auth_krb5: 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

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/lib/news/bin/auth/passwd/auth_krb5 - from package: inn2

You may install the required package with command apt-get install {package}
Error in other languages:
auth_krb5: bevel nie gevind nie
auth_krb5: comandă negăsită
auth_krb5: comando não encontrado
auth_krb5: commande introuvable
auth_krb5: command not found
auth_krb5: käsku ei ole
auth_krb5: không tìm thấy lệnh
auth_krb5: komanda nerasta
auth_krb5: Kommando nicht gefunden.
auth_krb5: kommandot finns inte
auth_krb5: komut yok
auth_krb5: nie znaleziono polecenia
auth_krb5: níor aimsíodh an t-ordú
auth_krb5: no se encontró la orden
auth_krb5: no s'ha trobat l'ordre
auth_krb5: opdracht niet gevonden
auth_krb5: parancs nem található
auth_krb5: perintah tidak ditemukan
auth_krb5: príkaz nenájdený
auth_krb5: příkaz nenalezen
auth_krb5: команда не найдена
auth_krb5: командата не е открита
auth_krb5: 命令找不到
auth_krb5: コマンドが見つかりません