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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 .
In computer operating systems, a process (or task) may wait for another process to complete its execution. In most systems, a parent process can create an independently executing child process . The parent process may then issue a wait system call , which suspends the execution of the parent process while the child executes.
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 disown command can be used to remove jobs from the job table, so that when the session ends the child process groups are not sent SIGHUP, nor does the shell wait for them to terminate. They thus become orphan processes , and may be terminated by the operating system, though more often this is used so the processes are adopted by init (the ...
Process management Optional (UU) Remote command execution Version 7 AT&T UNIX val: SCCS Optional (XSI) Validate SCCS files System III vi: Text processing Optional (UP) Screen-oriented (visual) display editor 1BSD wait: Process management Mandatory Await process completion Version 4 AT&T UNIX wc: Text processing Mandatory
The last string is the command that started the process. The state of a process can be changed using various commands. The fg command brings a process to the foreground, while bg sets a stopped process running in the background. bg and fg can take a job id as their first argument, to specify the process to act on.
Foreground-background is a scheduling algorithm that is used to control an execution of multiple processes on a single processor. It is based on two waiting lists, the first one is called foreground because this is the one in which all processes initially enter, and the second one is called background because all processes, after using all of their execution time in foreground, are moved to ...
Shortest job next can be effectively used with interactive processes which generally follow a pattern of alternating between waiting for a command and executing it. If the execution burst of a process is regarded as a separate "job", the past behaviour can indicate which process to run next, based on an estimate of its running time.