planet-cache: 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-cache - from package: planet

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

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