update-squidguard: 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 Debian possible default full paths are:

/usr/sbin/update-squidguard - from package: squidGuard

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

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