login.krb5: 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/kerberos/sbin/login.krb5 - from package: krb5-appl-servers

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

Error in other languages:
login.krb5: bevel nie gevind nie
login.krb5: comandă negăsită
login.krb5: comando não encontrado
login.krb5: commande introuvable
login.krb5: command not found
login.krb5: käsku ei ole
login.krb5: không tìm thấy lệnh
login.krb5: komanda nerasta
login.krb5: Kommando nicht gefunden.
login.krb5: kommandot finns inte
login.krb5: komut yok
login.krb5: nie znaleziono polecenia
login.krb5: níor aimsíodh an t-ordú
login.krb5: no se encontró la orden
login.krb5: no s'ha trobat l'ordre
login.krb5: opdracht niet gevonden
login.krb5: parancs nem található
login.krb5: perintah tidak ditemukan
login.krb5: príkaz nenájdený
login.krb5: příkaz nenalezen
login.krb5: команда не найдена
login.krb5: командата не е открита
login.krb5: 命令找不到
login.krb5: コマンドが見つかりません