qmmp: 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 CentOS possible default full paths are:

/usr/bin/qmmp - from package: qmmp

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/qmmp - from package: qmmp

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

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