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Most Unix systems have historically used init as the system process to which orphans are reparented, but in modern DragonFly BSD, FreeBSD, and Linux systems, an orphan process may be reparented to a "subreaper" process instead of init. [1] [2] A process can be orphaned unintentionally, such as when the parent process terminates or crashes.
In Unix-like operating systems, every process except process 0 (the swapper) is created when another process executes the fork() system call. The process that invoked fork is the parent process and the newly created process is the child process. Every process (except process 0) has one parent process, but can have many child processes.
Such situations are typically handled with a special "reaper" process [citation needed] that locates zombies and retrieves their exit status, allowing the operating system to then deallocate their resources. Conversely, a child process whose parent process terminates before it does becomes an orphan process. Such situations are typically ...
However, the process's entry in the process table remains. The parent can read the child's exit status by executing the wait system call, whereupon the zombie is removed. The wait call may be executed in sequential code, but it is commonly executed in a handler for the SIGCHLD signal, which the parent receives whenever a child has died.
A high-level overview of the Linux kernel's system call interface, which handles communication between its various components and the userspace. In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system [a] on which it is executed.
Version 7 Unix: /etc listing, showing init and rc Version 7 Unix: contents of an /etc/rc Bourne shell script. In Unix-based computer operating systems, init (short for initialization) is the first process started during booting of the operating system. Init is a daemon process that continues running
A child process inherits most of its attributes, such as file descriptors, from its parent. In Unix, a child process is typically created as a copy of the parent, using the fork system call. The child process can then overlay itself with a different program (using exec) as required. [1]
Likewise, a similar strategy is used to deal with a zombie process, which is a child process that has terminated but whose exit status is ignored by its parent process. Such a process becomes the child of a special parent process, which retrieves the child's exit status and allows the operating system to complete the termination of the dead ...