ksu.heimdal: command not found

Have You tried accessing the binary with the full path?

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/ksu.heimdal - from package: heimdal-clients
/usr/lib/debug/usr/bin/ksu.heimdal - from package: heimdal-dbg

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