ipset: 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/sbin/ipset - from package: ipset

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

On Debian possible default full paths are:

/sbin/ipset - from package: ipset

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

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