lookup: 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/bin/lookup - from package: lookup

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

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