unable to upgrade ubuntu from 14.04 to 16.04

[李白|字一日]

hi, all

I have tried many times to upgrade ubuntu from 14.04 to 16.04, but failed.
with command:
sudo update-manager -d

it seems it is due to the gnome/gtk problems:


debconf: 无法初始化前端界面：Gnome
debconf: (Can't locate Gtk2.pm in @INC (you may need to install the Gtk2
module) (@INC contains: /etc/perl /usr/local/lib/perl/5.18.2
/usr/local/share/perl/5.18.2 /usr/lib/perl5 /usr/share/perl5
/usr/lib/perl/5.18 /usr/share/perl/5.18 /usr/local/lib/site_perl .) at
/usr/share/perl5/Debconf/FrontEnd/Gnome.pm line 91.)
debconf: 返回前端界面：Dialog
debconf: 无法初始化前端界面：Gnome
debconf: (Can't locate Gtk2.pm in @INC (you may need to install the Gtk2
module) (@INC contains: /etc/perl /usr/local/lib/perl/5.18.2
/usr/local/share/perl/5.18.2 /usr/lib/perl5 /usr/share/perl5
/usr/lib/perl/5.18 /usr/share/perl/5.18 /usr/local/lib/site_perl .) at
/usr/share/perl5/Debconf/FrontEnd/Gnome.pm line 91.)
debconf: 返回前端界面：Dialog
debconf: 无法初始化前端界面：Gnome
debconf: (Can't locate Gtk2.pm in @INC (you may need to install the Gtk2
module) (@INC contains: /etc/perl /usr/local/lib/perl/5.18.2
/usr/local/share/perl/5.18.2 /usr/lib/perl5 /usr/share/perl5
/usr/lib/perl/5.18 /usr/share/perl/5.18 /usr/local/lib/site_perl .) at
/usr/share/perl5/Debconf/FrontEnd/Gnome.pm line 91.)
debconf: 返回前端界面：Dialog


after executed:
sudo apt-get install gtk2-engines

i get this message

正在检查新版 Ubuntu
/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeFetcher.py:86:
Warning: g_object_ref: assertion 'object->ref_count > 0' failed
  res = self.widgets.dialog_release_notes.run()
/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeFetcher.py:86:
Warning: g_object_unref: assertion 'object->ref_count > 0' failed
  res = self.widgets.dialog_release_notes.run()
使用 'xenial.tar.gz.gpg' 对 'xenial.tar.gz' 进行验证
正在提取 'xenial.tar.gz'

is there anyone know how to upgrade from 14.04 to 16.04?

thanks.
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