The GNU C Library
2.2 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 occurred and prevented
completion of the call. When this happens, you should try the call
You can choose to have functions resume after a signal that is handled,
rather than failing with
EINTR; see 24.5 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
- 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 26.5 Executing a File) occupy too much memory space. This condition never arises in the
- Macro: int ENOEXEC
- Invalid executable file format. This condition is detected by the
exec functions; see 26.5 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
- 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
- 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 13.15 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.
In the GNU system, this error never happens; you get a signal instead.
- 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 14.4 Hard Links) but
also when you rename a file with
rename (see section 14.7 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; you cannot open a directory for writing,
or create or remove hard links to it.
- 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.
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 section 22.2 Limiting Resource Usage.
- 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
13.5.1 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. 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 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 would become too large.
rename can cause this error if the file being renamed already has
as many links as it can take (see section 14.7 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
unless it has handled or blocked
- 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. 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:
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
select to find out
when the operation will be possible; see section 13.8 Waiting for Input or Output.
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.
A temporary resource shortage made an operation impossible.
can 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.
- Macro: int EWOULDBLOCK
- 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.
- Macro: int EINPROGRESS
- 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 16.9.1 Making a Connection) 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 section 13.8 Waiting for Input or Output.
- Macro: int EALREADY
- An operation is already in progress on an object that has non-blocking
- Macro: int ENOTSOCK
- A file that isn't a socket was specified when a socket is required.
- Macro: int EMSGSIZE
- The size of a message sent on a socket was larger than the supported
- Macro: int EPROTOTYPE
- The socket type does not support the requested communications protocol.
- Macro: int ENOPROTOOPT
- You specified a socket option that doesn't make sense for the
particular protocol being used by the socket. See section 16.12 Socket Options.
- Macro: int EPROTONOSUPPORT
- The socket domain does not support the requested communications protocol
(perhaps because the requested protocol is completely invalid).
See section 16.8.1 Creating a Socket.
- Macro: int ESOCKTNOSUPPORT
- The socket type is not supported.
- Macro: int EOPNOTSUPP
- 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. In the GNU system, 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.
- Macro: int EPFNOSUPPORT
- The socket communications protocol family you requested is not supported.
- Macro: int EAFNOSUPPORT
- The address family specified for a socket is not supported; it is
inconsistent with the protocol being used on the socket. See section 16. Sockets.
- Macro: int EADDRINUSE
- The requested socket address is already in use. See section 16.3 Socket Addresses.
- Macro: int EADDRNOTAVAIL
- 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 16.3 Socket Addresses.
- Macro: int ENETDOWN
- A socket operation failed because the network was down.
- Macro: int ENETUNREACH
- A socket operation failed because the subnet containing the remote host
- Macro: int ENETRESET
- A network connection was reset because the remote host crashed.
- Macro: int ECONNABORTED
- A network connection was aborted locally.
- Macro: int ECONNRESET
- A network connection was closed for reasons outside the control of the
local host, such as by the remote machine rebooting or an unrecoverable
- Macro: int ENOBUFS
- 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.
- Macro: int EISCONN
- You tried to connect a socket that is already connected.
See section 16.9.1 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. For a connectionless socket (for datagram
protocols, such as UDP), you get
- Macro: int EDESTADDRREQ
- 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
- Macro: int ESHUTDOWN
- The socket has already been shut down.
- Macro: int ETOOMANYREFS
- Macro: int ETIMEDOUT
- A socket operation with a specified timeout received no response during
the timeout period.
- Macro: int ECONNREFUSED
- 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.
- Macro: int ENAMETOOLONG
- Filename too long (longer than
PATH_MAX; see section 31.6 Limits on File System Capacity) or host name too long (in
sethostname; see section 30.1 Host Identification).
- Macro: int EHOSTDOWN
- The remote host for a requested network connection is down.
- Macro: int EHOSTUNREACH
- 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 EPROCLIM
- This means that the per-user limit on new process would be exceeded by
fork. See section 22.2 Limiting Resource Usage, for details on
- 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 EBADRPC
- Macro: int ERPCMISMATCH
- Macro: int EPROGUNAVAIL
- Macro: int EPROGMISMATCH
- Macro: int EPROCUNAVAIL
- Macro: int ENOLCK
- No locks available. This is used by the file locking facilities; see
13.15 File Locks. This error is never generated by the GNU system, but
it can result from an operation to an NFS server running another
- Macro: int EFTYPE
- 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 section 14.9.7 Assigning File Permissions.
- Macro: int EAUTH
- Macro: int ENEEDAUTH
- Macro: int ENOSYS
- 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.
- Macro: int ENOTSUP
- 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
If the entire function is not available at all in the implementation,
- Macro: int EILSEQ
- While decoding a multibyte character the function came along an invalid
or an incomplete sequence of bytes or the given wide character is invalid.
- Macro: int EBACKGROUND
- 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
it into a
SIGTTOU signal. See section 27. Job Control,
for information on process groups and these signals.
- Macro: int EDIED
- In the GNU system, 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.
- 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.
- Macro: int EGRATUITOUS
- This error code has no purpose.
- Macro: int EBADMSG
- Macro: int EIDRM
- Macro: int EMULTIHOP
- Macro: int ENODATA
- Macro: int ENOLINK
- Macro: int ENOMSG
- Macro: int ENOSR
- Macro: int ENOSTR
- Macro: int EOVERFLOW
- Macro: int EPROTO
- Macro: int ETIME
- Macro: int ECANCELED
- Operation canceled; an asynchronous operation was canceled before it
completed. See section 13.10 Perform I/O Operations in Parallel. When you call
the normal result is for the operations affected to complete with this
error; see section 13.10.4 Cancellation of AIO Operations.
The following error codes are defined by the Linux/i386 kernel.
They are not yet documented.
- Macro: int ERESTART
- Macro: int ECHRNG
- Macro: int EL2NSYNC
- Macro: int EL3HLT
- Macro: int EL3RST
- Macro: int ELNRNG
- Macro: int EUNATCH
- Macro: int ENOCSI
- Macro: int EL2HLT
- Macro: int EBADE
- Macro: int EBADR
- Macro: int EXFULL
- Macro: int ENOANO
- Macro: int EBADRQC
- Macro: int EBADSLT
- Macro: int EDEADLOCK
- Macro: int EBFONT
- Macro: int ENONET
- Macro: int ENOPKG
- Macro: int EADV
- Macro: int ESRMNT
- Macro: int ECOMM
- Macro: int EDOTDOT
- Macro: int ENOTUNIQ
- Macro: int EBADFD
- Macro: int EREMCHG
- Macro: int ELIBACC
- Macro: int ELIBBAD
- Macro: int ELIBSCN
- Macro: int ELIBMAX
- Macro: int ELIBEXEC
- Macro: int ESTRPIPE
- Macro: int EUCLEAN
- Macro: int ENOTNAM
- Macro: int ENAVAIL
- Macro: int EISNAM
- Macro: int EREMOTEIO
- Macro: int ENOMEDIUM
- Macro: int EMEDIUMTYPE