root@vdb10:/home/user# apt-get update
Ign:1 cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-1 20190706-10:24] buster InRelease
Ign:2 cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-2 20190706-10:24] buster InRelease
Ign:3 cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-3 20190706-10:24] buster InRelease
Err:4 cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-1 20190706-10:24] buster Release
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Err:5 cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-2 20190706-10:24] buster Release
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Err:6 cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-3 20190706-10:24] buster Release
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Get:7
http://security.debian.org/debian-security buster/updates InRelease [39.1 kB]
Get:8
http://security.debian.org/debian-security buster/updates/main Sources [12.7 kB]
Get:9
http://security.debian.org/debian-security buster/updates/main amd64 Packages [42.5 kB]
Get:10
http://security.debian.org/debian-security buster/updates/main Translation-en [20.0 kB]
Reading package lists... Done
E: The repository 'cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-1 20190706-10:24] buster 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.
E: The repository 'cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-2 20190706-10:24] buster 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.
E: The repository 'cdrom://[Debian GNU/Linux 10.0.0 _Buster_ - Official amd64 DVD Binary-3 20190706-10:24] buster 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.
root@vdb10:/home/user# apt-get install linux-headers
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package linux-headers is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'linux-headers' has no installation candidate
root@vdb10:/home/str#