Running PHP script from command line as background process

nohup php file.php > /dev/null 2>&1 &

The greater-thans (>) in commands like these redirect the program’s output somewhere. In this case, something is being redirected to /dev/null, and something is being redirected to &1

Standard in, out, and error

There are three standard sources of input and output for a program. Standard input usually comes from the keyboard if it’s an interactive program, or from another program if it’s processing the other program’s output. The program usually prints to standard output, and sometimes prints to standard error. These three file descriptors (you can think of them as “data pipes”) are often called STDIN, STDOUT, and STDERR.

Sometimes they’re not named, they’re numbered! The built-in numberings for them are 0, 1, and 2, in that order. By default, if you don’t name or number one explicitly, you’re talking about STDOUT.

the command above is redirecting the standard output to /dev/null, which is a place you can dump anything you don’t want, then redirecting standard error into standard output (you have to put an & in front of the destination when you do this).

The short explanation, therefore, is “all output from this command should be shoved into a black hole.” That’s one good way to make a program be really quiet!

& at the end puts the command in background.

ref: https://www.xaprb.com/blog/2006/06/06/what-does-devnull-21-mean/

Are you sure the script doesn't contain any errors? This is what normally makes "execution terminates very quickly".
First, append:

error_reporting(E_ALL); ini_set('display_errors', 1);

at the top of your script to display any errors it may have, then you can use :

nohup php filename.php &

nohup runs a command even if the session is disconnected or the user logs out.

OR

nohup php filename.php >/dev/null 2>&1 &

Same as above but doesn't create nohup.out file.

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You can also use:
ignore_user_abort(1);

Set whether a client disconnect should abort script execution

`set_time_limit(0);`

Limits the script maximum execution time, in this case it will run until the process finishes or the apache process restarts.

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#Notes The php and the filename.php paths may be provided as a full-path, instead of php and filename.php, you can use /usr/bin/php and /full/path/to/filename.php.
Full Path is recommended to avoid file not found errors.

the process may be closed when your session is closed.

try using nohup php filename.php