Manage the sound in Slint.

--- Sound on the command line ---

To adjust the volume not using a graphical tool there are several ways.
1. Type: alsamixer then:
use the page up key to increase the volume by 5%
use the page down key to decrease the volume by 5%
press Esc to leave the application.
alsmixer is a ncurses app, but you don't need all the features.
You can make the setting permanent typing as root:
alsactl store

2. Type: amixer <arguments>
For instance to set the main volume to 70% type: amixer sset Master 70%
To know more, type: 'man amixer' or 'amixer -h'

3. Type: pamixer <arguments>
For instance to set the volume to 70% for the default sink:
pamixer --set-volume 7O
To know more, type: pamixer -h

4. Type: ponymix <arguments>
For instance, to set the volume to 80% for the default sink:
ponymix set-volume 8O
To know more, type: ponymix --help

--- Control a running PulseAudio sound server ---

In a graphical environment use the application pavucontrol.
On the command line use one of the commands pactl or pacmd.
To know more:
man pactl
pactl --help
man pacmd
Warning: pacmd typed alone brings up an interective dialog. Press Ctrl+d
to exit from it but do not type exit, as that would kill PulseAudio!

--- Keep the same sound level after rebooting. ---

Just make the file /etc/rc.d/rc.alsa executable. As root:
chmod /etc/rc.d/rc.alsa

At startup, this script will restore the previous sound settings if
they were previously stored, else will set default volumes and store
them, so that they will be restored at next reboot.

If you don't want that this script to set the default volume type as root:
touch /var/lib/alsa/no.asound.state

You can change these default sound levels with alsamixer or amixer
then typing as root:
alsactl store
Then at next startup the script will restore them.

To know more:
man alsactl