Problem:
[root@localhost laravel_demo]# 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

– phpunit/phpunit 4.8.35 requires ext-dom * -> the requested PHP extension dom is missing from your system.

– phpunit/phpunit 4.8.35 requires ext-dom * -> the requested PHP extension dom is missing from your system.

– Installation request for phpunit/phpunit 4.8.35 -> satisfiable by phpunit/phpunit[4.8.35].

To enable extensions, verify that they are enabled in your .ini files:

– /etc/php.ini

– /etc/php.d/bz2.ini

– /etc/php.d/calendar.ini

– /etc/php.d/ctype.ini

– /etc/php.d/curl.ini

– /etc/php.d/exif.ini

– /etc/php.d/fileinfo.ini

– /etc/php.d/ftp.ini

– /etc/php.d/gd.ini

– /etc/php.d/gettext.ini

– /etc/php.d/gmp.ini

– /etc/php.d/iconv.ini

– /etc/php.d/json.ini

– /etc/php.d/ldap.ini

– /etc/php.d/mbstring.ini

– /etc/php.d/mcrypt.ini

– /etc/php.d/mysqli.ini

– /etc/php.d/pdo.ini

– /etc/php.d/pdo_mysql.ini

– /etc/php.d/pdo_sqlite.ini

– /etc/php.d/phar.ini

– /etc/php.d/shmop.ini

– /etc/php.d/simplexml.ini

– /etc/php.d/sockets.ini

– /etc/php.d/sqlite3.ini

– /etc/php.d/tokenizer.ini

– /etc/php.d/xml.ini

– /etc/php.d/zip.ini

You can also run `php –ini` inside terminal to see which files are used by PHP in CLI mode.

Solution:
[root@localhost ~]# yum search php70w    Check the packages available for installation
[root@localhost ~]# yum -y install php70w-xml.x86_64
[root@localhost ~]# systemctl restart httpd.service restart apache

Test:
[root@localhost ~]# systemctl restart httpd.service
[root@localhost ~]# cd /home/www/laravel_demo/
[root@localhost laravel_demo]# composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Package operations: 0 installs, 2 updates, 0 removals
– Updating symfony/event-dispatcher (v3.2.4 => v3.2.3): Downloading (100%)
– Updating symfony/yaml (v3.2.4 => v3.2.3): Downloading (100%)
Generating autoload files
> Illuminate\Foundation\ComposerScripts::postInstall
> php artisan optimize
Generating optimized class loader