dhis-register-p: 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/sbin/dhis-register-p - from package: dhis-tools-dns

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