ranger: 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/ranger - from package: ranger

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

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