mk-fifo-split: 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/mk-fifo-split - from package: maatkit

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

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