Bug #16756: File.chmod does not work on links.

• Status: Closed
• Assignee: Eregon (Benoit Daloze)
• Target version: -
• ruby -v: ruby-2.8.0-810d66f3e7
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[vo.x (Vit Ondruch)]

Now I observe different error after fix of #16749:

1)
File.lchmod changes the file mode of the link and not of the file ERROR
Errno::ENOTSUP: Operation not supported @ apply2files - /builddir/build/BUILD/ruby-2.8.0-810d66f3e7/rubyspec_temp/32136/359-file_chmod_test.lnk
/builddir/build/BUILD/ruby-2.8.0-810d66f3e7/spec/ruby/core/file/lchmod_spec.rb:21:in `lchmod'
/builddir/build/BUILD/ruby-2.8.0-810d66f3e7/spec/ruby/core/file/lchmod_spec.rb:21:in `block (3 levels) in <top (required)>'
/builddir/build/BUILD/ruby-2.8.0-810d66f3e7/spec/ruby/core/file/lchmod_spec.rb:3:in `<top (required)>'

It seems that glibc 2.31.9000 does not support lchmod above links. May be I should rather report this against glibc? Not sure ...

[vo.x (Vit Ondruch)]

I have reported this against glibc in Fedora:

https://bugzilla.redhat.com/show_bug.cgi?id=1820722

[fweimer (Florian Weimer)]

This is deliberate because Linux does not support changing the mode of a symbolic link (except for file systems with bugs). The error code ENOTSUP is mandated by POSIX for this case. You can still use lchmod to avoid following symbolic links even in the presence of races, so it's still useful.

[Eregon (Benoit Daloze)]

I'm unsure how to resolve this.
This means on Linux we have File.respond_to?(:lchmod) == true but it's basically unusable for its main purpose.

I guess we'll have to do similar as https://github.com/ruby/ruby/commit/a19228f878d955eaf2cce086bcf53f46fdf894b9, so accept both NotImplementedError and ENOTSUP and hardcode the fact Linux can't do lchmod(), because we can't detect it easily anymore.
This might break Ruby programs, notably those that would check File.respond_to?(:lchmod), and those calling lchmod but expecting only success or NotImplementedError but not ENOTSUP.

[Eregon (Benoit Daloze)]

• Status changed from Open to Closed

Should be fixed by https://github.com/ruby/spec/commit/7289ea3e3c22fb41b58d072e966420845cca6e9e