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) docu-
mentation.
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, di-
rectories, 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 spa-
ces. 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 permis-
sions 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 associ-
ated 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 pro-
cessing 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 at-
tribute namespace.
When the -q option is given attr will try to keep quiet. It will out-
put 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) pro-
gram will.
CAVEATS
The list option present in the IRIX version of this command is not sup-
ported. getfattr provides a mechanism to retrieve all of the attribute
names.
AUTHOR
Andreas Gruenbacher, <andreas.gruenbacher@gmail.com> and the SGI XFS
development team, <linux-xfs@oss.sgi.com>.
Please send your bug reports or comments to <https://savan-
nah.nongnu.org/bugs/?group=attr> or <acl-devel@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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