yppush: 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/sbin/yppush - from package: ypserv

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

On Debian possible default full paths are:

/usr/sbin/yppush - from package: nis

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

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