nxt_server: 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/nxt_server - from package: python-nxt

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

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