metaflac: 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/metaflac - from package: flac

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

On Debian possible default full paths are:

/usr/bin/metaflac - from package: flac

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

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