us: 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/us - from package: unicornscan

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

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