Ubuntu20.04+Nginx环境升级PHP8后Composer仍报版本不兼容问题

给Composer添加新依赖时本地运行一切正常，推送到Ubuntu 20.04服务器后出现如下报错：

Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 8.0.0".

已将服务器PHP版本升级到8.0.12，执行php -v返回结果如下：

# php -v 
PHP 8.0.12 (cli) (built: Oct 22 2021 12:34:48) ( NTS ) 
Copyright (c) The PHP Group 
Zend Engine v4.0.12, Copyright (c) Zend Technologies 
with Zend OPcache v8.0.12, Copyright (c), by Zend Technologies

排查Nginx错误日志发现如下记录：

Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 8.0.0". You are running 7.4.3. in /var/www/html/vendor/composer/platform_check.php on line 24" while reading response header from upstream, client: ........, server: _, request: "GET /login HTTP/1.1", upstream: "fastcgi://unix:/var/run/php/php7.4-fpm.sock:"

可见请求实际调用的是php7.4-fpm.sock，已尝试过如下操作仍未解决问题：

• 修改/etc/nginx/sites-available/default配置文件中PHP相关配置：

location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/var/run/php/php8.0-fpm.sock;
        # fastcgi_index index.php;
        # fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
        # fastcgi_read_timeout 300;
        # include fastcgi_params;
    }

配置已指定php8.0-fpm.sock，但仍调用PHP7.4版本

• 执行sudo apt-get autoremove删除php7.4-fpm相关文件后，出现502 bad gateway报错，日志显示：

connect() to unix:/var/run/php/php7.4-fpm.sock failed

• 执行composer install --ignore-platform-reqs，返回501内部错误

完整sites-available配置如下：

server {
    listen 80;
    server_name _ DOMAIN www.DOMAIN;
    root /var/www/html/public;

    add_header X-Frame-Options "SAMEORIGIN";
    add_header X-XSS-Protection "1; mode=block";
    add_header X-Content-Type-Options "nosniff";

    index index.html index.htm index.php;

    charset utf-8;

    location / {
        try_files $uri $uri/ /index.php$is_args$args;
    }

    location = /favicon.ico { access_log off; log_not_found off; }
    location = /robots.txt  { access_log off; log_not_found off; }

    error_page 404 /index.php;

    fastcgi_read_timeout 300;

    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/var/run/php/php8.0-fpm.sock;
        # fastcgi_index index.php;
        # fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
        # fastcgi_read_timeout 300;
        # include fastcgi_params;
    }

    location ~ /\.(?!well-known).* {
        deny all;
    }
}

问题核心是Nginx未加载更新后的站点配置，按以下步骤操作即可解决：

1. 确认php8.0-fpm服务正常运行：执行systemctl status php8.0-fpm检查状态，若未启动执行systemctl start php8.0-fpm && systemctl enable php8.0-fpm开启服务并设置开机自启
2. 更新Nginx站点软连接：执行ln -sf /etc/nginx/sites-available/default /etc/nginx/sites-enabled/default，确保sites-enabled目录下的配置指向你修改后的最新文件
3. 校验Nginx配置合法性：执行nginx -t，返回test is successful说明配置语法无错误
4. 重载Nginx配置：执行systemctl reload nginx让新配置生效
5. 验证结果：访问项目新增phpinfo页面即可查看Web端实际加载的PHP版本，确认是8.0版本后问题解决

内容的提问来源于stack exchange，提问作者Luuk Bakx