Question about libcurl3-gnutls 7.47.0-1ubuntu2.9

Version 7.47.0-1ubuntu2.9 of the curl (and libcurl*) packages in Ubuntu xenial was the current version between 2018-09-17 and 2018-10-31 and has meanwhile been superseded by higher version numbers (up to 7.47.0-1ubuntu2.19)

Instead of downgrading libcurl4-gnutls-dev to version 7.47.0-1ubuntu2 with a forced removal of other packages you should have better upgraded all packages to the newest version.

It seems that at a certain moment in time you had the xenial-security and/or xenial-updates repositories activated, and you are missing them now.

What you experience is a common problem that can happen when you deactivate a repository, but still have packages installed from that repository.

Remark: Are you aware that support for Ubuntu 16.04 will end this week (except for ESM)?

Thanks Manfred Hampl, that solved my question.

Thank you for your kindly help! It really helped me out of this situation.

However, I still cannot upgrade libcurl3-gnutls to the newest version 7.47.0-1ubuntu2.19. When I used "sudo apt-get install", I got this message

"E: Version '7.47.0-1ubuntu2.19' for 'libcurl3-gnutls' was not found"

I wonder if I should install the newest version by deb. I examined that the versions of other removed packages, like ros-kinetic-desktop-full is already the newest version. If I leave the libcurl3-gnutls version as version 7.47.0-1ubuntu2, will this version influence other packages version or the version of the packages I install in the future?

Thank you again for any kind help you can offer!

Manually installing from *.deb files is not recommended, because you may again run into dependency problems. Use the package management programs (e.g. apt or apt-get) whenever possible.

For updating all packages to the newest version there are the "apt upgrade" and "apt full-upgrade" commands and they should work well if the package management system is adequately configured.

What is the output of the commands

uname -a
lsb_release -crid
apt-cache policy libcurl3-gnutls
grep -e 'updates' -e 'security' /etc/apt/sources.list /etc/apt/sources.list.d/*.list

Hi,

Thank you for your kind help and sorry for the delayed response. I tried "apt upgrade" and "apt full-upgrade" with "apt-get update", but " libcurl3-gnutls" was not in the upgrade list. The response is as followed.

"The following NEW packages will be installed:
  amd64-microcode cgroup-lite intel-microcode iucode-tool libevent-core-2.0-5
  libevent-pthreads-2.0-5 linux-generic-lts-xenial linux-headers-4.4.0-148
  linux-headers-4.4.0-148-generic linux-headers-generic-lts-xenial
  linux-image-4.4.0-148-generic linux-image-generic-lts-xenial
  linux-modules-4.4.0-148-generic linux-modules-extra-4.4.0-148-generic
  python-rosdep-modules
The following packages will be upgraded:
  code git-core google-chrome-stable python-rosdep python-rospkg
  python-rospkg-modules ros-kinetic-ackermann-steering-controller
  ros-kinetic-control-toolbox ros-kinetic-diff-drive-controller
  ros-kinetic-effort-controllers ros-kinetic-force-torque-sensor-controller
  ros-kinetic-forward-command-controller ros-kinetic-gazebo-dev
  ros-kinetic-gazebo-msgs ros-kinetic-gazebo-plugins ros-kinetic-gazebo-ros
  ros-kinetic-gazebo-ros-control ros-kinetic-gazebo-ros-pkgs
  ros-kinetic-gripper-action-controller ros-kinetic-imu-sensor-controller
  ros-kinetic-industrial-robot-status-controller
  ros-kinetic-joint-state-controller ros-kinetic-joint-trajectory-controller
  ros-kinetic-position-controllers ros-kinetic-realtime-tools
  ros-kinetic-ros-controllers ros-kinetic-velocity-controllers seafile-daemon
  snap-confine snapd ubuntu-core-launcher
31 upgraded, 15 newly installed, 0 to remove and 0 not upgraded."

Then I tried the commands in the last conmments, and the response is as followed.

"~$ uname -a
Linux liaolab-ASM201 4.8.0-36-generic #36~16.04.1-Ubuntu SMP Sun Feb 5 09:39:57 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
liaolab@liaolab-ASM201:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 16.04.2 LTS
Release: 16.04
Codename: xenial
~$ apt-cache policy libcurl3-gnutls
libcurl3-gnutls:
  Installed: 7.47.0-1ubuntu2
  Candidate: 7.47.0-1ubuntu2
  Version table:
 *** 7.47.0-1ubuntu2 500
        500 http://mirrors.tuna.tsinghua.edu.cn/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status
     7.35.0-1ubuntu2.20 500
        500 http://us.archive.ubuntu.com/ubuntu trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu trusty-security/main amd64 Packages
     7.35.0-1ubuntu2 500
        500 http://us.archive.ubuntu.com/ubuntu trusty/main amd64 Packages
N: Ignoring file 'ros-latest.list122' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
liaolab@liaolab-ASM201:~$ grep -e 'updates' -e 'security' /etc/apt/source.list /etc/apt/sources/list.d/*.liast
grep: /etc/apt/source.list: No such file or directory
grep: /etc/apt/sources/list.d/*.liast: No such file or directory
~$ grep -e 'updates' -e 'security' /etc/apt/sources.list /etc/apt/sources.list.d/*.list
/etc/apt/sources.list:## Major bug fix updates produced after the final release of the
/etc/apt/sources.list:deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
/etc/apt/sources.list:deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
/etc/apt/sources.list:## review or updates from the Ubuntu security team.
/etc/apt/sources.list:deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
/etc/apt/sources.list:deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
/etc/apt/sources.list:## multiverse WILL NOT receive any review or updates from the Ubuntu
/etc/apt/sources.list:## security team.
/etc/apt/sources.list:deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
/etc/apt/sources.list:deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
/etc/apt/sources.list:## or updates from the Ubuntu security team.
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu trusty-security main restricted
/etc/apt/sources.list:deb-src http://security.ubuntu.com/ubuntu trusty-security main restricted
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu trusty-security universe
/etc/apt/sources.list:deb-src http://security.ubuntu.com/ubuntu trusty-security universe
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu trusty-security multiverse
/etc/apt/sources.list:deb-src http://security.ubuntu.com/ubuntu trusty-security multiverse"

Then I tried with "apt-get update' but I got these messages:

"Err:6 http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu xenial InRelease
  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)"

I wonder how I should do next or how I could fix the error with "apt-get update". Thank you very much for any help you can offer!

Your package management system is misconfigured.

You are running Ubuntu 16.04 xenial, but your sources.list configuration file contains references for Ubuntu 14.04 trusty. This is wrong.

Please copy/paste the output that you receive for the command

find /etc/apt -name '*.list' -exec bash -c 'echo -e "\n$1\n"; cat -n "$1"' _ '{}' \;

Thank you for you kind help and sorry for the delayed response. The output of this command is as followed:

"$ find /etc/apt -name '*.list' -exec bash -c 'echo -e "\n$1\n"; cat -n "$1"' _ '{}' \;

/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 [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main

/etc/apt/sources.list.d/seafile-ubuntu-seafile-client-xenial.list

     1 deb http://ppa.launchpad.net/seafile/seafile-client/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/seafile/seafile-client/ubuntu xenial main

/etc/apt/sources.list.d/ros-latest.list

     1 deb http://packages.ros.org/ros/ubuntu xenial main

/etc/apt/sources.list.d/vscode.list

     1 ### THIS FILE IS AUTOMATICALLY CONFIGURED ###
     2 # You may comment out this entry, but any other modifications may be lost.
     3 deb [arch=amd64,arm64,armhf] http://packages.microsoft.com/repos/code stable main

/etc/apt/sources.list.d/gazebo-stable.list

     1 deb http://packages.osrfoundation.org/gazebo/ubuntu-stable xenial main

/etc/apt/sources.list.d/sogoupinyin.list

     1 deb http://archive.ubuntukylin.com:10006/ubuntukylin xenial main

/etc/apt/sources.list.d/docky-core-ubuntu-stable-xenial.list

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

/etc/apt/sources.list.d/nilarimogard-ubuntu-webupd8-xenial.list

     1 deb http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu xenial main

/etc/apt/sources.list.d/git-core-ubuntu-ppa-xenial.list

     1 deb http://ppa.launchpad.net/git-core/ppa/ubuntu xenial main
     2 # deb-src http://ppa.launchpad.net/git-core/ppa/ubuntu xenial main

/etc/apt/sources.list

     1 # deb cdrom:[Ubuntu 14.04 LTS _Trusty Tahr_ - Release amd64+mac (20140417)]/ trusty 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://us.archive.ubuntu.com/ubuntu/ trusty main restricted
     6 deb-src http://us.archive.ubuntu.com/ubuntu/ trusty main restricted
     7
     8 ## Major bug fix updates produced after the final release of the
     9 ## distribution.
    10 deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
    11 deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
    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://us.archive.ubuntu.com/ubuntu/ trusty universe
    17 deb-src http://us.archive.ubuntu.com/ubuntu/ trusty universe
    18 deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
    19 deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
    20
    21 ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
    22 ## team, and may not be under a free licence. Please satisfy yourself as to
    23 ## your rights to use the software. Also, please note that software in
    24 ## multiverse WILL NOT receive any review or updates from the Ubuntu
    25 ## security team.
    26 deb http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
    27 deb-src http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
    28 deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
    29 deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
    30
    31 ## N.B. software from this repository may not have been tested as
    32 ## extensively as that contained in the main release, although it includes
    33 ## newer versions of some applications which may provide useful features.
    34 ## Also, please note that software in backports WILL NOT receive any review
    35 ## or updates from the Ubuntu security team.
    36 deb http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
    37 deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
    38
    39 deb http://security.ubuntu.com/ubuntu trusty-security main restricted
    40 deb-src http://security.ubuntu.com/ubuntu trusty-security main restricted
    41 deb http://security.ubuntu.com/ubuntu trusty-security universe
    42 deb-src http://security.ubuntu.com/ubuntu trusty-security universe
    43 deb http://security.ubuntu.com/ubuntu trusty-security multiverse
    44 deb-src http://security.ubuntu.com/ubuntu trusty-security multiverse
    45
    46 ## Uncomment the following two lines to add software from Canonical's
    47 ## 'partner' repository.
    48 ## This software is not part of Ubuntu, but is offered by Canonical and the
    49 ## respective vendors as a service to Ubuntu users.
    50 # deb http://archive.canonical.com/ubuntu trusty partner
    51 # deb-src http://archive.canonical.com/ubuntu trusty partner
    52
    53 ## This software is not part of Ubuntu, but is offered by third-party
    54 ## developers who want to ship their latest software.
    55 deb http://extras.ubuntu.com/ubuntu trusty main
    56 deb-src http://extras.ubuntu.com/ubuntu trusty main
    57 deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial universe restricted multiverse main
    58 deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial universe restricted multiverse main #Added by software-properties
"

Thank you very much for any help you can offer!

Open a terminal window and issue the command

sudo gedit /etc/apt/sources.list

In the editor window that opens change all occurrences of "trusty" by "xenial" except in the first line (leave the first line as it is).

Put a comment indicator in front of every line that starts wit deb-src,
changing from
deb-src http...
into
# deb-src http...

Delete the last two lines (those containing mirrors.tuna.tsinghua.edu.cn)

Save the file and close the editor.

Finally execute the command
sudo apt update
and copy/paste the output into the question document, that we can verify the results.

Thank you for your kind help! I have changed the list file as above and the output of "sudo apt update" is as followed.

"
Hit:1 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:2 http://archive.ubuntukylin.com:10006/ubuntukylin xenial InRelease
Hit:3 http://packages.osrfoundation.org/gazebo/ubuntu-stable xenial InRelease
Hit:4 http://ppa.launchpad.net/docky-core/stable/ubuntu xenial InRelease
Get:5 http://us.archive.ubuntu.com/ubuntu xenial InRelease [247 kB]
Hit:6 http://packages.ros.org/ros/ubuntu xenial InRelease
Hit:7 http://ppa.launchpad.net/git-core/ppa/ubuntu xenial InRelease
Hit:8 http://packages.microsoft.com/repos/code stable InRelease
Hit:9 http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu xenial InRelease
Get:10 http://security.ubuntu.com/ubuntu xenial-security InRelease [109 kB]
Hit:11 http://ppa.launchpad.net/seafile/seafile-client/ubuntu xenial InRelease
Get:12 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages [1,646 kB]
Get:13 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]
Ign:14 http://extras.ubuntu.com/ubuntu xenial InRelease
Err:15 http://extras.ubuntu.com/ubuntu xenial Release
  404 Not Found [IP: 91.189.88.91 80]
Get:16 http://security.ubuntu.com/ubuntu xenial-security/main i386 Packages [1,158 kB]
Get:17 http://us.archive.ubuntu.com/ubuntu xenial-backports InRelease [107 kB]
Get:18 http://security.ubuntu.com/ubuntu xenial-security/main Translation-en [380 kB]
Get:19 http://security.ubuntu.com/ubuntu xenial-security/main amd64 DEP-11 Metadata [93.6 kB]
Get:20 http://security.ubuntu.com/ubuntu xenial-security/main DEP-11 64x64 Icons [111 kB]
Get:21 http://security.ubuntu.com/ubuntu xenial-security/restricted amd64 Packages [9,824 B]
Get:22 http://security.ubuntu.com/ubuntu xenial-security/restricted i386 Packages [9,800 B]
Get:23 http://security.ubuntu.com/ubuntu xenial-security/restricted Translation-en [2,152 B]
Get:24 http://security.ubuntu.com/ubuntu xenial-security/restricted amd64 DEP-11 Metadata [200 B]
Get:25 http://security.ubuntu.com/ubuntu xenial-security/universe amd64 Packages [786 kB]
Get:26 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages [1,201 kB]
Get:27 http://security.ubuntu.com/ubuntu xenial-security/universe i386 Packages [665 kB]
Get:28 http://security.ubuntu.com/ubuntu xenial-security/universe Translation-en [226 kB]
Get:29 http://security.ubuntu.com/ubuntu xenial-security/universe amd64 DEP-11 Metadata [130 kB]
Get:30 http://security.ubuntu.com/ubuntu xenial-security/universe DEP-11 64x64 Icons [206 kB]
Get:31 http://security.ubuntu.com/ubuntu xenial-security/multiverse amd64 Packages [7,864 B]
Get:32 http://security.ubuntu.com/ubuntu xenial-security/multiverse i386 Packages [8,084 B]
Get:33 http://security.ubuntu.com/ubuntu xenial-security/multiverse Translation-en [2,672 B]
Get:34 http://security.ubuntu.com/ubuntu xenial-security/multiverse amd64 DEP-11 Metadata [2,468 B]
Get:35 http://security.ubuntu.com/ubuntu xenial-security/multiverse DEP-11 64x64 Icons [2,638 B]
Get:36 http://us.archive.ubuntu.com/ubuntu xenial/main i386 Packages [1,196 kB]
Get:37 http://us.archive.ubuntu.com/ubuntu xenial/main Translation-en [568 kB]
Get:38 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 DEP-11 Metadata [733 kB]
Get:39 http://us.archive.ubuntu.com/ubuntu xenial/main DEP-11 64x64 Icons [409 kB]
Get:40 http://us.archive.ubuntu.com/ubuntu xenial/restricted amd64 Packages [8,344 B]
Get:41 http://us.archive.ubuntu.com/ubuntu xenial/restricted i386 Packages [8,684 B]
Get:42 http://us.archive.ubuntu.com/ubuntu xenial/restricted Translation-en [2,908 B]
Get:43 http://us.archive.ubuntu.com/ubuntu xenial/restricted amd64 DEP-11 Metadata [186 B]
Get:44 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages [7,532 kB]
Get:45 http://us.archive.ubuntu.com/ubuntu xenial/universe i386 Packages [7,512 kB]
Get:46 http://us.archive.ubuntu.com/ubuntu xenial/universe Translation-en [4,354 kB]
Get:47 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 DEP-11 Metadata [3,410 kB]
Get:48 http://us.archive.ubuntu.com/ubuntu xenial/universe DEP-11 64x64 Icons [7,448 kB]
Get:49 http://us.archive.ubuntu.com/ubuntu xenial/multiverse amd64 Packages [144 kB]
Get:50 http://us.archive.ubuntu.com/ubuntu xenial/multiverse i386 Packages [140 kB]
Get:51 http://us.archive.ubuntu.com/ubuntu xenial/multiverse Translation-en [106 kB]
Get:52 http://us.archive.ubuntu.com/ubuntu xenial/multiverse amd64 DEP-11 Metadata [63.8 kB]
Get:53 http://us.archive.ubuntu.com/ubuntu xenial/multiverse DEP-11 64x64 Icons [230 kB]
Get:54 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages [2,048 kB]
Get:55 http://us.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages [1,524 kB]
Get:56 http://us.archive.ubuntu.com/ubuntu xenial-updates/main Translation-en [482 kB]
Get:57 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 DEP-11 Metadata [326 kB]
Get:58 http://us.archive.ubuntu.com/ubuntu xenial-updates/main DEP-11 64x64 Icons [252 kB]
Get:59 http://us.archive.ubuntu.com/ubuntu xenial-updates/restricted amd64 Packages [10.2 kB]
Get:60 http://us.archive.ubuntu.com/ubuntu xenial-updates/restricted i386 Packages [10.2 kB]
Get:61 http://us.archive.ubuntu.com/ubuntu xenial-updates/restricted Translation-en [2,272 B]
Get:62 http://us.archive.ubuntu.com/ubuntu xenial-updates/restricted amd64 DEP-11 Metadata [157 B]
Get:63 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 Packages [1,220 kB]
Get:64 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe i386 Packages [1,086 kB]
Get:65 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe Translation-en [358 kB]
Get:66 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 DEP-11 Metadata [281 kB]
Get:67 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe DEP-11 64x64 Icons [437 kB]
Get:68 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 Packages [22.6 kB]
Get:69 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse i386 Packages [21.4 kB]
Get:70 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse Translation-en [8,476 B]
Get:71 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 DEP-11 Metadata [5,960 B]
Get:72 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse DEP-11 64x64 Icons [14.3 kB]
Get:73 http://us.archive.ubuntu.com/ubuntu xenial-backports/main amd64 Packages [9,812 B]
Get:74 http://us.archive.ubuntu.com/ubuntu xenial-backports/main i386 Packages [9,784 B]
Get:75 http://us.archive.ubuntu.com/ubuntu xenial-backports/main Translation-en [4,456 B]
Get:76 http://us.archive.ubuntu.com/ubuntu xenial-backports/main amd64 DEP-11 Metadata [3,328 B]
Get:77 http://us.archive.ubuntu.com/ubuntu xenial-backports/main DEP-11 64x64 Icons [29 B]
Get:78 http://us.archive.ubuntu.com/ubuntu xenial-backports/restricted amd64 DEP-11 Metadata [194 B]
Get:79 http://us.archive.ubuntu.com/ubuntu xenial-backports/universe amd64 Packages [11.3 kB]
Get:80 http://us.archive.ubuntu.com/ubuntu xenial-backports/universe i386 Packages [10.9 kB]
Get:81 http://us.archive.ubuntu.com/ubuntu xenial-backports/universe Translation-en [4,476 B]
Get:82 http://us.archive.ubuntu.com/ubuntu xenial-backports/universe amd64 DEP-11 Metadata [6,616 B]
Get:83 http://us.archive.ubuntu.com/ubuntu xenial-backports/universe DEP-11 64x64 Icons [5,608 B]
Get:84 http://us.archive.ubuntu.com/ubuntu xenial-backports/multiverse amd64 DEP-11 Metadata [216 B]
Get:85 http://us.archive.ubuntu.com/ubuntu xenial-backports/multiverse DEP-11 64x64 Icons [29 B]
Reading package lists... Done
N: Ignoring file 'ros-latest.list122' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
E: The repository 'http://extras.ubuntu.com/ubuntu xenial Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
"
Thank you again!

Ok, this looks far better, but I have overlooked one additional error.

Proceed as follows:

open a terminal window and issue the following commands:

sudo rm /etc/apt/sources.list.d/ros-latest.list122
sudo gedit /etc/apt/sources.list

in the editor window that opens scroll down to the end and remove the last four lines (those about extras.ubuntu.com including the two comment lines before).

save the file, close the editor and issue the commands

sudo apt update
apt-cache policy libcurl4-gnutls-dev libcurl3-gnutls

and copy/paste the output that we can see the results.
I assume that you have already received a notice that several packages can be updated.

Thank you for your kind help. Part of the output of "sudo apt update" is as followed.

"
790 packages can be upgraded. Run 'apt list --upgradable' to see them.
"
 And the output of "apt-cache policy libcurl4-gnutls-dev libcurl3-gnutls" is as followed.

"
libcurl4-gnutls-dev:
  Installed: (none)
  Candidate: 7.47.0-1ubuntu2.19
  Version table:
     7.47.0-1ubuntu2.19 500
        500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
     7.47.0-1ubuntu2 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
libcurl3-gnutls:
  Installed: 7.47.0-1ubuntu2
  Candidate: 7.47.0-1ubuntu2.19
  Version table:
     7.47.0-1ubuntu2.19 500
        500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
 *** 7.47.0-1ubuntu2 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status
"

Thank you again for your help!

This looks good (unless there are warnings or errors in the part of "apt update" that you did not copy, which I do not expect).

I assume that you now can install libcurl4-gnutls-dev (version 7.47.0-1ubuntu2.19), and this will update libcurl3-gnutls to the same version.

"790 packages can be upgraded."
This shows that the configuration of your package management system was wrong and did not offer updates throughout the past years.
I recommend installing the available updates. This will automatically resolve any other dependency problem like the one with libcurl*-gnutls.

Thank you for your help and recommendation! The process of "apt update" seems correct, which has no warnings or errors. I will install the available updates later to resolve other dependency problem.

Many thanks for all your assistance! It really solves my problem and gives me encouragement.