shepherd: 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/sbin/shepherd - from package: sheepdog

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

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