Composer install error di Ubuntu server 16.04

Beberapa saat yang lalu menemukan error ketika pertamakali install Laravel di Ubuntu server 16.04 dengan php 7.1. Setelah clone dari repo Gitlab, kemudian insatall composer berhasil. ketika

 composer install

muncul error

Problem 1

   - Installation request for doctrine/inflector v1.3.0 -> satisfiable by doctrine/inflector[v1.3.0].

   - doctrine/inflector v1.3.0 requires php ^7.1 -> your PHP version (7.0.32) does not satisfy that requirement.

 Problem 2

   - Installation request for symfony/css-selector v4.1.6 -> satisfiable by symfony/css-selector[v4.1.6].

   - symfony/css-selector v4.1.6 requires php ^7.1.3 -> your PHP version (7.0.32) does not satisfy that requirement.

 Problem 3

   - Installation request for symfony/event-dispatcher v4.1.6 -> satisfiable by symfony/event-dispatcher[v4.1.6].

   - symfony/event-dispatcher v4.1.6 requires php ^7.1.3 -> your PHP version (7.0.32) does not satisfy that requirement.

 Problem 4

   - Installation request for symfony/translation v4.1.6 -> satisfiable by symfony/translation[v4.1.6].

   - symfony/translation v4.1.6 requires php ^7.1.3 -> your PHP version (7.0.32) does not satisfy that requirement.

 Problem 5

   - Installation request for doctrine/instantiator 1.1.0 -> satisfiable by doctrine/instantiator[1.1.0].

   - doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (7.0.32) does not satisfy that requirement.

 Problem 6

   - Installation request for myclabs/deep-copy 1.8.1 -> satisfiable by myclabs/deep-copy[1.8.1].

   - myclabs/deep-copy 1.8.1 requires php ^7.1 -> your PHP version (7.0.32) does not satisfy that requirement.

 Problem 7

   - Installation request for phar-io/manifest 1.0.1 -> satisfiable by phar-io/manifest[1.0.1].

   - phar-io/manifest 1.0.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.

 Problem 8

   - Installation request for phpunit/php-code-coverage 5.3.2 -> satisfiable by phpunit/php-code-coverage[5.3.2].

   - phpunit/php-code-coverage 5.3.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.

 Problem 9

   - Installation request for phpunit/phpunit 6.5.13 -> satisfiable by phpunit/phpunit[6.5.13].

   - phpunit/phpunit 6.5.13 requires ext-dom * -> the requested PHP extension dom is missing from your system.

 Problem 10

   - Installation request for theseer/tokenizer 1.1.0 -> satisfiable by theseer/tokenizer[1.1.0].

   - theseer/tokenizer 1.1.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

 Problem 11

   - doctrine/inflector v1.3.0 requires php ^7.1 -> your PHP version (7.0.32) does not satisfy that requirement.

   - laravel/framework v5.5.44 requires doctrine/inflector ~1.1 -> satisfiable by doctrine/inflector[v1.3.0].

   - Installation request for laravel/framework v5.5.44 -> satisfiable by laravel/framework[v5.5.44].

   ----------

   Do not run Composer as root/super user! See https://getcomposer.org/root for details

Loading composer repositories with package information

Updating dependencies (including require-dev)

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

  Problem 1

    - phpunit/phpunit 6.5.9 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.8 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.7 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.6 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.13 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.12 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.11 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.10 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.5.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.4.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.4.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.4.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.4.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.4.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.3.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.3.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.2.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.2.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.2.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.2.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.2.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.1.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.1.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.1.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.1.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.1.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.9 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.8 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.7 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.6 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.13 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.12 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.11 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.10 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - phpunit/phpunit 6.0.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.

    - Installation request for phpunit/phpunit ~6.0 -> satisfiable by phpunit/phpunit[6.0.0, 6.0.1, 6.0.10, 6.0.11, 6.0.12, 6.0.13, 6.0.2, 6.0.3, 6.0.4, 6.0.5, 6.0.6, 6.0.7, 6.0.8, 6.0.9, 6.1.0, 6.1.1, 6.1.2, 6.1.3, 6.1.4, 6.2.0, 6.2.1, 6.2.2, 6.2.3, 6.2.4, 6.3.0, 6.3.1, 6.4.0, 6.4.1, 6.4.2, 6.4.3, 6.4.4, 6.5.0, 6.5.1, 6.5.10, 6.5.11, 6.5.12, 6.5.13, 6.5.2, 6.5.3, 6.5.4, 6.5.5, 6.5.6, 6.5.7, 6.5.8, 6.5.9].

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

    - /etc/php/7.0/cli/php.ini

    - /etc/php/7.0/cli/conf.d/10-mysqlnd.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-mbstring.ini

    - /etc/php/7.0/cli/conf.d/20-mcrypt.ini

    - /etc/php/7.0/cli/conf.d/20-mysqli.ini

    - /etc/php/7.0/cli/conf.d/20-pdo_mysql.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

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

Setelah googling menemukan reverensi

https://stackoverflow.com/questions/43408604/php7-install-ext-dom-issue

dan saya ketik command

sudo apt-get update

sudo apt install php-xml

dan walaa.....

Error hilang...