mkhomedir_helper: 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:

/sbin/mkhomedir_helper - from package: pam

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

On Debian possible default full paths are:

/sbin/mkhomedir_helper - from package: libpam-modules-bin

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

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