root@debian:~# apt-get install htop
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  strace ltrace
The following NEW packages will be installed:
  htop
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 74.9 kB of archives.
After this operation, 216 kB of additional disk space will be used.
Err http://mirror.yandex.ru/debian/ wheezy/main htop amd64 1.0.1-1
  Could not resolve 'mirror.yandex.ru'
Failed to fetch http://mirror.yandex.ru/debian/pool/main/h/htop/htop_1.0.1-1_amd                                                                                                                                                             64.deb  Could not resolve 'mirror.yandex.ru'
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-mis                                                                                                                                                             sing?
root@debian:~# apt-get install screen
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  iselect screenie byobu
The following NEW packages will be installed:
  screen
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 668 kB of archives.
After this operation, 913 kB of additional disk space will be used.
Err http://security.debian.org/ wheezy/updates/main screen amd64 4.1.0~20120320g                                                                                                                                                             itdb59704-7+deb7u1
  Could not resolve 'security.debian.org'
Failed to fetch http://security.debian.org/pool/updates/main/s/screen/screen_4.1                                                                                                                                                             .0~20120320gitdb59704-7+deb7u1_amd64.deb  Could not resolve 'security.debian.org                                                                                                                                                             '
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-mis                                                                                                                                                             sing?
root@debian:~#