sur: command not found

Have You tried accessing the binary with the full path?

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/sur - from package: subtle

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