mount.gfs2: 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:

/sbin/mount.gfs2 - from package: gfs2-utils

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

On Debian possible default full paths are:

/sbin/mount.gfs2 - from package: gfs2-utils

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

Error in other languages:
mount.gfs2: bevel nie gevind nie
mount.gfs2: comandă negăsită
mount.gfs2: comando não encontrado
mount.gfs2: commande introuvable
mount.gfs2: command not found
mount.gfs2: käsku ei ole
mount.gfs2: không tìm thấy lệnh
mount.gfs2: komanda nerasta
mount.gfs2: Kommando nicht gefunden.
mount.gfs2: kommandot finns inte
mount.gfs2: komut yok
mount.gfs2: nie znaleziono polecenia
mount.gfs2: níor aimsíodh an t-ordú
mount.gfs2: no se encontró la orden
mount.gfs2: no s'ha trobat l'ordre
mount.gfs2: opdracht niet gevonden
mount.gfs2: parancs nem található
mount.gfs2: perintah tidak ditemukan
mount.gfs2: príkaz nenájdený
mount.gfs2: příkaz nenalezen
mount.gfs2: команда не найдена
mount.gfs2: командата не е открита
mount.gfs2: 命令找不到
mount.gfs2: コマンドが見つかりません