In order to avoid Debian to search for packages on a non-existent CDROM, which is most likely not present on a Linux VPS, you should change a simple parameter on the
Open and modify the file /etc/apt/sources.list
/etc/apt/sources.list file. You need to modify the aforementioned file if you get an output like this while using apt-get to install default packages:Media change: please insert the disc labeled
'Debian GNU/Linux 7.0.0 _Wheezy_ - Official amd64 CD Binary-1 20130504-14:44'
in the drive '/media/cdrom/' and press enter
Open and modify the file /etc/apt/sources.list
nano /etc/apt/sources.list
把这一行注释掉即可：
deb cdrom:[Debian GNU/Linux 8.2.0 _Jessie_ - Official amd64 CD Binary-1 20150906-11:13]/ jessie main