![]() Some processes, for example, the moc music player and the MySQL daemon, write their PID to a documented file location, to allow other processes to look it up. On Linux, the maximum process ID is given by the pseudo-file /proc/sys/kernel/pid_max. The process ID of a parent process is obtainable by a getppid() system call. The current process ID is provided by a getpid() system call, or as a variable $$ in shell. On some systems, like MPE/iX, the lowest available PID is used, sometimes in an effort to minimize the number of process information kernel pages in memory. As such, implementations that are particularly concerned about security may choose a different method of PID assignment. Some consider this to be a potential security vulnerability in that it allows information about the system to be extracted, or messages to be covertly passed between processes. However, for this and subsequent passes any PIDs still assigned to processes are skipped. In macOS and HP-UX, allocation restarts at 100. Once this limit is reached, allocation restarts at 300 and again increases. Process IDs, in the first place, are usually allocated on a sequential basis, beginning at 0 and rising to a maximum value which varies from system to system. More recent Unix systems typically have additional kernel components visible as 'processes', in which case PID 1 is actively reserved for the init process to maintain consistency with older systems. Originally, process ID 1 was not specifically reserved for init by any technical measures: it simply had this ID as a natural consequence of being the first process invoked by the kernel. ![]() Process ID 1 is usually the init process primarily responsible for starting and shutting down the system. There are two tasks with specially distinguished process IDs: swapper or sched has process ID 0 and is responsible for paging, and is actually part of the kernel rather than a normal user-mode process. The parent may, for example, wait for the child to terminate with the waitpid() function, or terminate the process with kill(). The PID is returned to the parent process, enabling it to refer to the child in further function calls. In Unix-like operating systems, new processes are created by the fork() system call. ( October 2017) ( Learn how and when to remove this template message) Please help to improve this section by introducing more precise citations. This section includes a list of general references, but it lacks sufficient corresponding inline citations.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |