coldreboot: 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:

/sbin/coldreboot - from package: kexec-tools

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

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