execstack: 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/execstack - from package: prelink

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

On Debian possible default full paths are:

/usr/sbin/execstack - from package: execstack

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

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