gperiodic: 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 Debian possible default full paths are:

/usr/bin/gperiodic - from package: gperiodic

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

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