Why my shell script is in standby in the background till I bring it back on the foreground?

Question

I have a shell script which is executing a php script (worker for beanstalkd).

Here is the script:

#!/bin/bash

if [ $# -eq 0 ]
then
   echo "You need to specify an argument"
   exit 0;
fi

CMD="/var/webserver/user/bin/console $@";
echo "$CMD";
nice $CMD;
ERR=$?

## Possibilities
# 97    - planned pause/restart
# 98    - planned restart
# 99    - planned stop, exit.
# 0     - unplanned restart (as returned by "exit;")
#        - Anything else is also unplanned paused/restart

if [ $ERR -eq 97 ]
then
   # a planned pause, then restart
   echo "97: PLANNED_PAUSE - wait 1";
   sleep 1;
   exec $0 $@;
fi

if [ $ERR -eq 98 ]
then
   # a planned restart - instantly
   echo "98: PLANNED_RESTART";
   exec $0 $@;
fi

if [ $ERR -eq 99 ]
then
   # planned complete exit
   echo "99: PLANNED_SHUTDOWN";
   exit 0;
fi

If I execute the script manually, like this:

[user@host]$ ./workers.sh

It's working perfectly, I can see the output of my PHP script. But if I detach the process from the console, like this:

[user@host]$ ./workers.sh &

It's not working anymore. However I can see the process in the background.

[user@host]$ jobs
[1]+  Stopped                 ./workers.sh email

The Queue jobs server is filling with jobs and none of them are processed until I bring the detached script in the foreground, like this:

[user@host]$ fg

At this moment I see all the job being process by my PHP script. I have no idea why this is happening. Could you help, please?

Thanks, Maxime

EDIT:

I've create a shell script to run x workers, I'm sharing it here. Not sure it's the best way to do it but it's working well at the moment:

#!/bin/bash

WORKER_PATH="/var/webserver/user/workers.sh"
declare -A Queue
Queue[email]=2
Queue[process-images]=5

for key in "${!Queue[@]}"
do
  echo "Launching ${Queue[$key]} instance(s) of $key Worker..."
  CMD="$WORKER_PATH $key"
  for (( l=1; l<=${Queue[$key]}; l++ ))
    do
        INSTANCE="$CMD $l"
        echo "lnch instance $INSTANCE"
        nice $INSTANCE > /dev/null 2> /dev/null &
    done
done

Answer 1

Background processes are not allowed to write to the terminal, which your script tries to do with the echo statements. You just need to redirect standard output to a file when you put it to the background.

[user@host]$ ./workers.sh > workers.output 2> workers.error &

(I've redirected standard error as well, just to be safe.)