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A process control block (PCB), also sometimes called a process descriptor, is a data structure used by a computer operating system to store all the information about a process. When a process is created (initialized or installed), the operating system creates a corresponding process control block, which specifies and tracks the process state (i ...
The PCB might be stored on a per-process stack in kernel memory (as opposed to the user-mode call stack), or there may be some specific operating system-defined data structure for this information. A handle to the PCB is added to a queue of processes that are ready to run, often called the ready queue .
A process moves into the running state when it is chosen for execution. The process's instructions are executed by one of the CPUs (or cores) of the system. There is at most one running process per CPU or core. A process can run in either of the two modes, namely kernel mode or user mode. [1] [2]
The context switch loads the process into the processor and changes the state to "running" while the previously "running" process is stored in a "waiting" state. If a process in the "running" state needs to wait for a resource (wait for user input or file to open, for example), it is assigned the "blocked" state. The process state is changed ...
This prevents other processes from reading or writing to the file (inode) [17] during the update operation, thereby avoiding data inconsistency or corruption. [18] Once the update operation is complete, the lock is released. Any subsequent access to the file (via the inode) by any processes will now point to the new version of the library.
The startup function startup_32() for the kernel (also called the swapper or process 0) establishes memory management (paging tables and memory paging), detects the type of CPU and any additional functionality such as floating point capabilities, and then switches to non-architecture specific Linux kernel functionality via a call to start ...
Modern Linux distributions include a /run directory as a temporary filesystem , which stores volatile runtime data, following the FHS version 3.0. According to the FHS version 2.3, such data were stored in /var/run , but this was a problem in some cases because this directory is not always available at early boot.
Some Linux distributions (e.g. Debian) do not have a tmpfs mounted on /tmp by default; in this case, files under /tmp will be stored in the same file system as /. And on almost all Linux distributions, a tmpfs is mounted on /run/ or /var/run/ to store temporary run-time files such as PID files and Unix domain sockets.