pgtune: 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/pgtune - from package: pgtune

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

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