ubuntu system upgrade PHP version

1. https://blog.csdn.net/qq_16885135/article/details/79747045     upgrade PHP7.2
2. https://www.cnblogs.com/lalalagq/p/10283528.html     Ubuntu system switching PHP versions
3. https://cloud.tencent.com/developer/ask/191230/answer/298856     PHP version 5.6 to 7 switch failure, possible viable solution
4. https://www.cnblogs.com/qk2014/p/8683493.html     see if php-fpm is on, how to open