fork() するときにファイル記述子は共有されますか?

fork(2) から :

  *  The child inherits copies of the parent’s set of open file  descrip-
     tors.   Each  file  descriptor  in the child refers to the same open
     file description (see open(2)) as the corresponding file  descriptor
     in  the parent.  This means that the two descriptors share open file
     status flags, current file offset, and signal-driven I/O  attributes
     (see the description of F_SETOWN and F_SETSIG in fcntl(2)).

それらは同じオフセットを共有しています。