ATTR(1) XFS Compatibility API ATTR(1)
NAME
attr - extended attributes on XFS filesystem objects
SYNOPSIS
attr [ -LRq ] -s attrname [ -V attrvalue ] pathname
attr [ -LRq ] -g attrname pathname
attr [ -LRq ] -r attrname pathname
OVERVIEW
Extended attributes implement the ability for a user to attach name:value pairs to objects
within the XFS filesystem.
They could be used to store meta-information about the file. For example "character-
set=kanji" could tell a document browser to use the Kanji character set when displaying
that document and "thumbnail=..." could provide a reduced resolution overview of a high
resolution graphic image.
This document describes the attr command, which is mostly compatible with the IRIX command
of the same name. It is thus aimed specifically at users of the XFS filesystem - for
filesystem independent extended attribute manipulation, consult the getfattr(1) and set-
fattr(1) documentation.
In the XFS filesystem, the names can be up to 256 bytes in length, terminated by the first
0 byte. The intent is that they be printable ASCII (or other character set) names for the
attribute. The values can be up to 64KB of arbitrary binary data.
Attributes can be attached to all types of XFS inodes: regular files, directories, sym-
bolic links, device nodes, etc.
XFS uses 2 disjoint attribute name spaces associated with every filesystem object. They
are the root and user address spaces. The root address space is accessable only to the
superuser, and then only by specifying a flag argument to the function call. Other users
will not see or be able to modify attributes in the root address space. The user address
space is protected by the normal file permissions mechanism, so the owner of the file can
decide who is able to see and/or modify the value of attributes on any particular file.
DESCRIPTION
The attr utility allows the manipulation of extended attributes associated with filesystem
objects from within shell scripts.
There are four main operations that attr can perform:
GET The -g attrname option tells attr to search the named object and print (to stdout)
the value associated with that attribute name. With the -q flag, stdout will be
exactly and only the value of the attribute, suitable for storage directly into a
file or processing via a piped command.
REMOVE The -r attrname option tells attr to remove an attribute with the given name from
the object if the attribute exists. There is no output on sucessful completion.
SET/CREATE
The -s attrname option tells attr to set the named attribute of the object to the
value read from stdin. If an attribute with that name already exists, its value
will be replaced with this one. If an attribute with that name does not already
exist, one will be created with this value. With the -V attrvalue flag, the
attribute will be set to have a value of attrvalue and stdin will not be read.
With the -q flag, stdout will not be used. Without the -q flag, a message showing
the attribute name and the entire value will be printed.
When the -L option is given and the named object is a symbolic link, operate on the
attributes of the object referenced by the symbolic link. Without this option, operate on
the attributes of the symbolic link itself.
When the -R option is given and the process has appropriate privileges, operate in the
root attribute namespace rather that the USER attribute namespace.
When the -q option is given attr will try to keep quiet. It will output error messages
(to stderr) but will not print status messages (to stdout).
NOTES
The standard file interchange/archive programs tar(1), and cpio(1) will not archive or
restore extended attributes, while the xfsdump(8) program will.
CAVEATS
The list option present in the IRIX version of this command is not supported. getfattr
provides a mechanism to retrieve all of the attribute names.
SEE ALSO
getfattr(1), setfattr(1), attr_get(3), attr_set(3), attr_multi(3), attr_remove(3),
attr(5), and xfsdump(8).
Dec 2001 Extended Attributes ATTR(1)
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