nnalg: 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 CentOS possible default full paths are:

/usr/bin/nnalg - from package: ncl

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/nnalg - from package: ncl-ncarg

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

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