How to upgrade ubuntu 18.04 to ubuntu 20.04 ?

[kalpana]

I try to upgrade ubuntu 18.04 with apache 2 under digital ocean to ubuntu 20.04

I try to follow steps in the https://help.ubuntu.com/community/FocalUpgrades article , but I got unexpected error

Please install all available updates for your release before upgrading

even after I upgraded the system:
Code:

Code Select Expand

root@remote-server:~# uname -r; uname -a
4.15.0-213-generic
Linux remote-server 4.15.0-213-generic #224-Ubuntu SMP Mon Jun 19 13:30:12 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

root@remote-server:~# do-release-upgrade
Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.

root@remote-server:~# sudo apt-get update
Ign:1 http://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/6.0 InRelease
Hit:2 http://ppa.launchpad.net/certbot/certbot/ubuntu bionic InRelease
Hit:3 http://security.ubuntu.com/ubuntu bionic-security InRelease
Get:4 https://download.docker.com/linux/ubuntu bionic InRelease [64.4 kB]
Hit:5 https://deb.nodesource.com/node_16.x bionic InRelease
Hit:6 http://ppa.launchpad.net/ondrej/php/ubuntu bionic InRelease
Hit:7 http://mirrors.digitalocean.com/ubuntu bionic InRelease
Hit:8 http://mirrors.digitalocean.com/ubuntu bionic-updates InRelease
Hit:9 http://mirrors.digitalocean.com/ubuntu bionic-backports InRelease
Hit:10 http://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/6.0 Release
Fetched 64.4 kB in 1s (70.6 kB/s)
Reading package lists... Done
root@remote-server:~# sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
  base-files docker-ce docker-ce-cli ubuntu-advantage-tools ubuntu-server
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.

root@remote-server:~# do-release-upgrade
Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.
How to fix this error and move next?