mk-purge-logs: 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-purge-logs - from package: maatkit

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

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