|WRITE(2)||Linux Programmer's Manual||WRITE(2)|
NAME¶write - write to a file descriptor
DESCRIPTION¶write() writes up to count bytes from the buffer pointed buf to the file referred to by the file descriptor fd.
RETURN VALUE¶On success, the number of bytes written is returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately.
- The file descriptor fd refers to a file other than a socket and has been marked nonblocking (O_NONBLOCK), and the write would block.
- EAGAIN or EWOULDBLOCK
- The file descriptor fd refers to a socket and has been marked nonblocking (O_NONBLOCK), and the write would block. POSIX.1-2001 allows either error to be returned for this case, and does not require these constants to have the same value, so a portable application should check for both possibilities.
- fd is not a valid file descriptor or is not open for writing.
- fd refers to a datagram socket for which a peer address has not been set using connect(2).
- The user's quota of disk blocks on the filesystem containing the file referred to by fd has been exhausted.
- buf is outside your accessible address space.
- An attempt was made to write a file that exceeds the implementation-defined maximum file size or the process's file size limit, or to write at a position past the maximum allowed offset.
- The call was interrupted by a signal before any data was written; see signal(7).
- fd is attached to an object which is unsuitable for writing; or the file was opened with the O_DIRECT flag, and either the address specified in buf, the value specified in count, or the current file offset is not suitably aligned.
- A low-level I/O error occurred while modifying the inode.
- The device containing the file referred to by fd has no room for the data.
- fd is connected to a pipe or socket whose reading end is closed. When this happens the writing process will also receive a SIGPIPE signal. (Thus, the write return value is seen only if the program catches, blocks or ignores this signal.)
CONFORMING TO¶SVr4, 4.3BSD, POSIX.1-2001.
NOTES¶A successful return from write() 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.
BUGS¶According to POSIX.1-2008/SUSv4 Section XSI 2.9.7 ("Thread Interactions with Regular File Operations"):
All of the following functions shall be atomic with respect to each other in the effects specified in POSIX.1-2008 when they operate on regular files or symbolic links: ...
SEE ALSO¶close(2), fcntl(2), fsync(2), ioctl(2), lseek(2), open(2), pwrite(2), read(2), select(2), writev(2), fwrite(3)
COLOPHON¶This page is part of release 3.74 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.