polygraph-server: 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-server - from package: polygraph

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

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