btrfsck: 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/btrfsck - from package: btrfs-progs

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

On Debian possible default full paths are:

/sbin/btrfsck - from package: btrfs-tools

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

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