Using ACLs to Protect ZFS Files

This chapter provides information about using access control lists (ACLs) to protect your ZFS files by providing more granular permissions than the standard UNIX permissions.

The following sections are provided in this chapter:

7.1. The NFSv4 ACL Model

Older versions of Solaris supported an ACL implementation that was primarily based on the POSIX-draft ACL specification. The POSIX-draft based ACLs are used to protect UFS files and are translated by versions of NFS prior to NFSv4.

With the introduction of NFSv4, a new ACL model fully supports the interoperability that NFSv4 offers between UNIX and non-UNIX clients. The new ACL implementation, as defined in the NFSv4 specification, provides much richer semantics that are based on NT-style ACLs.

The main differences of the new ACL model are as follows:

Based on the NFSv4 specification and similar to NT-style ACLs.
Provide much more granular set of access privileges. For more information, see ACL Access Privileges.
Set and displayed with the chmod and ls commands rather than the setfacl and getfacl commands.
Provide richer inheritance semantics for designating how access privileges are applied from directory to subdirectories, and so on. For more information, see ACL Inheritance.

Both ACL models provide more fine-grained access control than is available with the standard file permissions. Much like POSIX-draft ACLs, the new ACLs are composed of multiple Access Control Entries (ACEs).

POSIX-draft style ACLs use a single entry to define what permissions are allowed and what permissions are denied. The new ACL model has two types of ACEs that affect access checking: ALLOW and DENY. As such, you cannot infer from any single ACE that defines a set of permissions whether or not the permissions that weren't defined in that ACE are allowed or denied.

Translation between NFSv4-style ACLs and POSIX-draft ACLs is as follows:

If you use any ACL-aware utility, such as the cp, mv, tar, cpio, or rcp commands, to transfer UFS files with ACLs to a ZFS file system, the POSIX-draft ACLs are translated into the equivalent NFSv4-style ACLs.
Some NFSv4-style ACLs are translated to POSIX-draft ACLs. You see a message similar to the following if an NFSv4–style ACL isn't translated to a POSIX-draft ACL:
```
# cp -p filea /var/tmp
cp: failed to set acl entries on /var/tmp/filea
```
If you create a UFS tar or cpio archive with the preserve ACL option (tar -p or cpio -P) on a system that runs a current Solaris release, you will lose the ACLs when the archive is extracted on a system that runs a previous Solaris release.

All of the files are extracted with the correct file modes, but the ACL entries are ignored.
You can use the ufsrestore command to restore data into a ZFS file system, but the ACLs will be lost.
If you attempt to set an NFSv4-style ACL on a UFS file, you see a message similar to the following:
```
chmod: ERROR: ACL type's are different
```

If you attempt to set a POSIX-style ACL on a ZFS file, you will see messages similar to the following:

# getfacl filea
File system doesn't support aclent_t style ACL's.
See acl(5) for more information on Solaris ACL support.

For information about other limitations with ACLs and backup products, see Saving ZFS Data With Other Backup Products.

7.1.1. Syntax Descriptions for Setting ACLs

Two basic ACL formats are provided as follows:

Syntax for Setting Trivial ACLs

chmod [options] A[index]{+|=}owner@ |group@ |everyone@:access-permissions/...[:inheritance-flags]:deny | allow file

chmod [options] A-owner@, group@, everyone@:access-permissions/...[:inheritance-flags]:deny | allow file ...

chmod [options] A[index]- file

Syntax for Setting Non-Trivial ACLs

chmod [options] A[index]{+|=}user|group:name:access-permissions/...[:inheritance-flags]:deny | allow file

chmod [options] A-user|group:name:access-permissions/...[:inheritance-flags]:deny | allow file ...

chmod [options] A[index]- file

owner@, group@, everyone@: Identifies the ACL-entry-type for trivial ACL syntax. For a description of ACL-entry-types, see ACL Entry Types.
user or group:ACL-entry-ID=username or groupname: Identifies the ACL-entry-type for explicit ACL syntax. The user and group ACL-entry-type must also contain the ACL-entry-ID, username or groupname. For a description of ACL-entry-types, see ACL Entry Types.
access-permissions/.../: Identifies the access permissions that are granted or denied. For a description of ACL access privileges, see ACL Access Privileges.
inheritance-flags: Identifies an optional list of ACL inheritance flags. For a description of the ACL inheritance flags, see ACL Inheritance Flags.
deny | allow: Identifies whether the access permissions are granted or denied.

In the following example, the ACL-entry-ID value is not relevant:

group@:write_data/append_data/execute:deny

The following example includes an ACL-entry-ID because a specific user (ACL-entry-type) is included in the ACL.

0:user:gozer:list_directory/read_data/execute:allow

When an ACL entry is displayed, it looks similar to the following:

2:group@:write_data/append_data/execute:deny

The 2 or the index-ID designation in this example identifies the ACL entry in the larger ACL, which might have multiple entries for owner, specific UIDs, group, and everyone. You can specify the index-ID with the chmod command to identify which part of the ACL you want to modify. For example, you can identify index ID 3 as A3 to the chmod command, similar to the following:

chmod A3=user:venkman:read_acl:allow filename

ACL entry types, which are the ACL representations of owner, group, and other, are described in the following table.

ACL Entry Types
ACL Entry Type	Description
`owner@`	Specifies the access granted to the owner of the object.
`group@`	Specifies the access granted to the owning group of the object.
`everyone@`	Specifies the access granted to any user or group that does not match any other ACL entry.
`user`	With a user name, specifies the access granted to an additional user of the object. Must include the ACL-entry-ID, which contains a `username` or `userID`. If the value is not a valid numeric UID or `username`, the ACL entry type is invalid.
`group`	With a group name, specifies the access granted to an additional group of the object. Must include the ACL-entry-ID, which contains a `groupname` or `groupID`. If the value is not a valid numeric GID or `groupname`, the ACL entry type is invalid.

ACL access privileges are described in the following table.

ACL Access Privileges
Access Privilege	Compact Access Privilege	Description
add_file	w	Permission to add a new file to a directory.
add_subdirectory	p	On a directory, permission to create a subdirectory.
append_data	p	Placeholder. Not currently implemented.
delete	d	Permission to delete a file.
delete_child	D	Permission to delete a file or directory within a directory.
execute	x	Permission to execute a file or search the contents of a directory.
list_directory	r	Permission to list the contents of a directory.
read_acl	c	Permission to read the ACL (`ls`).
read_attributes	a	Permission to read basic attributes (non-ACLs) of a file. Think of basic attributes as the stat level attributes. Allowing this access mask bit means the entity can execute ls(1) and stat(2).
read_data	r	Permission to read the contents of the file.
read_xattr	R	Permission to read the extended attributes of a file or perform a lookup in the file's extended attributes directory.
synchronize	s	Placeholder. Not currently implemented.
write_xattr	W	Permission to create extended attributes or write to the extended attributes directory. Granting this permission to a user means that the user can create an extended attribute directory for a file. The attribute file's permissions control the user's access to the attribute.
write_data	w	Permission to modify or replace the contents of a file.
write_attributes	A	Permission to change the times associated with a file or directory to an arbitrary value.
write_acl	C	Permission to write the ACL or the ability to modify the ACL by using the `chmod` command.
write_owner	o	Permission to change the file's owner or group. Or, the ability to execute the `chown` or `chgrp` commands on the file. Permission to take ownership of a file or permission to change the group ownership of the file to a group of which the user is a member. If you want to change the file or group ownership to an arbitrary user or group, then the `PRIV_FILE_CHOWN` privilege is required.

7.1.2. ACL Inheritance

The purpose of using ACL inheritance is so that a newly created file or directory can inherit the ACLs they are intended to inherit, but without disregarding the existing permission bits on the parent directory.

By default, ACLs are not propagated. If you set an non-trivial ACL on a directory, it is not inherited to any subsequent directory. You must specify the inheritance of an ACL on a file or directory.

The optional inheritance flags are described in the following table.

ACL Inheritance Flags
Inheritance Flag	Compact Inheritance Flag	Description
file_inherit	f	Only inherit the ACL from the parent directory to the directory's files.
dir_inherit	d	Only inherit the ACL from the parent directory to the directory's subdirectories.
inherit_only	i	Inherit the ACL from the parent directory but applies only to newly created files or subdirectories and not the directory itself. This flag requires the `file_inherit` flag, the `dir_inherit` flag, or both, to indicate what to inherit.
no_propagate	n	Only inherit the ACL from the parent directory to the first-level contents of the directory, not the second-level or subsequent contents. This flag requires the `file_inherit` flag, the `dir_inherit` flag, or both, to indicate what to inherit.

In addition, you can set a default ACL inheritance policy on the file system that is more strict or less strict by using the aclinherit file system property. For more information, see the next section.

7.1.3. ACL Property Modes

The ZFS file system includes two property modes related to ACLs:

aclinherit – This property determines the behavior of ACL inheritance. Values include the following:
- discard – For new objects, no ACL entries are inherited when a file or directory is created. The ACL on the file or directory is equal to the permission mode of the file or directory.
- noallow – For new objects, only inheritable ACL entries that have an access type of deny are inherited.
- secure – For new objects, the write_owner and write_acl permissions are removed when an ACL entry is inherited.
- passthrough – For new objects, the inheritable ACL entries are inherited with no changes made to them. This mode, in effect, disables secure mode.
The default mode for the aclinherit is secure.
aclmode – This property modifies ACL behavior whenever a file or directory's mode is modified by the chmod command or when a file is initially created. Values include the following:
- discard – All ACL entries are removed except for the entries needed to define the mode of the file or directory.
- groupmask – User or group ACL permissions are reduced so that they are no greater than the group permission bits, unless it is a user entry that has the same UID as the owner of the file or directory. Then, the ACL permissions are reduced so that they are no greater than owner permission bits.
- passthrough – For new objects, the inheritable ACL entries are inherited with no changes made to the them.
The default mode for the aclmode property is groupmask.

7.2. Setting ACLs on ZFS Files

As implemented with ZFS, ACLs are composed of an array of ACL entries. ZFS provides a pure ACL model, where all files have an ACL. Typically, the ACL is trivial in that it only represents the traditional UNIX owner/group/other entries.

ZFS files still have permission bits and a mode, but these values are more of a cache of what the ACL represents. As such, if you change the permissions of the file, the file's ACL is updated accordingly. In addition, if you remove an non-trivial ACL that granted a user access to a file or directory, that user could still have access to the file or directory because of the file or directory's permission bits that grant access to group or everyone. All access control decisions are governed by the permissions represented in a file or directory's ACL.

The primary rules of ACL access on a ZFS file are as follows:

ZFS processes ACL entries in the order they are listed in the ACL, from the top down.
Only ACL entries that have a “who” that matches the requester of the access are processed.
Once an allow permission has been granted, it cannot be denied by a subsequent ACL deny entry in the same ACL permission set.
The owner of the file is granted the write_acl permission unconditionally, even if the permission is explicitly denied. Otherwise, any permission left unspecified is denied.

In the cases of deny permissions or when an access permission is missing, the privilege subsystem determines what access request is granted for the owner of the file or for superuser. This mechanism prevents owners of files from getting locked out of their files and enables superuser to modify files for recovery purposes.

If you set an non-trivial ACL on a directory, the ACL is not automatically inherited by the directory's children. If you set an non-trivial ACL and you want it inherited to the directory's children, you have to use the ACL inheritance flags. For more information, see ACL Inheritance Flags and Setting ACL Inheritance on ZFS Files in Verbose Format.

When you create a new file and depending on the umask value, a default trivial ACL, similar to the following, is applied:

$ ls -v file.1
-r--r--r--   1 root     root      206663 May  4 11:52 file.1
     0:owner@:write_data/append_data/execute:deny
     1:owner@:read_data/write_xattr/write_attributes/write_acl/write_owner
         :allow
     2:group@:write_data/append_data/execute:deny
     3:group@:read_data:allow
     4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

Note that each user category (owner@, group@, everyone@) in this example has two ACL entries. One entry for deny permissions, and one entry is for allow permissions.

A description of this file ACL is as follows:

0:owner@: The owner is denied execute permissions to the file (execute:deny).
1:owner@: The owner can read and modify the contents of the file (read_data/write_data/append_data). The owner can also modify the file's attributes such as timestamps, extended attributes, and ACLs (write_xattr/write_attributes /write_acl). In addition, the owner can modify the ownership of the file (write_owner:allow)
2:group@: The group is denied modify and execute permissions to the file (write_data/append_data/execute:deny).
3:group@: The group is granted read permissions to the file (read_data:allow).
4:everyone@: Everyone who is not user or group is denied permission to execute or modify the contents of the file and to modify any attributes of the file (write_data/append_data/write_xattr/execute/write_attributes/write_acl/write_owner:deny).
5:everyone@: Everyone who is not user or group is granted read permissions to the file, and the file's attributes (read_data/read_xattr/read_attributes/read_acl/synchronize:allow). The synchronize access permission is not currently implemented.

When a new directory is created and depending on the umask value, a default directory ACL is similar to the following:

$ ls -dv dir.1
drwxr-xr-x   2 root     root           2 Feb 23 10:37 dir.1
     0:owner@::deny
     1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     2:group@:add_file/write_data/add_subdirectory/append_data:deny
     3:group@:list_directory/read_data/execute:allow
     4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

A description of this directory ACL is as follows:

0:owner@: The owner deny list is empty for the directory (::deny).
1:owner@: The owner can read and modify the directory contents (list_directory/read_data/add_file/write_data/add_subdirectory/append_data), search the contents (execute), and modify the file's attributes such as timestamps, extended attributes, and ACLs (write_xattr/write_attributes/write_acl). In addition, the owner can modify the ownership of the directory (write_owner:allow).
2:group@: The group cannot add to or modify the directory contents (add_file/write_data/add_subdirectory/append_data:deny).
3:group@: The group can list and read the directory contents. In addition, the group has execute permission to search the directory contents (list_directory/read_data/execute:allow).
4:everyone@: Everyone who is not user or group is denied permission to add to or modify the contents of the directory (add_file/write_data/add_subdirectory/append_data). In addition, the permission to modify any attributes of the directory is denied. (write_xattr /write_attributes/write_acl/write_owner:deny).
5:everyone@: Everyone who is not user or group is granted read and execute permissions to the directory contents and the directory's attributes (list_directory/read_data/read_xattr/execute/read_attributes/read_acl/synchronize:allow). The synchronize access permission is not currently implemented.

7.3. Setting and Displaying ACLs on ZFS Files in Verbose Format

You can use the chmod command to modify ACLs on ZFS files. The following chmod syntax for modifying ACLs uses acl-specification to identify the format of the ACL. For a description of acl-specification, see Syntax Descriptions for Setting ACLs.

Adding ACL entries
- Adding an ACL entry for a user
```
% chmod A+acl-specification filename
```
- Adding an ACL entry by index-ID
```
% chmod Aindex-ID+acl-specification filename
```
  This syntax inserts the new ACL entry at the specified index-ID location.

Replacing an ACL entry

% chmod Aindex-ID=acl-specification filename

% chmod A=acl-specification filename

Removing ACL entries
- Removing an ACL entry by index-ID
```
% chmod Aindex-ID- filename
```
- Removing an ACL entry by user
```
% chmod A-acl-specification filename
```
- Removing all non-trivial ACEs from a file
```
% chmod A- filename
```

Verbose ACL information is displayed by using the ls -v command. For example:

# ls -v file.1
-rw-r--r--   1 root     root      206663 Feb 16 11:00 file.1
     0:owner@:execute:deny
     1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     2:group@:write_data/append_data/execute:deny
     3:group@:read_data:allow
     4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

For information about using the compact ACL format, see Setting and Displaying ACLs on ZFS Files in Compact Format.

This section provides examples of setting and displaying trivial ACLs.

In the following example, a trivial ACL exists on file.1:

# ls -v file.1
-rw-r--r--   1 root     root      206663 Feb 16 11:00 file.1
     0:owner@:execute:deny
     1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     2:group@:write_data/append_data/execute:deny
     3:group@:read_data:allow
     4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

In the following example, write_data permissions are granted for group@.

# chmod A2=group@:append_data/execute:deny file.1
# chmod A3=group@:read_data/write_data:allow file.1
# ls -v file.1
-rw-rw-r--   1 root     root           206663 May  3 16:36 file.1
     0:owner@:execute:deny
     1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     2:group@:append_data/execute:deny
     3:group@:read_data/write_data:allow
     4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

In the following example, permissions on file.1 are set back to 644.

# chmod 644 file.1
# ls -v file.1
-rw-r--r--   1 root     root           206663 May  3 16:36 file.1
     0:owner@:execute:deny
     1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     2:group@:write_data/append_data/execute:deny
     3:group@:read_data:allow
     4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

Modifying Trivial ACLs on ZFS Files

This section provides examples of setting and displaying non-trivial ACLs.

In the following example, read_data/execute permissions are added for the user gozer on the test.dir directory.

# chmod A+user:gozer:read_data/execute:allow test.dir
# ls -dv test.dir
drwxr-xr-x+  2 root     root           2 Feb 16 11:12 test.dir
     0:user:gozer:list_directory/read_data/execute:allow
     1:owner@::deny
     2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     3:group@:add_file/write_data/add_subdirectory/append_data:deny
     4:group@:list_directory/read_data/execute:allow
     5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

In the following example, read_data/execute permissions are removed for user gozer.

# chmod A0- test.dir
# ls -dv test.dir
drwxr-xr-x   2 root     root           2 Feb 16 11:12 test.dir
     0:owner@::deny
     1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     2:group@:add_file/write_data/add_subdirectory/append_data:deny
     3:group@:list_directory/read_data/execute:allow
     4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

Setting Non-Trivial ACLs on ZFS Files

These ACL examples illustrate the interaction between setting ACLs and then changing the file or directory's permission bits.

In the following example, a trivial ACL exists on file.2:

# ls -v file.2
-rw-r--r--   1 root     root        2703 Feb 16 11:16 file.2
     0:owner@:execute:deny
     1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     2:group@:write_data/append_data/execute:deny
     3:group@:read_data:allow
     4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     5:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

In the following example, ACL allow permissions are removed from everyone@.

# chmod A5- file.2
# ls -v file.2
-rw-r-----   1 root     root        2703 Feb 16 11:16 file.2
     0:owner@:execute:deny
     1:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     2:group@:write_data/append_data/execute:deny
     3:group@:read_data:allow
     4:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny

In this output, the file's permission bits are reset from 655 to 650. Read permissions for everyone@ have been effectively removed from the file's permissions bits when the ACL allow permissions are removed for everyone@.

In the following example, the existing ACL is replaced with read_data/write_data permissions for everyone@.

# chmod A=everyone@:read_data/write_data:allow file.3
# ls -v file.3
-rw-rw-rw-+  1 root     root        1532 Feb 16 11:18 file.3
     0:everyone@:read_data/write_data:allow

In this output, the chmod syntax effectively replaces the existing ACL with read_data/write_data:allow permissions to read/write permissions for owner, group, and everyone@. In this model, everyone@ specifies access to any user or group. Since no owner@ or group@ ACL entry exists to override the permissions for owner and group, the permission bits are set to 666.

In the following example, the existing ACL is replaced with read permissions for user gozer.

# chmod A=user:gozer:read_data:allow file.3
# ls -v file.3
----------+  1 root     root        1532 Feb 16 11:18 file.3
     0:user:gozer:read_data:allow

In this output, the file permissions are computed to be 000 because no ACL entries exist for owner@, group@, or everyone@, which represent the traditional permission components of a file. The owner of the file can resolve this problem by resetting the permissions (and the ACL) as follows:

# chmod 655 file.3
# ls -v file.3
-rw-r-xr-x+  1 root     root           0 Mar  8 13:24 file.3
     0:user:gozer::deny
     1:user:gozer:read_data:allow
     2:owner@:execute:deny
     3:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     4:group@:write_data/append_data:deny
     5:group@:read_data/execute:allow
     6:everyone@:write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:deny
     7:everyone@:read_data/read_xattr/execute/read_attributes/read_acl
         /synchronize:allow

ACL Interaction With Permissions on ZFS Files

You can use the chmod command to remove all non-trivial ACLs on a file or directory.

In the following example, 2 non-trivial ACEs exist on test5.dir.

# ls -dv test5.dir
drwxr-xr-x+  2 root     root           2 Feb 16 11:23 test5.dir
     0:user:gozer:read_data:file_inherit:deny
     1:user:lp:read_data:file_inherit:deny
     2:owner@::deny
     3:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     4:group@:add_file/write_data/add_subdirectory/append_data:deny
     5:group@:list_directory/read_data/execute:allow
     6:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     7:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

In the following example, the non-trivial ACLs for users gozer and lp are removed. The remaining ACL contains the six default values for owner@, group@, and everyone@.

# chmod A- test5.dir
# ls -dv test5.dir
drwxr-xr-x   2 root     root           2 Feb 16 11:23 test5.dir
     0:owner@::deny
     1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     2:group@:add_file/write_data/add_subdirectory/append_data:deny
     3:group@:list_directory/read_data/execute:allow
     4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

Restoring Trivial ACLs on ZFS Files

7.3.1. Setting ACL Inheritance on ZFS Files in Verbose Format

You can determine how ACLs are inherited or not inherited on files and directories. By default, ACLs are not propagated. If you set an non-trivial ACL on a directory, the ACL is not inherited by any subsequent directory. You must specify the inheritance of an ACL on a file or directory.

In addition, two ACL properties are provided that can be set globally on file systems: aclinherit and aclmode. By default, aclinherit is set to secure and aclmode is set to groupmask.

For more information, see ACL Inheritance.

By default, ACLs are not propagated through a directory structure.

In the following example, an non-trivial ACE of read_data/write_data/execute is applied for user gozer on test.dir.

# chmod A+user:gozer:read_data/write_data/execute:allow test.dir
# ls -dv test.dir
drwxr-xr-x+  2 root     root           2 Feb 17 14:45 test.dir
     0:user:gozer:list_directory/read_data/add_file/write_data/execute:allow
     1:owner@::deny
     2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     3:group@:add_file/write_data/add_subdirectory/append_data:deny
     4:group@:list_directory/read_data/execute:allow
     5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

If a test.dir subdirectory is created, the ACE for user gozer is not propagated. User gozer would only have access to sub.dir if the permissions on sub.dir granted him access as the file owner, group member, or everyone@.

# mkdir test.dir/sub.dir
# ls -dv test.dir/sub.dir
drwxr-xr-x   2 root     root           2 Feb 17 14:46 test.dir/sub.dir
     0:owner@::deny
     1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     2:group@:add_file/write_data/add_subdirectory/append_data:deny
     3:group@:list_directory/read_data/execute:allow
     4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

Default ACL Inheritance

This series of examples identify the file and directory ACEs that are applied when the file_inherit flag is set.

In the following example, read_data/write_data permissions are added for files in the test.dir directory for user gozer so that he has read access on any newly created files.

# chmod A+user:gozer:read_data/write_data:file_inherit:allow test2.dir
# ls -dv test2.dir
drwxr-xr-x+  2 root     root           2 Feb 17 14:47 test2.dir
     0:user:gozer:read_data/write_data:file_inherit:allow
     1:owner@::deny
     2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     3:group@:add_file/write_data/add_subdirectory/append_data:deny
     4:group@:list_directory/read_data/execute:allow
     5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

In the following example, user gozer's permissions are applied on the newly created test2.dir/file.2 file. The ACL inheritance granted, read_data:file_inherit:allow, means user gozer can read the contents of any newly created file.

# touch test2.dir/file.2
# ls -v test2.dir/file.2
-rw-r--r--+  1 root     root           0 Feb 17 14:49 test2.dir/file.2
     0:user:gozer:write_data:deny
     1:user:gozer:read_data/write_data:allow
     2:owner@:execute:deny
     3:owner@:read_data/write_data/append_data/write_xattr/write_attributes+
         /write_acl/write_owner:allow
     4:group@:write_data/append_data/execute:deny
     5:group@:read_data:allow
     6:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     7:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

Because the aclmode for this file is set to the default mode, groupmask, user gozer does not have write_data permission on file.2 because the group permission of the file does not allow it.

Note the inherit_only permission, which is applied when the file_inherit or dir_inherit flags are set, is used to propagate the ACL through the directory structure. As such, user gozer is only granted or denied permission from everyone@ permissions unless he is the owner of the file or a member of the owning group of the file. For example:

# mkdir test2.dir/subdir.2
# ls -dv test2.dir/subdir.2
drwxr-xr-x+  2 root     root           2 Feb 17 14:50 test2.dir/subdir.2
     0:user:gozer:list_directory/read_data/add_file/write_data:file_inherit
         /inherit_only:allow
     1:owner@::deny
     2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     3:group@:add_file/write_data/add_subdirectory/append_data:deny
     4:group@:list_directory/read_data/execute:allow
     5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

The following series of examples identify the file and directory ACLs that are applied when both the file_inherit and dir_inherit flags are set.

In the following example, user gozer is granted read, write, and execute permissions that are inherited for newly created files and directories.

# chmod A+user:gozer:read_data/write_data/execute:file_inherit/dir_inherit:allow test3.dir
# ls -dv test3.dir
drwxr-xr-x+  2 root     root           2 Feb 17 14:51 test3.dir
     0:user:gozer:list_directory/read_data/add_file/write_data/execute
         :file_inherit/dir_inherit:allow
     1:owner@::deny
     2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     3:group@:add_file/write_data/add_subdirectory/append_data:deny
     4:group@:list_directory/read_data/execute:allow
     5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

# touch test3.dir/file.3
# ls -v test3.dir/file.3
-rw-r--r--+  1 root     root           0 Feb 17 14:53 test3.dir/file.3
     0:user:gozer:write_data/execute:deny
     1:user:gozer:read_data/write_data/execute:allow
     2:owner@:execute:deny
     3:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     4:group@:write_data/append_data/execute:deny
     5:group@:read_data:allow
     6:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     7:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

# mkdir test3.dir/subdir.1
# ls -dv test3.dir/subdir.1
drwxr-xr-x+  2 root     root           2 May  4 15:00 test3.dir/subdir.1
     0:user:gozer:list_directory/read_data/add_file/write_data/execute
         :file_inherit/dir_inherit/inherit_only:allow
     1:user:gozer:add_file/write_data:deny
     2:user:gozer:list_directory/read_data/add_file/write_data/execute:allow
     3:owner@::deny
     4:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     5:group@:add_file/write_data/add_subdirectory/append_data:deny
     6:group@:list_directory/read_data/execute:allow
     7:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     8:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

In these examples, because the permission bits of the parent directory for group@ and everyone@ deny write and execute permissions, user gozer is denied write and execute permissions. The default aclmode property is secure, which means that write_data and execute permissions are not inherited.

In the following example, user gozer is granted read, write, and execute permissions that are inherited for newly created files, but are not propagated to subsequent contents of the directory.

# chmod A+user:gozer:read_data/write_data/execute:file_inherit/no_propagate:allow test4.dir
# ls -dv test4.dir
drwxr-xr-x+  2 root     root           2 Feb 17 14:54 test4.dir
     0:user:gozer:list_directory/read_data/add_file/write_data/execute
         :file_inherit/no_propagate:allow
     1:owner@::deny
     2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     3:group@:add_file/write_data/add_subdirectory/append_data:deny
     4:group@:list_directory/read_data/execute:allow
     5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

As the following example illustrates, when a new subdirectory is created, user gozer's read_data/write_data/execute permission for files are not propagated to the new sub4.dir directory.

# mkdir test4.dir/sub4.dir
# ls -dv test4.dir/sub4.dir
drwxr-xr-x   2 root     root           2 Feb 17 14:57 test4.dir/sub4.dir
     0:owner@::deny
     1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     2:group@:add_file/write_data/add_subdirectory/append_data:deny
     3:group@:list_directory/read_data/execute:allow
     4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     5:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

As the following example illustrates, gozer's read_data/write_data/execute permission for files is propagated to the newly created file.

# touch test4.dir/file.4
# ls -v test4.dir/file.4
-rw-r--r--+  1 root     root           0 May  4 15:02 test4.dir/file.4
     0:user:gozer:write_data/execute:deny
     1:user:gozer:read_data/write_data/execute:allow
     2:owner@:execute:deny
     3:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     4:group@:write_data/append_data/execute:deny
     5:group@:read_data:allow
     6:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     7:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

Granting ACL Inheritance on Files and Directories

If the aclmode property on the tank/cindy file system is set to passthrough, then user gozer would inherit the ACL applied on test4.dir for the newly created file.4 as follows:

# zfs set aclmode=passthrough tank/cindy
# touch test4.dir/file.4
# ls -v test4.dir/file.4
-rw-r--r--+  1 root     root           0 Feb 17 15:15 test4.dir/file.4
     0:user:gozer:read_data/write_data/execute:allow
     1:owner@:execute:deny
     2:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     3:group@:write_data/append_data/execute:deny
     4:group@:read_data:allow
     5:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     6:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

This output illustrates that the read_data/write_data/execute:allow:file_inherit/dir_inherit ACL that was set on the parent directory, test4.dir, is passed through to user gozer.

ACL Inheritance With ACL Mode Set to Passthrough

If the aclmode property on a file system is set to discard, then ACLs can potentially be discarded when the permission bits on a directory change. For example:

# zfs set aclmode=discard tank/cindy
# chmod A+user:gozer:read_data/write_data/execute:dir_inherit:allow test5.dir
# ls -dv test5.dir
drwxr-xr-x+  2 root     root           2 Feb 16 11:23 test5.dir
     0:user:gozer:list_directory/read_data/add_file/write_data/execute
         :dir_inherit:allow
     1:owner@::deny
     2:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     3:group@:add_file/write_data/add_subdirectory/append_data:deny
     4:group@:list_directory/read_data/execute:allow
     5:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     6:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

If, at a later time, you decide to tighten the permission bits on a directory, the non-trivial ACL is discarded. For example:

# chmod 744 test5.dir
# ls -dv test5.dir
drwxr--r--   2 root     root           2 Feb 16 11:23 test5.dir
     0:owner@::deny
     1:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     2:group@:add_file/write_data/add_subdirectory/append_data/execute:deny
     3:group@:list_directory/read_data:allow
     4:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /execute/write_attributes/write_acl/write_owner:deny
     5:everyone@:list_directory/read_data/read_xattr/read_attributes/read_acl
         /synchronize:allow

ACL Inheritance With ACL Mode Set to Discard

In the following example, two non-trivial ACLs with file inheritance are set. One ACL allows read_data permission, and one ACL denies read_data permission. This example also illustrates how you can specify two ACEs in the same chmod command.

# zfs set aclinherit=nonallow tank/cindy
# chmod A+user:gozer:read_data:file_inherit:deny,user:lp:read_data:file_inherit:allow test6.dir
# ls -dv test6.dir
drwxr-xr-x+  2 root     root           2 May  4 14:23 test6.dir
     0:user:gozer:read_data:file_inherit:deny
     1:user:lp:read_data:file_inherit:allow
     2:owner@::deny
     3:owner@:list_directory/read_data/add_file/write_data/add_subdirectory
         /append_data/write_xattr/execute/write_attributes/write_acl
         /write_owner:allow
     4:group@:add_file/write_data/add_subdirectory/append_data:deny
     5:group@:list_directory/read_data/execute:allow
     6:everyone@:add_file/write_data/add_subdirectory/append_data/write_xattr
         /write_attributes/write_acl/write_owner:deny
     7:everyone@:list_directory/read_data/read_xattr/execute/read_attributes
         /read_acl/synchronize:allow

As the following example shows, when a new file is created, the ACL that allows read_data permission is discarded.

# touch test6.dir/file.6
# ls -v test6.dir/file.6
-rw-r--r--+  1 root     root           0 May  4 13:44 test6.dir/file.6
     0:user:gozer:read_data:deny
     1:owner@:execute:deny
     2:owner@:read_data/write_data/append_data/write_xattr/write_attributes
         /write_acl/write_owner:allow
     3:group@:write_data/append_data/execute:deny
     4:group@:read_data:allow
     5:everyone@:write_data/append_data/write_xattr/execute/write_attributes
         /write_acl/write_owner:deny
     6:everyone@:read_data/read_xattr/read_attributes/read_acl/synchronize
         :allow

ACL Inheritance With ACL Inherit Mode Set to Noallow

7.4. Setting and Displaying ACLs on ZFS Files in Compact Format

You can set and display permissions on ZFS files in a compact format that uses 14 unique letters to represent the permissions. The letters that represent the compact permissions are listed in ACL Access Privileges and ACL Inheritance Flags.

You can display compact ACL listings for files and directories by using the ls -V command. For example:

# ls -V file.1
-rw-r--r--   1 root     root      206663 Feb 16 11:00 file.1
            owner@:--x-----------:------:deny
            owner@:rw-p---A-W-Co-:------:allow
            group@:-wxp----------:------:deny
            group@:r-------------:------:allow
         everyone@:-wxp---A-W-Co-:------:deny
         everyone@:r-----a-R-c--s:------:allow

The compact ACL output is described as follows:

owner@: The owner is denied execute permissions to the file (x=execute).
owner@: The owner can read and modify the contents of the file (rw=read_data/write_data), (p=append_data). The owner can also modify the file's attributes such as timestamps, extended attributes, and ACLs (A=write_xattr, W=write_attributes, C=write_acl). In addition, the owner can modify the ownership of the file (O=write_owner).
group@: The group is denied modify and execute permissions to the file (rw=read_data/write_data, p=append_data, and x=execute).
group@: The group is granted read permissions to the file (r=read_data).
everyone@: Everyone who is not user or group is denied permission to execute or modify the contents of the file, and to modify any attributes of the file (w=write_data, x=execute, p=append_data, A=write_xattr, W=write_attributes, C=write_acl, and o=write_owner).
everyone@: Everyone who is not user or group is granted read permissions to the file and the file's attributes (r=read_data, a=append_data, R=read_xattr, c=read_acl, and s=synchronize). The synchronize access permission is not currently implemented.

Compact ACL format provides the following advantages over verbose ACL format:

Permissions can be specified as positional arguments to the chmod command.
The hyphen (-) characters, which identify no permissions, can be removed and only the required letters need to be specified.
Both permissions and inheritance flags are set in the same fashion.

For information about using the verbose ACL format, see Setting and Displaying ACLs on ZFS Files in Verbose Format.

In the following example, a trivial ACL exists on file.1:

# ls -V file.1
-rw-r-xr-x   1 root     root      206663 Feb 16 11:00 file.1
            owner@:--x-----------:------:deny
            owner@:rw-p---A-W-Co-:------:allow
            group@:-w-p----------:------:deny
            group@:r-x-----------:------:allow
         everyone@:-w-p---A-W-Co-:------:deny
         everyone@:r-x---a-R-c--s:------:allow

In this example, read_data/execute permissions are added for the user gozer on file.1.

# chmod A+user:gozer:rx:allow file.1
# ls -V file.1
-rw-r-xr-x+  1 root     root      206663 Feb 16 11:00 file.1
        user:gozer:r-x-----------:------:allow
            owner@:--x-----------:------:deny
            owner@:rw-p---A-W-Co-:------:allow
            group@:-w-p----------:------:deny
            group@:r-x-----------:------:allow
         everyone@:-w-p---A-W-Co-:------:deny
         everyone@:r-x---a-R-c--s:------:allow

Another way to add the same permissions for user gozer is to insert a new ACL at a specific position, 4, for example. As such, the existing ACLs at positions 4–6 are pushed down. For example:

# chmod A4+user:gozer:rx:allow file.1
# ls -V file.1
-rw-r-xr-x+  1 root     root      206663 Feb 16 11:00 file.1
            owner@:--x-----------:------:deny
            owner@:rw-p---A-W-Co-:------:allow
            group@:-w-p----------:------:deny
            group@:r-x-----------:------:allow
        user:gozer:r-x-----------:------:allow
         everyone@:-w-p---A-W-Co-:------:deny
         everyone@:r-x---a-R-c--s:------:allow

In the following example, user gozer is granted read, write, and execute permissions that are inherited for newly created files and directories by using the compact ACL format.

# chmod A+user:gozer:rwx:fd:allow dir.2
# ls -dV dir.2
drwxr-xr-x+  2 root     root           2 Aug 28 13:21 dir.2
        user:gozer:rwx-----------:fd----:allow
            owner@:--------------:------:deny
            owner@:rwxp---A-W-Co-:------:allow
            group@:-w-p----------:------:deny
            group@:r-x-----------:------:allow
         everyone@:-w-p---A-W-Co-:------:deny
         everyone@:r-x---a-R-c--s:------:allow

You can also cut and paste permissions and inheritance flags from the ls -V output into the compact chmod format. For example, to duplicate the permissions and inheritance flags on dir.1 for user gozer to user cindys, copy and paste the permission and inheritance flags (rwx-----------:f-----:allow) into your chmod command. For example:

# chmod A+user:cindys:rwx-----------:fd----:allow dir.2
# ls -dv dir.2
drwxr-xr-x+  2 root     root           2 Aug 28 14:12 dir.2
       user:cindys:rwx-----------:fd----:allow
        user:gozer:rwx-----------:fd----:allow
            owner@:--------------:------:deny
            owner@:rwxp---A-W-Co-:------:allow
            group@:-w-p----------:------:deny
            group@:r-x-----------:------:allow
         everyone@:-w-p---A-W-Co-:------:deny
         everyone@:r-x---a-R-c--s:------:allow

Setting and Displaying ACLs in Compact Format