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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 other words, a read from an empty pipe will cause the calling thread to wait until at least one byte becomes available or an end-of-file is received as a result of the write handle of the pipe being closed. Likewise, a write to a full pipe will cause the calling thread to wait until space becomes available to store the data being written.
The jobs command will list the background jobs existing in the job table, along with their job number and job state (stopped or running). When a session ends when the user logs out (exits the shell, which terminates the session leader process), the shell process sends SIGHUP to all jobs, and waits for the process groups to end before ...
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.
When a child process terminates before the parent has called wait, the kernel retains some information about the process, such as its exit status, to enable its parent to call wait later. [3] Because the child is still consuming system resources but not executing it is known as a zombie process .
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.
Another relevant bash option is shopt huponexit, which automatically sends the HUP signal to jobs when the shell is exiting normally. [3] The AIX and Solaris versions of nohup have a -p option that modifies a running process to ignore future SIGHUP signals. Unlike the above-described disown builtin of bash, nohup -p accepts process IDs. [4]