synthread: 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/synthread - from package: argyll

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

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