genpng: 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/genpng - from package: lcov

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

On Debian possible default full paths are:

/usr/bin/genpng - from package: lcov

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

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