Returned value

If successful, the value fcntl() returns will depend on the action that was specified.

If unsuccessful, fcntl() returns -1 and sets errno to one of the following values:

Error Code

Description

EAGAIN

The process tried to set a lock with F_SETLK, but the lock is in conflict with a lock already set by some other process on an overlapping part of the file.

EBADF

fildes is not a valid open file descriptor; or the process tried to set a read lock on a file descriptor open for writing only; or the process tried to set a write lock on a file descriptor open for reading only; or the socket parameter is not a valid socket descriptor.

In an F_DUPFD2 operation, the third argument is negative, or greater than or equal to OPEN_MAX, which is the highest file descriptor value allowed for the process.

EDEADLK

The system detected the potential for deadlock in a F_SETLKW operation.

EINTR

fcntl() was interrupted by a signal during a F_SETLKW operation.

EINVAL

In an F_DUPFD operation, the third argument is negative or greater than or equal to OPEN_MAX, the highest file descriptor value allowed for the process. The OPEN_MAX value can be determined using pathconf().

In a locking operation, fildes refers to a file with a type that does not support locking, or the struct flock pointed to by the third argument has an incorrect form.

If an F_CLOSFD operation, the third argument, which specifies the upper limit, is less than filedes but is not equal to -1.

Behavior for sockets: The arg parameter is not a valid flag, or the cmd parameter is not a valid command.

EMFILE

In an F_DUPFD operation, the process has already reached its maximum number of file descriptors, or there are no available file descriptors greater than the specified third argument.

ENOLCK

In an F_SETLK or F_SETLKW operation, the specified file has already reached the maximum number of locked regions allowed by the system.

EOVERFLOW

One of the values to be returned cannot be represented correctly.

The cmd argument is F_GETLK, F_SETLK or F_SETLKW and the smallest or, if l_len is nonzero, the largest offset of any byte in the requested segment cannot be represented correctly in an object of type off_t.

EPERM

The operation was F_CLOSFD, but all the requested file descriptors were not closed.