ACLs

Question 1

What are ACLs used for?

Answer 1

Create granular permissions on a file/directory

Question 2

How can you tell if a file/directory has an extended ACL set on it?

Answer 2

Denoted by a + at the end of the permissions

Question 3

How do you set an ACL for a user/group on a file/directory?

Answer 3

setfacl -m u:{uid/username}:{r/w/x} file/directory

setfacl -m g:{gid/group}:{r/w/x} file/directory

Question 4

How do you view the ACL on a file/directory?

Answer 4

getfacl file/directory

Question 5

What is important to note when creating ACLs?

Answer 5

It uses the uid/gid, even if username/group is specified.

If the uid/gid of a username/group changes it will still apply to the id

Question 6

What is the mask in an ACL?

Answer 6

Maximum permissions for the file/directory

Even if user/group has higher permissions they are limited by the mask.

Question 7

How do you modify the mask on an ACL?

Answer 7

setfacl -m m::{r/w/x} file/directory

Question 8

How do you set default ACL permissions for child items within a directory?

Answer 8

setfacl -d -m u:{uid/user}:{r/w/x} directory
setfacl -m d:u:{uid/user}:{r/w/x} directory
setfacl -d -m g:{gid/group}:{r/w/x} directory
setfacl -m d:g:{gid/group}:{r/w/x} directory

Question 9

How do you remove default ACL permissions?

Answer 9

setfacl –remove-default file/directory

Question 10

How do you remove an ACL for a user/group?

Answer 10

setfacl -x u:{uid/user} file/directory

setfacl -x g:{gid/group} file/directory

Question 11

How do you remove a default ACL for a user/group?

Answer 11

setfacl -x d:u:{uid/user} file/directory

setfacl -x d:g:{gid/user} file/directory

Question 12

How would you copy the ACL of a file/directory and apply it to another?

Answer 12

getfacl file/folder | setfacl –set-file=- file/folder

*–set-file= sets the file to take ACL from, the - means to take standard input that is piped to the setfacl command

Question 13

What filesystems support ACLs?

Answer 13

ext4

xfs

Question 14

What are base permissions on an ACL?

Answer 14

Standard user|group|other permissions

No + at end of the permissions

Question 15

What is the equivalent of chmod 777 using ACL permissions?

Answer 15

setfacl -m u::rwx,g::rwx,o::rwx

Question 16

What is the equivalent of chmod 000 using ACL permissions?

Answer 16

setfacl -m u::—,g::—,o::—

Question 17

When performing a chmod on an ACL file/directory, what affects the mask?

Answer 17

A caveat of chmod g= is it affects the mask permissions.

Only the group permission does this

Question 18

What does a default ACL permission do?

Answer 18

Applied the permission to file/directories created within the folder. Not the folder itself.

Question 19

How do you create an ACL for the execute bit to only apply to directories?

Answer 19

i. e setfacl -m u:{uid/username}:X directory

* uppercase X

Question 20

How do you create an ACL to apply recursively?

Answer 20

i.e setfacl -R -m u:{uid/username}:{r/w/x} directory

Question 21

Does the cp command preserve ACL rules?

Answer 21

No

They will have to be reapplied with: getfacl file/directory | setfacl –set-file=- file/directory

Question 22

Does the mv command preserve ACL rules?

Answer 22

Yes