root: 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/root - from package: root

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

On Debian possible default full paths are:

/usr/bin/root - from package: root-system-bin

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

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