mkcp: 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

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/mkcp - from package: nilfs-tools

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