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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.
The parent process may then issue a wait system call, which suspends the execution of the parent process while the child executes. When the child process terminates, it returns an exit status to the operating system, which is then returned to the waiting parent process. The parent process then resumes execution.
Once all the boot and system drivers have been loaded, the kernel starts the session manager (smss.exe), which begins the login process. After the user has successfully logged into the machine, winlogon applies User and Computer Group Policy setting and runs startup programs declared in the Windows Registry and in "Startup" folders.
wait normally returns the exit status of the last job which terminated. It may also return 127 in the event that n specifies a non-existent job or zero if there were no jobs to wait for. Because wait needs to be aware of the job table of the current shell execution environment, it is usually implemented as a shell builtin .
Likewise, a similar strategy is used to deal with a zombie process, which is a child process that has terminated but whose exit status is ignored by its parent process. Such a process becomes the child of a special parent process, which retrieves the child's exit status and allows the operating system to complete the termination of the dead ...
But kill is something of a misnomer; the signal sent may have nothing to do with process killing. The kill command is a wrapper around the kill() system call, which sends signals to processes or process groups on the system, referenced by their numeric process IDs (PIDs) or process group IDs (PGIDs).
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 ...
In Windows NT operating systems, a Windows service is a computer program that operates in the background. [1] It is similar in concept to a Unix daemon. [1] A Windows service must conform to the interface rules and protocols of the Service Control Manager, the component responsible for managing Windows services.