我遇到了这个问题，使用laravel 5.4和PHP 7进行安装
您的要求无法解析为可安装的软件包。
问题1 - phpunit / phpunit 5.5.5需要ext-dom * - ＆gt;系统中缺少所请求的PHP扩展名dom。
- phpunit/phpunit 5.5.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.5.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.5.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.5.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.5.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.8 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.7 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.6 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.4.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.3.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.3.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.3.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.3.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.3.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.3.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.9 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.8 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.7 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.6 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.12 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.11 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.10 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.2.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.7 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.6 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.1.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.9 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.8 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.7 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.6 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.4 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.3 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.10 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.1 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- phpunit/phpunit 5.0.0 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- Installation request for phpunit/phpunit ~5.0 -> satisfiable by phpunit/phpunit[5.0.0, 5.0.1, 5.0.10, 5.0.2, 5.0.3, 5.0.4, 5.0.5, 5.0.6, 5.0.7, 5.0.8, 5.0.9, 5.1.0, 5.1.1, 5.1.2, 5.1.3, 5.1.4, 5.1.5, 5.1.6, 5.1.7, 5.2.0, 5.2.1, 5.2.10, 5.2.11, 5.2.12, 5.2.2, 5.2.3, 5.2.4, 5.2.5, 5.2.6, 5.2.7, 5.2.8, 5.2.9, 5.3.0, 5.3.1, 5.3.2, 5.3.3, 5.3.4, 5.3.5, 5.4.0, 5.4.1, 5.4.2, 5.4.3, 5.4.4, 5.4.5, 5.4.6, 5.4.7, 5.4.8, 5.5.0, 5.5.1, 5.5.2, 5.5.3, 5.5.4, 5.5.5].
要启用扩展程序，请验证它们是否已在这些.ini文件中启用：
- /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-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
您也可以在终端内运行php --ini以查看PHP在CLI模式下使用的文件。
答案 0 :(得分：0)
要解决此问题，我已进行了一些安装：
sudo apt-get install yum （你需要安装php dom扩展） 还有问题尚未解决，请执行此操作 sudo apt-get install php-xml