firstaidkit: 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/firstaidkit - from package: firstaidkit-engine

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

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