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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.
Components of some Linux desktop environments that are daemons include D-Bus, NetworkManager (here called unetwork), PulseAudio (usound), and Avahi.. In multitasking computer operating systems, a daemon (/ ˈ d iː m ən / or / ˈ d eɪ m ən /) [1] is a computer program that runs as a background process, rather than being under the direct control of an interactive user.
The other process, the parent, receives from fork the process identifier of the child, which is always a positive number. The parent process passes this identifier to the waitpid system call to suspend execution until the child has exited. When this has happened, the parent resumes execution and exits by means of the return statement.
When a process forks, a complete copy of the executing program is made into the new process. This new process is a child of the parent process, and has a new process identifier (PID). The fork() function returns the child's PID to the parent process. The fork() function returns 0 to the child process. This enables the two otherwise identical ...
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, new processes are created by the fork() system call. The PID is returned to the parent process, enabling it to refer to the child in further function calls. The parent may, for example, wait for the child to terminate with the waitpid() function, or terminate the process with kill().
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]
In Unix and other POSIX-compatible systems, the parent process can retrieve the exit status of a child process using the wait() family of system calls defined in wait.h. [10] Of these, the waitid() [11] call retrieves the full exit status, but the older wait() and waitpid() [12] calls retrieve only the least significant 8 bits of the exit status.