal confusion in the NFS system which is due to file system rearrangements on the server host. Repairing this condition usually requires unmounting and remounting the NFS file system on the local host.

Macro: int EREMOTE

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 the GNU system, making this error code impossible.)

Macro: int ENOLCK

No locks available. This is used by the file locking facilities; see section File Locks. This error never occurs in the GNU system.

Macro: int ENOSYS

Function not implemented. Some functions have commands or options defined that might not be supported in all implementations, and this is the kind of error you get if you request them and they are not supported.


In the GNU system, servers supporting the term protocol 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 read and write translate it into a SIGTTIN or SIGTTOU signal. See section Job Control, for information on process groups and these signals.

Macro: int ED

The experienced user will know what is wrong.

Macro: int EGREGIOUS

You did what?

Macro: int EIEIO

Go home and have a glass of warm, dairy-fresh milk.


This error code has no purpose.

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