parallel-nuke: 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 Debian possible default full paths are:

/usr/bin/parallel-nuke - from package: pssh

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

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