gfs2_mount: 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 Debian possible default full paths are:

/usr/sbin/gfs2_mount - from package: gfs2-utils

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

Error in other languages:
gfs2_mount: bevel nie gevind nie
gfs2_mount: comandă negăsită
gfs2_mount: comando não encontrado
gfs2_mount: commande introuvable
gfs2_mount: command not found
gfs2_mount: käsku ei ole
gfs2_mount: không tìm thấy lệnh
gfs2_mount: komanda nerasta
gfs2_mount: Kommando nicht gefunden.
gfs2_mount: kommandot finns inte
gfs2_mount: komut yok
gfs2_mount: nie znaleziono polecenia
gfs2_mount: níor aimsíodh an t-ordú
gfs2_mount: no se encontró la orden
gfs2_mount: no s'ha trobat l'ordre
gfs2_mount: opdracht niet gevonden
gfs2_mount: parancs nem található
gfs2_mount: perintah tidak ditemukan
gfs2_mount: príkaz nenájdený
gfs2_mount: příkaz nenalezen
gfs2_mount: команда не найдена
gfs2_mount: командата не е открита
gfs2_mount: 命令找不到
gfs2_mount: コマンドが見つかりません