laptop_mode: 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/sbin/laptop_mode - from package: laptop-mode-tools

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

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