sgclean: 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/sgclean - from package: squidGuard

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

On Debian possible default full paths are:

/usr/bin/sgclean - from package: squidGuard

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

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