gtk3-widget-factory: command not found

Have You tried accessing the binary with the full path?

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/bin/gtk3-widget-factory - from package: gtk-3-examples
/usr/lib/debug/usr/bin/gtk3-widget-factory - from package: libgtk-3-0-dbg

You may install the required package with command apt-get install {package}
Error in other languages:
gtk3-widget-factory: bevel nie gevind nie
gtk3-widget-factory: comandă negăsită
gtk3-widget-factory: comando não encontrado
gtk3-widget-factory: commande introuvable
gtk3-widget-factory: command not found
gtk3-widget-factory: käsku ei ole
gtk3-widget-factory: không tìm thấy lệnh
gtk3-widget-factory: komanda nerasta
gtk3-widget-factory: Kommando nicht gefunden.
gtk3-widget-factory: kommandot finns inte
gtk3-widget-factory: komut yok
gtk3-widget-factory: nie znaleziono polecenia
gtk3-widget-factory: níor aimsíodh an t-ordú
gtk3-widget-factory: no se encontró la orden
gtk3-widget-factory: no s'ha trobat l'ordre
gtk3-widget-factory: opdracht niet gevonden
gtk3-widget-factory: parancs nem található
gtk3-widget-factory: perintah tidak ditemukan
gtk3-widget-factory: príkaz nenájdený
gtk3-widget-factory: příkaz nenalezen
gtk3-widget-factory: команда не найдена
gtk3-widget-factory: командата не е открита
gtk3-widget-factory: 命令找不到
gtk3-widget-factory: コマンドが見つかりません