Linux - one command per day--chatt

DATE : 2012-12-22

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 +-=[acdeijstuADST].
       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  `acdeijstuADST'  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),   

                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.

       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  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 <[email protected]>.  It is currently
       being maintained by Theodore Ts'o <[email protected]>.

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 `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.

AILABILITY
       chattr  is  part  of  the  e2fsprogs  package  and  is  available  from  http://e2fsprogs.sourceforge.net.

SEE ALSO
       lsattr(1)

E2fsprogs version 1.41.12          May 2010                          CHATTR(1)