pg: 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/pg - from package: util-linux

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

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