pgagent: 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/pgagent - from package: pgagent

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

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