sg_senddiag: 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_senddiag - 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_senddiag - from package: sg3-utils

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

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