btrfstune: 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/btrfstune - from package: btrfs-progs

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

On Debian possible default full paths are:

/sbin/btrfstune - from package: btrfs-tools

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

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