yppoll: 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/yppoll - from package: yp-tools

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

On Debian possible default full paths are:

/usr/sbin/yppoll - from package: nis

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

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