Friday, April 25, 2014

Linux Acl in detail

Let's assume we have /dev/sda1 mounted on /data1 and we want to enable the acl option.

[root@server ~]# tune2fs -l /dev/sda1
To enable ACLs on a filesystem, we must set the fs default and remount:
[root@server ~]# tune2fs -o acl /dev/sda1
[root@server ~]# mount -o remount,acl /data1
Use getfacl to view ACLs:

[root@server ~]# touch /data1/foo.txt
[root@server ~]# getfacl /data1/foo.txt
getfacl: Removing leading '/' from absolute path names
# file: data1/foo.txt
# owner: root
# group: root
user::rw-
group::r--
other::r--
Use setfacl to set ACLs, with -m to modify and -x to remove a given ACL.
give user ram read+write+execute on a file:

[root@server ~]# setfacl -m u:ram:rwx /data1/foo.txt
give group peeps read+write on a file:
[root@server ~]# setfacl -m g:peeps:rw /data1/foo.txt
remove ram's ACL permissions:
[root@server ~]# setfacl -x u:ram /data1/foo.txt
set the default ACL permissions on a directory:
[root@server ~]# setfacl -m d:g:peeps:rw /data1/stuff/
revoke write permission for everyone:
[root@server ~]# setfacl -m m::rx /data1/foo.txt
When ACLs are present, an ls -l will show a plus sign to notify you:

[root@server ~]# ls -l /data1/foo.txt
-rw-rwxr--+ 1 root root 0 Dec 3 14:54 /data1/foo.txt
Note that the mv and cp -p commands will preserve ACLs. If you have defaults set on a parent directory, new files in that directory will inherit those settings.
If you want to remove all ACLs, reverting back to the base unix permissions of owner, group and other:

[root@server ~]# setfacl --remove-all /data1/foo.txt

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