grub-mkrescue: 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/grub-mkrescue - from package: grub-common

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

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