Command line script run in background goes in stopped state - linux

Question

I have a short php utility script, I run it from cli simply with:
php myscript.php
The script is always running, periodically performing some tasks (not relevant for the question). It doesn't need any input from the user.
After running it, I usually press CTRL+z and then run bg to put the process in background, and everything is fine.
If I run it as:
php myscript.php &
the script is put on background on start, but it is also put in a stopped state. Example:
[1] 11513
[1]+ Stopped php myscript.php
even running bg at this point doesn't help, I have to run fg, then CTRL+z and bg again to make it work.
This is the php script:
<?
while(true){
echo 'hi '.time()."\n";
sleep(30);
}
?>
My problem is that I cannot run it directly in background, because the system stops it, and I don't understand why. How can I fix this?
update:
I made a bash version of the same script, and it can be run and put in background (running and not stopped) just by launching it with the & in the end (script.sh &)
script.sh:
#!/bin/bash
while true; do
echo `date`
sleep 30
done
Why the php script is being stopped after launching it in background, and the bash script doesn't?
What could cause this different behaviour?

Answer 1

I found what is causing the issue. In PHP, if the readline module is enabled, any command line script will expect an input, even if the script is written to NOT wait for user input.
To check if you have readline support enabled, just run:
php --info |grep "Readline Support"
and check the output. If you get Readline Support => enabled then you have readline enabled and you may experience the problem described in the original question.
The proper way to use the cli when is then to explicitly specify that php is not using the terminal for input:
php myscript.php < /dev/null &
Further info: http://php.net/manual/en/book.readline.php
Alternatives:
./test.php >/dev/null &
or (more creative):
nohup php test.php > /dev/null 2>&1 &
(p.s.: I still believe this question belongs to ServerFault, btw.. problem solved!)

Answer 2

Usually, the process what do you send to background with the & and the script waiting for an input from the terminal, going into the stopped state.
E.g. have a bash script valecho:
#!/bin/sh
read val
echo $val
runnig it as:
./valecho &
the script will stop.
When run it as
echo hello | ./valecho &
will correctly run and finish.
So, check your php - probably wants some input from the stdin
Edit - based on comment:
i'm not an php developer - but just tried the next script (p.php)
<?php
while(true){
   echo 'hi '.time()."\n";
   sleep(3);
}
?>
with the command:
php -f p.php &
and running nicely... so... sry for confusion...

Answer 3

From http://php.net/manual/en/book.readline.php :
When readline is enabled, php switches the terminal mode to accept line-buffered input. This means that the proper way to use the cli when you pipe to an interactive command is to explicitly specify that php is not using the terminal for input:
php myscript.php < /dev/null &
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