planet: 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/planet - from package: planet

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

On Debian possible default full paths are:

/usr/bin/planet - from package: planet-venus

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

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