checksec: 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/checksec - from package: checksec

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

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