btreplay: 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:

/usr/bin/btreplay - from package: blktrace

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

On Debian possible default full paths are:

/usr/sbin/btreplay - from package: blktrace

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

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