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After Linux kernel 3.4 this is no longer true, in fact processes can issue the prctl() system call with the PR_SET_CHILD_SUBREAPER option, and as a result they, not process #1, will become the parent of any of their orphaned descendant processes. This is the way of working of modern service managers and daemon supervision utilities including ...
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.
In a strictly technical sense, a Unix-like system process is a daemon when its parent process terminates and the daemon is assigned the init process (process number 1) as its parent process and has no controlling terminal. However, more generally, a daemon may be any background process, whether a child of the init process or not.
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 ...
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]
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.
When the shell fork s a new child process for a command pipeline, both the parent shell process and the child process immediately make the child process the leader of the process group for the command pipeline. This ensures that the child is the leader of the process group before either the parent or child relies on this being the case.
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.