chattr(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ATTRIBUTES | AUTHOR | BUGS AND LIMITATIONS | AVAILABILITY | SEE ALSO | COLOPHON

CHATTR(1)                  General Commands Manual                 CHATTR(1)

NAME         top

       chattr - change file attributes on a Linux file system

SYNOPSIS         top

       chattr [ -RVf ] [ -v version ] [ -p project ] [ mode ] files...

DESCRIPTION         top

       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         top

       -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         top

       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         top

       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         top

       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         top

       chattr is part of the e2fsprogs package and is available from
       http://e2fsprogs.sourceforge.net.

SEE ALSO         top

       lsattr(1), btrfs(5), ext4(5), xfs(5).

COLOPHON         top

       This page is part of the e2fsprogs (utilities for ext2/3/4
       filesystems) project.  Information about the project can be found at
       ⟨http://e2fsprogs.sourceforge.net/⟩.  It is not known how to report
       bugs for this man page; if you know, please send a mail to
       man-pages@man7.org.  This page was obtained from the project's
       upstream Git repository
       ⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on 2020-06-09.
       (At that time, the date of the most recent commit that was found in
       the repository was 2020-03-21.)  If you discover any rendering prob‐
       lems in this HTML version of the page, or you believe there is a bet‐
       ter or more up-to-date source for the page, or you have corrections
       or improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to man-pages@man7.org

E2fsprogs version 1.46-WIP       March 2020                        CHATTR(1)

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