subtle: 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/subtle - from package: subtle

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

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