Galera, boa noite. Alguém pode me ajudar? Estou com uns problemas ao criar um projeto, na verdade as dependências até são criadas porém aparece uns avisos estranhos, crio que não seja normal.

Avisos:

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for laravel/framework v5.2.39 -> satisfiable by laravel/framework[v5.2.39].
    - laravel/framework v5.2.39 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
  Problem 2
    - Installation request for phpunit/phpunit 4.8.26 -> satisfiable by phpunit/phpunit[4.8.26].
    - phpunit/phpunit 4.8.26 requires ext-dom * -> the requested PHP extension dom is missing from your system.

Criando o projeto:

carlos@carlos-S400CA:~/Documentos$ laravel new estoque
Crafting application...
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 v5.2.39 -> satisfiable by laravel/framework[v5.2.39].
    - laravel/framework v5.2.39 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
  Problem 2
    - Installation request for phpunit/phpunit 4.8.26 -> satisfiable by phpunit/phpunit[4.8.26].
    - phpunit/phpunit 4.8.26 requires ext-dom * -> the requested PHP extension dom is missing from your system.

  To enable extensions, verify that they are enabled in those .ini files:
    - /etc/php/7.0/cli/php.ini
    - /etc/php/7.0/cli/conf.d/10-opcache.ini
    - /etc/php/7.0/cli/conf.d/10-pdo.ini
    - /etc/php/7.0/cli/conf.d/20-calendar.ini
    - /etc/php/7.0/cli/conf.d/20-ctype.ini
    - /etc/php/7.0/cli/conf.d/20-exif.ini
    - /etc/php/7.0/cli/conf.d/20-fileinfo.ini
    - /etc/php/7.0/cli/conf.d/20-ftp.ini
    - /etc/php/7.0/cli/conf.d/20-gettext.ini
    - /etc/php/7.0/cli/conf.d/20-iconv.ini
    - /etc/php/7.0/cli/conf.d/20-json.ini
    - /etc/php/7.0/cli/conf.d/20-phar.ini
    - /etc/php/7.0/cli/conf.d/20-posix.ini
    - /etc/php/7.0/cli/conf.d/20-readline.ini
    - /etc/php/7.0/cli/conf.d/20-shmop.ini
    - /etc/php/7.0/cli/conf.d/20-sockets.ini
    - /etc/php/7.0/cli/conf.d/20-sysvmsg.ini
    - /etc/php/7.0/cli/conf.d/20-sysvsem.ini
    - /etc/php/7.0/cli/conf.d/20-sysvshm.ini
    - /etc/php/7.0/cli/conf.d/20-tokenizer.ini
    - /etc/php/7.0/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.
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