mpdexit: 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/mpdexit - from package: mpich2

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

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