navlog-viewer: 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 Debian possible default full paths are:

/usr/bin/navlog-viewer - from package: mrpt-apps

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

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