php artisan command not working in ubuntu

Question

When i do php artisan or php artisan serve in my laravel project it shows some error and I don't know how to solve it. I tried removing composer and again installing it also doing composer update but it does not seem to solve the problem. Operationg System: Ubuntu 20.04 LTS

My Error:

wiggly@Wiggly-Faun:~/Desktop/Web Designing/websites/Ticketing$ php artisan serve
PHP Warning:  require(/home/wiggly/Desktop/Web 
Designing/websites/Ticketing/vendor/autoload.php): failed to open stream: No such file or 
directory in /home/wiggly/Desktop/Web Designing/websites/Ticketing/artisan on line 18
PHP Fatal error:  require(): Failed opening required '/home/wiggly/Desktop/Web 
Designing/websites/Ticketing/vendor/autoload.php' (include_path='.:/usr/share/php') in 
/home/wiggly/Desktop/Web Designing/websites/Ticketing/artisan on line 18

When I do composer install inside my project is shows:

wiggly@Wiggly-Faun:~/Desktop/Web Designing/websites/Ticketing$ 
composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of 
packages.

Problem 1
- Installation request for laravel/framework v7.18.0 -> satisfiable 
by laravel/framework[v7.18.0].
- laravel/framework v7.18.0 requires ext-mbstring * -> the requested 
PHP extension mbstring is missing from your system.
Problem 2
- Installation request for league/commonmark 1.5.1 -> satisfiable by 
league/commonmark[1.5.1].
- league/commonmark 1.5.1 requires ext-mbstring * -> the requested 
PHP extension mbstring is missing from your system.
Problem 3
- Installation request for tijsverkoyen/css-to-inline-styles 2.2.2 - 
> satisfiable by tijsverkoyen/css-to-inline-styles[2.2.2].
- tijsverkoyen/css-to-inline-styles 2.2.2 requires ext-dom * -> the 
requested PHP extension dom is missing from your system.
Problem 4
- Installation request for facade/ignition 2.0.7 -> satisfiable by 
facade/ignition[2.0.7].
- facade/ignition 2.0.7 requires ext-mbstring * -> the requested PHP 
extension mbstring is missing from your system.
Problem 5
- Installation request for phar-io/manifest 1.0.3 -> satisfiable by 
phar-io/manifest[1.0.3].
- phar-io/manifest 1.0.3 requires ext-dom * -> the requested PHP 
extension dom is missing from your system.
Problem 6
- Installation request for phpunit/php-code-coverage 7.0.10 -> 
satisfiable by phpunit/php-code-coverage[7.0.10].
- phpunit/php-code-coverage 7.0.10 requires ext-dom * -> the 
requested PHP extension dom is missing from your system.
Problem 7
- Installation request for phpunit/phpunit 8.5.8 -> satisfiable by 
phpunit/phpunit[8.5.8].
- phpunit/phpunit 8.5.8 requires ext-dom * -> the requested PHP 
extension dom is missing from your system.
Problem 8
- Installation request for scrivo/highlight.php v9.18.1.1 -> 
satisfiable by scrivo/highlight.php[v9.18.1.1].
- scrivo/highlight.php v9.18.1.1 requires ext-mbstring * -> the 
requested PHP extension mbstring is missing from your system.
Problem 9
- Installation request for theseer/tokenizer 1.1.3 -> satisfiable by 
theseer/tokenizer[1.1.3].
- theseer/tokenizer 1.1.3 requires ext-dom * -> the requested PHP 
extension dom is missing from your system.
Problem 10
- laravel/framework v7.18.0 requires ext-mbstring * -> the requested 
PHP extension mbstring is missing from your system.
- facade/flare-client-php 1.3.2 requires illuminate/pipeline 
^5.5|^6.0|^7.0 -> satisfiable by laravel/framework[v7.18.0].
- Installation request for facade/flare-client-php 1.3.2 -> 
satisfiable by facade/flare-client-php[1.3.2].

To enable extensions, verify that they are enabled in your .ini 
files:
- /etc/php/7.4/cli/php.ini
- /etc/php/7.4/cli/conf.d/10-opcache.ini
- /etc/php/7.4/cli/conf.d/10-pdo.ini
- /etc/php/7.4/cli/conf.d/20-calendar.ini
- /etc/php/7.4/cli/conf.d/20-ctype.ini
- /etc/php/7.4/cli/conf.d/20-exif.ini
- /etc/php/7.4/cli/conf.d/20-ffi.ini
- /etc/php/7.4/cli/conf.d/20-fileinfo.ini
- /etc/php/7.4/cli/conf.d/20-ftp.ini
- /etc/php/7.4/cli/conf.d/20-gettext.ini
- /etc/php/7.4/cli/conf.d/20-iconv.ini
- /etc/php/7.4/cli/conf.d/20-json.ini
- /etc/php/7.4/cli/conf.d/20-phar.ini
- /etc/php/7.4/cli/conf.d/20-posix.ini
- /etc/php/7.4/cli/conf.d/20-readline.ini
- /etc/php/7.4/cli/conf.d/20-shmop.ini
- /etc/php/7.4/cli/conf.d/20-sockets.ini
- /etc/php/7.4/cli/conf.d/20-sysvmsg.ini
- /etc/php/7.4/cli/conf.d/20-sysvsem.ini
- /etc/php/7.4/cli/conf.d/20-sysvshm.ini
- /etc/php/7.4/cli/conf.d/20-tokenizer.ini
- /etc/php/7.4/cli/conf.d/20-zip.ini
You can also run `php --ini` inside terminal to see which files are 
used by PHP in CLI mode.

Answer 1

Did you installed all the necessary vendor packages locally? Does your "vendor" directory exists?

Don't forget to use:

composer install

in the project directory to install necessary vendor packages.

Also, make sure you have installed necessary PHP extensions, such as mbstring and xml, you may install them via:

sudo apt install php-xml php-mbstring

Hopefullly this helps solve your question.