mrvlogin: 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
/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/lib/rancid/bin/mrvlogin - from package: rancid

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