问题说明：

执行composer install遇到错误：Your requirements could not be resolved to an installable set of packages. 这是因为不匹配composer.json要求的版本。

$ composer install
 
Your requirements could not be resolved to an installable set of packages.
 
  Problem 1
    - laravel-notification-channels/webpush 3.0.0 requires minishlink/web-push ^2.0 -> satisfiable by minishlink/web-push[v2.0.0, v2.0.1].
    - laravel-notification-channels/webpush 3.0.1 requires minishlink/web-push ^2.0 -> satisfiable by minishlink/web-push[v2.0.0, v2.0.1].
    - minishlink/web-push v2.0.0 requires mdanter/ecc ^0.5.0 -> satisfiable by mdanter/ecc[v0.5.0, v0.5.1, v0.5.2].
    - minishlink/web-push v2.0.1 requires mdanter/ecc ^0.5.0 -> satisfiable by mdanter/ecc[v0.5.0, v0.5.1, v0.5.2].
    - mdanter/ecc v0.5.2 requires ext-gmp * -> the requested PHP extension gmp is missing from your system.
    - mdanter/ecc v0.5.1 requires ext-gmp * -> the requested PHP extension gmp is missing from your system.
    - mdanter/ecc v0.5.0 requires ext-gmp * -> the requested PHP extension gmp is missing from your system.
    - Installation request for laravel-notification-channels/webpush ^3.0 -> satisfiable by laravel-notification-channels/webpush[3.0.0, 3.0.1].
 
  To enable extensions, verify that they are enabled in your .ini files:
    - /usr/local/php7.2.9/etc/php.ini
  You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

提示我的PHP 7版本太高，不符合composer.json需要的版本，但是在PHP 7下应该也是可以运行的，composer可以设置忽略版本匹配，命令是：

$ composer install --ignore-platform-reqs

或者

$ composer update --ignore-platform-reqs

问题二.

说明：报关于php gmp扩展问题

$ 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
    - mdanter/ecc v0.5.2 requires ext-gmp * -> the requested PHP extension gmp is missing from your system.
    - mdanter/ecc v0.5.2 requires ext-gmp * -> the requested PHP extension gmp is missing from your system.
    - Installation request for mdanter/ecc v0.5.2 -> satisfiable by mdanter/ecc[v0.5.2].
 
  To enable extensions, verify that they are enabled in your .ini files:
    - /usr/local/php7.2.9/etc/php.ini
  You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

解决

说明：安装php gmp扩展库

$ yum install -y gmp-devel
 
$ cd /usr/local/php-fpm7.2.9/ext/gmp/
 
$ /usr/local/php-fpm7.2.9/bin/phpize
 
$ ./configure --with-php-config=/usr/local/php-fpm7.2.9/bin/php-config --with-gmp
 
$ make && make install
 
 
 
#在php.ini
 
加入：
 
extension=gmp.so
 
 
#重启php
/etc/ini.t/php-fpm restart

内存相关的报错

$ composer update nothing
 
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)
Package operations: 28 installs, 0 updates, 0 removals
  - Installing symfony/yaml (v3.4.23): The following exception is caused by a lack of memory or swap, or not having swap configured
Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for details
 
PHP Warning:  proc_open(): fork failed - Cannot allocate memory in phar:///usr/bin/composer/vendor/symfony/console/Application.php on line 952
 
Warning: proc_open(): fork failed - Cannot allocate memory in phar:///usr/bin/composer/vendor/symfony/console/Application.php on line 952
                                                     
  [ErrorException]                                   
  proc_open(): fork failed - Cannot allocate memory

解决：

增加虚拟内存,重新再执行composer install or composer update nothing 就不会报错啦

$ dd if=/dev/zero of=/tmp/newdisk bs=1024 count=1024000
$ du -sh /tmp/newdisk
$ mkswap /tmp/newdisk
$ chmod 0600 /tmp/newdisk
$ swapon /tmp/newdisk