gml2gv: 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/gml2gv - from package: graphviz

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

On Debian possible default full paths are:

/usr/bin/gml2gv - from package: graphviz

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

Error in other languages:
gml2gv: bevel nie gevind nie
gml2gv: comandă negăsită
gml2gv: comando não encontrado
gml2gv: commande introuvable
gml2gv: command not found
gml2gv: käsku ei ole
gml2gv: không tìm thấy lệnh
gml2gv: komanda nerasta
gml2gv: Kommando nicht gefunden.
gml2gv: kommandot finns inte
gml2gv: komut yok
gml2gv: nie znaleziono polecenia
gml2gv: níor aimsíodh an t-ordú
gml2gv: no se encontró la orden
gml2gv: no s'ha trobat l'ordre
gml2gv: opdracht niet gevonden
gml2gv: parancs nem található
gml2gv: perintah tidak ditemukan
gml2gv: príkaz nenájdený
gml2gv: příkaz nenalezen
gml2gv: команда не найдена
gml2gv: командата не е открита
gml2gv: 命令找不到
gml2gv: コマンドが見つかりません