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Full Discussion: Shell script runs fine in Solaris, in Linux hangs at wait command
Top Forums Shell Programming and Scripting Shell script runs fine in Solaris, in Linux hangs at wait command Post 302467452 by DGPickett on Friday 29th of October 2010 11:39:12 AM
Old 10-29-2010
I guess wait on LINUX waits for everything. I wonder if nohup helps to move the script away. It might be an interesting man page read or such, to find out whether it is waiting for all processes on the tty or on the process group. But yes, collecting pids and waiting for them one at a time is best, as you get the exit return $? of each child from "wait $child_pid".

If the exit status is not a biggie, or you check that through log files, you can skill the wait and monitor the children through shared stdout and stderr, like this:
Code:
(
this&
that&
the_other&
) 2>&1 | cat >>$shared_log

This monitors not only the children but their children and so on, as long as they do not redirect both stdout and stderr. Even when "wait $child_pid" returns, the child may have antecedents still running, background or up-pipeline processes that close stdout but do not immediately exit, or someone down-pipeline exits cutting them off! $! is just the parent or last in pipeline pid.
Code:
sleep 99 | sleep 5 & wait $!    # wait waits for sleep 5 but sleep 99 is still running.

(sleep 99 & sleep 5 ) & wait $!    # wait waits for sleep 5 but sleep 99 is still running.

The ability of processes other than $! to get errors not reported on $? is one reason to rely on logs, or write a very attentive wrapper script to keep an eye on the children and report $? for all. Sometimes I get really formal, for money and my job security and all that. This is fine for interactive, but not so wise unattended:
Code:
cmd1|cmd2|cmd3

Code:
>$fail_log
(
  cmd1
  zret=$?
  if [ $zret != 0 ]
  then
   echo cmd1 returned $zret >>$fail_log
  fi
 ) | (
  cmd2
  zret=$?
  if [ $zret != 0 ]
  then
   echo cmd2 returned $zret >>$fail_log
  fi
 ) | (
  cmd3 . . . .
 )

if [ -s $fail_log ]
then
 exit 1
fi

Last edited by DGPickett; 10-29-2010 at 12:52 PM..
 

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LEARN ABOUT DEBIAN

wait

wait(3) 						     Library Functions Manual							   wait(3)

NAME

       wait - check child process status

SYNTAX

       #include <wait.h>

       int wait_nohang(&wstat);
       int wait_stop(&wstat);
       int wait_stopnohang(&wstat);
       int wait_pid(&wstat,pid);

       int wait_exitcode(wstat);
       int wait_crashed(wstat);
       int wait_stopped(wstat);
       int wait_stopsig(wstat);

       int pid;
       int wstat;

DESCRIPTION

       wait_nohang  looks  for	zombies (child processes that have exited).  If it sees a zombie, it eliminates the zombie, puts the zombie's exit
       status into wstat, and returns the zombie's process ID.	If there are several zombies, wait_nohang picks one.  If there are children but no
       zombies, wait_nohang returns 0.	If there are no children, wait_nohang returns -1, setting errno appropriately.

       wait_stopnohang is similar to wait_nohang, but it also looks for children that have stopped.

       wait_stop is similar to wait_stopnohang, but if there are children it will pause waiting for one of them to stop or exit.

       wait_pid waits for child process pid to exit.  It eliminates any zombie that shows up in the meantime, discarding the exit status.

       wait_stop and wait_pid retry upon error_intr.

STATUS PARSING

       If the child stopped, wait_stopped is nonzero; wait_stopsig is the signal that caused the child to stop.

       If the child exited by crashing, wait_stopped is zero; wait_crashed is nonzero.

       If the child exited normally, wait_stopped is zero; wait_crashed is zero; and wait_exitcode is the child's exit code.

SEE ALSO

       wait(2), error(3)

																	   wait(3)
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