如果我通过系统工具运行软件更新程序，我会收到：
并非所有更新都可以安装，请运行部分升级以安装尽可能多的更新。
我可以选择：“设置”、“部分升级”和“继续”。
如果我单击“继续”，我会收到：“此计算机上的软件已是最新的”。
如果我点击“部分升级”，我会收到：“无法安装 lubuntu-core。无法安装所需的软件包”。我可以点击“确定”，如果这样做，我会收到：“是否要开始升级？”。要删除的软件包中有 arduino、texworks 和其他软件包（我不明白为什么！）。
有什么建议吗？
输出sudo apt-get update：
Get:1 http://cran.mirror.garr.it xenial/ InRelease [3.590 B]
Hit http://archive.ubuntu.com xenial InRelease
Hit http://security.ubuntu.com xenial-security InRelease
Ign http://cran.mirror.garr.it xenial/ InRelease
Hit http://archive.ubuntu.com xenial-updates InRelease
Ign http://cran.mirror.garr.it xenial/ Packages/DiffIndex
Hit http://archive.ubuntu.com xenial/main amd64 Packages
Hit http://security.ubuntu.com xenial-security/main amd64 Packages
Hit http://archive.ubuntu.com xenial/main i386 Packages
Hit http://security.ubuntu.com xenial-security/main i386 Packages
Hit http://archive.ubuntu.com xenial/main Translation-en
Hit http://security.ubuntu.com xenial-security/main Translation-en
Hit http://archive.ubuntu.com xenial/main Translation-it
Hit http://cran.mirror.garr.it xenial/ Packages
Hit http://archive.ubuntu.com xenial-updates/main amd64 Packages
Hit http://archive.ubuntu.com xenial-updates/main i386 Packages
Hit http://archive.ubuntu.com xenial-updates/main Translation-en
Ign http://cran.mirror.garr.it xenial/ Translation-en_US
Ign http://cran.mirror.garr.it xenial/ Translation-en
Ign http://cran.mirror.garr.it xenial/ Translation-it
Fetched 3.590 B in 6s (573 B/s)
Reading package lists... Done
N: Ignoring file '50unattended-upgrades.ucf-old' in directory '/etc/apt/apt.conf.d/' as it has an invalid filename extension
W: GPG error: http://cran.mirror.garr.it xenial/ InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 51716619E084DAB9
输出sudo apt-get upgrade：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... The following packages were automatically installed and are no longer required:
libavahi-client-dev libavahi-common-dev libdbus-1-dev libllvm3.6v5 libpango1.0-0 python-cffi python-ply python-pycparser
Use 'apt-get autoremove' to remove them.
Done
The following packages have been kept back:
apt apt-transport-https apt-utils aptitude aptitude-common apturl apturl-common bind9-host bluez-obexd cups cups-bsd cups-client cups-core-drivers cups-daemon
cups-filters cups-filters-core-drivers curl debhelper default-jre default-jre-headless dnsutils emacs24 emacs24-bin-common emacs24-common findutils gdebi-core
gir1.2-gtk-3.0 glib-networking glib-networking-common glib-networking-services gstreamer1.0-plugins-base gstreamer1.0-plugins-good gstreamer1.0-x gvfs gvfs-backends
gvfs-bin gvfs-common gvfs-daemons gvfs-fuse gvfs-libs inkscape isc-dhcp-client isc-dhcp-common libappindicator1 libcups2 libcupscgi1 libcupsimage2 libcupsmime1
libcupsppdc1 libcurl3-gnutls libgail18 libgd3 libgnomevfs2-0 libgnomevfs2-common libgnomevfs2-extra libgnutls-openssl27 libgpgme11 libgpod4
libgstreamer-plugins-base1.0-0 libgstreamer-plugins-good1.0-0 libgstreamer1.0-0 libgtk-3-0 libgtk-3-bin libgtk2.0-0 libgtk2.0-bin libgtkmm-3.0-1v5
libhsqldb1.8.0-java libhunspell-1.3-0 libinput10 libjs-jquery libldap-2.4-2 libmirclient9 libneon27-gnutls libnm-glib-vpn1 libnm-glib4 libnm-gtk-common libnm-gtk0
libnm-util2 libnm0 libpoppler-qt4-4 libqt4-dbus libqt4-declarative libqt4-designer libqt4-network libqt4-opengl libqt4-qt3support libqt4-script libqt4-scripttools
libqt4-sql libqt4-svg libqt4-xml libqt4-xmlpatterns libqt5core5a libqt5dbus5 libqt5gui5 libqt5network5 libqt5printsupport5 libqt5qml5 libqt5quick5 libqt5sql5
libqt5sql5-sqlite libqt5svg5 libqt5widgets5 libqt5xml5 libqtcore4 libqtdbus4 libqtgui4 librtmp1 libsmbclient libvdpau1 libvncclient1 libvte-2.91-0
libvte-2.91-common libwbclient0 libwpd-0.10-10 libyelp0 lp-solve lsb-release network-manager network-manager-gnome ntfs-3g ntfs-3g-dev printer-driver-gutenprint
procps python-apt python-gi python-service-identity python3-apt qdbus qml-module-qtquick-controls qml-module-qtquick-dialogs qml-module-qtquick-layouts
qml-module-qtquick-privatewidgets qml-module-qtquick-window2 qml-module-qtquick2 qpdf ruby samba-libs ttf-ancient-fonts-symbola tzdata upower yelp zenity
zenity-common
0 upgraded, 0 newly installed, 0 to remove and 144 not upgraded.
N: Ignoring file '50unattended-upgrades.ucf-old' in directory '/etc/apt/apt.conf.d/' as it has an invalid filename extension