It's hard to have multiple processes logging to the same file, but using pipes Posix defines writes shorter than PIPE_BUF to be atomic. On linux this is 1024 B

It's hard to have multiple processes logging to the same file, but using pipes Posix defines writes shorter than PIPE_BUF to be atomic. On linux this is 1024 Bytes. So if log less than 1024 bytes per message from multiple processes, you can ensure they won't scramble their messages. http://manpages.courier-mta.org/htmlman7/pipe.7.html http://manpages.courier-mta.org/htmlman7/pipe.7.html > POSIX.1-2001 says that write(2)s of less than PIPE_BUF bytes must be atomic: the output data is written to the pipe as a contiguous sequence. Writes of more than PIPE_BUF bytes may be nonatomic: the kernel may interleave the data with data written by other processes. POSIX.1-2001 requires PIPE_BUF to be at least 512 bytes. (On Linux, PIPE_BUF is 4096 bytes.) The precise semantics depend on whether the file descriptor is nonblocking (O_NONBLOCK), whether there are multiple writers to the pipe, and on n, the number of bytes to be written.