nikola: 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/nikola - from package: nikola

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

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