CHATTR(1)

NAME
chattr - change file attributes on a Linux file system

SYNOPSIS
chattr [ -RVf ] [ -v version ] [ -b cluster_size ] [ -m compression_method ] [ mode ] files...

DESCRIPTION
chattr changes the file attributes on a Linux file system.

The format of a symbolic mode is +-=[acdeijstuABDESTXZ].

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 `acdeijstuABDESTXZ' 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), contains compressed clusters (B), synchronous directory updates (D), compression error (E), synchronous updates (S), top of directory hierarchy (T), disable de/compression on I/O (X), and requires compression (Z).

The following attributes are read-only, and may be listed by lsattr(1) but not modified by chattr: huge file (h), contains compressed clusters (B), 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.

-b cluster_size
    Set the cluster size for compressed files. The only supported cluster sizes are 4, 8, 16 or 32 blocks per cluster. Depending on the file system and/or the kernel, some of these values may not be supported.

-m compression_method
    Set the algorithm used for compression. Currently, the only supported algorithms are `bzip2', `lzo1x1', `lzrw3a', `lzv1', and `gzip1', `gzip2', ..., `gzip9' (where the number is equivalent to the compression level used for gzip). The name `lzv' is an alias for `lzv1', `gzip' is an alias for `gzip6', `lzo' is an alias for `lzo1x1', and `bzip' is an alias for `bzip2'. Not all kernels have support for all compression methods.

There are also some `pseudo-compression methods': `defer', `none' (an alias for `defer'), `never', and `auto' (which, at present, is just an alias for the kernel's default compression method). Depending on the kernel in use, some of these values may not be supported.

Unless the file is uncompressed (ie. compressed with method `none' or `defer'), changing the compression algorithm will not cause existing compressed clusters to be recompressed using that algorithm; it only changes the default algorithm that will be used for any new or newly- modified clusters.

Setting the compression method to `never' will immediately decompress the entire file and disallow any further algorithm changes while the `c' attribute remains set.

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. The `B' attribute is used by the experimental compression patches to indicate that a file contains compressed clusters (or more accurately, that it contains clusters that the kernel regards as compressed, although in practice they may be `compressed' using algorithm `none'). The `B' attribute may not be set or reset using chattr(1), although it can be displayed by lsattr(1).

A file with the `c' attribute set is automatically compressed on the disk by the kernel as soon as possible. A read from this file returns uncompressed data. A write to this file is followed by an attempt to compress the data written. Note: please make sure to read the bugs and limitations section at the end of this document.

Clearing the `c' attribute will cause a file to be decompressed as soon as possible, although it may not clear the `B' attribute unless `-m never' is also specified.

Directories also can be marked with the `c' attribute; in such a case, nothing is compressed, but any newly created file in the directory will automatically be marked with the `c' attribute. Similarly, a directory can be given an algorithm name and/or cluster size, so that newly created files will use this algorithm / cluster size. New files in the directory will only inherit the flags if they get a new inode, not if they are simply given a new link in that directory (e.g. with `mv' or `ln').

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.

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.

The `Z' attribute is used by the experimental compression patches to indicate a compressed file is dirty (ie. that compression or decompression is pending). 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>. Modifications to display information related to file compression were written by Antoine de Maricourt <dumesnil@etca.fr>.

BUGS AND LIMITATIONS
The `c', 's', and `u' attributes are not honored by the ext2 and ext3 filesystems as implemented in the current mainline Linux kernels. These attributes may be implemented in future versions of the ext2 and ext3 filesystems.

The `c' attribute is implemented in the kernel if the e2compr patch has been applied. The -m and -b options are also accepted only if the patch has been applied.

It is currently not possible to change the cluster size for an already compressed file. You must first decompress the file, and then compress it again with the new cluster size.

Changing the compression algorithm will not recompress the already compressed clusters with the new algorithm. Only newly written data will be compressed with the new algorithm. If you want to recompress the complete file with the new algorithm, you must first decompress it, and then recompress it with the new algorithm.

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
This version of chattr is modified for the e2compr project. The original version is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.

SEE ALSO
lsattr(1) e2compress(1) (not for use with e2compr-0.4), e2ratio(1),