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This was after apt update, apt-dist-upgrade:

root@_____:~# cat /etc/os-release 
NAME="Ubuntu"
VERSION="16.04.6 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.6 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
VERSION_CODENAME=xenial
UBUNTU_CODENAME=xenial

root@_____:~# do-release-upgrade 
Checking for a new Ubuntu release
No new release found.
Karel Adams
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  • Did you try to update from 16.04? Is this output after the update? What is the output of `cat /etc/apt/sources.list`? And what about `cat /etc/update-manager/release-upgrades`? – Kulfy Jan 05 '20 at 09:47
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    @Kufly: sources.list shows nothing unexpected, all lines (except comments, of course) begin with "deb http:" and all contain "xenial". As for the update-manager file, it only has one single line, apart from the comments: "Prompt=never". I compared with another Ubuntu, already at 18.04, and found no difference. – Karel Adams Jan 05 '20 at 09:56
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    Your Ubuntu would never get updated to newer version of Ubuntu unless you change prompt to `lts` (to get upgrades to LTS releases only) or `normal` (to get any upgrade to any release including non-LTS releases). – Kulfy Jan 05 '20 at 10:07
  • Yes, changing the "Prompt=never" to "Prompt=lts" in etc/update-manager/release-upgrades did the trick; upgrade has been started now. Put this as an "answer" and I'll be glad to endorse it. – Karel Adams Jan 05 '20 at 10:17

1 Answers1

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Step 1: Upgrade the packages to the latest version for 16.04 decreases the chance of something going wrong during the upgrade to version 18.04. Run the command below 

sudo apt update && sudo apt upgrade

Step 2: Install the Ubuntu Update Manager.

sudo apt install update-manager-core

Step 3: Upgrade Ubuntu

sudo do-release-upgrade

Step 4: After the upgrade is complete, a restart will be required.

Step 5:To check what version of Ubuntu is currently installed, use the command below.

lsb_release -a

If that does not work, you need to follow these steps

Step 1: Edit apt configuration

Press Ctrl Alt T to open terminal Now, type 

sudo nano /etc/apt/apt.conf

Step 2: Change the config:

APT::Default-Release *;

Note If the apt.conf file does not exist, create your own user file in /etc/apt/apt.conf.d so you can guarantee that it won't be overwritten by package updates. Use the command to create the file

sudo touch /etc/apt/apt.conf.d/apt.conf

Then to edit your file run

sudo nano /etc/apt/apt.conf.d/apt.conf

Add this line to the file

 APT::Default-Release *;
Tejas Lotlikar
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    Needlees to say that the standard procedure had already been tried, also the update-manger-core was already in place so it did not get any upgrade. The alternate procedure did not work, either. /etc/apt/apt.conf did not exist, so I created one in /etc/apt/apt.conf.d, with the suggested content. Renewed apt update && apt upgrade did install libappstream4, so the whole apt chain is working ok. Still, do-release-upgrade comes back with the same "No new release found." – Karel Adams Jan 05 '20 at 09:52
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    @KarelAdams, might be but I do not see that in the question. – vanadium Jan 05 '20 at 11:29