gnome-terminal: 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/gnome-terminal - from package: gnome-terminal

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

On Debian possible default full paths are:

/usr/bin/gnome-terminal - from package: gnome-terminal

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

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