S3ACL(1p)

User Contributed Perl Documentation

S3ACL(1p)

NAME¶

s3acl - Display or manipulate the ACL of AWS S3 buckets and items

SYNOPSIS¶

s3acl [options] [[bucket|bucket/key] ...]

 Options:
   --access-key    AWS Access Key ID
   --secret-key    AWS Secret Access Key
   --get           Output the ACL to STDOUT
     --xml           in raw XML form instead of parsed form
   --set           Modify the ACL
     --clear                remove all grants from the ACL
     --add grant,grant,...  add grants to the ACL
     --del grant,grant,...  remove matching grants from the ACL
     --xml                  apply the XML ACL from STDIN to the item
     --acl-short cannedacl  apply the "canned" ACL to the item
 Environment:
   AWS_ACCESS_KEY_ID
   AWS_ACCESS_KEY_SECRET

OPTIONS¶

--help

Print a brief help message and exits.

--man

Prints the manual page and exits.

--verbose

Output what is being done as it is done.

--access-key and --secret-key

Specify the "AWS Access Key Identifiers" for the AWS account. --access-key is the "Access Key ID", and --secret-key is the "Secret Access Key". These are effectively the "username" and "password" to the AWS account, and should be kept confidential.

The access keys MUST be specified, either via these command line parameters, or via the AWS_ACCESS_KEY_ID and AWS_ACCESS_KEY_SECRET environment variables.

Specifying them on the command line overrides the environment variables.

--secure

Uses SSL/TLS HTTPS to communicate with the AWS service, instead of HTTP.

--get

Retrieve and display the ACL for each specified bucket or item.

--xml

When used with the --get option, outputs to stdout the raw XML, instead of parsed format. This raw XML is documented in the "Amazon S3 Developer Guide".

If more than one bucket or item is specified, the XML ACL for each will be output, concatenated together. This is probably not very useful.

The raw XML output can be used as input for the --set option, like so:

  s3acl --get --xml bucketA | s3acl --set --xml bucketB bucketC

This does not work when specifying more than one bucket or item to the --get option, because the concatenation of multiple XML ACLs is not a valid XML ACL.

--set

Instead of displaying the ACL, modify it. An ACL can be modified by using --clear, --add, and --del, or by using --xml, or by using --acl-short.

--clear

Removes all of the grants from the ACL. This includes access by the owner of the bucket or item. This is done before the --add or --del options are applied, no matter what order options are specified on the command line.

It is usually accompanied by the --add option to add some grants back to the now empty ACL.

--del

Remove matching grants from the ACL. This is done before the --add option is applied, no matter what order options are specified on the command line.

Grants are specified in parsed form, and then joined together by commas with no whitespace.

There is an extension to the parsed grant format. If the grantee is specified as "ANY", then it matches any and all grantees in the ACL. If the permission is specified as "ANY", then it matches any permission. Thus

  s3acl --set --del ANY:READ mybucket

removes all grants that give READ permission, and

  s3acl --set --del someuserid:ANY mybucket

removes all grants to the user someuserid

  s3acl --set --del ANY:ANY mybucket

does the same thing as

  s3acl --set --clear mybucket

Due to a limitation in the semantics of the S3 API, it is not possible to delete a grantee by email address, only by canonical ID.

--add

Add the specified grants to the ACL. Grants are specified in parsed form, and then joined together by commas with no whitespace.

It is possible to add the same grant to a bucket or item more than once. This is a surprising behavior of the S3 service.

--xml

When used with --set, and instead of using <--clear>, <--del>, and --add, read a raw XML ACL from STDIN, and then apply it to each given bucket or item. This will completely overwrite the existing ACL for each given bucket or item.

--acl-short

Instead of using <--clear>, <--del>, and --add, or using <--xml>, apply a "canned ACL" to each given bucket or item. This will completely overwrite the existing ACL for each given bucket or item.

The following canned ACLs are currently defined by S3:

private: Owner gets "FULL_CONTROL". No one else has any access rights. This is the default for newly created buckets and items.
public-read: Owner gets "FULL_CONTROL". The anonymous principal is granted "READ" access.
public-read-write: Owner gets "FULL_CONTROL".
The anonymous principal is granted "READ" and "WRITE" access. This is a useful policy to apply to a bucket, if you intend for any anonymous user to PUT objects into the bucket.
authenticated-read: Owner gets "FULL_CONTROL" . Any principal authenticated as a registered Amazon S3 user is granted "READ" access.

bucket or bucket/key

One or more bucket names or bucket and key names, specifies an item. As many as possible will be be processed.

If just a bucket name is given, the ACL for that bucket is retrieved or modified.

If a bucket name and a key, separated by a slash, is given, the ACL for that key in that bucket is retrieved or modified.

If a bucket name begins with one or more dashes, it might be mistaken for a command line option. If this is the case, separate the command line options from the bucket or bucket/key names with two dashes, like so:

  s3acl --get -- --bucketname/keyname

ENVIRONMENT VARIABLES¶

AWS_ACCESS_KEY_ID and AWS_ACCESS_KEY_SECRET

Specify the "AWS Access Key Identifiers" for the AWS account. AWS_ACCESS_KEY_ID contains the "Access Key ID", and AWS_ACCESS_KEY_SECRET contains the "Secret Access Key". These are effectively the "username" and "password" to the AWS service, and should be kept confidential.

The access keys MUST be specified, either via these environment variables, or via the --access-key and --secret-key command line parameters.

If the command line parameters are set, they override these environment variables.

CONFIGURATION FILE¶

The configuration options will be read from the file "~/.s3-tools" if it exists. The format is the same as the command line options with one option per line. For example, the file could contain:

    --access-key <AWS access key>
    --secret-key <AWS secret key>
    --secure

This example configuration file would specify the AWS access keys and that a secure connection using HTTPS should be used for all communications.

DESCRIPTION¶

Retrieves and outputs the Access Control List (ACL) of buckets and of items in buckets in the Amazon Simple Storage Service (S3).

Principals¶

(Much of the following text is taken from the "Amazon S3 Developer Guide (API Version 2006-03-01)".)

Every bucket and item has an Access Control List (ACL). When a request is made, S3 determines the principal making the request, and then checks the access control list to see if that principal is authorized to make the request. If the ACL contains an entry authorizing that principal to make this request, the request is allowed to proceed, otherwise an error is returned.

A principal may be someone with an AWS S3 account who has logged in, or "authenticated". The principal might be the creator and owner of the bucket or item. Or the principal might be some anonymous web browser out on the internet.

ACL is sequence of grants. A grant is 1 grantee and 1 permission.¶

An access control list is a sequence of grants. It may contain up to 100 grants. A grant is composed of one grantee, which is a description of the principal who will be allowed access, and one permission, which is a description of what that principal is allowed to do with that bucket or item.

User Grantee¶

A user grantee must be registered as an Amazon.com customer, but does not have to be registered as an AWS customer.

When an ACL is read, the user grantee will be displayed in a canonical format, which consists of 64 hex characters. The exception is if the grantee is the owner. Amazon still stores and returns the grantee in canonical form, but this tool displays it as "OWNER".

Group Grantee¶

The only groups available are those pre-defined by S3. In the current release of S3, you cannot create your own group. There are currently two pre-defined groups.

The first is represented by the string "WORLD" by this tool. All principals, whether they are anonymous or authenticated, are considered part of this group.

The second is represented by the string "USERS" by this tool. Every non-anonymous principal is considered part of the group. Note that permission granted by virtue of this grant does not trump other access control considerations. For example, if a user is registered with AWS, they may be part of this group, but if they have not subscribed to S3, they will still not be granted access.

There is also a special pseudo group with the string "ANY". It is used by the --del option to match against a ACL item to select for deletion.

If Amazon updates S3 to define any additional groups before this tool is updated, they will be represented as a URI surrounded by angle brackets.

Owner¶

Every bucket and item in S3 has an owner attribute associated with it. The owner the user that created the bucket or item. The only way to change the owner of a bucket is to delete the bucket and create it again under a different user identity. The only way to change the owner of an item is to overwrite the item using a different identity.

The owner of a bucket or item is subject to the access control policy of that bucket or item just like everybody else, with two notable exceptions: The owner of a resource always has the ability to read and write the ACL of that resource, no matter what the associated ACL says. For example, as the owner of an item, you could remove yourself from the associated access control list, and find that you can no longer read the item's data and metadata. However, by virtue of being owner, you always have the right to re-grant yourself permissions to it. This policy prevents the situation where an item becomes "stranded," with nobody able to ever modify or even delete it.

Permissions¶

The permission in a grant describes the type of access to be granted to the respective grantee. The following permissions are supported:

READ: When applied to a bucket, this grants permission to list the bucket. When applied to an item, this grants permission to read the item data and/or metadata.
WRITE: When applied to a bucket, this grants permission to create, overwrite, and delete any item in the bucket. This permission is not supported for items (it is reserved for future use).
READ_ACP: Grants permission to read the access control policy (ACL and owner) for the applicable bucket or item. The owner of a bucket or item always has this permission implicitly.
WRITE_ACP: Grants permission to overwrite the ACP for the applicable bucket or item. The owner of a bucket or item always has this permission implicitly. Note that granting this permission is equivalent to granting FULL_CONTROL, because the grant recipient can now make any whatever changes to the ACP he or she likes!
FULL_CONTROL: This permission is short-hand for the union of READ, WRITE, READ_ACP, and WRITE_ACP permissions. It does not convey additional rights, and is provided only for convenience. It is probably unwise to give this permission to WORLD.
ANY: This is not really a permission, but is used by the --del option. It matches any permission to select a grant for deletion.

Default ACL¶

If no ACL is provided at the time a bucket is created or an item written then a default ACL is created. The default ACL for new resources consists of a single grant that gives the owner of the resource (i.e. the principal making the request to create the bucket or to write the item) FULL_CONTROL permission. Note that if you overwrite an existing item, the ACL for the existing item is always overwritten as well, and defaulted back to OWNER:FULL_CONTROL if no explicit ACL is provided.

Raw XML ACL Format¶

The XML ACL format is documented in the "Amazon S3 Developer Guide".

Parsed ACL Format¶

This tool parses the raw XML ACL format into a more readable form.

A parsed ACL consists of several lines. Comments are lines that begin with a hash character. Lines that are not comments are grants.

For buckets, the comments give the bucket name, and the Amazon canonical user string for the owner.

For items, the comments give the bucket name, the item key, and the Amazon canonical user string for the owner.

A grant is grantee string and a permission string, separated with a colon character. A grantee can be one of the strings "OWNER", "WORLD", or "USERS", or a URI wrapped in angle brackets, or the email address of an Amazon user, or a Amazon canonical user string, which is 64 hex characters. A permission is one of the strings "READ", "WRITE", "READ_ACP", "WRITE_ACP", or "FULL_CONTROL".

  $ ./s3getacl example
  # bucket: example
  # owner: 5a1568e09392dad4b4ceb54f29f0a64d651a531350d6f720fbd2367eed995f08
  OWNER:FULL_CONTROL
  a00490decea9d0ad76e5ef8b450b3efa63861adccfb9197cfb42f837eb222df2:WRITE
  USERS:READ
  WORLD:READ
  $ ./s3getacl example/thingee
  # bucket: example
  # item: thingee
  # owner: 5a1568e09392dad4b4ceb54f29f0a64d651a531350d6f720fbd2367eed995f08
  OWNER:FULL_CONTROL
  $ _

BUGS¶

Report bugs to Mark Atwood mark@fallenpegasus.com.

Occasionally the S3 service will randomly fail for no externally apparent reason. When that happens, this tool should retry, with a delay and a backoff.

Access to the S3 service can be authenticated with a X.509 certificate, instead of via the "AWS Access Key Identifiers". This tool should support that.

It might be useful to be able to specify the "AWS Access Key Identifiers" in the user's "~/.netrc" file. This tool should support that.

Errors and warnings are very "Perl-ish", and can be confusing.

Trying to access a bucket or item that does not exist or is not accessible by the user generates less than helpful error messages.

Net::Amazon::S3 already uses XML::LibXML and XML::LibXML::XPathContext, so this tool should use those instead of using XML::Writer, to have fewer module dependences.

It is possible to add the same grant to a bucket or item more than once. This is a surprising behavior of the S3 service. Both identical grants will be removed by using the --del option.