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 +-=[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      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_IMMUTABLE capability can set or clear this attri-
              bute.

       A      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.

       c      A file with the 'c' attribute set is automatically compressed on
              the  disk  by  the kernel.  A read from this file returns uncom-
              pressed data.  A write to this file compresses data before stor-
              ing  them  on the disk.  Note: please make sure to read the bugs
              and limitations section at the end of this document.

       C      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 attri-
              bute set.)

       d      A file with the 'd' attribute set is not a candidate for  backup
              when the dump(8) program is run.

       D      When  a  directory  with  the 'D' attribute set is modified, the
              changes are written synchronously to the disk; this  is  equiva-
              lent  to  the  'dirsync' mount option applied to a subset of the
              files.

       e      The 'e' attribute indicates that the file is using  extents  for
              mapping  the  blocks  on  disk.   It  may  not  be removed using
              chattr(1).

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

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

       i      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 possess-
              ing the CAP_LINUX_IMMUTABLE capability can set or clear this at-
              tribute.

       I      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 cleared using chattr(1), although it can be displayed by
              lsattr(1).

       j      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.

       N      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).

       P      A directory with the 'P' attribute set will enforce a hierarchi-
              cal  structure  for project id's.  This means that files and di-
              rectories created 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  ids  must  match.  In addition, a hard link to file can
              only be created when the project id for the file and the  desti-
              nation directory match.

       s      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 doc-
              ument.

       S      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.

       t      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  neces-
              sary for applications such as LILO which read the filesystem di-
              rectly, and which don't understand tail-merged files.  Note:  As
              of  this  writing,  the  ext2, ext3, and ext4 filesystems do not
              support tail-merging.

       T      A directory with the 'T' attribute will be deemed to be the  top
              of directory hierarchies for the purposes of the Orlov block al-
              locator.  This is a hint to the block allocator used by ext3 and
              ext4  that  the  subdirectories under this directory are not re-
              lated, 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.

       u      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.

       V      A file with the 'V' attribute set  has  fs-verity  enabled.   It
              cannot be written to, and the filesystem will automatically ver-
              ify all data read from it against a cryptographic hash that cov-
              ers  the  entire  file's contents, 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 1.45.6          March 2020                         CHATTR(1)

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