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 +-=[aAcCdDeFijmPsStTux].

       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 'aAcCdDeFijmPsStTux' 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 journaling
       (j), don't compress (m), project hierarchy (P), secure deletion (s),
       synchronous updates (S), no tail-merging (t), top of directory hierarchy
       (T), undeletable (u), and direct access for files (x).

       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 file systems; refer to
       file system-specific man pages such as btrfs(5), ext4(5), and xfs(5) for
       more file system-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.  (Note: For
              btrfs, If the 'c' flag is set, then the 'C' flag cannot be set.
              Also conflicts with btrfs mount option 'nodatasum')

       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. If the 'C' flag
              is set, then the 'c' flag cannot be 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 file system.  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 file system 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.

       m      A file with the 'm' attribute is excluded from compression on file
              systems that support per-file compression.

       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
              file systems which support tail-merging).  This is necessary for
              applications such as LILO which read the file system directly, and
              which don't understand tail-merged files.  Note: As of this
              writing, the ext2, ext3, and ext4 file systems 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.

       x      The 'x' attribute can be set on a directory or file.  If the
              attribute is set on an existing directory, it will be inherited by
              all files and subdirectories that are subsequently created in the
              directory.  If an existing directory has contained some files and
              subdirectories, modifying the attribute on the parent directory
              doesn't change the attributes on these files and subdirectories.

       V      A file with the 'V' attribute set has fs-verity enabled.  It
              cannot be written to, and the file system 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 file systems 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 1.46.4           August 2021                         CHATTR(1)