When you create a user, a group will be created with the same name and will be set as newly created user's primary group.
You can find out what your primary group name is using:
id -gn
The file which defines which group is your primary group lives at: /etc/passwd
, run bellow command to get corresponding line to your user:
getent passwd $USER
it should look like:
username:x:1000:1000:Your Name,,,:/home/username:/bin/bash
Pay attention to second (1000), it's your primary user's group id.
or find out what groups your user is a member of using:
id -Gn
The file contains details about groups lives at: /etc/group
, this command should show you the details about your user's primary group:
grep "^$USER" /etc/group
Same as:
getent group $USER
The result looks like:
groupname:x:1000:
Remember the 1000 from before? this is the group id which has been set as your primary group in /etc/passwd
.
Then when you create new files, they would be owned by your user, and your primary group (which is same as your username and only one user is a member of that group, which is your user).