Problem: npm install -g fails with EACCES (two forms, two fixes) —— Trove problem library

What you will run into

npm install -g <pkg> reports npm ERR! code EACCES; you think "permission issue, add sudo" — and next time even the cache can't be written (Your cache folder contains root-owned files), making it worse.

The error actually has two forms with different paths and completely different fixes — check where path points before acting.

Why this happens

npm global installs write to two locations: the global package directory (npm prefix -g, e.g. /usr/local/lib/node_modules) and the cache (~/.npm):

Form 1 is the norm for non-root users installing global packages (system node lives in /usr/local or /usr); form 2 is the after-effect of having used sudo before. Both errors carry EACCES + errno -13, but the fixes differ.

Global npm installs write to two locations: the global package directory (node_modules under npm prefix -g) and the cache (~/.npm).

EACCES means "the current user cannot write to the target directory": form 1's global directory is owned by root (system node lives in /usr/local or /usr), so non-root writes are rejected;

form 2 comes from a historical sudo npm install that made root the owner of ~/.npm cache files, after which normal-user cache writes fail.

Both forms show EACCES/errno -13, but the causes and fixes differ completely — form 1 is "directory ownership", form 2 is "cache ownership poisoned".

Deterministic takeaway: an error path containing node_modules = form 1; containing _cacache/.npm = form 2;

the correct fix for form 1 is npm config set prefix ~/.npm-global (move the global dir into the user home and add to PATH — do not force-install with sudo), and for form 2 sudo chown -R $(whoami) ~/.npm (restore cache ownership);

fixed diagnostic: ls -ld the target directory and compare with the error path.

Step by step

1. Read the error's path to identify the form — Diagnose

npm install -g yaml 2>&1 | grep -E "path|EACCES"

path /usr/local/lib/... → form 1; path /home/<user>/.npm/_cacache → form 2.

2. Form 1: move the global prefix to your user directory (recommended) — Required

npm config set prefix ~/.npm-global
export PATH="$HOME/.npm-global/bin:$PATH"

Add export PATH=... to ~/.bashrc so global packages install into your own directory from now on, never touching system dirs.

3. Form 2: give ~/.npm back to yourself — Required

sudo chown -R $(whoami) ~/.npm

npm's error message usually suggests the matching chown command. If you don't care about old cache, rm -rf ~/.npm and let it rebuild.

4. Alternatives — Advanced

• Manage node with nvm: node lives under ~/.nvm, global packages are naturally writable;
• sudo npm install -g works but isn't recommended — it keeps manufacturing form 2.

How to confirm it works

npm install -g yaml && yaml --help

No more EACCES and yaml runs (prints usage) means success. Measured: after form-1 fix added 1 package; after form-2 chown changed 1 package.

Other environments

Symptom

npm install -g <pkg> fails with a permission error, in two typical forms:

# Form 1: no write permission on the global package dir (most common)
npm ERR! code EACCES
npm ERR! syscall mkdir
npm ERR! path /usr/local/lib/node_modules/yaml
npm ERR! Error: EACCES: permission denied, mkdir '/usr/local/lib/node_modules/yaml'

# Form 2: cache dir owned by root (after using sudo)
npm ERR! code EACCES
npm ERR! syscall mkdir
npm ERR! path /home/<user>/.npm/_cacache
npm ERR! Your cache folder contains root-owned files, due to a bug in
npm ERR! previous versions of npm which has since been addressed.

Key traits: both forms carry npm ERR! code EACCES + errno -13; exit code is usually 243; Form 1 happens for non-root users installing globally (system node under /usr/local or /usr, dirs owned by root); Form 2 is common after ever running sudo npm install (root-owned files mixed into ~/.npm, regular users can no longer write).

Cause

Global installs write two locations: the global package dir (npm prefix -g, e.g. /usr/local/lib/node_modules) and the cache (~/.npm). The former is root-owned while your user isn't root → Form 1; the latter got root-owned files/dirs (sudo leftovers) → Form 2. Same EACCES, different paths, different fixes — check what path says first.

Solution

1. Form 1: move the global prefix into your home (recommended, one-time):

   npm config set prefix ~/.npm-global
   export PATH="$HOME/.npm-global/bin:$PATH"   # add to ~/.bashrc

Global installs now go to your own directory and never touch system dirs.

1. Form 1 alternatives: manage node with nvm (node lives in ~/.nvm, global dirs are naturally writable); or sudo npm install -g (works but not recommended — it creates Form 2).
2. Form 2: give ~/.npm back to yourself:

   sudo chown -R $(whoami) ~/.npm

(npm's own error suggests the exact chown command.) If you don't need the old cache, rm -rf ~/.npm and let it rebuild.

1. Verify: npm install -g <pkg> succeeds and the command runs (e.g. yaml prints usage).