gfs_control: 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/sbin/gfs_control - from package: cman

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

On Debian possible default full paths are:

/usr/sbin/gfs_control - from package: gfs2-cluster

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

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