heimdal-su: 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/heimdal-su - from package: heimdal-workstation

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

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