chattr(1)



CHATTR(1)                   General Commands Manual                  CHATTR(1)

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 +-=[aAcCdDeijPsStTu].

       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 'aAcCdDeijPsStTu' 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),
       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), and
       inline data (N).

       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 open 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 sys-
       tems.

       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 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  on  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).

       The  'E'  attribute  is  used by the experimental encryption patches to
       indicate that the file has been encrypted.  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,  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 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).

       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  reset
       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  cre-
       ated  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 on 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 or ext3 filesys-
       tems do not (yet, except in very experimental  patches)  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.

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  ker-
       nels.   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).

E2fsprogs version 1.44.4          August 2018                        CHATTR(1)

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