extrema: command not found

Have You tried accessing the binary with the full path?

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/extrema - from package: extrema

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