not: 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 Debian possible default full paths are:

/usr/lib/llvm-3.4/bin/not - from package: llvm-3.4-tools
/usr/lib/llvm-3.5/bin/not - from package: llvm-3.5-tools

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

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