Ruby on RailsのUbuntuでの環境構築中にエラー

「現場で使えるRuby on Rails 5 速習実践ガイド」の2章に従って、windows10でUbuntuにrbenvをインストールするところまでは良かったのですが、その後rbenv install 2.7.2とするとエラーが発生します。

kjo68eik@Kajio:~$ rbenv -v
rbenv 1.1.2-36-g60c9339
kjo68eik@Kajio:~$ git clone https://github.com/rbenv/ruby-build.git "$(rbenv root)"/plugins/ruby-build
Cloning into '/home/kjo68eik/.rbenv/plugins/ruby-build'...
remote: Enumerating objects: 1, done.
remote: Counting objects: 100% (1/1), done.
remote: Total 11168 (delta 0), reused 0 (delta 0), pack-reused 11167
Receiving objects: 100% (11168/11168), 2.35 MiB | 2.10 MiB/s, done.
Resolving deltas: 100% (7368/7368), done.
kjo68eik@Kajio:~$ sudo apt-get install autoconf bison build-essential libssl-dev libyaml-dev libreadline6-dev zlib1g-dev
 libncurses5-dev libffi-dev libgdbm3 libgdbm-dev
[sudo] password for kjo68eik:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'libreadline-dev' instead of 'libreadline6-dev'
E: Unable to locate package libgdbm3
kjo68eik@Kajio:~$ rbenv install 2.7.2
Downloading ruby-2.7.2.tar.bz2...
-> https://cache.ruby-lang.org/pub/ruby/2.7/ruby-2.7.2.tar.bz2
Installing ruby-2.7.2...

BUILD FAILED (Ubuntu 20.04 using ruby-build 20201118)

Inspect or clean up the working tree at /tmp/ruby-build.20201201184918.12219.Y7t4YQ
Results logged to /tmp/ruby-build.20201201184918.12219.log

Last 10 log lines:
checking for ruby... false
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking target system type... x86_64-pc-linux-gnu
checking for gcc... no
checking for cc... no
checking for cl.exe... no
configure: error: in `/tmp/ruby-build.20201201184918.12219.Y7t4YQ/ruby-2.7.2':
configure: error: no acceptable C compiler found in $PATH
See `config.log' for more details

その後、C compilerが必要（？）とのことでググって以下を実行しました。

sudo apt install gcc
sudo apt install make-doc

そしてもう一度rbenv install 2.7.2したところ、

BUILD FAILED (Ubuntu 20.04 using ruby-build 20201118)

Inspect or clean up the working tree at /tmp/ruby-build.20201201205155.20088.o1C9N3
Results logged to /tmp/ruby-build.20201201205155.20088.log

Last 10 log lines:
        from ./tool/rbinstall.rb:846:in `block (2 levels) in install_default_gem'
        from ./tool/rbinstall.rb:279:in `open_for_install'
        from ./tool/rbinstall.rb:845:in `block in install_default_gem'
        from ./tool/rbinstall.rb:835:in `each'
        from ./tool/rbinstall.rb:835:in `install_default_gem'
        from ./tool/rbinstall.rb:799:in `block in <main>'
        from ./tool/rbinstall.rb:950:in `block in <main>'
        from ./tool/rbinstall.rb:947:in `each'
        from ./tool/rbinstall.rb:947:in `<main>'
make: *** [uncommon.mk:373: do-install-all] Error 1

こうなりましたが、ここから進めません。
libffi-devのインストール失敗が気になったのでsudo apt-get install libffi-devを実行したら以下のログが表示され、その後もう一度rubyのインストールを試みましたが、エラーは変わりませんでした。

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  libffi-dev
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 57.0 kB of archives.
After this operation, 312 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu focal/main amd64 libffi-dev amd64 3.3-4 [57.0 kB]
Fetched 57.0 kB in 1s (44.1 kB/s)
Selecting previously unselected package libffi-dev:amd64.
(Reading database ... 36618 files and directories currently installed.)
Preparing to unpack .../libffi-dev_3.3-4_amd64.deb ...
Unpacking libffi-dev:amd64 (3.3-4) ...
Setting up libffi-dev:amd64 (3.3-4) ...
Processing triggers for install-info (6.7.0.dfsg.2-5) ...
Processing triggers for man-db (2.9.1-1) ...