Allowing a group Read-Write Access to a directory

FolderA will first need to be part of groupA - the folder's owner or root can perform this operation

chgrp groupA ./folderA

Then groupA will need rwx permissions of the folder

chmod g+rwx  ./folderA

There are options in the chgrp and chmod commands to recurse into the directory if required.

My own experience in this area here. Tested on Ubuntu 18.04.

Allow to write in the system folder

Give write permission to /etc/nginx/ folder.

# Check 'webmasters' group doen't exist
cat /etc/group | grep webmasters
# Create 'webmasters' group
sudo addgroup webmasters
# Add users to 'webmasters' group
sudo usermod -a -G webmasters username
sudo usermod -a -G webmasters vozman
sudo usermod -a -G webmasters romanroskach

# Group assignment changes won't take effect
# until the users log out and back in.

# Create directory
sudo mkdir /etc/nginx/
# Check directory permissions
ls -al /etc | grep nginx
drwxr-xr-x   2 root root     4096 Dec  5 18:30 nginx

# Change group owner of the directory
sudo chgrp -R webmasters /etc/nginx/
# Check that the group owner is changed
ls -al /etc | grep nginx
drwxr-xr-x   2 root webmasters   4096 Dec  5 18:30 nginx

# Give write permission to the group
sudo chmod -R g+w /etc/nginx/
# Check
ls -al /etc | grep nginx
drwxrwxr-x   2 root webmasters   4096 Dec  5 18:30 nginx

# Try to create file
sudo -u username touch /etc/nginx/test.txt  # should work
sudo -u username touch /etc/test.txt  # Permission denied

Give write permission to /etc/systemd/system/ folder.

# List ACLs
getfacl /etc/systemd/system

getfacl: Removing leading '/' from absolute path names
# file: etc/systemd/system
# owner: root
# group: root
user::rwx
group::r-x
other::r-x

# Add 'webmasters' group to an ACL
sudo setfacl -m g:webmasters:rwx /etc/systemd/system

# Check
getfacl /etc/systemd/system

getfacl: Removing leading '/' from absolute path names
# file: etc/systemd/system
# owner: root
# group: root
user::rwx
group::r-x
group:webmasters:rwx
mask::rwx
other::r-x

sudo -u username touch /etc/systemd/system/test.txt  # should work
sudo -u username touch /etc/systemd/test.txt  # Permission denied

Original how-to.