Isso deve resolver seu problema:
sudo apt-get update --fix-missing
sudo apt-get install npm
Espero que isso funcione!
Tentei instalar o npm no Ubuntu 14.04, mas o seguinte erro ocorreu
gwt@gwt-Aspire-E1-571:~$ sudo apt-get install npm
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
npm : Depends: nodejs but it is not going to be installed
Depends: node-abbrev (>= 1.0.4) but it is not going to be installed
Depends: node-ansi but it is not going to be installed
Depends: node-archy but it is not going to be installed
Depends: node-block-stream but it is not going to be installed
Depends: node-fstream (>= 0.1.22) but it is not going to be installed
Depends: node-fstream-ignore but it is not going to be installed
Depends: node-github-url-from-git but it is not going to be installed
Depends: node-glob (>= 3.1.21) but it is not going to be installed
Depends: node-graceful-fs (>= 2.0.0) but it is not going to be installed
Depends: node-inherits but it is not going to be installed
Depends: node-ini (>= 1.1.0) but it is not going to be installed
Depends: node-lockfile but it is not going to be installed
Depends: node-lru-cache (>= 2.3.0) but it is not going to be installed
Depends: node-minimatch (>= 0.2.11) but it is not going to be installed
Depends: node-mkdirp (>= 0.3.3) but it is not going to be installed
Depends: node-gyp (>= 0.10.9) but it is not going to be installed
Depends: node-nopt (>= 2.1.1) but it is not going to be installed
Depends: node-npmlog but it is not going to be installed
Depends: node-once but it is not going to be installed
Depends: node-osenv but it is not going to be installed
Depends: node-read but it is not going to be installed
Depends: node-read-package-json (>= 1.1.0) but it is not going to be installed
Depends: node-request (>= 2.25.0) but it is not going to be installed
Depends: node-retry but it is not going to be installed
Depends: node-rimraf (>= 2.2.2) but it is not going to be installed
Depends: node-semver (>= 2.1.0) but it is not going to be installed
Depends: node-sha but it is not going to be installed
Depends: node-slide but it is not going to be installed
Depends: node-tar (>= 0.1.18) 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.
gwt@gwt-Aspire-E1-571:~$
Por gentileza, aconselhe uma solução para esse problema, uma vez que não é possível prosseguir.
Isso deve resolver seu problema:
sudo apt-get update --fix-missing
sudo apt-get install npm
Espero que isso funcione!