POSIX Access Control Lists
POSIX Access Control Lists (ACLs) allows you to assign different permissions for different users or
groups even though they do not correspond to the original owner or the owning group.
For example: User john creates a file but does not want to allow anyone to do anything with this
file, except another user, antony (even though there are other users that belong to the group john).
This means, in addition to the file owner, the file group, and others, additional users and groups can
be granted or denied access by using POSIX ACLs.
Activating POSIX ACLs Support
To use POSIX ACLs for a file or directory, the partition of the file or directory must be mounted with
POSIX ACLs support.
Activating POSIX ACLs Support on Sever
To mount the backend export directories for POSIX ACLs support, use the following command:
# mount -o acl device-namepartition
For example:
# mount -o acl /dev/sda1 /export1
Alternatively, if the partition is listed in the /etc/fstab file, add the following entry for the partition
to include the POSIX ACLs option:
LABEL=/work /export1 ext3 rw, acl 14
Activating POSIX ACLs Support on Client
To mount the glusterfs volumes for POSIX ACLs support, use the following command:
# mount –t glusterfs -o acl severname:volume-idmount point
For example:
# mount -t glusterfs -o acl 198.192.198.234:glustervolume /mnt/gluster
Setting POSIX ACLs
You can set two types of POSIX ACLs, that is, access ACLs and default ACLs. You can use
access ACLs to grant permission for a specific file or directory. You can use default ACLs only
on a directory but if a file inside that directory does not have an ACLs, it inherits the permissions of
the default ACLs of the directory.
You can set ACLs for per user, per group, for users not in the user group for the file, and via the
effective right mask.
Setting Access ACLs
You can apply access ACLs to grant permission for both files and directories.
To set or modify Access ACLs
You can set or modify access ACLs use the following command:
# setfacl –m entry type file
The ACL entry types are the POSIX ACLs representations of owner, group, and other.
Permissions must be a combination of the characters r (read), w (write), and x (execute). You must
specify the ACL entry in the following format and can specify multiple entry types separated by
commas.
ACL Entry
Description
u:uid:<permission>
Sets the access ACLs for a user. You can specify user name or UID
g:gid:<permission>
Sets the access ACLs for a group. You can specify group name or GID.
m:<permission>
Sets the effective rights mask. The mask is the combination of all access permissions of the owning group and all of the user and group entries.
o:<permission>
Sets the access ACLs for users other than the ones in the group for the file.
If a file or directory already has an POSIX ACLs, and the setfacl command is used, the additional
permissions are added to the existing POSIX ACLs or the existing rule is modified.
For example, to give read and write permissions to user antony:
# setfacl -m u:antony:rw /mnt/gluster/data/testfile
Setting Default ACLs
You can apply default ACLs only to directories. They determine the permissions of a file system
objects that inherits from its parent directory when it is created.
To set default ACLs
You can set default ACLs for files and directories using the following command:
# setfacl –m –-set entry type directory
For example, to set the default ACLs for the /data directory to read for users not in the user group:
# setfacl –m --set o::r /mnt/gluster/data
An access ACLs set for an individual file can override the default ACLs permissions.
Effects of a Default ACLs
The following are the ways in which the permissions of a directory's default ACLs are passed to the
files and subdirectories in it:
A subdirectory inherits the default ACLs of the parent directory both as its default ACLs and as an
access ACLs.
A file inherits the default ACLs as its access ACLs.
Retrieving POSIX ACLs
You can view the existing POSIX ACLs for a file or directory.
To view existing POSIX ACLs
View the existing access ACLs of a file using the following command:
# getfacl path/filename
For example, to view the existing POSIX ACLs for sample.jpg
# getfacl /mnt/gluster/data/test/sample.jpg
# owner: antony
# group: antony
user::rw-
group::rw-
other::r--
View the default ACLs of a directory using the following command:
# getfacl directory name
For example, to view the existing ACLs for /data/doc
# getfacl /mnt/gluster/data/doc
# owner: antony
# group: antony
user::rw-
user:john:r--
group::r--
mask::r--
other::r--
default:user::rwx
default:user:antony:rwx
default:group::r-x
default:mask::rwx
default:other::r-x
Removing POSIX ACLs
To remove all the permissions for a user, groups, or others, use the following command:
# setfacl -x ACL entry type file
For example, to remove all permissions from the user antony:
# setfacl -x u:antony /mnt/gluster/data/test-file
Samba and ACLs
If you are using Samba to access GlusterFS FUSE mount, then POSIX ACLs are enabled by default.
Samba has been compiled with the --with-acl-support option, so no special flags are required
when accessing or mounting a Samba share.
NFS and ACLs
Currently we do not support ACLs configuration through NFS, i.e. setfacl and getfacl commands do
not work. However, ACLs permissions set using Gluster Native Client applies on NFS mounts.