GNOME Software can be a little harder to debug than other applications, because it is typically started early in a user’s session, and it runs in the background.
If gnome-software is already running and you want to enable debug output from this point onward, run:
gnome-software --verbose
This will tell the running instance to enable verbose logging, without needing to restart.
By default, all log messages from gnome-software are sent to the systemd journal. Messages, warnings and errors are always logged; debug and info messages are only logged if verbose output is enabled.
To view the messages from the currently running gnome-software process, run:
journalctl --user --boot "$(which gnome-software)"
If you are starting gnome-software manually, you have a little more control over log output.
The --verbose command line argument will enable verbose mode for the newly
started process. If run from a terminal, all log messages will be printed on the
terminal rather than being sent to the systemd journal. As with journal logging,
debug and info messages will only be printed if they are enabled.
An alternative to the --verbose argument are the following environment
variables:
GS_DEBUG=1GS_DEBUG_NO_TIME=1G_MESSAGES_DEBUG=*
GS_DEBUG and GS_DEBUG_NO_TIME are equivalent to --verbose, enabling output
of all log messages. Normally messages are printed with timestamps, but
GS_DEBUG_NO_TIME disables that if you want to save space.
G_MESSAGES_DEBUG=all is equivalent to the above, but other values can be
passed to it to filter debug log output to certain message domains.
Verbose debug output may be made persistent by modifying the autostart
configuration file for GNOME Software to add --verbose to it:
cp /etc/xdg/autostart/org.gnome.Software.desktop ~/.config/autostart/
sed -i '/^Exec=/ s/$/ --verbose/' ~/.config/autostart/org.gnome.Software.desktop
Note that this will produce a lot of debug output which will consume a noticeable amount of space in your systemd journal over time.