gmpc: 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/gmpc - from package: gmpc

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

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