尝试使用命令升级软件包：
sudo apt-get dist-upgrade
但它说网址未找到。我也尝试检查 URL，但显示 404 未找到。
ubuntu@ubuntu-alienware17-r5:~$ sudo apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
libpq5
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 108 kB of archives.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
Err:1 http://security.ubuntu.com/ubuntu bionic-security/main amd64 libpq5 amd64 10.9-0ubuntu0.18.04.1
404 Not Found [IP: 91.189.91.23 80]
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/p/postgresql-10/libpq5_10.9-0ubuntu0.18.04.1_amd64.deb 404 Not Found [IP: 91.189.91.23 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?