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 +-=[aAcCdDeFijPsStTu].
The operator '+' causes the selected attributes to be added to the ex-
isting attributes of the files; '-' causes them to be removed; and '='
causes them to be the only attributes that the files have.
The letters 'aAcCdDeFijPsStTu' 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 directory updates (D), extent format (e),
case-insensitive directory lookups (F), immutable (i), data journalling
(j), project hierarchy (P), secure deletion (s), synchronous updates
(S), no tail-merging (t), top of directory hierarchy (T), and un-
deletable (u).
The following attributes are read-only, and may be listed by lsattr(1)
but not modified by chattr: encrypted (E), indexed directory (I), in-
line data (N), and verity (V).
Not all flags are supported or utilized by all filesystems; refer to
filesystem-specific man pages such as btrfs(5), ext4(5), and xfs(5) for
more filesystem-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 attri-
bute.
A When a file with the 'A' attribute set is accessed, its atime
record is not modified. 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 uncom-
pressed data. A write to this file compresses data before stor-
ing them on the disk. Note: please make sure to read the bugs
and limitations section at the end of this document.
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 attri-
bute 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 equiva-
lent 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 en-
crypted by the filesystem. 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-insensi-
tive fashion. This attribute can only be changed in empty di-
rectories 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 modified, and the file can not be
opened in write mode. Only the superuser or a process possess-
ing the CAP_LINUX_IMMUTABLE capability can set or clear this at-
tribute.
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 journal 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 filesystem 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 possessing the
CAP_SYS_RESOURCE capability can set or clear this attribute.
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 hierarchi-
cal structure for project id's. This means that files and di-
rectories 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 desti-
nation directory match.
s When a file with the 's' attribute set is deleted, its blocks
are zeroed and written back to the disk. Note: please make sure
to read the bugs and limitations section at the end of this doc-
ument.
S When a file with the 'S' attribute set is modified, the changes
are written synchronously 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 filesystems which support tail-merging). This is neces-
sary for applications such as LILO which read the filesystem di-
rectly, and which don't understand tail-merged files. Note: As
of this writing, the ext2, ext3, and ext4 filesystems do not
support tail-merging.
T A directory with the 'T' attribute will be deemed to be the top
of directory hierarchies for the purposes of the Orlov block al-
locator. This is a hint to the block allocator used by ext3 and
ext4 that the subdirectories under this directory are not re-
lated, 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 subdirectories 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.
V A file with the 'V' attribute set has fs-verity enabled. It
cannot be written to, and the filesystem will automatically ver-
ify all data read from it against a cryptographic hash that cov-
ers 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@linux.org>. It is currently
being maintained by Theodore Ts'o <tytso@alum.mit.edu>.
BUGS AND LIMITATIONS
The 'c', 's', and 'u' attributes are not honored by the ext2, ext3,
and ext4 filesystems as implemented in the current mainline Linux ker-
nels. 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.sourceforge.net.
SEE ALSO
lsattr(1), btrfs(5), ext4(5), xfs(5).
E2fsprogs version 1.45.6 March 2020 CHATTR(1)