Manual Pages  — WRITE

write, writev, pwrite, pwritev – write output

LIBRARY SYNOPSIS DESCRIPTION RETURN VALUES ERRORS SEE ALSO STANDARDS HISTORY BUGS

Standard C Library (libc, -lc)

#include <unistd.h>

ssize_t
write(int fd, const void *buf, size_t nbytes);

ssize_t
pwrite(int fd, const void *buf, size_t nbytes, off_t offset);

#include <sys/uio.h>

ssize_t
writev(int fd, const struct iovec *iov, int iovcnt);

ssize_t
pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset);

Upon successful completion the number of bytes which were written is returned. Otherwise a -1 is returned and the global variable errno is set to indicate the error.

The write(), writev(), pwrite() and pwritev() system calls will fail and the file pointer will remain unchanged if:

[EBADF]
	The fd argument is not a valid descriptor open for writing.
[EPIPE]
	An attempt is made to write to a pipe that is not open for reading by any process.
[EPIPE]
	An attempt is made to write to a socket of type SOCK_STREAM that is not connected to a peer socket.
[EFBIG]
	An attempt was made to write a file that exceeds the process's file size limit or the maximum file size.
[EFAULT]
	Part of iov or data to be written to the file points outside the process's allocated address space.
[EINVAL]
	The pointer associated with fd was negative.
[ENOSPC]
	There is no free space remaining on the file system containing the file.
[EDQUOT]
	The user's quota of disk blocks on the file system containing the file has been exhausted.
[EIO]	An I/O error occurred while reading from or writing to the file system.
[EINTR]
	A signal interrupted the write before it could be completed.
[EAGAIN]
	The file was marked for non-blocking I/O, and no data could be written immediately.
[EROFS]
	An attempt was made to write over a disk label area at the beginning of a slice. Use disklabel(8) -W to enable writing on the disk label area.
[EINVAL]
	The value nbytes is greater than SSIZE_MAX (or greater than INT_MAX, if the sysctl debug.iosize_max_clamp is non-zero).
[EINTEGRITY]
	The backing store for fd detected corrupted data while reading. (For example, writing a partial filesystem block may require first reading the existing block which may trigger this error.)

In addition, writev() and pwritev() may return one of the following errors:

[EDESTADDRREQ]
	The destination is no longer available when writing to a Unix domain datagram socket on which connect(2) had been used to set a destination address.
[EINVAL]
	The iovcnt argument was less than or equal to 0, or greater than IOV_MAX.
[EINVAL]
	One of the iov_len values in the iov array was negative.
[EINVAL]
	The sum of the iov_len values in the iov array overflowed a 32-bit integer.
[ENOBUFS]
	The mbuf pool has been completely exhausted when writing to a socket.

The pwrite() and pwritev() system calls may also return the following errors:

[EINVAL]
	The offset value was negative.
[ESPIPE]
	The file descriptor is associated with a pipe, socket, or FIFO.

The write() system call is expected to conform to IEEE Std 1003.1-90 ("POSIX.1"). The writev() and pwrite() system calls are expected to conform to -xpg4.2.

The pwritev() system call appeared in FreeBSD 6.0 . The pwrite() function appeared in AT&T V.4 . The writev() system call appeared in BSD 4.2 . The write() function appeared in AT&T v1 .

The pwrite() system call appends the file without changing the file offset if O_APPEND is set, contrary to IEEE Std 1003.1-2008 ("POSIX.1") where pwrite() writes into offset regardless of whether O_APPEND is set.