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
       existing 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
       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),
       inline 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
              attribute.

       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
              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.

       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
              attribute 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
              equivalent 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
              encrypted 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-
              insensitive fashion.  This attribute can only be changed in
              empty directories 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
              possessing the CAP_LINUX_IMMUTABLE capability can set or clear
              this attribute.

       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
              hierarchical structure for project id's.  This means that files
              and directories 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 destination 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
              document.

       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
              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.

       T      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.

       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
              verify all data read from it against a cryptographic hash that
              covers 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
       kernels.  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)