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twice, running the desired process in the grandchild, and immediately terminating the child. The grandchild process is now orphaned, and is not adopted by its grandparent, but rather by init. Higher-level alternatives circumvent the shell's hangup handling, either telling the child process to ignore
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and occurs automatically. Even though technically the process has a system process as its parent, it is still called an orphan process since the process that originally created it no longer exists. In other systems orphaned processes are immediately terminated by the kernel. Most Unix systems have
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in either case). In any event, the session id (process id of the session leader, the shell) does not change, and the process id of the session that has ended is still in use until all orphaned processes either terminate or change session id (by starting a new session via
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It is sometimes desirable to intentionally orphan a process, usually to allow a long-running job to complete without further user attention, or to start an indefinitely running service or agent; such processes (without an associated session) are known as
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From Linux 3.4 onwards 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
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Expiration is a technique where each process is allotted a certain amount of time to finish before being killed. If need be a process may "ask" for more time to finish before the allotted time expires.
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A server process is also said to be orphaned when the client that initiated the request unexpectedly crashes after making the request while leaving the server process running.
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These orphaned processes waste server resources and can potentially leave a server starved for resources. However, there are several solutions to the orphan process problem:
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so that processes not designed to be used as services respond correctly to system signals. An alternative to keep processes running without orphaning them is to use a
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any orphaned process will be immediately adopted by an implementation-defined system process: the kernel sets the parent to this process. This operation is called
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Reincarnation is a technique in which machines periodically try to locate the parents of any remote computations; at which point orphaned processes are killed.
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and run the processes in a detached session (or a session that becomes detached), so the session is not terminated and the process is not orphaned.
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mechanism in most Unix-like operating systems can be used to help protect against accidental orphaning, where in coordination with the user's
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A process can be orphaned unintentionally, such as when the parent process terminates or crashes. The
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ends, and the shell sends SIGHUP to all its jobs (internal representation of process groups).
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Termination is the most commonly used technique; in this case the orphan is killed.
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To simplify system administration, it is often desirable to use a
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