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.
“No such process.” No process matches the specified process ID.
“Interrupted system 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.
“Input/output error.” Usually used for physical read or write errors.
“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
exec functions (see Executing a File) occupy too much memory space. This condition never arises on
“Exec format error.”
Invalid executable file format. This condition is detected by the
exec functions; 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).
“No child processes.” This error happens on operations that are supposed to manipulate child processes, when there aren’t any processes to manipulate.
“Resource 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.
“Cannot allocate memory.” The system cannot allocate more virtual memory because its capacity is full.
“Permission denied.” The file permissions do not allow the attempted operation.
“Bad address.” An invalid pointer was detected. On GNU/Hurd systems, this error never happens; you get a signal instead.
“Block device required.” 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.
“Device or 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.
“Invalid cross-device link.”
An attempt to make an improper link across file systems was detected.
This happens not only when you use
link (see Hard Links) but
also when you rename a file with
rename (see Renaming Files).
“No such device.” The wrong type of device was given to a function that expects a particular sort of device.
“Not a directory.” A file that isn’t a directory was specified when a directory is required.
“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.
“Too many open files.” 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_NOFILE limit or make it unlimited;
see Limits on Resources.
“Too many open files in system.” 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 ioctl for device.” Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.
“Text file busy.” 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.
“File too large.” The size of a file would be larger than allowed by the system.
“No space left on device.” Write operation on a file failed because the disk is full.
“Illegal seek.” Invalid seek operation (such as on a pipe).
“Read-only file system.” An attempt was made to modify something on a read-only file system.
“Too many links.”
The link count of a single file would become too large.
rename can cause this error if the file being renamed already has
as many links as it can take (see Renaming Files).
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
unless it has handled or blocked
“Numerical argument out of domain.” Used by mathematical functions when an argument value does not fall into the domain over which the function is defined.
“Numerical result out of range.” 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
EWOULDBLOCK is another name for
they are always the same in the GNU C Library.
This error can happen in a few different situations:
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
EAGAIN. To make your program portable, you should
check for both codes and treat them the same.
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.
“Operation would block.”
In the GNU C Library, this is another name for
The values are always the same, on every operating system.
C libraries in many older Unix systems have
EWOULDBLOCK as a
separate error code.
“Operation now in progress.”
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
EINPROGRESS to indicate that
the operation has begun and will take some time. Attempts to manipulate
the object before the call completes return
EALREADY. You can
select function to find out when the pending operation
has completed; see Waiting for I/O.
“Operation already in progress.” An operation is already in progress on an object that has non-blocking mode selected.
“Socket operation on non-socket.” A file that isn’t a socket was specified when a socket is required.
“Message too long.” The size of a message sent on a socket was larger than the supported maximum size.
“Protocol wrong type for socket.” The socket type does not support the requested communications protocol.
“Protocol not available.” You specified a socket option that doesn’t make sense for the particular protocol being used by the socket. See Socket Options.
“Protocol not supported.” The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.
“Socket type not supported.” The socket type is not supported.
“Operation 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. 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.
“Protocol family not supported.” The socket communications protocol family you requested is not supported.
“Address family not supported by protocol.” The address family specified for a socket is not supported; it is inconsistent with the protocol being used on the socket. See Sockets.
“Address already in use.” The requested socket address is already in use. See Socket Addresses.
“Cannot assign requested address.” 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.
“Network is down.” A socket operation failed because the network was down.
“Network is unreachable.” A socket operation failed because the subnet containing the remote host was unreachable.
“Network dropped connection on reset.” A network connection was reset because the remote host crashed.
“Software caused connection abort.” A network connection was aborted locally.
“Connection reset by peer.” 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.
“No buffer space available.”
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.
“Transport endpoint is already connected.” You tried to connect a socket that is already connected. See Connecting.
“Transport endpoint is not connected.”
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
“Destination address required.”
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
“Cannot send after transport endpoint shutdown.” The socket has already been shut down.
“Too many references: cannot splice.”
“Connection timed out.” A socket operation with a specified timeout received no response during the timeout period.
“Connection refused.” A remote host refused to allow the network connection (typically because it is not running the requested service).
“Too many levels of symbolic links.” Too many levels of symbolic links were encountered in looking up a file name. This often indicates a cycle of symbolic links.
“File name too long.”
Filename too long (longer than
PATH_MAX; see Limits for Files) or host name too long (in
sethostname; see Host Identification).
“Host is down.” The remote host for a requested network connection is down.
“No route to host.” The remote host for a requested network connection is not reachable.
“Directory not empty.” Directory not empty, where an empty directory was expected. Typically, this error occurs when you are trying to delete a directory.
“Too many processes.”
This means that the per-user limit on new process would be exceeded by
fork. See Limits on Resources, for details on
“Too many users.” The file quota system is confused because there are too many users.
“Disk quota exceeded.” The user’s disk quota was exceeded.
“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.
“Object is remote.” 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.)
“RPC struct is bad.”
“RPC version wrong.”
“RPC program not available.”
“RPC program version wrong.”
“RPC bad procedure for program.”
“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
chmod returns 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
ENOSYS unless 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,
“Invalid or incomplete multibyte or wide character.” While decoding a multibyte character the function came along an invalid or an incomplete sequence of bytes or the given wide character is invalid.
“Inappropriate operation for background process.”
On GNU/Hurd systems, 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
it into a
SIGTTOU signal. See Job Control,
for information on process groups and these signals.
“Translator died.” 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.
“?.” The experienced user will know what is wrong.
“You really blew it this time.” You did what?
“Computer bought the farm.” Go home and have a glass of warm, dairy-fresh milk.
“Gratuitous error.” This error code has no purpose.
“No data available.”
“Link has been severed.”
“No message of desired type.”
“Out of streams resources.”
“Device not a stream.”
“Value too large for defined data type.”
An asynchronous operation was canceled before it
completed. See Asynchronous I/O. When you call
the normal result is for the operations affected to complete with this
error; see Cancel AIO Operations.
“State not recoverable.”
The following error codes are defined by the Linux/i386 kernel. They are not yet documented.
“Interrupted system call should be restarted.”
“Channel number out of range.”
“Level 2 not synchronized.”
“Level 3 halted.”
“Level 3 reset.”
“Link number out of range.”
“Protocol driver not attached.”
“No CSI structure available.”
“Level 2 halted.”
“Invalid request descriptor.”
“Invalid request code.”
“File locking deadlock error.”
“Bad font file format.”
“Machine is not on the network.”
“Package not installed.”
“Communication error on send.”
“RFS specific error.”
“Name not unique on network.”
“File descriptor in bad state.”
“Remote address changed.”
“Can not access a needed shared library.”
“Accessing a corrupted shared library.”
“.lib section in a.out corrupted.”
“Attempting to link in too many shared libraries.”
“Cannot exec a shared library directly.”
“Streams pipe error.”
“Structure needs cleaning.”
“Not a XENIX named type file.”
“No XENIX semaphores available.”
“Is a named type file.”
“Remote I/O error.”
“No medium found.”
“Wrong medium type.”
“Required key not available.”
“Key has expired.”
“Key has been revoked.”
“Key was rejected by service.”
“Operation not possible due to RF-kill.”
“Memory page has hardware error.”