root試してみましたが問題ないようです。
応答待ちになるということはファイアーウォールやプロキシあたりで引っかかってたりしませんか?
[root@ae5b1eef2c8e /]# npm install express --save
npm WARN package.json none@1.0.0 No description
npm WARN package.json none@1.0.0 No repository field.
npm WARN package.json none@1.0.0 No README data
express@4.15.2 node_modules/express
├── setprototypeof@1.0.3
├── escape-html@1.0.3
├── array-flatten@1.1.1
├── cookie-signature@1.0.6
├── utils-merge@1.0.0
├── encodeurl@1.0.1
├── content-type@1.0.2
├── merge-descriptors@1.0.1
├── methods@1.1.2
├── cookie@0.3.1
├── content-disposition@0.5.2
├── path-to-regexp@0.1.7
├── etag@1.8.0
├── serve-static@1.12.1
├── vary@1.1.1
├── fresh@0.5.0
├── parseurl@1.3.1
├── range-parser@1.2.0
├── statuses@1.3.1
├── depd@1.1.0
├── qs@6.4.0
├── debug@2.6.1 (ms@0.7.2)
├── on-finished@2.3.0 (ee-first@1.1.1)
├── proxy-addr@1.1.4 (forwarded@0.1.0, ipaddr.js@1.3.0)
├── finalhandler@1.0.2 (unpipe@1.0.0, debug@2.6.4)
├── type-is@1.6.15 (media-typer@0.3.0, mime-types@2.1.15)
├── accepts@1.3.3 (negotiator@0.6.1, mime-types@2.1.15)
└── send@0.15.1 (destroy@1.0.4, ms@0.7.2, mime@1.3.4, http-errors@1.6.1)
[root@ae5b1eef2c8e /]# npm install socket.io --save
npm WARN package.json none@1.0.0 No description
npm WARN package.json none@1.0.0 No repository field.
npm WARN package.json none@1.0.0 No README data
socket.io@1.7.3 node_modules/socket.io
├── object-assign@4.1.0
├── socket.io-adapter@0.5.0
├── debug@2.3.3 (ms@0.7.2)
├── has-binary@0.1.7 (isarray@0.0.1)
├── engine.io@1.8.3 (cookie@0.3.1, base64id@1.0.0, engine.io-parser@1.3.2, ws@1.1.2, accepts@1.3.3)
├── socket.io-parser@2.3.1 (isarray@0.0.1, json3@3.3.2, component-emitter@1.1.2, debug@2.2.0)
└── socket.io-client@1.7.3 (to-array@0.1.4, component-emitter@1.2.1, indexof@0.0.1, object-component@0.0.3, component-bind@1.0.0, backo2@1.0.2, parseuri@0.0.5, engine.io-client@1.8.3)
[root@ae5b1eef2c8e /]# node -v
v4.8.2
[root@ae5b1eef2c8e /]# npm -v
2.15.11
[root@ae5b1eef2c8e /]#