btrfs-find-root: 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/btrfs-find-root - from package: btrfs-progs

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

On Debian possible default full paths are:

/sbin/btrfs-find-root - from package: btrfs-tools

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

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