unbuffer: 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/unbuffer - from package: expect

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

On Debian possible default full paths are:

/usr/bin/unbuffer - from package: expect

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

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