我知道很多主题都有相同的问题，但我已经尝试了所有的方法，但都不适用。所以我尝试在我的ubuntu stretch上安装php7.4。我已经完成了我在互联网上找到的以下命令：
apt install ca-certificates apt-transport-https wget gnupg
wget -q https://packages.sury.org/php/apt.gpg -O- | apt-key add -
echo "deb https://packages.sury.org/php/ buster main" | tee /etc/apt/sources.list.d/php.list
apt update
apt install php7.4
然后我得到错误：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
php7.4 : Depends: libapache2-mod-php7.4 but it is not going to be installed or
php7.4-fpm but it is not going to be installed or
php7.4-cgi but it is not going to be installed
Depends: php7.4-common but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
我看到有人跟踪错误，试图安装导致问题的dependencies。所以我做了
apt install php7.4-common
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
php7.4-common : Depends: libc6 (>= 2.27) but 2.24-11+deb9u4 is to be installed
E: Unable to correct problems, you have held broken packages.
我在某个地方看到它可能是我的/etc/apt/sources.list中的某个东西，所以它在这里：
# Generated by distrobuilder
deb http://deb.debian.org/debian stretch main
deb http://security.debian.org/debian-security stretch/updates main
我被卡住了，我不知道怎么了。你能帮忙吗？感谢
请为Ubuntu尝试以下命令：
sudo apt install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt update