pgpool: 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/pgpool - from package: postgresql-pgpool-II

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

On Debian possible default full paths are:

/usr/sbin/pgpool - from package: pgpool2

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

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