krb5_newrealm: 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 Debian possible default full paths are:

/usr/sbin/krb5_newrealm - from package: krb5-admin-server

You may install the required package with command apt-get install {package}

Error in other languages:
krb5_newrealm: bevel nie gevind nie
krb5_newrealm: comandă negăsită
krb5_newrealm: comando não encontrado
krb5_newrealm: commande introuvable
krb5_newrealm: command not found
krb5_newrealm: käsku ei ole
krb5_newrealm: không tìm thấy lệnh
krb5_newrealm: komanda nerasta
krb5_newrealm: Kommando nicht gefunden.
krb5_newrealm: kommandot finns inte
krb5_newrealm: komut yok
krb5_newrealm: nie znaleziono polecenia
krb5_newrealm: níor aimsíodh an t-ordú
krb5_newrealm: no se encontró la orden
krb5_newrealm: no s'ha trobat l'ordre
krb5_newrealm: opdracht niet gevonden
krb5_newrealm: parancs nem található
krb5_newrealm: perintah tidak ditemukan
krb5_newrealm: príkaz nenájdený
krb5_newrealm: příkaz nenalezen
krb5_newrealm: команда не найдена
krb5_newrealm: командата не е открита
krb5_newrealm: 命令找不到
krb5_newrealm: コマンドが見つかりません