расширенные атрибуты объектов файловой системы XFS (extended attributes on XFS filesystem objects)
Имя (Name)
attr - extended attributes on XFS filesystem objects
Синопсис (Synopsis)
attr [ -LRSq ] -s attrname [ -V attrvalue ] pathname
attr [ -LRSq ] -g attrname pathname
attr [ -LRSq ] -r attrname pathname
attr [ -LRSq ] -l pathname
Обзор (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.
Описание (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).
Примечание (Note)
The standard file interchange/archive programs tar(1), and
cpio(1) will not archive or restore extended attributes, while
the xfsdump(8) program will.
Предостережение (Caveat)
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.
