npm install failing
I have the same error if not privileged, so I must use sudo when using the -g flag
If sudo don't recongize npm you can try:
passing the complete route of npm
$ sudo $(which npm) install -g socket.iopreserving the environment with -E flag
$ sudo -E npm install -g socket.io
Upd:
Note that is recommended to use the -g flag only for executables and install locally (without the flag) the libraries that are required in your code. Privileges are required for copying the executables to /usr/bin or, in your case /usr/local/bin
Note too that in the socket.io site, the -g flag is not included for the installation command ;)
Read more: http://blog.nodejs.org/2011/03/23/npm-1-0-global-vs-local-installation/