npm: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/npm - from package: npm
/usr/lib/node_modules/npm/bin/npm - from package: npm

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/npm - from package: npm

You may install the required package with command apt-get install {package}

Error in other languages:
npm: bevel nie gevind nie
npm: comandă negăsită
npm: comando não encontrado
npm: commande introuvable
npm: command not found
npm: käsku ei ole
npm: không tìm thấy lệnh
npm: komanda nerasta
npm: Kommando nicht gefunden.
npm: kommandot finns inte
npm: komut yok
npm: nie znaleziono polecenia
npm: níor aimsíodh an t-ordú
npm: no se encontró la orden
npm: no s'ha trobat l'ordre
npm: opdracht niet gevonden
npm: parancs nem található
npm: perintah tidak ditemukan
npm: príkaz nenájdený
npm: příkaz nenalezen
npm: команда не найдена
npm: командата не е открита
npm: 命令找不到
npm: コマンドが見つかりません