mirror of https://github.com/mkerrisk/man-pages
163 lines
4.7 KiB
Groff
163 lines
4.7 KiB
Groff
.\" Copyright (C) Andreas Gruenbacher, February 2001
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.\" Copyright (C) Silicon Graphics Inc, September 2001
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.\"
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.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, see
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.\" <http://www.gnu.org/licenses/>.
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.\" %%%LICENSE_END
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.\"
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.TH GETXATTR 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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getxattr, lgetxattr, fgetxattr \- retrieve an extended attribute value
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.SH SYNOPSIS
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.fam C
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.nf
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.B #include <sys/xattr.h>
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.PP
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.BI "ssize_t getxattr(const char *" path ", const char *" name ,
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.BI " void *" value ", size_t " size );
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.BI "ssize_t lgetxattr(const char *" path ", const char *" name ,
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.BI " void *" value ", size_t " size );
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.BI "ssize_t fgetxattr(int " fd ", const char *" name ,
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.BI " void *" value ", size_t " size );
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.fi
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.fam T
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.SH DESCRIPTION
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Extended attributes are
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.IR name :\c
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.I value
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pairs associated with inodes (files, directories, symbolic links, etc.).
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They are extensions to the normal attributes which are associated
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with all inodes in the system (i.e., the
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.BR stat (2)
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data).
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A complete overview of extended attributes concepts can be found in
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.BR xattr (7).
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.PP
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.BR getxattr ()
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retrieves the value of the extended attribute identified by
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.I name
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and associated with the given
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.I path
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in the filesystem.
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The attribute value is placed in the buffer pointed to by
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.IR value ;
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.I size
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specifies the size of that buffer.
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The return value of the call is the number of bytes placed in
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.IR value .
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.PP
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.BR lgetxattr ()
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is identical to
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.BR getxattr (),
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except in the case of a symbolic link, where the link itself is
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interrogated, not the file that it refers to.
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.PP
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.BR fgetxattr ()
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is identical to
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.BR getxattr (),
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only the open file referred to by
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.I fd
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(as returned by
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.BR open (2))
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is interrogated in place of
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.IR path .
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.PP
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An extended attribute
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.I name
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is a null-terminated string.
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The name includes a namespace prefix; there may be several, disjoint
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namespaces associated with an individual inode.
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The value of an extended attribute is a chunk of arbitrary textual or
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binary data that was assigned using
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.BR setxattr (2).
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.PP
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If
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.I size
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is specified as zero, these calls return the current size of the
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named extended attribute (and leave
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.I value
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unchanged).
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This can be used to determine the size of the buffer that
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should be supplied in a subsequent call.
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(But, bear in mind that there is a possibility that the
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attribute value may change between the two calls,
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so that it is still necessary to check the return status
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from the second call.)
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.SH RETURN VALUE
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On success, these calls return a nonnegative value which is
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the size (in bytes) of the extended attribute value.
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On failure, \-1 is returned and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B E2BIG
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The size of the attribute value is larger than the maximum size allowed; the
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attribute cannot be retrieved.
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This can happen on filesystems that support
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very large attribute values such as NFSv4, for example.
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.TP
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.B ENODATA
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The named attribute does not exist, or the process has no access to
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this attribute.
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.\" .RB ( ENOATTR
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.\" is defined to be a synonym for
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.\" .BR ENODATA
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.\" in
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.\" .IR <attr/attributes.h> .)
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.TP
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.B ENOTSUP
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Extended attributes are not supported by the filesystem, or are disabled.
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.TP
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.B ERANGE
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The
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.I size
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of the
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.I value
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buffer is too small to hold the result.
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.PP
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In addition, the errors documented in
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.BR stat (2)
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can also occur.
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.SH VERSIONS
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These system calls have been available on Linux since kernel 2.4;
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glibc support is provided since version 2.3.
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.SH CONFORMING TO
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These system calls are Linux-specific.
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.\" .SH AUTHORS
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.\" Andreas Gruenbacher,
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.\" .RI < a.gruenbacher@computer.org >
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.\" and the SGI XFS development team,
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.\" .RI < linux-xfs@oss.sgi.com >.
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.\" Please send any bug reports or comments to these addresses.
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.SH EXAMPLES
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See
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.BR listxattr (2).
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.SH SEE ALSO
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.BR getfattr (1),
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.BR setfattr (1),
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.BR listxattr (2),
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.BR open (2),
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.BR removexattr (2),
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.BR setxattr (2),
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.BR stat (2),
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.BR symlink (7),
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.BR xattr (7)
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