:~$ sudo apt install bind9
[sudo] password for ceru:
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: The package libgdm1 needs to be reinstalled, but I can't find an archive for it.
:~$ sudo apt install dnsutils
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: The package libgdm1 needs to be reinstalled, but I can't find an archive for it.
尝试 sudo apt update 后，结果显示：
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/u2t/bleedingedge/ubuntu cosmic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
有人能帮我解决这个问题吗？我是 Linux 新手，所有安装都遇到问题，这是其中一个问题。谢谢。