hp_ud_grade: 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/hp_ud_grade - from package: healpix

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

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