Provided by: e2fsprogs_1.42.9-3ubuntu1.3_amd64 
NAME
chattr - change file attributes on a Linux file system
SYNOPSIS
chattr [ -RVf ] [ -v version ] [ mode ] files...
DESCRIPTION
chattr changes the file attributes on a Linux file system.
The format of a symbolic mode is +-=[acdeijstuACDST].
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 `acdeijstuACDST' select the new attributes for the files: append only (a), compressed (c), no
dump (d), extent format (e), immutable (i), data journalling (j), secure deletion (s), no tail-merging
(t), undeletable (u), no atime updates (A), no copy on write (C), synchronous directory updates (D),
synchronous updates (S), and top of directory hierarchy (T).
The following attributes are read-only, and may be listed by lsattr(1) but not modified by chattr: huge
file (h), compression error (E), indexed directory (I), compression raw access (X), and compressed dirty
file (Z).
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.
ATTRIBUTES
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 `a' attribute set can only be open in append mode for writing. Only the superuser or a
process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
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 the No_COW attribute.)
When a directory with the `D' attribute set is modified, the changes are written synchronously on the
disk; this is equivalent to the `dirsync' mount option applied to a subset of the files.
A file with the `d' attribute set is not candidate for backup when the dump(8) program is run.
The 'E' attribute is used by the experimental compression patches to indicate that a compressed file has
a compression error. It may not be set or reset using chattr(1), although it can be displayed by
lsattr(1).
The 'e' attribute indicates that the file is using extents for mapping the blocks on disk. It may not be
removed using chattr(1).
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 reset using chattr(1), although it can be displayed by lsattr(1).
The 'h' attribute indicates the file is storing its blocks in units of the filesystem blocksize instead
of in units of sectors, and means that the file is (or at one time was) larger than 2TB. It may not be
set or reset using chattr(1), although it can be displayed by lsattr(1).
A file with the `i' attribute cannot be modified: it cannot be deleted or renamed, no link can be created
to this file and no data can be written to the file. Only the superuser or a process possessing the
CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
A file with the `j' attribute has all of its data written to the ext3 journal before being written to the
file itself, if the filesystem is mounted with the "data=ordered" or "data=writeback" options. 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.
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 on the disk;
this is equivalent to the `sync' mount option applied to a subset of the files.
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.
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 or ext3 filesystems do not (yet, except in very experimental patches) support
tail-merging.
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.
The 'X' attribute is used by the experimental compression patches to indicate that a raw contents of a
compressed file can be accessed directly. It currently may not be set or reset using chattr(1), although
it can be displayed by lsattr(1).
The 'Z' attribute is used by the experimental compression patches to indicate a compressed file is dirty.
It may not be set or reset 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.
The `j' option is only useful if the filesystem is mounted as ext3.
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)