pssh: 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/pssh - from package: pssh

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

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