我做了什么：
当我运行此apt安装Composer
root@sewa:~/sewa# apt install composer
Reading package lists... Done
Building dependency tree
Reading state information... Done
composer is already the newest version (1.6.3-1).
0 upgraded, 0 newly installed, 0 to remove and 26 not upgraded.
但是运行composer install时我无法安装作曲家，会出现类似这样的错误消息
root@sewa:~/sewa# composer install
Do not run Composer as root/super user! See https://getcomposer.org/root for details
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 dompdf/dompdf v0.8.5 -> satisfiable by dompdf/dompdf[v0.8.5].
- dompdf/dompdf v0.8.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.
Problem 2
- Installation request for laravel/framework v6.18.2 -> satisfiable by laravel/framework[v6.18.2].
- laravel/framework v6.18.2 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
Problem 3
- Installation request for league/commonmark 1.3.1 -> satisfiable by league/commonmark[1.3.1].
- league/commonmark 1.3.1 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
Problem 4
- 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 5
- Installation request for facade/ignition 1.16.1 -> satisfiable by facade/ignition[1.16.1].
- facade/ignition 1.16.1 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
Problem 6
- 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 7
- 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 8
- Installation request for phpunit/phpunit 8.5.2 -> satisfiable by phpunit/phpunit[8.5.2].
- phpunit/phpunit 8.5.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
Problem 9
- 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 10
- 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 11
- dompdf/dompdf v0.8.5 requires ext-dom * -> the requested PHP extension dom is missing from your system.
- barryvdh/laravel-dompdf v0.8.6 requires dompdf/dompdf ^0.8 -> satisfiable by dompdf/dompdf[v0.8.5].
- Installation request for barryvdh/laravel-dompdf v0.8.6 -> satisfiable by barryvdh/laravel-dompdf[v0.8.6].
To enable extensions, verify that they are enabled in your .ini files:
- /etc/php/7.2/cli/php.ini
- /etc/php/7.2/cli/conf.d/10-mysqlnd.ini
- /etc/php/7.2/cli/conf.d/10-opcache.ini
- /etc/php/7.2/cli/conf.d/10-pdo.ini
- /etc/php/7.2/cli/conf.d/20-apcu.ini
- /etc/php/7.2/cli/conf.d/20-apcu_bc.ini
- /etc/php/7.2/cli/conf.d/20-calendar.ini
- /etc/php/7.2/cli/conf.d/20-ctype.ini
- /etc/php/7.2/cli/conf.d/20-exif.ini
- /etc/php/7.2/cli/conf.d/20-fileinfo.ini
- /etc/php/7.2/cli/conf.d/20-ftp.ini
- /etc/php/7.2/cli/conf.d/20-gd.ini
- /etc/php/7.2/cli/conf.d/20-gettext.ini
- /etc/php/7.2/cli/conf.d/20-iconv.ini
- /etc/php/7.2/cli/conf.d/20-json.ini
- /etc/php/7.2/cli/conf.d/20-mysqli.ini
- /etc/php/7.2/cli/conf.d/20-pdo_mysql.ini
- /etc/php/7.2/cli/conf.d/20-phar.ini
- /etc/php/7.2/cli/conf.d/20-posix.ini
- /etc/php/7.2/cli/conf.d/20-readline.ini
- /etc/php/7.2/cli/conf.d/20-shmop.ini
- /etc/php/7.2/cli/conf.d/20-sockets.ini
- /etc/php/7.2/cli/conf.d/20-sysvmsg.ini
- /etc/php/7.2/cli/conf.d/20-sysvsem.ini
- /etc/php/7.2/cli/conf.d/20-sysvshm.ini
- /etc/php/7.2/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.
我要解决的错误
答案 0 :(得分：1)
安装以下php扩展名-
php7.2-mbstring php7.2-dom
运行以下命令进行安装-
sudo apt install php7.2-mbstring php7.2-dom
然后重新启动apache-
sudo systemctl reload apache2