sg_scan: 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_scan - 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_scan - from package: sg3-utils

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

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