gcore: 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/gcore - from package: gdb

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

On Debian possible default full paths are:

/usr/bin/gcore - from package: gdb-minimal
/usr/bin/gcore - from package: gdb

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

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