package manager troubleshooting terminal output

https://help.ubuntu.com/community/PackageManagerTroubleshootingProcedure#Step_5_List_of_Terminal_commands_to_execute

Please post full terminal output of ALL commands in step 5 here:

https://answers.launchpad.net/ubuntu/+source/apt/+question/233867

I'm sorry for the delay!!

rajat@rajat-MS-7529:~$ sudo grep -R proxy /etc/apt/*
[sudo] password for rajat:
rajat@rajat-MS-7529:~$ grep proxy /etc/environment
rajat@rajat-MS-7529:~$ echo $http_proxy

rajat@rajat-MS-7529:~$ echo $ftp_proxy

rajat@rajat-MS-7529:~$ grep proxy /etc/bash.bashrc
rajat@rajat-MS-7529:~$ grep proxy ~/.bashrc
rajat@rajat-MS-7529:~$ cat /etc/apt/apt.conf
rajat@rajat-MS-7529:~$ sudo fuser -vvv /var/lib/dpkg/lock
rajat@rajat-MS-7529:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=12.04
DISTRIB_CODENAME=precise
DISTRIB_DESCRIPTION="Ubuntu 12.04.2 LTS"
rajat@rajat-MS-7529:~$ uname -a
Linux rajat-MS-7529 3.2.0-49-generic-pae #75-Ubuntu SMP Tue Jun 18 18:00:21 UTC 2013 i686 i686 i386 GNU/Linux
rajat@rajat-MS-7529:~$ sudo rm /var/lib/apt/lists/lock
rajat@rajat-MS-7529:~$ sudo rm /var/lib/dpkg/lock
rajat@rajat-MS-7529:~$ sudo cp -arf /var/lib/dpkg /var/lib/dpkg.backup
rajat@rajat-MS-7529:~$ sudo mv /var/lib/dpkg/status /var/lib/dpkg/status-bad
rajat@rajat-MS-7529:~$ sudo cp /var/lib/dpkg/status-old /var/lib/dpkg/status || sudo cp /var/backups/apt.extended_states.0 /var/lib/dpkg/status
rajat@rajat-MS-7529:~$ sudo mv /var/lib/dpkg/available /var/lib/dpkg/available-bad
rajat@rajat-MS-7529:~$ sudo cp /var/lib/dpkg/available-old /var/lib/dpkg/available
rajat@rajat-MS-7529:~$ sudo rm -rf /var/lib/dpkg/updates/*
rajat@rajat-MS-7529:~$ sudo rm -rf /var/lib/apt/lists
rajat@rajat-MS-7529:~$ sudo rm /var/cache/apt/*.bin
rajat@rajat-MS-7529:~$ sudo mkdir /var/lib/apt/lists
rajat@rajat-MS-7529:~$ sudo mkdir /var/lib/apt/lists/partial
rajat@rajat-MS-7529:~$ LANG=C;sudo apt-get clean
rajat@rajat-MS-7529:~$ LANG=C;sudo apt-get autoclean
Reading package lists... Done
Building dependency tree
Reading state information... Done
rajat@rajat-MS-7529:~$ LANG=C;sudo apt-get --purge autoremove
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
  rtmpdump*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 143 kB disk space will be freed.
Do you want to continue [Y/n]? Y
(Reading database ... 231018 files and directories currently installed.)
Removing rtmpdump ...
Processing triggers for man-db ...
rajat@rajat-MS-7529:~$ LANG=C;sudo apt-get --fix-missing update -o APT::Cache-Limit=100000000
Get:1 http://archive.ubuntu.com precise Release.gpg [198 B]
Get:2 http://archive.ubuntu.com precise-updates Release.gpg [198 B]
Get:3 http://archive.ubuntu.com precise-security Release.gpg [198 B]
Get:4 http://archive.ubuntu.com precise Release [49.6 kB]
Get:5 http://archive.ubuntu.com precise-updates Release [49.6 kB]
Get:6 http://archive.ubuntu.com precise-security Release [49.6 kB]
Get:7 http://archive.ubuntu.com precise/universe Sources [5019 kB]
Get:8 http://archive.ubuntu.com precise/main Sources [934 kB]
Get:9 http://archive.ubuntu.com precise/restricted Sources [5470 B]
Get:10 http://archive.ubuntu.com precise/multiverse Sources [155 kB]
Get:11 http://archive.ubuntu.com precise/main i386 Packages [1274 kB]
Get:12 http://archive.ubuntu.com precise/multiverse i386 Packages [121 kB]
Get:13 http://archive.ubuntu.com precise/universe i386 Packages [4796 kB]
Get:14 http://archive.ubuntu.com precise/main TranslationIndex [3706 B]
Get:15 http://archive.ubuntu.com precise/multiverse TranslationIndex [2676 B]
Get:16 http://archive.ubuntu.com precise/universe TranslationIndex [2922 B]
Get:17 http://archive.ubuntu.com precise-updates/universe Sources [93.9 kB]
Get:18 http://archive.ubuntu.com precise-updates/main Sources [412 kB]
Get:19 http://archive.ubuntu.com precise-updates/multiverse Sources [6582 B]
Get:20 http://archive.ubuntu.com precise-updates/main i386 Packages [692 kB]
Get:21 http://archive.ubuntu.com precise-updates/multiverse i386 Packages [13.8 kB]
Get:22 http://archive.ubuntu.com precise-updates/universe i386 Packages [215 kB]
Get:23 http://archive.ubuntu.com precise-updates/main TranslationIndex [3564 B]
Get:24 http://archive.ubuntu.com precise-updates/multiverse TranslationIndex [2605 B]
Get:25 http://archive.ubuntu.com precise-updates/universe TranslationIndex [2850 B]
Get:26 http://archive.ubuntu.com precise-security/universe Sources [28.0 kB]
Get:27 http://archive.ubuntu.com precise-security/main Sources [85.0 kB]
Get:28 http://archive.ubuntu.com precise-security/multiverse Sources [1383 B]
Get:29 http://archive.ubuntu.com precise-security/main i386 Packages [320 kB]
Get:30 http://archive.ubuntu.com precise-security/multiverse i386 Packages [2371 B]
Get:31 http://archive.ubuntu.com precise-security/universe i386 Packages [83.7 kB]
Get:32 http://archive.ubuntu.com precise-security/main TranslationIndex [74 B]
Get:33 http://archive.ubuntu.com precise-security/multiverse TranslationIndex [71 B]
Get:34 http://archive.ubuntu.com precise-security/universe TranslationIndex [73 B]
Get:35 http://archive.ubuntu.com precise/main Translation-en [726 kB]
Get:36 http://archive.ubuntu.com precise/multiverse Translation-en [93.4 kB]
Get:37 http://archive.ubuntu.com precise/universe Translation-en [3341 kB]
Get:38 http://archive.ubuntu.com precise-updates/main Translation-en [304 kB]
Get:39 http://archive.ubuntu.com precise-updates/multiverse Translation-en [7834 B]
Get:40 http://archive.ubuntu.com precise-updates/universe Translation-en [125 kB]
Get:41 http://archive.ubuntu.com precise-security/main Translation-en [148 kB]
Get:42 http://archive.ubuntu.com precise-security/multiverse Translation-en [995 B]
Get:43 http://archive.ubuntu.com precise-security/universe Translation-en [51.8 kB]
Fetched 19.2 MB in 55s (344 kB/s)
Reading package lists... Done
rajat@rajat-MS-7529:~$ sudo dpkg --configure -a
rajat@rajat-MS-7529:~$ sudo dpkg --clear-avail
rajat@rajat-MS-7529:~$ LANG=C;sudo apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 39 not upgraded.
rajat@rajat-MS-7529:~$ LANG=C;sudo apt-get --fix-missing install
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 39 not upgraded.
rajat@rajat-MS-7529:~$ LANG=C;sudo apt-get update -o APT::Cache-Limit=100000000 && sudo apt-get dist-upgrade
Hit http://archive.ubuntu.com precise Release.gpg
Hit http://archive.ubuntu.com precise-updates Release.gpg
Hit http://archive.ubuntu.com precise-security Release.gpg
Hit http://archive.ubuntu.com precise Release
Hit http://archive.ubuntu.com precise-updates Release
Hit http://archive.ubuntu.com precise-security Release
Hit http://archive.ubuntu.com precise/universe Sources
Hit http://archive.ubuntu.com precise/main Sources
Hit http://archive.ubuntu.com precise/restricted Sources
Hit http://archive.ubuntu.com precise/multiverse Sources
Hit http://archive.ubuntu.com precise/main i386 Packages
Hit http://archive.ubuntu.com precise/multiverse i386 Packages
Hit http://archive.ubuntu.com precise/universe i386 Packages
Hit http://archive.ubuntu.com precise/main TranslationIndex
Hit http://archive.ubuntu.com precise/multiverse TranslationIndex
Hit http://archive.ubuntu.com precise/universe TranslationIndex
Hit http://archive.ubuntu.com precise-updates/universe Sources
Hit http://archive.ubuntu.com precise-updates/main Sources
Hit http://archive.ubuntu.com precise-updates/multiverse Sources
Hit http://archive.ubuntu.com precise-updates/main i386 Packages
Hit http://archive.ubuntu.com precise-updates/multiverse i386 Packages
Hit http://archive.ubuntu.com precise-updates/universe i386 Packages
Hit http://archive.ubuntu.com precise-updates/main TranslationIndex
Hit http://archive.ubuntu.com precise-updates/multiverse TranslationIndex
Hit http://archive.ubuntu.com precise-updates/universe TranslationIndex
Hit http://archive.ubuntu.com precise-security/universe Sources
Hit http://archive.ubuntu.com precise-security/main Sources
Hit http://archive.ubuntu.com precise-security/multiverse Sources
Hit http://archive.ubuntu.com precise-security/main i386 Packages
Hit http://archive.ubuntu.com precise-security/multiverse i386 Packages
Hit http://archive.ubuntu.com precise-security/universe i386 Packages
Hit http://archive.ubuntu.com precise-security/main TranslationIndex
Hit http://archive.ubuntu.com precise-security/multiverse TranslationIndex
Hit http://archive.ubuntu.com precise-security/universe TranslationIndex
Hit http://archive.ubuntu.com precise/main Translation-en
Hit http://archive.ubuntu.com precise/multiverse Translation-en
Hit http://archive.ubuntu.com precise/universe Translation-en
Hit http://archive.ubuntu.com precise-updates/main Translation-en
Hit http://archive.ubuntu.com precise-updates/multiverse Translation-en
Hit http://archive.ubuntu.com precise-updates/universe Translation-en
Hit http://archive.ubuntu.com precise-security/main Translation-en
Hit http://archive.ubuntu.com precise-security/multiverse Translation-en
Hit http://archive.ubuntu.com precise-security/universe Translation-en
Reading package lists... Done
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following NEW packages will be installed:
  linux-headers-3.2.0-51 linux-headers-3.2.0-51-generic-pae
  linux-image-3.2.0-51-generic-pae
The following packages will be upgraded:
  apport apport-gtk apt apt-transport-https apt-utils evince evince-common
  gir1.2-dbusmenu-glib-0.4 gir1.2-dbusmenu-gtk-0.4 gir1.2-gudev-1.0
  grub-common grub-pc grub-pc-bin grub2-common jockey-common jockey-gtk
  libapt-inst1.4 libapt-pkg4.12 libdbusmenu-glib4 libdbusmenu-gtk3-4
  libdbusmenu-gtk4 libevince3-3 libgudev-1.0-0 liblightdm-gobject-1-0 libudev0
  lightdm linux-generic-pae linux-headers-generic-pae linux-image-generic-pae
  lsb-base lsb-release python-apport python-problem-report remmina
  remmina-common remmina-plugin-rdp remmina-plugin-vnc udev whoopsie
39 upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
Need to get 58.8 MB of archives.
After this operation, 181 MB of additional disk space will be used.
Do you want to continue [Y/n]? Y
Get:1 http://archive.ubuntu.com/ubuntu/ precise-updates/main apt i386 0.8.16~exp12ubuntu10.12 [1096 kB]
Get:2 http://archive.ubuntu.com/ubuntu/ precise-updates/main libapt-inst1.4 i386 0.8.16~exp12ubuntu10.12 [102 kB]
Get:3 http://archive.ubuntu.com/ubuntu/ precise-updates/main libudev0 i386 175-0ubuntu9.4 [32.3 kB]
Get:4 http://archive.ubuntu.com/ubuntu/ precise-updates/main gir1.2-dbusmenu-gtk-0.4 i386 0.6.2-0ubuntu0.2 [3292 B]
Get:5 http://archive.ubuntu.com/ubuntu/ precise-updates/main libdbusmenu-gtk4 i386 0.6.2-0ubuntu0.2 [31.1 kB]
Get:6 http://archive.ubuntu.com/ubuntu/ precise-updates/main gir1.2-dbusmenu-glib-0.4 i386 0.6.2-0ubuntu0.2 [7142 B]
Get:7 http://archive.ubuntu.com/ubuntu/ precise-updates/main libdbusmenu-glib4 i386 0.6.2-0ubuntu0.2 [47.3 kB]
Get:8 http://archive.ubuntu.com/ubuntu/ precise-updates/main libdbusmenu-gtk3-4 i386 0.6.2-0ubuntu0.2 [31.2 kB]
Get:9 http://archive.ubuntu.com/ubuntu/ precise-updates/main libgudev-1.0-0 i386 1:175-0ubuntu9.4 [14.6 kB]
Get:10 http://archive.ubuntu.com/ubuntu/ precise-updates/main libapt-pkg4.12 i386 0.8.16~exp12ubuntu10.12 [944 kB]
Get:11 http://archive.ubuntu.com/ubuntu/ precise-updates/main lightdm i386 1.2.3-0ubuntu2.3 [98.2 kB]
Get:12 http://archive.ubuntu.com/ubuntu/ precise-updates/main linux-image-3.2.0-51-generic-pae i386 3.2.0-51.77 [38.3 MB]
Get:13 http://archive.ubuntu.com/ubuntu/ precise-updates/main whoopsie i386 0.1.33 [26.4 kB]
Get:14 http://archive.ubuntu.com/ubuntu/ precise-updates/main lsb-base all 4.0-0ubuntu20.3 [10.5 kB]
Get:15 http://archive.ubuntu.com/ubuntu/ precise-updates/main apt-utils i386 0.8.16~exp12ubuntu10.12 [194 kB]
Get:16 http://archive.ubuntu.com/ubuntu/ precise-updates/main lsb-release all 4.0-0ubuntu20.3 [11.0 kB]
Get:17 http://archive.ubuntu.com/ubuntu/ precise-updates/main udev i386 175-0ubuntu9.4 [350 kB]
Get:18 http://archive.ubuntu.com/ubuntu/ precise-updates/main apt-transport-https i386 0.8.16~exp12ubuntu10.12 [16.3 kB]
Get:19 http://archive.ubuntu.com/ubuntu/ precise-updates/main python-problem-report all 2.0.1-0ubuntu17.4 [9342 B]
Get:20 http://archive.ubuntu.com/ubuntu/ precise-updates/main python-apport all 2.0.1-0ubuntu17.4 [81.1 kB]
Get:21 http://archive.ubuntu.com/ubuntu/ precise-updates/main apport all 2.0.1-0ubuntu17.4 [147 kB]
Get:22 http://archive.ubuntu.com/ubuntu/ precise-updates/main apport-gtk all 2.0.1-0ubuntu17.4 [9200 B]
Get:23 http://archive.ubuntu.com/ubuntu/ precise-updates/main evince i386 3.4.0-0ubuntu1.7 [207 kB]
Get:24 http://archive.ubuntu.com/ubuntu/ precise-updates/main libevince3-3 i386 3.4.0-0ubuntu1.7 [357 kB]
Get:25 http://archive.ubuntu.com/ubuntu/ precise-updates/main evince-common all 3.4.0-0ubuntu1.7 [476 kB]
Get:26 http://archive.ubuntu.com/ubuntu/ precise-updates/main gir1.2-gudev-1.0 i386 175-0ubuntu9.4 [3972 B]
Get:27 http://archive.ubuntu.com/ubuntu/ precise-updates/main grub-pc i386 1.99-21ubuntu3.10 [140 kB]
Get:28 http://archive.ubuntu.com/ubuntu/ precise-updates/main grub-pc-bin i386 1.99-21ubuntu3.10 [876 kB]
Get:29 http://archive.ubuntu.com/ubuntu/ precise-updates/main grub2-common i386 1.99-21ubuntu3.10 [94.3 kB]
Get:30 http://archive.ubuntu.com/ubuntu/ precise-updates/main grub-common i386 1.99-21ubuntu3.10 [2096 kB]
Get:31 http://archive.ubuntu.com/ubuntu/ precise-updates/main jockey-gtk all 0.9.7-0ubuntu7.9 [9116 B]
Get:32 http://archive.ubuntu.com/ubuntu/ precise-updates/main jockey-common all 0.9.7-0ubuntu7.9 [129 kB]
Get:33 http://archive.ubuntu.com/ubuntu/ precise-updates/main liblightdm-gobject-1-0 i386 1.2.3-0ubuntu2.3 [32.0 kB]
Get:34 http://archive.ubuntu.com/ubuntu/ precise-updates/main linux-generic-pae i386 3.2.0.51.61 [1724 B]
Get:35 http://archive.ubuntu.com/ubuntu/ precise-updates/main linux-image-generic-pae i386 3.2.0.51.61 [2354 B]
Get:36 http://archive.ubuntu.com/ubuntu/ precise-updates/main linux-headers-3.2.0-51 all 3.2.0-51.77 [11.7 MB]
Get:37 http://archive.ubuntu.com/ubuntu/ precise-updates/main linux-headers-3.2.0-51-generic-pae i386 3.2.0-51.77 [974 kB]
Get:38 http://archive.ubuntu.com/ubuntu/ precise-updates/main linux-headers-generic-pae i386 3.2.0.51.61 [2348 B]
Get:39 http://archive.ubuntu.com/ubuntu/ precise-updates/main remmina-plugin-rdp i386 1.0.0-1ubuntu6.3 [31.6 kB]
Get:40 http://archive.ubuntu.com/ubuntu/ precise-updates/main remmina-plugin-vnc i386 1.0.0-1ubuntu6.3 [20.1 kB]
Get:41 http://archive.ubuntu.com/ubuntu/ precise-updates/main remmina i386 1.0.0-1ubuntu6.3 [134 kB]
Get:42 http://archive.ubuntu.com/ubuntu/ precise-updates/main remmina-common all 1.0.0-1ubuntu6.3 [47.7 kB]
Fetched 57.9 MB in 1min 16s (755 kB/s)
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/a/apt/libapt-pkg4.12_0.8.16~exp12ubuntu10.12_i386.deb Size mismatch
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
rajat@rajat-MS-7529:~$ find /etc/apt -name '*.list' -exec bash -c 'echo -e "\n$1\n"; cat -n "$1"' _ '{}' \;

/etc/apt/sources.list

     1 # deb cdrom:[Ubuntu 12.04.1 LTS _Precise Pangolin_ - Release i386 (20120817.3)]/ precise main restricted
     2
     3 # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
     4 # newer versions of the distribution.
     5 deb http://archive.ubuntu.com/ubuntu precise main multiverse
     6 deb-src http://archive.ubuntu.com/ubuntu precise universe main restricted multiverse #Added by software-properties
     7
     8 ## Major bug fix updates produced after the final release of the
     9 ## distribution.
    10 deb http://archive.ubuntu.com/ubuntu precise-updates main multiverse
    11 deb-src http://archive.ubuntu.com/ubuntu precise-updates universe main multiverse #Added by software-properties
    12
    13 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
    14 ## team. Also, please note that software in universe WILL NOT receive any
    15 ## review or updates from the Ubuntu security team.
    16 deb http://archive.ubuntu.com/ubuntu precise universe
    17 deb http://archive.ubuntu.com/ubuntu precise-updates universe
    18
    19 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
    20 ## team, and may not be under a free licence. Please satisfy yourself as to
    21 ## your rights to use the software. Also, please note that software in
    22 ## multiverse WILL NOT receive any review or updates from the Ubuntu
    23 ## security team.
    24
    25 ## N.B. software from this repository may not have been tested as
    26 ## extensively as that contained in the main release, although it includes
    27 ## newer versions of some applications which may provide useful features.
    28 ## Also, please note that software in backports WILL NOT receive any review
    29 ## or updates from the Ubuntu security team.
    30
    31 deb http://archive.ubuntu.com/ubuntu precise-security main multiverse
    32 deb-src http://archive.ubuntu.com/ubuntu precise-security universe main multiverse #Added by software-properties
    33 deb http://archive.ubuntu.com/ubuntu precise-security universe
    34
    35 ## Uncomment the following two lines to add software from Canonical's
    36 ## 'partner' repository.
    37 ## This software is not part of Ubuntu, but is offered by Canonical and the
    38 ## respective vendors as a service to Ubuntu users.
    39 # deb http://archive.canonical.com/ubuntu precise partner
    40 # deb-src http://archive.canonical.com/ubuntu precise partner
    41
    42 ## This software is not part of Ubuntu, but is offered by third-party
    43 ## developers who want to ship their latest software.
    44 # deb http://extras.ubuntu.com/ubuntu precise main
    45 # deb-src http://extras.ubuntu.com/ubuntu precise main

/etc/apt/sources.list.d/google-talkplugin.list

     1 ### THIS FILE IS AUTOMATICALLY CONFIGURED ###
     2 # You may comment out this entry, but any other modifications may be lost.
     3 # deb http://dl.google.com/linux/talkplugin/deb/ stable main

/etc/apt/sources.list.d/docky-core-stable-precise.list

     1 # deb http://ppa.launchpad.net/docky-core/stable/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/docky-core/stable/ubuntu precise main

/etc/apt/sources.list.d/noobslab-ppa-gimp-precise.list

     1 # deb http://ppa.launchpad.net/noobslab/ppa-gimp/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/noobslab/ppa-gimp/ubuntu precise main

/etc/apt/sources.list.d/google-chrome.list

     1 ### THIS FILE IS AUTOMATICALLY CONFIGURED ###
     2 # You may comment out this entry, but any other modifications may be lost.
     3 # deb http://dl.google.com/linux/chrome/deb/ stable main

/etc/apt/sources.list.d/ubuntu-wine-ppa-precise.list

     1 # deb http://ppa.launchpad.net/ubuntu-wine/ppa/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/ubuntu-wine/ppa/ubuntu precise main

/etc/apt/sources.list.d/ubuntu-sdk-team-ppa-precise.list

     1 # deb http://ppa.launchpad.net/ubuntu-sdk-team/ppa/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/ubuntu-sdk-team/ppa/ubuntu precise main

/etc/apt/sources.list.d/steam.list

     1 # deb http://repo.steampowered.com/steam/ precise steam
     2 # deb-src http://repo.steampowered.com/steam/ precise steam

/etc/apt/sources.list.d/teejee2008-ppa-precise.list

     1 # deb http://ppa.launchpad.net/teejee2008/ppa/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/teejee2008/ppa/ubuntu precise main

/etc/apt/sources.list.d/ian-berke-ppa-drawers-precise.list

     1 # deb http://ppa.launchpad.net/ian-berke/ppa-drawers/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/ian-berke/ppa-drawers/ubuntu precise main

/etc/apt/sources.list.d/webupd8team-unstable-precise.list

     1 # deb http://ppa.launchpad.net/webupd8team/unstable/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/webupd8team/unstable/ubuntu precise main

/etc/apt/sources.list.d/dropbox.list

     1 # deb http://linux.dropbox.com/ubuntu precise main

/etc/apt/sources.list.d/snwh-moka-icon-theme-daily-precise.list

     1 # deb http://ppa.launchpad.net/snwh/moka-icon-theme-daily/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/snwh/moka-icon-theme-daily/ubuntu precise main

/etc/apt/sources.list.d/private-ppa.launchpad.net_commercial-ppa-uploaders_screencloud_ubuntu.list

     1 # deb https://private-ppa.launchpad.net/commercial-ppa-uploaders/screencloud/ubuntu precise main #Added by software-center; credentials stored in /etc/apt/auth.conf

/etc/apt/sources.list.d/precise-partner.list

     1 # deb http://archive.canonical.com/ubuntu precise partner #Added by software-center

/etc/apt/sources.list.d/langdalepl-gvfs-mtp-precise.list

     1 # deb http://ppa.launchpad.net/langdalepl/gvfs-mtp/ubuntu precise main
     2 # deb-src http://ppa.launchpad.net/langdalepl/gvfs-mtp/ubuntu precise main
rajat@rajat-MS-7529:~$

Terminal output looks ok except for this:

Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/a/apt/libapt-pkg4.12_0.8.16~exp12ubuntu10.12_i386.deb Size mismatch

The download of libapt-pkg4.12_0.8.16~exp12ubuntu10.12_i386.deb is probably incomplete, so the file is probably corrupt and you need to download it once more.

But the troubleshooting procedure seems to have solved any issues you were having before.

Is the issue solved?

You never mentioned what the initial error message was...

I received your Email message to my private Email account.

If you want to learn more about Ubuntu, I suggest reading these guides:

https://help.ubuntu.com/community/ExternalGuides

The problem was .......the update manager couldn't download the updates and the software-center wasn't opening...A error was notified in the notification bar...anyways now the software center's working fine, but recently when I updated the system via update-manager I get this error

"Failed to download package files...
Check your internet connection
Details
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/a/apt/libapt-pkg4.12_0.8.16~exp12ubuntu10.12_i386.deb Size mismatch"
The one you mentioned above..HOW to solve this problem now!!

Try running these commands in a Terminal:

sudo apt-get clean

sudo apt-get autoclean

Then switch to a different mirror repository in Ubuntu Software Center, which is explained here:

http://askubuntu.com/questions/53084/how-do-i-change-which-mirror-i-get-updates-and-software-from

Then run this command:

sudo apt-get update

Then retry upgrading.

Source: http://www.ubuntulinuxhelp.com/quick-fix-for-the-size-mismatch-when-updating-ubuntu-linux/