Acl (Access Control List)

Acl (Access Control List)

Files and directories have permission sets for the owner of the file, the group associated with the file, and all other users for the system. However, these permission sets have limitations. For example, different permissions cannot be configured for different users. Thus, Access Control Lists (ACLs) were implemented.

The Red Hat Enterprise Linux kernel provides ACL support for the ext3 file system and NFS-exported file systems. ACLs are also recognized on ext3 file systems accessed via Samba.

Along with support in the kernel, the acl package is required to implement ACLs. It contains the utilities used to add, modify, remove, and retrieve ACL information.

The cp and mv commands copy or move any ACLs associated with files and directories.

 Mounting File Systems

Before using ACLs for a file or directory, the partition for the file or directory must be mounted with ACL support. If it is a local ext3 file system, it can mounted with the following command:

mount -t ext3 -o acl device-name partition

For example:

mount -t ext3 -o acl /dev/VolGroup00/LogVol02 /work

Alternatively, if the partition is listed in the /etc/fstab file, the entry for the partition can include the acl option:

# vi /etc/fstab

LABEL=/        /     ext3      defaults,acl     1  1

:wq (save and exit)

# mount -o remount,rw /

# mkdir work

# cd work

# cat >aclwork.txt

Ctrl + D

Login with other user and open the file.

# getfacl /root/work/aclwork.txt  (Command will show the permission on the file.)

# setfacl -m u:user1:r-x /root/work/aclwork.txt (Will set the permission on the file.)

# getfacl /root/work/aclwork.txt

Login with user1 and try to open the file.

# setfacl -x u:user1 /root/work/aclwork.txt  (command will remove the acl permission from the file).