cssh: 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/cssh - from package: clusterssh

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

On Debian possible default full paths are:

/usr/bin/cssh - from package: clusterssh

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

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