planets: 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/planets - from package: planets

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

On Debian possible default full paths are:

/usr/bin/planets - from package: planets

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

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