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When a process calls fork, it is deemed the parent process and the newly created process is its child. After the fork, both processes not only run the same program, but they resume execution as though both had called the system call. They can then inspect the call's return value to determine their status, child or parent, and act accordingly.
fork() is the name of the system call that the parent process uses to "divide" itself ("fork") into two identical processes. After calling fork(), the created child process is an exact copy of the parent except for the return value of the fork() call. This includes open files, register state, and all memory allocations, which includes the ...
For instance, this includes Unix and Unix-like operating systems, such as GNU variants, distributions of Linux and BSD, and macOS, and compilers such as GCC and LLVM. On Unix-like systems, the interface defined by unistd.h is typically made up largely of system call wrapper functions such as fork, pipe and I/O primitives (read, write, close, etc.).
In the Linux kernel, in which there is a very slim difference between processes and POSIX threads, there are two kinds of parent processes, namely real parent and parent. Parent is the process that receives the SIGCHLD signal on child's termination, whereas real parent is the thread that actually created this child process in a multithreaded ...
Linux 2.6 kernels adhere to this behavior, and FreeBSD supports both of these methods since version 5.0. [5] However, because of historical differences between System V and BSD behaviors with regard to ignoring SIGCHLD, calling wait remains the most portable paradigm for cleaning up after forked child processes.
The return value indicates the exit status of the spawned program. A value of zero indicates that the spawned program executed successfully. A positive value indicates that the spawned program executed, but was aborted or ended in error, the value returned is the exit status of the child process. A negative value indicates that the spawned ...
name=value. where name is the environment variable name, and value is the value of that variable. The final element of the envp array must be null. In the execl, execlp, execv, and execvp calls, the new process image inherits the current environment variables.
Each of these child processes (detected by the fact that fork() returned zero) prints a message, sleeps, and exits. All of the children are created at essentially the same time (since the parent is doing very little in the loop), so it is somewhat random when each of them gets scheduled for the first time - thus the scrambled order of their ...