doubly underlined terminal output is hardly readable

[bam80]

It was first reported for systemd but the problem might be somewhere else:

systemd version the issue has been seen with

systemd 256 (256.11-1.fc41)

Used distribution

Fedora 41

Component

systemd

Expected behaviour you didn't see

ANSI-colored terminal output should look readable and nice on any terminal emulators, even on non-Linux console ones.
Particularly, it's expected there should be no visual regression on terminals properly supporting "Double-underline" (SGR 21) Select Graphic Rendition control sequence, e.g. VTE-based ones.

Unexpected behaviour you saw

On any VTE-based terminal (e.g., Gnome's default) systemd boot output is full of double-underlines which looks ugly and hard-readable:

Apparently, SGR 21 ("Double-underline") attribute is used.
In Linux console, it renders in cyan color instead (as double-underline output is not supported), so it looks rather acceptable there.

Steps to reproduce the problem

• Download Fedora Workstation (e.g. 41):
  https://fedoraproject.org/workstation/download
• In VTE-based terminal emulator (e.g. Ptyxis), run the ISO in Qemu with -serial mon:stdio option and console=tty0 console=ttyS0 kernel command line.
• In the terminal, you'll get double-underlined output similar to the screenshot at some point of boot.
  At the same time, in Qemu VGA-emulating window you can notice the terminal output looks pretty well, with cyan color instead of the underlines.

Suggested solution

In bulk outputs, consider using any other SGR parameter instead of Double-underline or Underline:
Bold, Faint, Italic (this one might look nice), Set foreground color, etc.