fsck.btrfs: 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 Debian possible default full paths are:

/sbin/fsck.btrfs - from package: btrfs-tools

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

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