我正在尝试在相对较新（1 周）的 Ubuntu Server 18.04 上安装 Nextcloud。当尝试 apt 安装必要的依赖项时，出现以下错误：
tomas@homeserver:~$ sudo apt install php7.2-xml php7.2-cgi php-7.2-cli php7.2-mysql php7.2-mbstring php7.2-gd php7.2-curl php7.2-zip
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package php-7.2-cli
E: Couldn't find any package by glob 'php-7.2-cli'
E: Couldn't find any package by regex 'php-7.2-cli'
E: Unable to locate package php7.2-mbstring
E: Couldn't find any package by glob 'php7.2-mbstring'
E: Couldn't find any package by regex 'php7.2-mbstring'
E: Unable to locate package php7.2-zip
E: Couldn't find any package by glob 'php7.2-zip'
E: Couldn't find any package by regex 'php7.2-zip'
tomas@homeserver:~$ sudo apt-get install apache2 mariadb-server libapache2-mod-php7.0
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package mariadb-server
E: Unable to locate package libapache2-mod-php7.0
E: Couldn't find any package by glob 'libapache2-mod-php7.0'
E: Couldn't find any package by regex 'libapache2-mod-php7.0'
为什么我的系统无法在存储库中找到这些？