thin_metadata_size: 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:

/sbin/thin_metadata_size - from package: device-mapper-persistent-data
/usr/sbin/thin_metadata_size - from package: device-mapper-persistent-data

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

On Debian possible default full paths are:

/usr/sbin/thin_metadata_size - from package: thin-provisioning-tools

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

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