Today, when I launched Steam, it didn’t work. I ran steam in a terminal and go this error:

Running Steam on ubuntu 17.10 64-bit
STEAM_RUNTIME is enabled automatically
Installing breakpad exception handler for appid(steam)/version(1513371133)
libGL: Can't open configuration file /home/thykof/.drirc: Aucun fichier ou dossier de ce type.

…

libGL error: unable to load driver: r600_dri.so
libGL error: failed to load driver: r600
...
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast

I made some searches on Qwant and found a lot of time this answer:

rm ~/.local/share/Steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libstdc**.so.6

rm ~/.local/share/Steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libgcc_s.so.1

It had worked for the askers on the forums, but in my case, it didn’t work.

I finally found the solution, given by abelthorne here.

find ~/.steam/root/ \( -name "libgcc_s.so*" -o -name "libstdc**.so*" -o -name "libxcb.so*" \) -print -delete
find ~/.local/share/Steam/ \( -name "libgcc_s.so*" -o -name "libstdc**.so*" -o -name "libxcb.so*" \) -print -delete

Actually, the problem was about OpenGL and graphic card drivers. I might have changed something somewhere, probably when I was trying to set up GPU mining for Minergate (cf. this post).