WRITESection: Linux Programmer's Manual (2)
Index Return to Main Contents
NAMEwrite - write to a file descriptor
DESCRIPTIONwrite() writes up to count bytes to the file referenced by the file descriptor fd from the buffer starting at buf. POSIX requires that a read(2) which can be proved to occur after a write() has returned returns the new data. Note that not all file systems are POSIX conforming.
RETURN VALUEOn success, the number of bytes written are returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately.
If count is zero and fd refers to a regular file, then write () may return a failure status if one of the errors below is detected. If no errors are detected, 0 will be returned without causing any other effect. If count is zero and fd refers to a file other than a regular file, the results are not specified.
- Non-blocking I/O has been selected using O_NONBLOCK and the write would block.
- fd is not a valid file descriptor or is not open for writing.
- 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' 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.
- 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 TOSVr4, 4.3BSD, POSIX.1-2001.
NOTESA 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.
SEE ALSOclose(2), fcntl(2), fsync(2), ioctl(2), lseek(2), open(2), pwrite(2), read(2), select(2), writev(2), fwrite(3)