stellarium: 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 CentOS possible default full paths are:

/usr/bin/stellarium - from package: stellarium

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/stellarium - from package: stellarium

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

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