chattr man page on Gentoo

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CHATTR(1)							     CHATTR(1)

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-merg‐
       ing (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 sys‐
       tems.

       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 direc‐
       tory 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 supe‐
       ruser 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 filesys‐
       tems 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 and  ext3
       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)

E2fsprogs version 1.42.7	 January 2013			     CHATTR(1)
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