cmus: 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/cmus - from package: cmus

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

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