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CHATTR(1) General Commands Manual CHATTR(1)
NAME
chattr - change file attributes on a Linux file system
SYNOPSIS
chattr [ -RVf ] [ -v version ] [ -p project ] [ mode ] files...
DESCRIPTION
chattr changes the file attributes on a Linux file system.
The format of a symbolic mode is +-=[aAcCdDeFijmPsStTux].
The operator '+' causes the selected attributes to be added to the existing attributes of
the files; '-' causes them to be removed; and '=' causes them to be the only attributes
that the files have.
The letters 'aAcCdDeFijmPsStTux' select the new attributes for the files: append only (a),
no atime updates (A), compressed (c), no copy on write (C), no dump (d), synchronous di-
rectory updates (D), extent format (e), case-insensitive directory lookups (F), immutable
(i), data journaling (j), don't compress (m), project hierarchy (P), secure deletion (s),
synchronous updates (S), no tail-merging (t), top of directory hierarchy (T), undeletable
(u), and direct access for files (x).
The following attributes are read-only, and may be listed by lsattr(1) but not modified by
chattr: encrypted (E), indexed directory (I), inline data (N), and verity (V).
Not all flags are supported or utilized by all file systems; refer to file system-specific
man pages such as btrfs(5), ext4(5), and xfs(5) for more file system-specific details.
OPTIONS
-R Recursively change attributes of directories and their contents.
-V Be verbose with chattr's output and print the program version.
-f Suppress most error messages.
-v version
Set the file's version/generation number.
-p project
Set the file's project number.
ATTRIBUTES
a A file with the 'a' attribute set can only be opened in append mode for writing.
Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can
set or clear this attribute.
A When a file with the 'A' attribute set is accessed, its atime record is not modi-
fied. This avoids a certain amount of disk I/O for laptop systems.
c A file with the 'c' attribute set is automatically compressed on the disk by the
kernel. A read from this file returns uncompressed data. A write to this file
compresses data before storing them on the disk. Note: please make sure to read
the bugs and limitations section at the end of this document. (Note: For btrfs, If
the 'c' flag is set, then the 'C' flag cannot be set. Also conflicts with btrfs
mount option 'nodatasum')
C A file with the 'C' attribute set will not be subject to copy-on-write updates.
This flag is only supported on file systems which perform copy-on-write. (Note:
For btrfs, the 'C' flag should be set on new or empty files. If it is set on a
file which already has data blocks, it is undefined when the blocks assigned to the
file will be fully stable. If the 'C' flag is set on a directory, it will have no
effect on the directory, but new files created in that directory will have the
No_COW attribute set. If the 'C' flag is set, then the 'c' flag cannot be set.)
d A file with the 'd' attribute set is not a candidate for backup when the dump(8)
program is run.
D When a directory with the 'D' attribute set is modified, the changes are written
synchronously to the disk; this is equivalent to the 'dirsync' mount option applied
to a subset of the files.
e The 'e' attribute indicates that the file is using extents for mapping the blocks
on disk. It may not be removed using chattr(1).
E A file, directory, or symlink with the 'E' attribute set is encrypted by the file
system. This attribute may not be set or cleared using chattr(1), although it can
be displayed by lsattr(1).
F A directory with the 'F' attribute set indicates that all the path lookups inside
that directory are made in a case-insensitive fashion. This attribute can only be
changed in empty directories on file systems with the casefold feature enabled.
i A file with the 'i' attribute cannot be modified: it cannot be deleted or renamed,
no link can be created to this file, most of the file's metadata can not be modi-
fied, and the file can not be opened in write mode. Only the superuser or a
process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attri-
bute.
I The 'I' attribute is used by the htree code to indicate that a directory is being
indexed using hashed trees. It may not be set or cleared using chattr(1), although
it can be displayed by lsattr(1).
j A file with the 'j' attribute has all of its data written to the ext3 or ext4 jour-
nal before being written to the file itself, if the file system is mounted with the
"data=ordered" or "data=writeback" options and the file system has a journal. When
the file system is mounted with the "data=journal" option all file data is already
journalled and this attribute has no effect. Only the superuser or a process pos-
sessing the CAP_SYS_RESOURCE capability can set or clear this attribute.
m A file with the 'm' attribute is excluded from compression on file systems that
support per-file compression.
N A file with the 'N' attribute set indicates that the file has data stored inline,
within the inode itself. It may not be set or cleared using chattr(1), although it
can be displayed by lsattr(1).
P A directory with the 'P' attribute set will enforce a hierarchical structure for
project id's. This means that files and directories created in the directory will
inherit the project id of the directory, rename operations are constrained so when
a file or directory is moved into another directory, that the project ids must
match. In addition, a hard link to file can only be created when the project id
for the file and the destination directory match.
s When a file with the 's' attribute set is deleted, its blocks are zeroed and writ-
ten back to the disk. Note: please make sure to read the bugs and limitations sec-
tion at the end of this document.
S When a file with the 'S' attribute set is modified, the changes are written syn-
chronously to the disk; this is equivalent to the 'sync' mount option applied to a
subset of the files.
t A file with the 't' attribute will not have a partial block fragment at the end of
the file merged with other files (for those file systems which support tail-merg-
ing). This is necessary for applications such as LILO which read the file system
directly, and which don't understand tail-merged files. Note: As of this writing,
the ext2, ext3, and ext4 file systems do not support tail-merging.
T A directory with the 'T' attribute will be deemed to be the top of directory hier-
archies for the purposes of the Orlov block allocator. This is a hint to the block
allocator used by ext3 and ext4 that the subdirectories under this directory are
not related, and thus should be spread apart for allocation purposes. For example
it is a very good idea to set the 'T' attribute on the /home directory, so that
/home/john and /home/mary are placed into separate block groups. For directories
where this attribute is not set, the Orlov block allocator will try to group subdi-
rectories closer together where possible.
u When a file with the 'u' attribute set is deleted, its contents are saved. This
allows the user to ask for its undeletion. Note: please make sure to read the bugs
and limitations section at the end of this document.
x The 'x' attribute can be set on a directory or file. If the attribute is set on an
existing directory, it will be inherited by all files and subdirectories that are
subsequently created in the directory. If an existing directory has contained some
files and subdirectories, modifying the attribute on the parent directory doesn't
change the attributes on these files and subdirectories.
V A file with the 'V' attribute set has fs-verity enabled. It cannot be written to,
and the file system will automatically verify all data read from it against a cryp-
tographic hash that covers the entire file's contents, e.g. via a Merkle tree.
This makes it possible to efficiently authenticate the file. This attribute may
not be set or cleared using chattr(1), although it can be displayed by lsattr(1).
AUTHOR
chattr was written by Remy Card <Remy.Card AT linux.org>. It is currently being maintained
by Theodore Ts'o <tytso AT alum.edu>.
BUGS AND LIMITATIONS
The 'c', 's', and 'u' attributes are not honored by the ext2, ext3, and ext4 file systems
as implemented in the current mainline Linux kernels. Setting 'a' and 'i' attributes will
not affect the ability to write to already existing file descriptors.
The 'j' option is only useful for ext3 and ext4 file systems.
The 'D' option is only useful on Linux kernel 2.5.19 and later.
AVAILABILITY
chattr is part of the e2fsprogs package and is available from http://e2fsprogs.source-
forge.net.
SEE ALSO
lsattr(1), btrfs(5), ext4(5), xfs(5).
E2fsprogs version 1.46.5 December 2021 CHATTR(1)
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