plasma-overlay: 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/plasma-overlay - from package: kdebase-workspace

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

On Debian possible default full paths are:

/usr/bin/plasma-overlay - from package: kde-workspace-bin

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

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