mensis: 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/mensis - from package: mensis

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