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Linux ACL Permissions

Overview

“Access Control List (ACL) provides an additional, more flexible permission mechanism for file systems.
It is designed to assist with UNIX file permissions.
ACL allows you to give permissions for any user or group to any disc resource.” (Wikipedia)

Enable ACL on file system

Most likely is that the ACL option is already enabled on your file system but to be sure you can verify using the next command:

#make sure to replace sda2 with the name of your device
tune2fs -l /dev/sda2 | grep options

The output should be:

Default mount options:    user_xattr acl

In order to enable ACL on a file system use tune2fs command:

#make sure to replace sda2 with the name of your device
tune2fs -o acl /dev/sda2

View Linux ACL Permissions

ls command

With ls command you can see if there are any ACL permissions on a file, you will see a ‘+’ sign:

ls -l /folder-file

#Output:
-rw-rwxr--+ 1 root root 0 Mar 15 05:27 folder-file

Now we use getfacl command to see the ACL permissions.

getfacl command

You can use getfacl to view the current ACL permissions of a file or folder.

getfacl /folder-file

#Output
# file: folder-file
# owner: root
# group: root
user::rw-
user:nfsnobody:rwx
group::r--
mask::rwx
other::r--

setfacl command

#setfacl -m u:username:permissions /folder-file
setfacl -m u:bob:rwx /folder-file

#setfacl -m u:uid:permissions /folder-file
setfacl -m u:12345:rwx /folder-file

#setfacl -m g:groupname:permissions /folder-file
setfacl -m g:company:rx /folder-file

#setfacl -m g:gid:permissions /folder-file
setfacl -m g:12345:rx /folder-file

Remove all ACL permissions:

setfacl -b

Remove a specific ACL entry by username, uid, group or gid:

setfacl -x "bob"

Enjoy!

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