attr man page on aLinux

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ATTR(1)			     XFS Compatibility API		       ATTR(1)

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.

       They could be used to store meta-information about the file.  For exam‐
       ple  "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 setfattr(1) docu‐
       mentation.

       In the XFS filesystem, the names can be up to 256 bytes in length, ter‐
       minated	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 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 mecha‐
       nism, 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 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.

       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  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.

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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