viewnior: 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/viewnior - from package: viewnior

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

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