skyviewer: command not found

Have You tried accessing the binary with the full path?

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/skyviewer - from package: skyviewer

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