Steam created a 92 GB file in /tmp/dumps/marian_stdout.txt, where "marian" is my username.

The file looks like this:

STEAM_RUNTIME is enabled automatically
Pins up-to-date!
/home/marian/.local/share/Steam/ubuntu12_32/steam
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Gtk-Message: 20:54:07.495: Failed to load module "gail"
Gtk-Message: 20:54:07.495: Failed to load module "atk-bridge"
Installing breakpad exception handler for appid(steam)/version(1586022601)
STEAM_RUNTIME_HEAVY: ./steam-runtime-heavy
[2020-04-17 20:54:07] Startup - updater built Apr  4 2020 00:37:13
[2020-04-17 20:54:07] Verifying installation...
[2020-04-17 20:54:07] Verification complete
surface_linux.cpp (2093) : Assertion Failed: None of the authentication protocols specified are supported
surface_linux.cpp (2093) : Assertion Failed: None of the authentication protocols specified are supported
Installing breakpad exception handler for appid(steam)/version(1586022601)
assert_20200417205407_5.dmp[3190]: Uploading dump (out-of-process)
/tmp/dumps/assert_20200417205407_5.dmp
[0417/205407.712301:INFO:crash_reporting.cc(247)] Crash reporting enabled for process: browser
[0417/205407.736265:WARNING:crash_reporting.cc(286)] Failed to set crash key: UserID with value: 0
[0417/205407.736328:WARNING:crash_reporting.cc(286)] Failed to set crash key: BuildID with value: 1585960908
[0417/205407.736333:WARNING:crash_reporting.cc(286)] Failed to set crash key: SteamUniverse with value: Public
[0417/205407.736338:WARNING:crash_reporting.cc(286)] Failed to set crash key: Vendor with value: Valve
/usr/lib/x86_64-linux-gnu/gio/modules/libdconfsettings.so: undefined symbol: g_log_structured_standard
Failed to load module: /usr/lib/x86_64-linux-gnu/gio/modules/libdconfsettings.so
GLib-GIO-Message: Using the 'memory' GSettings backend.  Your settings will not be saved or shared with other applications.
[0417/205407.807075:WARNING:crash_reporting.cc(286)] Failed to set crash key: UserID with value: 0
[0417/205407.807134:WARNING:crash_reporting.cc(286)] Failed to set crash key: BuildID with value: 1585960908
[0417/205407.807138:WARNING:crash_reporting.cc(286)] Failed to set crash key: SteamUniverse with value: Public
[0417/205407.807142:WARNING:crash_reporting.cc(286)] Failed to set crash key: Vendor with value: Valve
[0417/205407.807711:INFO:crash_reporting.cc(247)] Crash reporting enabled for process: gpu-process
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
CApplicationManagerPopulateThread took 3 milliseconds to initialize (will have waited on CAppInfoCacheReadFromDiskThread)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
Installing breakpad exception handler for appid(steam)/version(1586022601)
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type
type unknown not a basic type

The rest of the file is just 92 GB of type unknown not a basic type.

Your system information

• Steam client version (build number or date):
• Distribution: Ubuntu 19.10
• Opted into Steam client beta?: No
• Have you checked for system updates?: Updates were installed while Steam was running