Tentei instalar o nodejs e o npm no ubuntu 12.04. Eu pesquisei e fiz isso. Agora, não consegui instalar o npm na máquina.
sudo apt-get install npm
O que me dá isso
The following packages have unmet dependencies:
npm : Depends: nodejs but it is not going to be installed
Depends: nodejs-dev
Depends: node-request but it is not going to be installed
Depends: node-mkdirp but it is not going to be installed
Depends: node-minimatch but it is not going to be installed
Depends: node-semver but it is not going to be installed
Depends: node-ini but it is not going to be installed
Depends: node-graceful-fs but it is not going to be installed
Depends: node-abbrev but it is not going to be installed
Depends: node-nopt but it is not going to be installed
Depends: node-fstream but it is not going to be installed
Depends: node-rimraf but it is not going to be installed
Depends: node-tar but it is not going to be installed
Depends: node-which but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
apt-get install npm
deve ser evitado (!). Verifique senpm -v
existe antes de tentar instalar .... (leia mais abaixo na resposta da @ MarcoCerpi)