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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
commit | fc22b3d6507c6745911b9dfcc68f1e665ae13dbc (patch) | |
tree | ce1e3bce06471410239a6f41282e328770aa404a /upstream/opensuse-tumbleweed/man7/xattr.7 | |
parent | Initial commit. (diff) | |
download | manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.tar.xz manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.zip |
Adding upstream version 4.22.0.upstream/4.22.0
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'upstream/opensuse-tumbleweed/man7/xattr.7')
-rw-r--r-- | upstream/opensuse-tumbleweed/man7/xattr.7 | 180 |
1 files changed, 180 insertions, 0 deletions
diff --git a/upstream/opensuse-tumbleweed/man7/xattr.7 b/upstream/opensuse-tumbleweed/man7/xattr.7 new file mode 100644 index 00000000..c2f12c95 --- /dev/null +++ b/upstream/opensuse-tumbleweed/man7/xattr.7 @@ -0,0 +1,180 @@ +.\" Extended attributes manual page +.\" +.\" Copyright (C) 2000, 2002, 2007 Andreas Gruenbacher <agruen@suse.de> +.\" Copyright (C) 2001, 2002, 2004, 2007 Silicon Graphics, Inc. +.\" All rights reserved. +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.\" +.TH xattr 7 2023-02-05 "Linux man-pages 6.05.01" +.SH NAME +xattr \- Extended attributes +.SH DESCRIPTION +Extended attributes are name:value pairs associated permanently with +files and directories, similar to the environment strings associated +with a process. +An attribute may be defined or undefined. +If it is defined, its value may be empty or non-empty. +.PP +Extended attributes are extensions to the normal attributes which are +associated with all inodes in the system (i.e., the +.BR stat (2) +data). +They are often used to provide additional functionality +to a filesystem\[em]for example, additional security features such as +Access Control Lists (ACLs) may be implemented using extended attributes. +.PP +Users with search access to a file or directory may use +.BR listxattr (2) +to retrieve a list of attribute names defined for that file or directory. +.PP +Extended attributes are accessed as atomic objects. +Reading +.RB ( getxattr (2)) +retrieves the whole value of an attribute and stores it in a buffer. +Writing +.RB ( setxattr (2)) +replaces any previous value with the new value. +.PP +Space consumed for extended attributes may be counted towards the disk quotas +of the file owner and file group. +.SS Extended attribute namespaces +Attribute names are null-terminated strings. +The attribute name is always specified in the fully qualified +.I namespace.attribute +form, for example, +.IR user.mime_type , +.IR trusted.md5sum , +.IR system.posix_acl_access , +or +.IR security.selinux . +.PP +The namespace mechanism is used to define different classes of extended +attributes. +These different classes exist for several reasons; +for example, the permissions +and capabilities required for manipulating extended attributes of one +namespace may differ to another. +.PP +Currently, the +.IR security , +.IR system , +.IR trusted , +and +.I user +extended attribute classes are defined as described below. +Additional classes may be added in the future. +.SS Extended security attributes +The security attribute namespace is used by kernel security modules, +such as Security Enhanced Linux, and also to implement file capabilities (see +.BR capabilities (7)). +Read and write access permissions to security attributes depend on the +policy implemented for each security attribute by the security module. +When no security module is loaded, all processes have read access to +extended security attributes, and write access is limited to processes +that have the +.B CAP_SYS_ADMIN +capability. +.SS System extended attributes +System extended attributes are used by the kernel to store system +objects such as Access Control Lists. +Read and write +access permissions to system attributes depend on the policy implemented +for each system attribute implemented by filesystems in the kernel. +.SS Trusted extended attributes +Trusted extended attributes are visible and accessible only to processes that +have the +.B CAP_SYS_ADMIN +capability. +Attributes in this class are used to implement mechanisms in user +space (i.e., outside the kernel) which keep information in extended attributes +to which ordinary processes should not have access. +.SS User extended attributes +User extended attributes may be assigned to files and directories for +storing arbitrary additional information such as the mime type, +character set or encoding of a file. +The access permissions for user +attributes are defined by the file permission bits: +read permission is required to retrieve the attribute value, +and writer permission is required to change it. +.PP +The file permission bits of regular files and directories are +interpreted differently from the file permission bits of special files +and symbolic links. +For regular files and directories the file +permission bits define access to the file's contents, while for device special +files they define access to the device described by the special file. +The file permissions of symbolic links are not used in access checks. +These differences would allow users to consume filesystem resources in +a way not controllable by disk quotas for group or world writable +special files and directories. +.PP +For this reason, +user extended attributes are allowed only for regular files and directories, +and access to user extended attributes is restricted to the +owner and to users with appropriate capabilities for directories with the +sticky bit set (see the +.BR chmod (1) +manual page for an explanation of the sticky bit). +.SS Filesystem differences +The kernel and the filesystem may place limits on the maximum number +and size of extended attributes that can be associated with a file. +The VFS-imposed limits on attribute names and values are 255 bytes +and 64\ kB, respectively. +The list of attribute names that +can be returned is also limited to 64\ kB +(see BUGS in +.BR listxattr (2)). +.PP +Some filesystems, such as Reiserfs (and, historically, ext2 and ext3), +require the filesystem to be mounted with the +.B user_xattr +mount option in order for user extended attributes to be used. +.PP +In the current ext2, ext3, and ext4 filesystem implementations, +the total bytes used by the names and values of all of a file's +extended attributes must fit in a single filesystem block (1024, 2048 +or 4096 bytes, depending on the block size specified when the +filesystem was created). +.PP +In the Btrfs, XFS, and Reiserfs filesystem implementations, there is no +practical limit on the number of extended attributes +associated with a file, and the algorithms used to store extended +attribute information on disk are scalable. +.PP +In the JFS, XFS, and Reiserfs filesystem implementations, +the limit on bytes used in an EA value is the ceiling imposed by the VFS. +.PP +In the Btrfs filesystem implementation, +the total bytes used for the name, value, and implementation overhead bytes +is limited to the filesystem +.I nodesize +value (16\ kB by default). +.SH STANDARDS +Extended attributes are not specified in POSIX.1, but some other systems +(e.g., the BSDs and Solaris) provide a similar feature. +.SH NOTES +Since the filesystems on which extended attributes are stored might also +be used on architectures with a different byte order and machine word +size, care should be taken to store attribute values in an +architecture-independent format. +.PP +This page was formerly named +.BR attr (5). +.\" .SH AUTHORS +.\" Andreas Gruenbacher, +.\" .RI < a.gruenbacher@bestbits.at > +.\" and the SGI XFS development team, +.\" .RI < linux-xfs@oss.sgi.com >. +.SH SEE ALSO +.BR attr (1), +.BR getfattr (1), +.BR setfattr (1), +.BR getxattr (2), +.BR ioctl_iflags (2), +.BR listxattr (2), +.BR removexattr (2), +.BR setxattr (2), +.BR acl (5), +.BR capabilities (7), +.BR selinux (8) |