eqn2graph: 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/eqn2graph - from package: groff

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

On Debian possible default full paths are:

/usr/bin/eqn2graph - from package: groff

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

Error in other languages:
eqn2graph: bevel nie gevind nie
eqn2graph: comandă negăsită
eqn2graph: comando não encontrado
eqn2graph: commande introuvable
eqn2graph: command not found
eqn2graph: käsku ei ole
eqn2graph: không tìm thấy lệnh
eqn2graph: komanda nerasta
eqn2graph: Kommando nicht gefunden.
eqn2graph: kommandot finns inte
eqn2graph: komut yok
eqn2graph: nie znaleziono polecenia
eqn2graph: níor aimsíodh an t-ordú
eqn2graph: no se encontró la orden
eqn2graph: no s'ha trobat l'ordre
eqn2graph: opdracht niet gevonden
eqn2graph: parancs nem található
eqn2graph: perintah tidak ditemukan
eqn2graph: príkaz nenájdený
eqn2graph: příkaz nenalezen
eqn2graph: команда не найдена
eqn2graph: командата не е открита
eqn2graph: 命令找不到
eqn2graph: コマンドが見つかりません