mtnopt: 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/mtnopt - from package: monotone

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

On Debian possible default full paths are:

/usr/bin/mtnopt - from package: monotone

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

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