Access Control Lists

Most everything here comes directly from the RHEL 5 Deployment Guide. This reference can't be stressed enough for preparation for the RHCE Exam.

There are two types of ACLs. Access and Default.

  • Access ACLs are associated with a file or directory
  • Default ACLs are associated with a directory and are optional. They take precedence when a file in the directory does not have an access ACL. Default ACLs cannot be associated with a file.

Access ACLs

They can be configured:

  • Per User
  • Per Group
  • Via an effective rights mask
  • For users not in the user group for the file

To set ACLs, use the setfacl command 

setfacl -m <rules> <files>

<rules> can be:

  • u:<uid>:<perms> - UID can be user name or user id
  • g:<gid>:<perms> - GID can be group name or group id
  • m:<perms> - Effective Rights Mask
  • o:<perms> - ACLs for users other than those in the group for the file

To Remove an ACL 

setfacl -x <rules> <files>

Default ACLs

To Set 

setfacl -m d:<rules> <directory>

Viewing ACLs

To View ACLs 

getfacl <file>

Note: tar and dump do not back up ACLs. Use star to achieve this.

Also: If the filesystem is not mounted with the -o acl option, ACLs will be unavailable.

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