Ubuntu 20.04下apt-get安装qemu-system-x86时软件包版本不匹配导致下载失败的问题求助

各位好，我在Ubuntu 20.04系统上尝试用apt-get安装qemu-system-x86时遇到了棘手的问题：apt-get想要获取的软件包版本和仓库里实际存在的版本不一致，导致部分包下载失败，报404错误。

具体来说，apt-get试图拉取的是qemu-system-common_4.2-3ubuntu6.21_amd64.deb这类版本，但仓库里现在只有qemu-system-common_4.2-3ubuntu6.24_amd64.deb，版本号对不上。

以下是我执行安装命令时的完整终端输出：

$ sudo apt-get install qemu-system-x86

Reading package lists... Done

Building dependency tree

Reading state information... Done

The following additional packages will be installed:

cpu-checker ipxe-qemu ipxe-qemu-256k-compat-efi-roms msr-tools ovmf qemu-system-common qemu-system-data qemu-system-gui seabios

Suggested packages:

samba vde2

The following NEW packages will be installed:

cpu-checker ipxe-qemu ipxe-qemu-256k-compat-efi-roms msr-tools ovmf qemu-system-common qemu-system-data qemu-system-gui qemu-system-x86 seabios

0 upgraded, 10 newly installed, 0 to remove and 228 not upgraded.

Need to get 12.5 MB of archives.

After this operation, 51.5 MB of additional disk space will be used.

Do you want to continue? [Y/n]

Get:1 http://ca.archive.ubuntu.com/ubuntu focal/main amd64 msr-tools amd64 1.3-3 [10.0 kB]

Get:2 http://ca.archive.ubuntu.com/ubuntu focal/main amd64 cpu-checker amd64 0.7-1.1 [6,936 B]

Get:3 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 ipxe-qemu all 1.0.0+git-20190109.133f4c4-0ubuntu3.2 [930 kB]

Get:4 http://ca.archive.ubuntu.com/ubuntu focal/main amd64 ipxe-qemu-256k-compat-efi-roms all 1.0.0+git-20150424.a25a16d-0ubuntu4 [552 kB]

Ign:5 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-common amd64 1:4.2-3ubuntu6.21

Ign:6 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-data all 1:4.2-3ubuntu6.21

Ign:7 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-gui amd64 1:4.2-3ubuntu6.21

Get:8 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 seabios all 1.13.0-1ubuntu1.1 [138 kB]

Ign:9 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-x86 amd64 1:4.2-3ubuntu6.21

Get:10 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 ovmf all 0~20191122.bd85bf54-2ubuntu3.3 [2,490 kB]

Ign:6 http://ca.archive.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-data all 1:4.2-3ubuntu6.21

Err:5 http://security.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-common amd64 1:4.2-3ubuntu6.21

404  Not Found [IP: 2001:67c:1562::15 80]

Err:7 http://security.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-gui amd64 1:4.2-3ubuntu6.21

404  Not Found [IP: 2001:67c:1562::15 80]

Err:9 http://security.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-x86 amd64 1:4.2-3ubuntu6.21

404  Not Found [IP: 2001:67c:1562::15 80]

Ign:6 http://security.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-data all 1:4.2-3ubuntu6.21

Err:6 http://security.ubuntu.com/ubuntu focal-updates/main amd64 qemu-system-data all 1:4.2-3ubuntu6.21

404  Not Found [IP: 2001:67c:1562::15 80]

Fetched 4,127 kB in 2s (2,089 kB/s)

E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/q/qemu/qemu-system-common_4.2-3ubuntu6.21_amd64.deb  404  Not Found [IP: 2001:67c:1562::15 80]

E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/q/qemu/qemu-system-data_4.2-3ubuntu6.21_all.deb  404  Not Found [IP: 2001:67c:1562::15 80]

E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/q/qemu/qemu-system-gui_4.2-3ubuntu6.21_amd64.deb  404  Not Found [IP: 2001:67c:1562::15 80]

E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/q/qemu/qemu-system-x86_4.2-3ubuntu6.21_amd64.deb  404  Not Found [IP: 2001:67c:1562::15 80]

E: Unable to fetch some archives, try running apt-get update or apt-get --fix-missing.

按照错误提示里的建议，我已经尝试过运行apt-get update和apt-get --fix-missing，但问题还是没解决。

我的系统版本信息如下：

$ lsb_release -a

LSB Version:    core-11.1.0ubuntu2-noarch:security-11.1.0ubuntu2-noarch

Distributor ID: Ubuntu

Description:    Ubuntu 20.04.2 LTS

Release:    20.04

Codename:   focal

有没有大佬能帮忙看看这个问题怎么解决？非常感谢！

备注：内容来源于stack exchange，提问作者Mathieu Poirier