polygraph-client: 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/polygraph-client - from package: polygraph

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

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