Node:Linked Channels, Next:Independent Channels, Up:Stream/Descriptor Precautions
Channels that come from a single opening share the same file position;
we call them linked channels. Linked channels result when you
make a stream from a descriptor using fdopen
, when you get a
descriptor from a stream with fileno
, when you copy a descriptor
with dup
or dup2
, and when descriptors are inherited
during fork
. For files that don't support random access, such as
terminals and pipes, all channels are effectively linked. On
random-access files, all append-type output streams are effectively
linked to each other.
If you have been using a stream for I/O, and you want to do I/O using
another channel (either a stream or a descriptor) that is linked to it,
you must first clean up the stream that you have been using.
See Cleaning Streams.
Terminating a process, or executing a new program in the process,
destroys all the streams in the process. If descriptors linked to these
streams persist in other processes, their file positions become
undefined as a result. To prevent this, you must clean up the streams
before destroying them.