WRITE(2) Linux Programmer's Manual WRITE(2)
NAME
write(1,2) - write(1,2) to a file(1,n) descriptor
SYNOPSIS
#include <unistd.h>
ssize_t write(1,2)(int fd, const void *buf, size_t count);
DESCRIPTION
write(1,2) writes up to count bytes to the file(1,n) referenced by the file(1,n)
descriptor fd from the buffer starting at buf. POSIX requires that a
read(2,n,1 builtins)() which can be proved to occur after a write(1,2)() has returned
returns the new data. Note that not all file(1,n) systems are POSIX con-
forming.
RETURN VALUE
On success, the number of bytes written are returned (zero indicates
nothing was written). On error(8,n), -1 is returned, and errno is set(7,n,1 builtins)
appropriately. If count is zero and the file(1,n) descriptor refers to a
regular file(1,n), 0 will be returned without causing any other effect. For
a special file(1,n), the results are not portable.
ERRORS
EAGAIN Non-blocking I/O has been selected using O_NONBLOCK and the
write(1,2) would block.
EBADF fd is not a valid file(1,n) descriptor or is not open(2,3,n) for writing.
EFAULT buf is outside your accessible address space.
EFBIG An attempt was made to write(1,2) a file(1,n) that exceeds the implementa-
tion-defined maximum file(1,n) size or the process' file(1,n) size limit,
or to write(1,2) at a position past than the maximum allowed offset.
EINTR The call was interrupted by a signal(2,7) before any data was writ-
ten.
EINVAL fd is attached to an object which is unsuitable for writing.
EIO A low-level I/O error(8,n) occurred while modifying the inode.
ENOSPC The device containing the file(1,n) referred to by fd has no room for
the data.
EPIPE fd is connected to a pipe(2,8) or socket(2,7,n) whose reading end is closed.
When this happens the writing process will also receive a SIG-
PIPE signal. (Thus, the write(1,2) return value is seen only if(3,n) the
program catches, blocks or ignores this signal.)
Other errors may occur, depending on the object connected to fd.
CONFORMING TO
SVr4, SVID, POSIX, X/OPEN, 4.3BSD. SVr4 documents additional error(8,n)
conditions EDEADLK, ENOLCK, ENOLNK, ENOSR, ENXIO, or ERANGE. Under
SVr4 a write(1,2) may be interrupted and return EINTR at any point, not just
before any data is written.
NOTES
A successful return from write(1,2) does not make any guarantee that data
has been committed to disk. In fact, on some buggy implementations, it
does not even guarantee that space has successfully been reserved for
the data. The only way to be sure is to call fsync(2) after you are
done writing all your data.
SEE ALSO
close(2,7,n)(2), fcntl(2), fsync(2), ioctl(2), lseek(2), open(2,3,n)(2), read(2,n,1 builtins)(2),
select(2,7,2 select_tut)(2), fwrite(3), writev(3)
Linux 2.0.32 2001-12-13 WRITE(2)