gnulib-tool: 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/bin/gnulib-tool - from package: gnulib

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

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