Alguns pacotes não puderam ser instalados

Question

Estou tentando configurar um servidor de e-mail para um projeto da escola e quero instalar o postfix, quando eu executei apt-get install postfix um erro ocorreu.

Eu executei o upgrade do apt-get update também, antes disso, surgiu também um erro NO_PUBKEY 16126d3a3e5c1192 .

Resultados de apt-cache policy ssl-cert postfix; lsb_release -a :

ssl-cert:
  Installed: (none)
  Candidate: (none)
  Version table:

postfix:
  Installed: (none)
  Candidate: 2.11.0-1ubuntu1
  Version table:
     2.11.0-1ubuntu1 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64
 Packages

No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.3 LTS
Release:        14.04
Codename:       trusty

apt-get install ssl-cert :

Reading package lists... Done
Building dependency tree
Reading state information... Done
Package ssl-cert 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 'ssl-cert' has no installation candidate

    

Answer 1

Seu problema NO_PUBKEY

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 16126d3a3e5c1192
sudo apt-get update

E você não tem o repositório main habilitado

sudo apt-add-repository main
sudo apt-get update
sudo apt-get install postfix

E se software-properties-common não estiver instalado (precisamos de apt-add-repository )

cd
wget http://mirrors.kernel.org/ubuntu/pool/main/s/software-properties/software-properties-common_0.92.37.5_all.deb
sudo dpkg -i software-properties-common_0.92.37.5_all.deb
sudo apt-get update
sudo apt-get install -f

Ou use este /etc/apt/sources.list e não se esqueça de começar

sudo apt-get update
sudo apt-get install -f

após substituir o conteúdo com as linhas abaixo

# See http://heus.archive.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu trusty restricted universe main multiverse
deb-src http://us.archive.ubuntu.com/ubuntu trusty main universe restricted multiverse #Added by software-properties

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu trusty-updates restricted universe main multiverse
deb-src http://us.archive.ubuntu.com/ubuntu trusty-updates restricted universe main multiverse #Added by software-properties

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.

deb http://us.archive.ubuntu.com/ubuntu trusty-security restricted universe main multiverse
deb-src http://us.archive.ubuntu.com/ubuntu trusty-security restricted universe main multiverse #Added by software-properties

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://us.archive.canonical.com/ubuntu trusty partner
# deb-src http://us.archive.canonical.com/ubuntu trusty partner

deb http://us.archive.ubuntu.com/ubuntu trusty-backports main universe restricted multiverse
deb-src http://us.archive.ubuntu.com/ubuntu trusty-backports main universe restricted multiverse #Added by software-properties