gkrellmd: 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/sbin/gkrellmd - from package: gkrellm-daemon

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

On Debian possible default full paths are:

/usr/bin/gkrellmd - from package: gkrellmd

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

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