chattr

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 +-=[aAcCdDeFijPsStTu].

       The  operator '+' causes the selected attributes to be added to the ex-
       isting attributes of the files; '-' causes them to be removed; and  '='
       causes them to be the only attributes that the files have.

       The letters 'aAcCdDeFijPsStTu' 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),
       case-insensitive directory lookups (F), immutable (i), data journalling
       (j),  project  hierarchy  (P), secure deletion (s), synchronous updates
       (S), no tail-merging (t), top  of  directory  hierarchy  (T),  and  un-
       deletable (u).

       The  following attributes are read-only, and may be listed by lsattr(1)
       but not modified by chattr: encrypted (E), indexed directory  (I),  in-
       line data (N), and verity (V).

       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 opened in append mode for
       writing.  Only the superuser or a process possessing the  CAP_LINUX_IM-
       MUTABLE 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 a 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 to  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).

       A file, directory, or symlink with the 'E' attribute set  is  encrypted
       by  the  filesystem.   This  attribute  may not be set or cleared using
       chattr(1), although it can be displayed by lsattr(1).

       A directory with the 'F' attribute set  indicates  that  all  the  path
       lookups  inside  that directory are made in a case-insensitive fashion.
       This attribute can only be changed in empty directories on file systems
       with the casefold feature enabled.

       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_IM-
       MUTABLE 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 cleared
       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  cleared
       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, re-
       name 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 ze-
       roed 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 to 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, ext3, and ext4
       filesystems do not support tail-merging.

       A directory with the 'T' attribute will be deemed to be the top of  di-
       rectory  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.

       A  file with the 'V' attribute set has fs-verity enabled.  It cannot be
       written to, and the filesystem will automatically verify all data  read
       from it against a cryptographic hash that covers the entire file's con-
       tents, e.g. via a Merkle tree.  This makes it possible  to  efficiently
       authenticate  the file.  This attribute may not be set or cleared 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  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 1.45.5         January 2020                        CHATTR(1)