regtree: 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 CentOS possible default full paths are:

/usr/bin/regtree - from package: samba4-client

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/regtree - from package: registry-tools

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

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