DEV Community: Dominic Koech

Linux Directory Structure Overview

Dominic Koech — Thu, 15 Sep 2022 05:14:19 +0000

Linux is an extremely useful tool, particularly for developers and cybersecurity professionals. Knowing the ins and outs of the Linux system and how things are organized in it is thus advantageous.
In this article, I'll walk you through the Linux file system's directory structure. This article is intended for people who are still new to the Linux operating system.

In the design of its system, Linux employs the Filesystem Hierarchy Standard (FHS). In this standard, all system files and directories are stored in the root directory(/), regardless of whether they are on virtual or physical devices.

/

This is the top-level directory. It contains all of the files in your Linux file system. It is similar to the C: directory in Windows.

/boot

This directory contains boot-related files. These are the files that are required to boot the system. Before the kernel begins executing user-mode programs, data found here is processed. Grub Boot loader files and vmlinux are two examples of such files.

/bin

This directory contains essential user binaries, also known as "executable programs" by some. One thing to keep in mind is that /bin contains shells such as bash and zsh, as well as common Linux commands such as ps, ls, rm, and so on that all users can use. Browsers and other binaries are kept in /usr/bin/.

/dev

Device files are stored in the /dev directory. Device files are hardware devices that are connected to your Linux system and with which applications interact via I/O system calls. This demonstrates an important aspect of the Linux filesystem: everything is either a file or a directory.
The /dev/null device file is one to be aware of. Anything sent here vanishes; it's like a "black hole."

/etc

This directory contains Linux System configuration files, such as boot loader configuration files.

/etc/opt stores configuration for add-on packages
/etc/SGML stores configuration for software that processes SGML
/etc/xll stores configuration for the X Window System
/etc/XML stores configuration for software that processes XML
/etc/passwd stored encrypted user passwords

Configuration files affecting specific users are in the user's home directory.

/home

This directory contains each user's home folder. The data and configuration files are stored in folders named after the user's username.

/lib

This directory contains kernel modules and shared system libraries required by /bin and /sbin. The filenames in this directory are in the ld* or lib*.so.* format.

/found+lost

Any corrupted files discovered while rebooting are saved in this directory. This allows you to recover as much data as possible.

/media

This is the location where removable devices are mounted. USB disks, CD/DVD ROM (mounted at /media/cdrom), floppy disks (mounted at /media/floppy), and other similar devices are examples. The contents of those devices are accessible from this page. ### /media

/mnt

This is where sysadmins mount temporary file systems while using them. Network shares are one example.

/opt

Packages for add-on applications can be found here. These are proprietary/third-party applications that are not available in the distribution repository.

/proc

It contains data on system processes, the kernel, and configuration parameters. Because it is a virtual filesystem, it does not contain any'real' files.

/root

This is the root user's home directory. It should be noted that only the root user has permission to write in this directory.

/run

It saves volatile data that occurs during runtime.

/sbin

This directory contains binaries that a system administrator uses to perform system maintenance and/or administrative tasks.

/srv

This directory contains data files for the system's services. For example, apache server or FTP server website files.

/sys

Modern Linux systems include this directory. It's a virtual filesystem that stores data on hardware devices, drivers, and kernel features.

/tmp

The system or the user creates the temporary application files in this store. Every time the system reboots, these files are deleted.

/usr

Users' binaries, programs, utilities, and files are stored in this directory.

User binary files are located in /usr/bin.
System binaries used by system administrators, such as sshd and userdel, are located in /usr/sbin.
/usr/lib contains libraries for /usr/bin and /usr/sbin.
Source-installed programs are located in /usr/local.
The standard include files are located in /usr/include.
The kernel's source code can be found in /usr/src.
Documentation that is shared by all libraries can be found in /usr/share.

/var

This directory contains variable files. These are files whose contents will be changed as the system runs. System log files, lock files, print queues, and so on are examples of such files.

/var/cache - This directory stores cached files from application programs.
/var/lib - This directory contains dynamic data libraries and files.
/var/log - This directory contains log files.
/var/opt - variable data of /opt/ packages
/var/mail - This directory stores mailbox files.
/var/spool - Queued tasks are stored in this directory.
/var/run - Stores information about the system since it was booted up.
/var/tmp - It stores temporary files saved between system reboots.
/var/log - This directory contains lock files created by programs to indicate that a specific file or device is in use.

Summary

I hope this article has given you a general understanding of how top-level Linux directories are organized.

I appreciate your time.

Deploying Python Telegram Bot On Heroku Without Using Flask

Dominic Koech — Mon, 22 Aug 2022 06:01:57 +0000

You've already built your telegram bot and it's running perfectly in your local machine, now you want to deploy and run it on Heroku without having to use the flask framework. In this article, I'll give you a step-to-step guide on how to do exactly that.

Prerequisites

You should have the following:-

Heroku account.You can create one at https://signup.heroku.com/
A telegram bot that is working in your local machine. (If you don't have one, no worries, I'll guide you on how to make a simple one).

Let's get started...

Open where you have the code that runs your telegram bot, in case you don't have one already you can copy the code below for a simple bot that I've created that echoes a text sent to it.

from telegram.ext import *
from telegram import *

TOKEN = 'Your API Key'


def echo_message(update, context):
    update.message.reply_text(f'{update.message.text}')


def main():
    updater = Updater(TOKEN, use_context=True)
    disp = updater.dispatcher
    disp.add_handler(MessageHandler(Filters.regex(r'.*'), echo_message))
    updater.start_polling()
    updater.idle()


if __name__ == '__main__':
    main()

Creating an app on Heroku

Log into Heroku and head over to dashboard >> new >> create a new app. Enter your app name and select your region then click create. For me, I'll use 'testingnotes' as my app name and USA as my region.

Select settings then scroll down to domains and copy the URL for your app that you'll be given, you'll use this later on.

You'll get your URL here:-

Modifying your telegram bot code

To deploy the telegram bot on Heroku, make the following changes in your python code.

At the top of the code add the following lines:-

import os

TOKEN = os.environ.get('TOKEN')
PORT = int(os.environ.get('PORT',88))

The changes made enable you to get the API key and PORT (port which the bot will be listening to) from the environment variables.

At the end of the code remove updater.start_polling() and add the following lines:-

    updater.start_webhook(listen="0.0.0.0",
                          port=int(PORT),
                          url_path=TOKEN,
                          webhook_url='app URL that you copied from Heroku + TOKEN)
    updater.idle()

Create a profile and name it 'Procfile' without using any extensions and add the following to it:

web: python3 main.py $PORT

'main.py' is the python file that starts the bot.

Create a requirements.txt file by typing the following commands in your virtual environment:

pip freeze > requirements.txt

The code for your bot should be looking like this now:

from telegram.ext import *
from telegram import *
import os

TOKEN = os.environ.get('TOKEN')

PORT = int(os.environ.get('PORT', 88))

def echo_message(update, context):
    update.message.reply_text(f'{update.message.text}')


def main():
    updater = Updater(TOKEN, use_context=True)
    disp = updater.dispatcher
    disp.add_handler(MessageHandler(Filters.regex(r'.*'), echo_message))
    updater.start_webhook(listen="0.0.0.0",
                          port=int(PORT),
                          url_path=TOKEN,
                          webhook_url='https://testingnotes.herokuapp.com/' + TOKEN)

    updater.idle()


if __name__ == '__main__':
    main()

Deploying

Open the terminal, move to where the project folder is and type the following commands:

$ Heroku login
$ git init
$ heroku git:remote -a appname
$ git add.
$ git commit -am "make it better"
$ git push Heroku master

If the deployment is successful you'll see the following message.

Head to settings then Config Vars. Add 'TOKEN' as the key and then put your API key as the value.

You'll put the API key here:-

Now head back to telegram and interact with your bot. It should be working.

Python Input Validation Using PyInputPlus Module

Dominic Koech — Sun, 26 Jun 2022 14:40:00 +0000

In this article, I'll be covering how to validate user inputs in python using PyInputPlus.

Introduction

Input validation is checking whether the value given by the user is of the correct format i.e if an email is to be provided by the user then the code should not accept anything other than an email. Improper input validation will cause bugs and vulnerabilities in the system.

PyInputPlus is a python module created by AI Sweigart that takes user input and checks whether it is valid. If invalid input is provided, it will keep on asking for input until a valid input is given.PyInputplus has functions such as inputStr(), inputInt(), InputDate() among others which are used in validating user input.

Installation

To install the module type the command below in your terminal:

pip install --user pyinputplus

To use it in your code add the following at the beginning of your code:

import pyinputplus as pyip

Pyinputplus is a long name hence we use pyip to save us time.

Functions in PyInputPlus

1. inputNum()

This function only accepts integers and floating-point numbers from the user.

>>> import pyinputplus as pyip
>>> result = pyip.inputNum()
who
'who' is not a number.
22
>>> result
22

>>> result = pyip.inputNum()
22.4
>>> result
22.4

From the snippets above you can see that 'who' is rejected because it is a string while 22.4 and 22 are accepted since they are floating-point values and integers respectively.

2. inputInt()

This function only accepts integer values and will reject floating-point values and strings.

>>> import pyinputplus as pyip
>>> result = pyip.inputInt()
mike
'mike' is not an integer.
22.4
'22.4' is not an integer.
30
>>> result
30

From the snippet above 'mike' will be rejected because it is a string and '22.4' will be rejected because it is a floating-point value.

3. inputStr()

This function is similar to the input() function but has features of PyInputPlus functions.

>>> import pyinputplus as pyip
>>> result = pyip.inputStr()
34
>>> result
'34'
>>> result = pyip.inputStr()
mike
>>> result
'mike'
>>> result = pyip.inputStr()
22.4
>>> result
'22.4'

In the snippet above you see that integers, strings, and floats are accepted as inputs but are returned as strings.

4. inputChoice()

This function gives users a list of choices from which to choose and only accepts one of the choices.

>>> import pyinputplus as pyip
>>> result = pyip.inputChoice(['bee','dog','sheep'])
Please select one of: bee, dog, sheep
mike
'mike' is not a valid choice.
Please select one of: bee, dog, sheep
12
'12' is not a valid choice.
Please select one of: bee, dog, sheep
dog
>>> result
'dog'

From the snippet above 'mike' and '12' are rejected because they are not in the list provided as an argument. You can provide a list or a tuple as an argument in the function.

5. inputMenu()

It works the same as the inputChoice function but provides a menu that is numbered from which the user should choose.

>>> import pyinputplus as pyip
>>> result = pyip.inputMenu(['bee','dog','sheep'])
Please select one of the following:
* bee
* dog
* sheep
cow
'cow' is not a valid choice.
Please select one of the following:
* bee
* dog
* sheep
12
'12' is not a valid choice.
Please select one of the following:
* bee
* dog
* sheep
bee
>>> result
'bee'

In the snippet above a menu is provided to the user from which they should choose one item from it.'12' and 'cow' is rejected because they are not in the list provided while 'dog' is accepted as the input.

>>> result = pyip.inputMenu(['bee','dog','sheep'], numbered=True)
Please select one of the following:
1. bee
2. dog
3. sheep
2
>>> result
'dog'

Setting the numbered parameter to true numbers the menu items and you can choose an item by giving the corresponding number. A tuple can also be provided as an argument instead of a list.

6. inputDatetime(), inputDate() and inputTime()

These functions ensure the user only provides an input which is a date, time, or both.

>>> import pyinputplus as pyip
>>> result = pyip.inputTime()
12
'12' is not a valid time.
ss
'ss' is not a valid time.
12:00
>>> str(result)
'12:00:00'

In the above snippet the inputTime() function only accepts time in the format hours, minutes then seconds separated by colons. The input into the str() function to change it to a string.'12' and 'ss' are rejected since they are not in the correct format.

>>> result = pyip.inputDate()
12121212
'12121212' is not a valid date.
ww
'ww' is not a valid date.
12/12/2020
>>> str(result)
'2020-12-12'

In the above snippet only dates in the format day,month, year separated by forwarding slashes are accepted as valid user inputs.

>>> result = pyip.inputDatetime()
12:00 12/12/2020
'12:00 12/12/2020' is not a valid date and time.
12/12/2020
'12/12/2020' is not a valid date and time.
12:00
'12:00' is not a valid date and time.
12/12/2020 12:00
>>> str(result)
'2020-12-12 12:00:00'

From the snippet above the only accepted user input is date followed by time, reversing it, the input will be rejected. Date alone or time alone will be rejected.

7. inputFloat()

This function only accepts floating-point values as the only valid user input.

8. inputPassword()

In this function, as the user provides an input, * characters will be displayed to ensure sensitive information such as passwords is not displayed on the screen.

9. inputYesNo()

In this funtion only Yes and No accepted as valid input.

10. inputBool()

In this function True or False is the only accepted user input.

11. inputFilepath()

It ensures that only a file path and filename are entered by the user.

12. inputEmail()

This function accepts only valid email addresses as user input.

13. inputCustom()

Using this function you can create your validation logic by passing a function as an argument to this function.

14. help()

It helps you get more information on other pyinputplus functions. You pass the function's name as an argument.

Common parameters PyInputPlus funtions

min/max/greaterThan/lessThan parameters

These parameters are used in inputNum() , inputInt() , and inputFloat() functions.They help you to specify the range os accepted user input values.

prompt parameter

A text to be displayed before prompting the user for an input.

>>> import pyinputplus as pyip
>>> response = pyip.inputInt(prompt='Enter your age:')
Enter your age:23
>>> response
23

blank parameter

When set to True, the user does not need to enter anything as the input. By default, the blank parameter is set to False.

limit, timeout, and default parameters

The limit parameter specified the number of tries a user is given to enter an input after which it raises a pyinputplus.RetryLimitException exception if the number of limits has been exceeded and no valid input is given.

>>> import pyinputplus as pyip
>>> response = pyip.inputInt(limit=3)
rr
'rr' is not an integer.
rr
'rr' is not an integer.
rr
'rr' is not an integer.
Traceback (most recent call last):
    --snip---
    raise limitOrTimeoutException
pyinputplus.RetryLimitException

The timeout parameter specifies how many seconds to wait for a user inpt before raising a pyinputplus.TimeoutException exception.

>>> import pyinputplus as pyip
>>> response = pyip.inputInt(timeout=5)
23
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
   --snip--
    raise TimeoutException()
pyinputplus.TimeoutException

When you pass a value to the default parameter, the value will be returned instead of raising an exception.

allowRegexes and blockRegexes parameters

AllowRegexes parameter takes a regular expression that specifies what input is to be allowed. Blockregexes parameter takes a regex that specifies what user input should not be accepted. The parameter can take a list of regexes.

>>> result = pyip.inputStr(allowRegexes=[r'^fo.*'])

>>> result = pyip.inputStr(blockRegexes=[r'.*s$'])

Conclusion

Apart from the functions and parameters listed above, others can be found in the official documentation.
As seen PyInputPlus makes the work of validating user input very simple and easy.

Thanks for reading.