instant: 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/instant - from package: docbook-to-man

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

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