pnuke: 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/bin/pnuke - from package: pssh

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

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