science-viewing: 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/science-viewing - from package: science-viewing

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

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