attr - Online in the Cloud

PROGRAM:

NAME

attr - extended attributes on XFS filesystem objects

SYNOPSIS

attr [ -LRSq ] -s attrname [ -V attrvalue ] pathname

attr [ -LRSq ] -g attrname pathname

attr [ -LRSq ] -r attrname pathname

attr [ -LRSq ] -l pathname

OVERVIEW

Extended attributes implement the ability for a user to attach name:value pairs to objects
within the XFS filesystem.

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
setfattr(1) documentation.

Extended attributes can 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.

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,
symbolic 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 accessible 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.

LIST The -l option tells attr to list the names of all the attributes that are
associated with the object, and the number of bytes in the value of each of those
attributes. With the -q flag, stdout will be a simple list of only the attribute
names, one per line, suitable for input into a script.

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 successful 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.

The -S option is similar, except it specifies use of the security 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.

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