lnav: 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/lnav - from package: lnav

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

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