Permission issue when opening ardour

When opening Ardour normally it get stuck at this stage
$ ardour6

WARNING: Your system has a limit for maximum amount of locked memory!
         This might cause Ardour to run out of memory before your system runs
         out of memory. You can view the memory limit with 'ulimit -l', and it
         is normally controlled by /etc/security/limits.conf

Ardour6.9.0 (built using 6.9 and GCC version 11.2.0)
Ardour: [INFO]: Your system is configured to limit Ardour to 524288 open files
Ardour: [INFO]: Loading system configuration file /etc/ardour6/system_config
Ardour: [INFO]: CPU vendor: GenuineIntel
Ardour: [INFO]: AVX-capable processor
Ardour: [INFO]: AVX with FMA capable processor
Ardour: [INFO]: CPU brand: Intel(R) Core(TM) i3-10100 CPU @ 3.60GHz
Ardour: [INFO]: Using AVX and FMA optimized routines
Ardour: [INFO]: Loading plugin meta data file /usr/share/ardour6/plugin_metadata/plugin_tags
Ardour: [INFO]: Loading default ui configuration file /etc/ardour6/default_ui_config
Ardour: [INFO]: Loading 452 MIDI patches from /usr/share/ardour6/patchfiles
Ardour: [INFO]: Loading color file /usr/share/ardour6/themes/dark-ardour.colors

Although opening with sudo allows it to work nromally
$ sudo ardour6

Ardour6.9.0 (built using 6.9 and GCC version 11.2.0)
Ardour: [INFO]: Your system is configured to limit Ardour to 524288 open files
Ardour: [INFO]: Loading system configuration file /etc/ardour6/system_config
Ardour: [INFO]: CPU vendor: GenuineIntel
Ardour: [INFO]: AVX-capable processor
Ardour: [INFO]: AVX with FMA capable processor
Ardour: [INFO]: CPU brand: Intel(R) Core(TM) i3-10100 CPU @ 3.60GHz
Ardour: [INFO]: Using AVX and FMA optimized routines
Ardour: [INFO]: Loading plugin meta data file /usr/share/ardour6/plugin_metadata/plugin_tags
Ardour: [INFO]: Loading default ui configuration file /etc/ardour6/default_ui_config
Ardour: [INFO]: Loading user ui configuration file /root/.config/ardour6/ui_config
Ardour: [INFO]: Loading 452 MIDI patches from /usr/share/ardour6/patchfiles
Ardour: [INFO]: Loading color file /usr/share/ardour6/themes/dark-ardour.colors
Ardour: [INFO]: Loading ui configuration file /etc/ardour6/clearlooks.rc
Ardour: [INFO]: Loading bindings from /etc/ardour6/ardour.keys
Loading ui configuration file /etc/ardour6/clearlooks.rc
set default folder to /root
Found nothing along /root/.config/ardour6/templates:/usr/share/ardour6/templates
Scanning folders for bundled LV2s: /usr/lib64/ardour6/LV2
Set cursor set to default

Try
mv ~/.config/ardour6 ~/.config/ardour6.backup
before starting Ardour, in case you have something weird in your config.

Also make sure you have permission to read /etc/ardour6/clearlooks.rc and /etc/ardour6/ardour.keys

And see 0005605: Hangs while starting at loading UI config files - Ardour Bug Tracker and the suggestion to setting
export GTK2_RC_FILES=/usr/share/themes/Adwaita/gtk-2.0/gtkrc
or maybe
GTK2_RC_FILES=/nonexistent
in case that still an issue

Are you running the official Ardour package or one from your distro?
If it’s the latter you should see if the official package exhibits the same problem. If it doesn’t it’s something weird going on with your distro’s version.

https://tracker.ardour.org/view.php?id=5605#c18109

Likely caused by your system’s GTK color theme. You can try the GTK2_RC_FILES workaround mentioned in the bug report, or get the official binary from Get Ardour | ardour which does not have this issue.

as root (or sudo):

usermod -a -G audio username

Then re-login.