CENTOS Linux User Group Management

Note: I frequently update this post whenever there are changes in my setup.

Show users
# cat /etc/passwd

Show groups
# cat /etc/group

Add user from group 
# usermod -a -G [groupname] [username]
or
# gpasswd -a [username] [groupname]

Delete user from group
# gpasswd -d [username] [groupname]

Change Directory owner
# chgrp [groupname] [foldername]


How to change Owner/Group permissions

# chown [username]:[groupname]

should change the ownership and group to what you want.

# chown -R [username]:[groupname] [directory/file]

should change the ownership of the directory, and the entire subtree under it.


Here is a list of what the shorthand represents:

Identities
u — the user who owns the file (that is, the owner)

g — the group to which the user belongs

o — others (not the owner or the owner's group)

a — everyone or all (u, g, and o)

Permissions
r — read access

w — write access

x — execute access

Actions
+ — adds the permission

- — removes the permission

= — makes it the only permission

Note that to create (or delete) a file in a directory, the user or group must have write permission to the directory. And to list a directory, the user or group must have 'x' permission to the directory.

# chmod ug+rwx [directory/file]

# chmod -R ug+rw [directory/file]

might do what you want.

But read the man pages previously recommended to make sure. And be especially careful with -R. Also, never use a '.*' wildcard for this sort of thing. It will do something very bad that you were not expecting.

References:

https://www.centos.org/docs/4/html/rhel-sbs-en-4/s1-navigating-ownership.html

man chown
man chgrp
man chmod

https://tecadmin.net/tutorial/linux/linux-modify-user/