s9edoc: 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/s9edoc - from package: scheme9

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

Error in other languages:
s9edoc: bevel nie gevind nie
s9edoc: comandă negăsită
s9edoc: comando não encontrado
s9edoc: commande introuvable
s9edoc: command not found
s9edoc: käsku ei ole
s9edoc: không tìm thấy lệnh
s9edoc: komanda nerasta
s9edoc: Kommando nicht gefunden.
s9edoc: kommandot finns inte
s9edoc: komut yok
s9edoc: nie znaleziono polecenia
s9edoc: níor aimsíodh an t-ordú
s9edoc: no se encontró la orden
s9edoc: no s'ha trobat l'ordre
s9edoc: opdracht niet gevonden
s9edoc: parancs nem található
s9edoc: perintah tidak ditemukan
s9edoc: príkaz nenájdený
s9edoc: příkaz nenalezen
s9edoc: команда не найдена
s9edoc: командата не е открита
s9edoc: 命令找不到
s9edoc: コマンドが見つかりません