Run multiple instance of a program in parallel

You could use a script. Save the following as run-parallel.sh, and make it executable (chmod +x run-parallel.sh):

#! /bin/bash
trap "pkill -P $$; kill -INT $$" INT

while read n
do
    "$@" &
done < <(seq 1000)
wait

Explanation:

• trap ... INT sets a command to be run when the SIGINT signal is received (which is the signal generated when you press CtrlC).
• $$ is the PID of the current process (that is, of the script itself). pkill -P $$ kills those processes whose parent process i the script.
• It is convention that a program which catches SIGINT kill itself using SIGINT once it has tidied up. Hence, the kill -INT $$.
• seq 1000 generates numbers from 1 to 1000.
• The while loop runs the command provided as arguments to the script once for each number from seq, and sends them to the background.
• Then we wait until all of the background processes finish executing.

Run it thus:

./run-parallel.sh php process.php

You can use xargs. Just print the name of the process you want 100 times and pass it to xargs:

perl -e 'print "/path/to/process.php\n" x 100' | xargs -P 100 -I {} php {} 

The Perl command simply prints /path/to/process.php followed by a newline 100 times. This is then passed to xargs which is told to launch up to 100 parallel commands (-P 100). The -I {} tells xargs to replace the string {} with its input. Therefore, php {} is expanded to php /path/to/process.php. Since everything is done by xargs, a single Ctrl+C will kill all of them, and all output is printed to the same terminal.