close closes a file descriptor, so that it no longer refers to any file
and may be reused. Any locks held on the file it was associated with, and
owned by the process, are removed (regardless of the file descriptor that was
used to obtain the lock).
If fd is the last copy of a particular file descriptor the resources
associated with it are freed; if the descriptor was the last reference to a
file which has been removed using unlink(2) the file is deleted.
Not checking the return value of close is a common but nevertheless serious
programming error. It is quite possible that errors on a previous
write(2) operation are first reported at the final close. Not
checking the return value when closing the file may lead to silent loss of
data. This can especially be observed with NFS and with disk quota.
A successful close does not guarantee that the data has been successfully saved
to disk, as the kernel defers writes. It is not common for a filesystem to
flush the buffers when the stream is closed. If you need to be sure that the
data is physically stored use fsync(2). (It will depend on the disk
hardware at this point.)