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Question

fork系统调用是否为子进程分配新的用户结构？它确实为子进程分配新的进程结构。

Answer 1

http://svn.freebsd.org/base/ release/7.1.0/sys/kern/kern_fork.c

http://www.freebsd.org/cgi/man.cgi?query=fork&apropos=0&sektion=0&manpath=FreeBSD +7.1-RELEASE&format=html

DESCRIPTION
     The fork() system call causes creation of a new process.  The new process
     (child process) is an exact copy of the calling process (parent process)
     except for the following:

       +o   The child process has a unique process ID.

       +o   The child process has a different parent process ID (i.e., the
           process ID of the parent process).

       +o   The child process has its own copy of the parent's descriptors.
           These descriptors reference the same underlying objects, so
           that, for instance, file pointers in file objects are shared
           between the child and the parent, so that an lseek(2) on a
           descriptor in the child process can affect a subsequent read(2)
           or write(2) by the parent.  This descriptor copying is also
           used by the shell to establish standard input and output for
           newly created processes as well as to set up pipes.

       +o   The child process' resource utilizations are set to 0; see
           setrlimit(2).

       +o   All interval timers are cleared; see setitimer(2).