ausearch: 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:

/sbin/ausearch - from package: audit

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

On Debian possible default full paths are:

/sbin/ausearch - from package: auditd

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

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