Provided by: e2fsprogs_1.45.5-2ubuntu1.2_amd64 
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 existing 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
undeletable (u).
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 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 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.
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.
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.
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.)
A file with the 'd' attribute set is not a candidate for backup when the dump(8) program
is run.
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.
The 'e' attribute indicates that the file is using extents for mapping the blocks on disk.
It may not be removed using chattr(1).
A file, directory, or symlink with the 'E' attribute set is encrypted by the filesystem.
This attribute may not be set or cleared using chattr(1), although it can be displayed by
lsattr(1).
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.
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.
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).
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.
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).
A directory with the 'P' attribute set will enforce a hierarchical structure for project
id's. This means that files and directory 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 id's much match. In addition, a hard
link to file can only be created when the project id for the file and the destination
directory match.
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.
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.
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
necessary for applications such as LILO which read the filesystem directly, and which
don't understand tail-merged files. Note: As of this writing, the ext2, ext3, and ext4
filesystems do not support tail-merging.
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.
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.
A file with the 'V' attribute set has fs-verity enabled. It cannot be written to, and the
filesystem 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).
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 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.sourceforge.net.
SEE ALSO
lsattr(1), btrfs(5), ext4(5), xfs(5).