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300 lines
9.4 KiB
Groff
300 lines
9.4 KiB
Groff
.\" -*- nroff -*-
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.TH CHATTR 1 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
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.SH NAME
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chattr \- change file attributes on a Linux file system
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.SH SYNOPSIS
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.B chattr
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[
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.B \-RVf
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]
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[
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.B \-v
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.I version
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]
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[
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.B \-p
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.I project
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]
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[
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.I mode
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]
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.I files...
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.SH DESCRIPTION
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.B chattr
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changes the file attributes on a Linux file system.
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.PP
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The format of a symbolic
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.I mode
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is
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.BR +-= [ aAcCdDeFijmPsStTux ].
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.PP
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The operator
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.RB ' + '
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causes the selected attributes to be added to the
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existing attributes of the files;
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.RB ' - '
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causes them to be removed; and
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.RB ' = '
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causes them to be the only attributes that the files have.
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.PP
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The letters
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.RB ' aAcCdDeFijmPsStTux '
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select the new attributes for the files:
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append only
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.RB ( a ),
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no atime updates
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.RB ( A ),
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compressed
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.RB ( c ),
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no copy on write
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.RB ( C ),
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no dump
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.RB ( d ),
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synchronous directory updates
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.RB ( D ),
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extent format
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.RB ( e ),
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case-insensitive directory lookups
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.RB ( F ),
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immutable
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.RB ( i ),
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data journaling
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.RB ( j ),
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don't compress
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.RB ( m ),
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project hierarchy
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.RB ( P ),
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secure deletion
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.RB ( s ),
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synchronous updates
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.RB ( S ),
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no tail-merging
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.RB ( t ),
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top of directory hierarchy
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.RB ( T ),
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undeletable
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.RB ( u ),
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and direct access for files
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.RB ( x ).
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.PP
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The following attributes are read-only, and may be listed by
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.BR lsattr (1)
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but not modified by chattr:
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encrypted
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.RB ( E ),
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indexed directory
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.RB ( I ),
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inline data
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.RB ( N ),
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and verity
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.RB ( V ).
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.PP
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Not all flags are supported or utilized by all file systems; refer to
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file system-specific man pages such as
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.BR btrfs (5),
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.BR ext4 (5),
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.BR mkfs.f2fs (8),
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and
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.BR xfs (5)
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for more file system-specific details.
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.SH OPTIONS
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.TP
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.B \-R
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Recursively change attributes of directories and their contents.
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.TP
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.B \-V
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Be verbose with chattr's output and print the program version.
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.TP
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.B \-f
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Suppress most error messages.
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.TP
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.BI \-v " version"
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Set the file's version/generation number.
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.TP
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.BI \-p " project"
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Set the file's project number.
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.SH ATTRIBUTES
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.TP
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.B a
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A file with the 'a' attribute set can only be opened in append mode for
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writing. Only the superuser or a process possessing the
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CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
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.TP
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.B A
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When a file with the 'A' attribute set is accessed, its atime record is
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not modified. This avoids a certain amount of disk I/O for laptop
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systems.
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.TP
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.B c
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A file with the 'c' attribute set is automatically compressed on the disk
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by the kernel. A read from this file returns uncompressed data. A write to
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this file compresses data before storing them on the disk. Note: please
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make sure to read the bugs and limitations section at the end of this
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document. (Note: For btrfs, If the 'c' flag is set, then the 'C' flag
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cannot be set. Also conflicts with btrfs mount option 'nodatasum')
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.TP
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.B C
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A file with the 'C' attribute set will not be subject to copy-on-write
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updates. This flag is only supported on file systems which perform
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copy-on-write. (Note: For btrfs, the 'C' flag should be
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set on new or empty files. If it is set on a file which already has
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data blocks, it is undefined when the blocks assigned to the file will
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be fully stable. If the 'C' flag is set on a directory, it will have no
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effect on the directory, but new files created in that directory will
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have the No_COW attribute set. If the 'C' flag is set, then the 'c' flag
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cannot be set.)
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.TP
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.B d
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A file with the 'd' attribute set is not a candidate for backup when the
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.BR dump (8)
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program is run.
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.TP
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.B D
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When a directory with the 'D' attribute set is modified,
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the changes are written synchronously to the disk; this is equivalent to
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the 'dirsync' mount option applied to a subset of the files.
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.TP
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.B e
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The 'e' attribute indicates that the file is using extents for mapping
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the blocks on disk. It may not be removed using
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.BR chattr (1).
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.TP
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.B E
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A file, directory, or symlink with the 'E' attribute set is encrypted by the
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file system. This attribute may not be set or cleared using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.TP
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.B F
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A directory with the 'F' attribute set indicates that all the path
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lookups inside that directory are made in a case-insensitive fashion.
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This attribute can only be changed in empty directories on file systems
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with the casefold feature enabled.
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.TP
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.B i
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A file with the 'i' attribute cannot be modified: it cannot be deleted or
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renamed, no link can be created to this file, most of the file's
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metadata can not be modified, and the file can not be opened in write mode.
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Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE
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capability can set or clear this attribute.
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.TP
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.B I
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The 'I' attribute is used by the htree code to indicate that a directory
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is being indexed using hashed trees. It may not be set or cleared using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.TP
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.B j
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A file with the 'j' attribute has all of its data written to the ext3 or
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ext4 journal before being written to the file itself, if the file system
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is mounted with the "data=ordered" or "data=writeback" options and the
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file system has a journal. When the file system is mounted with the
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"data=journal" option all file data is already journalled and this
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attribute has no effect. Only the superuser or a process possessing the
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CAP_SYS_RESOURCE capability can set or clear this attribute.
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.TP
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.B m
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A file with the 'm' attribute is excluded from compression on file
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systems that support per-file compression.
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.TP
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.B N
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A file with the 'N' attribute set indicates that the file has data
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stored inline, within the inode itself. It may not be set or cleared
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using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.TP
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.B P
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A directory with the 'P' attribute set will enforce a hierarchical
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structure for project id's. This means that files and directories created
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in the directory will inherit the project id of the directory, rename
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operations are constrained so when a file or directory is moved into
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another directory, that the project ids must match. In addition, a
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hard link to file can only be created when the project id for the file
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and the destination directory match.
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.TP
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.B s
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When a file with the 's' attribute set is deleted, its blocks are zeroed
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and written back to the disk. Note: please make sure to read the bugs
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and limitations section at the end of this document.
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.TP
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.B S
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When a file with the 'S' attribute set is modified,
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the changes are written synchronously to the disk; this is equivalent to
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the 'sync' mount option applied to a subset of the files.
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.TP
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.B t
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A file with the 't' attribute will not have a partial block fragment at
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the end of the file merged with other files (for those file systems which
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support tail-merging). This is necessary for applications such as LILO
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which read the file system directly, and which don't understand tail-merged
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files. Note: As of this writing, the ext2, ext3, and ext4 file systems do
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not support tail-merging.
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.TP
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.B T
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A directory with the 'T' attribute will be deemed to be the top of
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directory hierarchies for the purposes of the Orlov block allocator.
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This is a hint to the block allocator used by ext3 and ext4 that the
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subdirectories under this directory are not related, and thus should be
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spread apart for allocation purposes. For example it is a very good
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idea to set the 'T' attribute on the /home directory, so that /home/john
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and /home/mary are placed into separate block groups. For directories
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where this attribute is not set, the Orlov block allocator will try to
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group subdirectories closer together where possible.
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.TP
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.B u
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When a file with the 'u' attribute set is deleted, its contents are
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saved. This allows the user to ask for its undeletion. Note: please
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make sure to read the bugs and limitations section at the end of this
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document.
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.TP
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.B x
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A file with the 'x' requests the use of direct access (dax) mode, if the
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kernel supports DAX. This can be overridden by the 'dax=never' mount
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option. For more information see the kernel documentation for dax:
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<https://www.kernel.org/doc/html/latest/filesystems/dax.html>.
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.IP
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If the attribute is set on an existing directory, it will be inherited
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by all files and subdirectories that are subsequently created in the
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directory. If an existing directory has contained some files and
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subdirectories, modifying the attribute on the parent directory doesn't
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change the attributes on these files and subdirectories.
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.TP
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.B V
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A file with the 'V' attribute set has fs-verity enabled. It cannot be
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written to, and the file system will automatically verify all data read
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from it against a cryptographic hash that covers the entire file's
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contents, e.g. via a Merkle tree. This makes it possible to efficiently
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authenticate the file. This attribute may not be set or cleared using
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.BR chattr (1),
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although it can be displayed by
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.BR lsattr (1).
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.PP
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.SH AUTHOR
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.B chattr
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was written by Remy Card <Remy.Card@linux.org>. It is currently being
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maintained by Theodore Ts'o <tytso@alum.mit.edu>.
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.SH BUGS AND LIMITATIONS
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The 'c', 's', and 'u' attributes are not honored
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by the ext2, ext3, and ext4 file systems as implemented in the current
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mainline Linux kernels.
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Setting 'a' and 'i' attributes will not affect the ability to write
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to already existing file descriptors.
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.PP
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The 'j' option is only useful for ext3 and ext4 file systems.
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.PP
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The 'D' option is only useful on Linux kernel 2.5.19 and later.
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.SH AVAILABILITY
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.B chattr
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is part of the e2fsprogs package and is available from
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http://e2fsprogs.sourceforge.net.
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.SH SEE ALSO
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.BR lsattr (1),
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.BR btrfs (5),
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.BR ext4 (5),
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.BR mkfs.f2fs (8),
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.BR xfs (5).
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