nnview: 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/nnview - from package: nn

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

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