# Create the groups
sudo groupadd testGroupA
sudo groupadd testGroupB
# Create the user and add to groupA
sudo useradd -m -g testGroupA testUserA
sudo usermod -aG  testGroupB testUserA
# Create a file owned by testUserA and testGroupA
sudo touch /lfs/test/file.txt
sudo chown testUserA:testGroupA /lfs/test/file.txt
sudo chmod 444 /lfs/test/file.txt
# Verify the ownership
echo "Initial file ownership:"
ls -l /lfs/test/file.txt
# Change the group ownership to groupB using chgrp
sudo -u testUserA chgrp testGroupB /lfs/test/file.txt
# Verify the new ownership
echo "Updated file ownership:"
ls -l /lfs/test/file.txt 

ubuntu@ip-10-0-159-248:~$ ls -l /lfs/test/file1.txt
-r--r--r-- 1 testUserA testGroupA 0 Dec 24 05:16 /lfs/test/file1.txt
ubuntu@ip-10-0-159-248:~$ 
ubuntu@ip-10-0-159-248:~$ # Change the group ownership to groupB using chgrp
ubuntu@ip-10-0-159-248:~$ sudo -u testUserA chgrp testGroupB /lfs/test/file1.txt
ubuntu@ip-10-0-159-248:~$ 
ubuntu@ip-10-0-159-248:~$ # Verify the new ownership
ubuntu@ip-10-0-159-248:~$ echo "Updated file ownership:"
Updated file ownership:
ubuntu@ip-10-0-159-248:~$ ls -l /lfs/test/file1.txt
-r--r--r-- 1 testUserA testGroupB 0 Dec 24 05:16 /lfs/test/file1.txt

Initial file ownership:
-r--r--r-- 1 testUserA testGroupA 0 Dec 24 05:22 /lfs/test/file.txt
chgrp: changing group of '/lfs/test/file.txt': Permission denied
Updated file ownership:
-r--r--r-- 1 testUserA testGroupA 0 Dec 24 05:22 /lfs/test/file.txt
Script complete.