The shell itself executes wait, without creating a new process. If you get the error message cannot fork,too many processes, try using the wait command to clean up your background processes. If this doesn't help, the system process table is probably full or you have too many active foreground processes. There is a limit to the number of process IDs associated with your login, and to the number the system can keep track of.
Not all the processes of a pipeline with three or more stages are children of the shell, and thus cannot be waited for.
Wait for your background process whose process ID is pid and report its termination status. If pid is omitted, all your shell's currently active background processes are waited for and the return code will be 0. The wait utility accepts a job identifier, when Job Control is enabled (jsh), and the argument, jobid, is preceded by a percent sign (%).
If pid is not an active process ID, the wait utility will return immediately and the return code will be 0.
Wait for your background processes.
When an asynchronous list is started by the shell, the process ID of the last command in each element of the asynchronous list becomes known in the current shell execution environment.
If the wait utility is invoked with no operands, it will wait until all process IDs known to the invoking shell have terminated and exit with an exit status of 0.
If one or more pid or jobid operands are specified that represent known process IDs (or jobids), the wait utility will wait until all of them have terminated. If one or more pid or jobid operands are specified that represent unknown process IDs (or jobids), wait will treat them as if they were known process IDs (or jobids) that exited with exit status 127. The exit status returned by the wait utility will be the exit status of the process requested by the last pid or jobid operand.
The known process IDs are applicable only for invocations of wait in the current shell execution environment.
The following operands are supported:
One of the following:
The unsigned decimal integer process ID of a command, for which the utility is to wait for the termination.
A job control job ID that identifies a background process group to be waited for. The job control job ID notation is applicable only for invocations of wait in the current shell execution environment, and only on systems supporting the job control option.
On most implementations, wait is a shell built-in. If it is called in a subshell or separate utility execution environment, such as one of the following,
(wait) nohup wait ... find . -exec wait ... \;
it will return immediately because there will be no known process IDs to wait for in those environments.
Although the exact value used when a process is terminated by a signal is unspecified, if it is known that a signal terminated a process, a script can still reliably figure out which signal is using kill, as shown by the following (/bin/ksh and /usr/xpg4/bin/sh):
sleep 1000& pid=$! kill -kill $pid wait $pid echo $pid was terminated by a SIG$(kill -l $(($?-128))) signal.
If the following sequence of commands is run in less than 31 seconds (/bin/ksh and /usr/xpg4/bin/sh):
sleep 257 | sleep 31 & jobs -l %%
then either of the following commands will return the exit status of the second sleep in the pipeline:
wait <pid of sleep 31> wait %%
See environ(5) for descriptions of the following environment variables that affect the execution of wait: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|