disc-cover: 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/disc-cover - from package: disc-cover

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

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