gstack: 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/gstack - from package: gdb

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

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