aide: 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/aide - from package: aide

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

On Debian possible default full paths are:

/usr/bin/aide - from package: aide-dynamic
/usr/bin/aide - from package: aide
/usr/bin/aide - from package: aide-xen

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

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