Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Pages: 31. Chapters: Close (system call), Dirent.h, Dup (system call), Fcntl.h, Fork-exec, Fork (operating system), Getaddrinfo, Getopt, Glob (programming), Mmap, Native POSIX Thread Library, Open (system call), POSIX Threads, Read (system call), Select (Unix), Sigaction, Spawn (computing), Spurious wakeup, Stat (system call), Sync (Unix), Sys/stat.h, Unistd.h, Utime.h, Wait (system call), Write (system call). Excerpt: In computing, when a process forks, it creates a copy of itself. Under Unix-like operating systems, this is created with the fork() system call. The original process that calls fork() is the parent process, and the newly created process is the child process. Both processes return from the system call and execute the next instruction. The fork operation creates a separate address space for the child. The child process has an exact copy of all the memory segments of the parent process, though if copy-on-write semantics are implemented actual physical memory may not be assigned (i.e., both processes may share the same physical memory segments for a while). Both the parent and child processes possess the same code segments, but execute independently of each other. The system call takes no arguments. If it returns a negative value, the creation of a child process was not successful. Otherwise, in the child process, the return value of fork() is zero, whereas the return value in the parent process is the process identifier of the newly created child process (a positive value). Since both processes continue executing the same program, they typically distinguish the parent from the child by testing the return value of fork(). Forking is an important part of Unix, critical to the support of its design philosophy, which encourages the development of filters. In Unix, a filter is a (usually small) program that reads its input from stdin, and writes its output to stdout. A pipeline of these commands can be strung together by a shell to create new commands. For example, one can string together the output of the find(1) command and the input of the wc(1) command to create a new command that will print a count of files ending in ".cpp" found in the current directory and any subdirectories, as follows: In order to accomplish this, the shell forks itself, and uses pipes, a form of interprocess communication, to tie the output of the find command to the input of the wc command. First
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