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A set of processes, comprising a shell pipeline, and any processes descended from it, that are all in the same process group. A job can be referred to by a handle [ b ] called the job control job ID or simply job ID , which is used by shell builtins to refer to the job.
Location of the "O(1) scheduler" (a process scheduler) in a simplified structure of the Linux kernel. An O(1) scheduler (pronounced "O of 1 scheduler", "Big O of 1 scheduler", or "constant time scheduler") is a kernel scheduling design that can schedule processes within a constant amount of time, regardless of how many processes are running on the operating system.
The process scheduler is a part of the operating system that decides which process runs at a certain point in time. It usually has the ability to pause a running process, move it to the back of the running queue and start a new process; such a scheduler is known as a preemptive scheduler, otherwise it is a cooperative scheduler. [5]
A task (i.e., a synonym for thread) is the minimal entity that Linux can schedule. However, it can also manage groups of threads, whole multi-threaded processes, and even all the processes of a given user. This design leads to the concept of schedulable entities, where tasks are grouped and managed by the scheduler as a whole.
A process can define how to handle incoming POSIX signals. If a process does not define a behaviour for a signal, then the default handler for that signal is being used. The table below lists some default actions for POSIX-compliant UNIX systems, such as FreeBSD, OpenBSD and Linux.
In February 2003 Andrea Arcangeli put forward his idea for a Stochastic Fair Queueing I/O scheduler to Jens Axboe who then implemented it. Jens Axboe made improvements to his first implementation, calling the new version the Completely Fair Queueing scheduler, and produced a patch to apply it to the 2.5.60 development series kernel.
When the active array contains no more processes, the scheduler swaps the active and expired arrays, hence the name O(1) scheduler. In UNIX or Linux, the sar command is used to check the run queue. The vmstat UNIX or Linux command can also be used to determine the number of processes that are queued to run or waiting to run. These appear in the ...
This special process detects when an orphan process terminates and then retrieves its exit status, allowing the system to deallocate the terminated child process. If a child process receives a signal, a waiting parent will then continue execution leaving an orphan process behind.