stdbuf: 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/stdbuf - from package: coreutils

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

On Debian possible default full paths are:

/usr/bin/stdbuf - from package: coreutils

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

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