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ATTR(1) XFS Compatibility API ATTR(1)
NAME
attr - extended attributes on 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 filesystem.
This document describes the attr command, which is mostly compatible with the IRIX command
of the same name. It was originally aimed specifically at users of the XFS filesystem,
even though it can be used now on any filesystem that supports extended attributes, but
for the generic and more portable interface 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 supported filesystems, 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 inodes: regular files, directories, symbolic
links, device nodes, etc.
Extended attributes use 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 par-
ticular 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 associ-
ated with the object, and the number of bytes in the value of each of those at-
tributes. 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 attri-
bute 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 at-
tribute 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 at-
tributes 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 re-
store 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.
AUTHOR
Andreas Gruenbacher, <andreas.gruenbacher AT gmail.com> and the SGI XFS development team,
<linux-xfs AT oss.com>.
Please send your bug reports or comments to <https://savannah.nongnu.org/bugs/?group=attr>
or <acl-devel AT nongnu.org>.
SEE ALSO
getfattr(1), setfattr(1), attr_get(3), attr_set(3), attr_multi(3), attr_remove(3),
attr(5), xfsdump(8)
Dec 2001 Extended Attributes ATTR(1)
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