sg_rbuf: 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/sg_rbuf - from package: sg3_utils

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

On Debian possible default full paths are:

/usr/bin/sg_rbuf - from package: sg3-utils

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

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