root@debian:~# apt-get update
忽略:1 cdrom://[Debian GNU/Linux 11.3.0 _Bullseye_ - Official amd64 DVD Binary-1 20220326-11:23] bullseye InRelease
错误:2 cdrom://[Debian GNU/Linux 11.3.0 _Bullseye_ - Official amd64 DVD Binary-1 20220326-11:23] bullseye Release
  请使用 apt-cdrom，通过它可以让 APT 识别该盘片。apt-get upgdate 不能被用来加入新的盘片。
错误:3 http://security.debian.org/debian-security bullseye-security InRelease
  暂时不能解析域名“security.debian.org”
正在读取软件包列表... 完成
E: 仓库 “cdrom://[Debian GNU/Linux 11.3.0 _Bullseye_ - Official amd64 DVD Binary-1 20220326-11:23] bullseye Release” 没有 Release 文件。
N: 无法安全地用该源进行更新，所以默认禁用该源。
N: 参见 apt-secure(8) 手册以了解仓库创建和用户配置方面的细节。

• 问题原因：

从上面可以看出镜像源出现了问题，默认从cdrom获取镜像源，由于我们光驱中并没有放置安装光盘，因此需要修改镜像源。

• 解决办法：

 查看当前镜像源配置文件 sources.list

root@debian:~# cat /etc/apt/sources.list
# deb cdrom:[Debian GNU/Linux 11.3.0 _Bullseye_ - Official amd64 DVD Binary-1 20220326-11:23]/ bullseye contrib main

deb cdrom:[Debian GNU/Linux 11.3.0 _Bullseye_ - Official amd64 DVD Binary-1 20220326-11:23]/ bullseye contrib main

deb http://security.debian.org/debian-security bullseye-security main contrib
deb-src http://security.debian.org/debian-security bullseye-security main contrib

# bullseye-updates, to get updates before a point release is made;
# see https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_updates_and_backports
# A network mirror was not selected during install.  The following entries
# are provided as examples, but you should amend them as appropriate
# for your mirror of choice.
#
# deb http://deb.debian.org/debian/ bullseye-updates main contrib
# deb-src http://deb.debian.org/debian/ bullseye-updates main contrib

替换镜像源，注释掉原有的镜像源，这里存放了阿里云、腾讯云、网易三个镜像源，只启用阿里云的镜像源，如下修改：

root@debian:/etc/apt# cat sources.list
# deb cdrom:[Debian GNU/Linux 11.3.0 _Bullseye_ - Official amd64 DVD Binary-1 20220326-11:23]/ bullseye contrib main

#deb cdrom:[Debian GNU/Linux 11.3.0 _Bullseye_ - Official amd64 DVD Binary-1 20220326-11:23]/ bullseye contrib main

#deb http://security.debian.org/debian-security bullseye-security main contrib
#deb-src http://security.debian.org/debian-security bullseye-security main contrib

# bullseye-updates, to get updates before a point release is made;
# see https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_updates_and_backports
# A network mirror was not selected during install.  The following entries
# are provided as examples, but you should amend them as appropriate
# for your mirror of choice.
#
# deb http://deb.debian.org/debian/ bullseye-updates main contrib
# deb-src http://deb.debian.org/debian/ bullseye-updates main contrib


#Aliyun Apt Source 阿里云镜像源
deb http://mirrors.aliyun.com/debian/ bullseye main contrib
deb-src http://mirrors.aliyun.com/debian/ bullseye main contrib
deb http://mirrors.aliyun.com/debian/ bullseye-updates main contrib
deb-src http://mirrors.aliyun.com/debian/ bullseye-updates main contrib
deb http://mirrors.aliyun.com/debian/ bullseye-backports main contrib
deb-src http://mirrors.aliyun.com/debian/ bullseye-backports main contrib
deb http://mirrors.aliyun.com/debian/ bullseye-proposed-updates main contrib
deb-src http://mirrors.aliyun.com/debian/ bullseye-proposed-updates main contrib


#Tencent Apt Source 腾讯云镜像源
#deb https://mirrors.tencent.com/debian/ bullseye main non-free contrib
#deb-src https://mirrors.tencent.com/debian/ bullseye main non-free contrib
#deb https://mirrors.tencent.com/debian-security/ bullseye-security main
#deb-src https://mirrors.tencent.com/debian-security/ bullseye-security main
#deb https://mirrors.tencent.com/debian/ bullseye-updates main non-free contrib
#deb-src https://mirrors.tencent.com/debian/ bullseye-updates main non-free contrib
#deb https://mirrors.tencent.com/debian/ bullseye-backports main non-free contrib
#deb-src https://mirrors.tencent.com/debian/ bullseye-backports main non-free contrib

#163 Apt Source 网易镜像源
#deb https://mirrors.163.com/debian/ bullseye main non-free contrib
#deb-src https://mirrors.163.com/debian/ bullseye main non-free contrib
#deb https://mirrors.163.com/debian-security/ bullseye-security main
#deb-src https://mirrors.163.com/debian-security/ bullseye-security main
#deb https://mirrors.163.com/debian/ bullseye-updates main non-free contrib
#deb-src https://mirrors.163.com/debian/ bullseye-updates main non-free contrib
#deb https://mirrors.163.com/debian/ bullseye-backports main non-free contrib
#deb-src https://mirrors.163.com/debian/ bullseye-backports main non-free contrib

重新更新镜像源缓存，出现如下错误

root@debian:~# apt-get update
错误:1 http://mirrors.aliyun.com/debian bullseye InRelease
  暂时不能解析域名“mirrors.aliyun.com”
错误:2 http://mirrors.aliyun.com/debian bullseye-updates InRelease
  暂时不能解析域名“mirrors.aliyun.com”
错误:3 http://mirrors.aliyun.com/debian bullseye-backports InRelease
  暂时不能解析域名“mirrors.aliyun.com”
错误:4 http://mirrors.aliyun.com/debian bullseye-proposed-updates InRelease
  暂时不能解析域名“mirrors.aliyun.com”
正在读取软件包列表... 完成
W: 无法下载 http://mirrors.aliyun.com/debian/dists/bullseye/InRelease  暂时不能解析域名“mirrors.aliyun.com”
W: 无法下载 http://mirrors.aliyun.com/debian/dists/bullseye-updates/InRelease  暂时不能解析域名“mirrors.aliyun.com”
W: 无法下载 http://mirrors.aliyun.com/debian/dists/bullseye-backports/InRelease  暂时不能解析域名“mirrors.aliyun.com”
W: 无法下载 http://mirrors.aliyun.com/debian/dists/bullseye-proposed-updates/InRelease  暂时不能解析域名“mirrors.aliyun.com”
W: 部分索引文件下载失败。如果忽略它们，那将转而使用旧的索引文件。

修改DNS配置文件

​
root@debian:~# nano /etc/resolv.conf                                                                                                                         
nameserver 114.114.114.114
nameserver 8.8.8.8

root@debian:~# nano /etc/network/interface
修改
nameserver 114.114.114.114

Ctrl+X退出保存配置，并重启服务器。然后再次更新镜像源就没问题了。

root@debian:~# apt-get update
获取:1 http://mirrors.aliyun.com/debian bullseye InRelease [116 kB]
获取:2 http://mirrors.aliyun.com/debian bullseye-updates InRelease [39.4 kB]
获取:3 http://mirrors.aliyun.com/debian bullseye-backports InRelease [44.2 kB]
获取:4 http://mirrors.aliyun.com/debian bullseye-proposed-updates InRelease [44.6 kB]
获取:5 http://mirrors.aliyun.com/debian bullseye/main Sources [8,627 kB]
获取:6 http://mirrors.aliyun.com/debian bullseye/contrib Sources [43.0 kB]                                                                                                                                                              
获取:7 http://mirrors.aliyun.com/debian bullseye/main amd64 Packages [8,182 kB]                                                                                                                                                         
获取:8 http://mirrors.aliyun.com/debian bullseye/main Translation-en [6,241 kB]                                                                                                                                                         
获取:9 http://mirrors.aliyun.com/debian bullseye/main Translation-zh_CN [114 kB]                                                                                                                                                        
获取:10 http://mirrors.aliyun.com/debian bullseye/main Translation-zh [1,215 B]                                                                                                                                                         
获取:11 http://mirrors.aliyun.com/debian bullseye/contrib amd64 Packages [50.5 kB]                                                                                                                                                      
获取:12 http://mirrors.aliyun.com/debian bullseye/contrib Translation-en [46.9 kB]                                                                                                                                                      
获取:13 http://mirrors.aliyun.com/debian bullseye-updates/main Sources [1,868 B]                                                                                                                                                        
获取:14 http://mirrors.aliyun.com/debian bullseye-updates/main amd64 Packages [2,592 B]                                                                                                                                                 
获取:15 http://mirrors.aliyun.com/debian bullseye-updates/main Translation-en [2,343 B]                                                                                                                                                 
获取:16 http://mirrors.aliyun.com/debian bullseye-backports/main Sources [281 kB]                                                                                                                                                       
获取:17 http://mirrors.aliyun.com/debian bullseye-backports/contrib Sources [2,556 B]                                                                                                                                                   
获取:18 http://mirrors.aliyun.com/debian bullseye-backports/main amd64 Packages [302 kB]                                                                                                                                                
获取:19 http://mirrors.aliyun.com/debian bullseye-backports/main Translation-en [233 kB]                                                                                                                                                
获取:20 http://mirrors.aliyun.com/debian bullseye-backports/contrib amd64 Packages [4,704 B]                                                                                                                                         
获取:21 http://mirrors.aliyun.com/debian bullseye-backports/contrib Translation-en [4,196 B]                                                                                                                                            
获取:22 http://mirrors.aliyun.com/debian bullseye-proposed-updates/contrib Sources [1,264 B]                                                                                                                                            
获取:23 http://mirrors.aliyun.com/debian bullseye-proposed-updates/main Sources [56.3 kB]                                                                                                                                               
获取:24 http://mirrors.aliyun.com/debian bullseye-proposed-updates/main amd64 Packages [85.9 kB]                                                                                                                                        
获取:25 http://mirrors.aliyun.com/debian bullseye-proposed-updates/main Translation-en [56.6 kB]                                                                                                                                        
获取:26 http://mirrors.aliyun.com/debian bullseye-proposed-updates/contrib amd64 Packages [1,320 B]                                                                                                                                     
获取:27 http://mirrors.aliyun.com/debian bullseye-proposed-updates/contrib Translation-en [925 B]                                                                                                                                       
已下载 24.6 MB，耗时 44秒 (564 kB/s)                                                                                                                                                                                                    
正在读取软件包列表... 完成

最后我们要执行

root@debian:~# apt-get upgrade

注意：update是更新软件列表，upgrade是更新软件。