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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 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.
However, the process's entry in the process table remains. The parent can read the child's exit status by executing the wait system call, whereupon the zombie is removed. The wait call may be executed in sequential code, but it is commonly executed in a handler for the SIGCHLD signal, which the parent receives whenever a child has died.
Version 7 AT&T UNIX fc: Misc Optional (UP) Process the command history list fg: Process management Optional (UP) Run jobs in the foreground file: Filesystem Mandatory Determine file type Version 4 AT&T UNIX find: Filesystem Mandatory Find files Version 1 AT&T UNIX fold: Text processing Mandatory Filter for folding lines 1BSD fuser: Process ...
Command-line completion generally only works in interactive mode. That is, it cannot be invoked to complete partially typed commands in scripts or batch files, even if the completion is unambiguous. The name tab completion comes from the fact that command-line completion is often invoked by pressing the tab key.
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 back to "waiting" when the process no longer needs to wait (in a blocked state). Once the process finishes execution, or is terminated by the operating system, it ...
In computer science and software engineering, busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary on systems that lacked a ...
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.