Failed to build Ruby 2.7.7 on CentOS 6.9

[madsen]

When I ran rbenv install 2.7.7 on a CentOS 6.9 machine, I got

BUILD FAILED (CentOS 6.9 using ruby-build 20230306)

Inspect or clean up the working tree at /tmp/ruby-build.20230307101935.29825.7C0ZvU
Results logged to /tmp/ruby-build.20230307101935.29825.log

Last 10 log lines:
/tmp/ruby-build.20230307101935.29825.7C0ZvU/ruby-2.7.7/tool/lib/vcs.rb:632: syntax error, unexpected ':', expecting '='
...r, out: NullDevice, exception: false)
                              ^
/tmp/ruby-build.20230307101935.29825.7C0ZvU/ruby-2.7.7/tool/lib/vcs.rb:638: syntax error, unexpected ':', expecting ')'
        cmd_pipe(env, cmd, chdir: @srcdir) do |r|
                                 ^

I eventually figured out that this was because /usr/bin/ruby is 1.8.7. I tried export RBENV_VERSION=2.6.3 (the most recent version on this server) before running rbenv install, but that didn't help.

What did help was mv -iv /usr/bin/ruby{,NO}. After that, rbenv install 2.7.7 worked fine, and I could then mv -iv /usr/bin/ruby{NO,}. But I don't think I should have to do that.