该如何用语句完成以下问题

该如何用语句完成以下问题，第一问我知道该如何创建，第二问该怎么属于呢

还是好好复习基础 和 努力学习。
这几题操作如下：

[root@servera ~]# groupadd group1
[root@servera ~]# groupadd group2
[root@servera ~]# 
[root@servera ~]# useradd user1 -G group1
[root@servera ~]# useradd user2 -G group2
[root@servera ~]# 
[root@servera ~]# 
[root@servera ~]# mkdir /home/dir1
[root@servera ~]# touch /home/dir1/group1_file.txt
[root@servera ~]# chgrp group1 /home/dir1/group1_file.txt 
[root@servera ~]# 
[root@servera ~]# su - user1
[user1@servera ~]$ echo "user1'file" > u1_file.txt
[user1@servera ~]$ cat !$
cat u1_file.txt
user1'file
[user1@servera ~]$ exit
logout
[root@servera ~]# su - user2
[user2@servera ~]$ echo "user2'file" > u2_file.txt
[user2@servera ~]$ exit
logout
[root@servera ~]# 
[root@servera ~]# su - user1 
Last login: Tue Mar 15 21:32:44 CST 2022 on pts/0
[user1@servera ~]$ echo "userl edited" >> u1_file.txt 
[user1@servera ~]$ cat u1_file.txt 
user1'file
userl edited
[user1@servera ~]$ exit
logout
[root@servera ~]# su - user2
Last login: Tue Mar 15 21:33:27 CST 2022 on pts/0
[user2@servera ~]$ echo "user2 edited user1' file" >> u2_file.txt 
[user2@servera ~]$ cat u2_file.txt 
user2'file
user2 edited user1' file