There is something not clear on relationship between file properties and user and group.
root@debian:/home/debian# ls -l /home/linuxsir total 4 -rw-r--r-- 1 linuxsir root 1549 Feb 23 19:16 test.txt
I draw a conclusion that the directory /home/linuxisir contain one file named test.txt, linuxsir is its owner ,and linuxsir belong to the root group.
root@debian:/home/debian# cat /etc/group root:x:0: linuxsir:x:1004: postgres:x:120: my_test_group1:x:1005:linuxsir,linuxsir2
From cat /etc/group , linuxsir do not belong to group root?
How to think of this matter properly?