s9c2html: 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/s9c2html - from package: scheme9

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

Error in other languages:
s9c2html: bevel nie gevind nie
s9c2html: comandă negăsită
s9c2html: comando não encontrado
s9c2html: commande introuvable
s9c2html: command not found
s9c2html: käsku ei ole
s9c2html: không tìm thấy lệnh
s9c2html: komanda nerasta
s9c2html: Kommando nicht gefunden.
s9c2html: kommandot finns inte
s9c2html: komut yok
s9c2html: nie znaleziono polecenia
s9c2html: níor aimsíodh an t-ordú
s9c2html: no se encontró la orden
s9c2html: no s'ha trobat l'ordre
s9c2html: opdracht niet gevonden
s9c2html: parancs nem található
s9c2html: perintah tidak ditemukan
s9c2html: príkaz nenájdený
s9c2html: příkaz nenalezen
s9c2html: команда не найдена
s9c2html: командата не е открита
s9c2html: 命令找不到
s9c2html: コマンドが見つかりません