freebsd-mkdep: 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/freebsd-mkdep - from package: freebsd-buildutils

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

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