Skip to main content

Run Python Scripts Using PHP in a Linux Environment

How to run python or other scripts using PHP or other popular web programming languages in a Linux environment?

Problem

We want to access the PHP program through a web server application (Apache/Nginx). The PHP program needs to run other scripts stored in the same machine.


Sample Problem
  • PHP program is located in /var/www/html/index.php
  • Python program is located in /var/www/html/capture.py
  • Python program will access Pi Camera, capture an image, and store it in /var/www/html/assets/photo.jpg

Solution
index.php should access and run capture.py script. The script is as follows:

$output = shell_exec("python /var/www/html/capture.py");

Execution of external program using shell_exec() or exec() will block the program. The next line of PHP codes will be run after the external program returns an output. So, we shouldn't run an excessive amount of external programs. Clients will wait too long on their browser.

If our application actually needs many external programs to be run, we can make an external program be run as a background process. As a result, we can't retrieve any output of the process directly and we don't need to store the return value of shell_exec() method into a variable.

shell_exec("python /var/www/html/capture.py &> /dev/null &");

capture.py will access Pi Camera and store the captured image.

#!/usr/bin/env python

from picamera import PiCamera
from time import sleep

camera = PiCamera()
sleep(5)
camera.capture('/var/www/html/assets/photo.jpg')

As we access the PHP program through a web server, we are recognized as www-data by the system. It can be different if we change the configuration of our webserver to use another user account.

We need to change ownership of capture.py file by running this command:

chown www-data:www-data /var/www/html/capture.py

Since our python program will store an image file in a directory, the directory should also be owned by www-data.

chown -R www-data:www-data /var/www/html/assets

Have we finished it yet? If we try to access our program via browser, it will result in nothing.

Unfortunately, our simple python program is not an ordinary program. It actually needs to access other programs in the Linux system that provide accessibility to our Pi Camera. Python fails to provide the report to us about this failure.

If we use the default program provided by Raspberry Pi to capture an image e.g. raspistill -o photo.jpg and run it by PHP application as an external program, we will get a message that said: "failed to open vchiq instance". The solution is as follows:

chmod 0666 /dev/vchiq

It's simple. Let's try to access our PHP application.

VCHIQ is a command interface between the running Linux kernel and peripherals related to the video controller. /dev/vhciq provides generic access to those commands for utilizing the camera. It's a decently dangerous interface to expose to random programs, that's why it has restrictive permissions by default.


If you think this article is useful, please share it with your colleagues.

Comments

Popular posts from this blog

Configuring Swap Memory on Ubuntu Using Ansible

If we maintain a Linux machine with a low memory capacity while we are required to run an application with high memory consumption, enabling swap memory is an option. Ansible can be utilized as a helper tool to automate the creation of swap memory. A swap file can be allocated in the available storage of the machine. The swap file then can be assigned as a swap memory. Firstly, we should prepare the inventory file. The following snippet is an example, you must provide your own configuration. [server] 192.168.1.2 [server:vars] ansible_user=root ansible_ssh_private_key_file=~/.ssh/id_rsa Secondly, we need to prepare the task file that contains not only the tasks but also some variables and connection information. For instance, we set /swapfile  as the name of our swap file. We also set the swap memory size to 2GB and the swappiness level to 60. - hosts: server become: true vars: swap_vars: size: 2G swappiness: 60 For simplicity, we only check the exi

Rangkaian Sensor Infrared dengan Photo Dioda

Keunggulan photodioda dibandingkan LDR adalah photodioda lebih tidak rentan terhadap noise karena hanya menerima sinar infrared, sedangkan LDR menerima seluruh cahaya yang ada termasuk infrared. Rangkaian yang akan kita gunakan adalah seperti gambar di bawah ini. Pada saat intensitas Infrared yang diterima Photodiode besar maka tahanan Photodiode menjadi kecil, sedangkan jika intensitas Infrared yang diterima Photodiode kecil maka tahanan yang dimiliki photodiode besar. Jika  tahanan photodiode kecil  maka tegangan  V- akan kecil . Misal tahanan photodiode mengecil menjadi 10kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 10 / (10+10) x Vcc V- = (1/2) x 5 Volt V- = 2.5 Volt Sedangkan jika  tahanan photodiode besar  maka tegangan  V- akan besar  (mendekati nilai Vcc). Misal tahanan photodiode menjadi 150kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 150 / (150+10) x Vcc V- = (150/160) x 5

Installing VSCode Server Manually on Ubuntu

I've ever gotten stuck on updating the VSCode server on my remote server because of an unstable connection between my remote server and visualstudio.com that host the updated server source codes. The download and update process failed over and over so I couldn't remotely access my remote files through VSCode. The solution is by downloading the server source codes through a host with a stable connection which in my case I downloaded from a cloud VPS server. Then I transfer the downloaded source codes as a compressed file to my remote server through SCP. Once the file had been on my remote sever, I extracted them and align the configuration. The more detailed steps are as follows. First, we should get the commit ID of our current VSCode application by clicking on the About option on the Help menu. The commit ID is a hexadecimal number like  92da9481c0904c6adfe372c12da3b7748d74bdcb . Then we can download the compressed server source codes as a single file from the host.

Resize VirtualBox LVM Storage

VirtualBox is a free solution to host virtual machines on your computer. It provides configuration options for many components on our machine such as memory, storage, networking, etc. It also allows us to resize our machine storage after its operating system is installed. LVM is a volume manager in a Linux platform that helps us to allocate partitions in the system and configure the storage size that will be utilized for a specific volume group. There are some points to be noticed when we work with LVM on VirtualBox to resize our storage. These are some steps that need to be performed. 1. Stop your machine before resizing the storage. 2. Set new storage size using GUI by selecting " File > Virtual Media Manager > Properties " then find the desired virtual hard disk name that will be resized. OR , by running a CLI program located in " Program Files\Oracle\VirtualBox\VBoxManage.exe ".  cd "/c/Program Files/Oracle/VirtualBox" ./VBoxManage.exe list

Managing MongoDB Records Using NestJS and Mongoose

NestJS is a framework for developing Node.js-based applications. It provides an additional abstraction layer on top of Express or other HTTP handlers and gives developers a stable foundation to build applications with structured procedures. Meanwhile, Mongoose is a schema modeling helper based on Node.js for MongoDB. There are several main steps to be performed for allowing our program to handle MongoDB records. First, we need to add the dependencies which are @nestjs/mongoose , mongoose , and @types/mongoose . Then, we need to define the connection configuration on the application module decorator. import { MongooseModule } from '@nestjs/mongoose'; @Module({ imports: [ MongooseModule.forRoot('mongodb://localhost:27017/mydb'), ], controllers: [AppController], providers: [AppService], }) Next, we create the schema definition using helpers provided by NestJS and Mongoose. The following snippet is an example with a declaration of index setting and an o

Generate API Documentation Using Swagger Module in NestJS

Swagger provides us a standard to generate API documentation based on the Open API specification. If we use NestJS for building our API providers, we can utilize a tool provided by NestJS in the  @nestjs/swagger  module to generate the documentation automatically in the built time. This module also requires the swagger-ui-express module if we use Express as the NestJS base HTTP handler. Set Swagger configuration First, we need to define Swagger options and instantiate the documentation provider on the main.ts file. import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger'; // sample application instance const app = await NestFactory.create(AppModule); // setup Swagger options const options = new DocumentBuilder() .setTitle('Coffee') .setVersion('1.0') .setDescription('Learn NestJS with coffee') .build(); // build the document const document = SwaggerModule.createDocument(app, options); // provide an endpoint