chattr - change file attributes on a Linux file system
chattr [ -RVf ] [ -v version ] [
-p project ] [ mode ] files...
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 directory 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),
mkfs.f2fs(8), and xfs(5) for more file system-specific
details.
- -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.
- 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 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 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 modified, 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 attribute.
- 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 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 possessing 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 written back to the disk. Note: please make sure to read the bugs and
limitations section at the end of this document.
- 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 file systems which
support tail-merging). 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 hierarchies 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
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.
- x
- A file with the 'x' requests the use of direct access (dax) mode, if the
kernel supports DAX. This can be overridden by the 'dax=never' mount
option. For more information see the kernel documentation for dax:
<https://www.kernel.org/doc/html/latest/filesystems/dax.html>.
- 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 cryptographic 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).
chattr was written by Remy Card
<Remy.Card@linux.org>. It is currently being maintained by Theodore
Ts'o <tytso@alum.mit.edu>.
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.
chattr is part of the e2fsprogs package and is available
from http://e2fsprogs.sourceforge.net.