CHATTR(1) General Commands Manual CHATTR(1)
NAME
chattr - change file attributes on a Linux file system
SYNOPSIS
chattr [ -RVf ] [ -v version ] [ mode ] files...
DESCRIPTION
chattr changes the file attributes on a Linux file system.
The format of a symbolic mode is +-=[aAcCdDeijsStTu].
The operator '+' causes the selected attributes to be added to the existing attributes of the files; '-'
causes them to be removed; and
The letters 'aAcCdDeijsStTu' 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),
immutable (i), data journalling (j), 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: compression
error (E), huge file (h), indexed directory (I), inline data (N), compression raw access (X), and compressed
dirty file (Z).
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.
ATTRIBUTES
A file with the 'a' attribute set can only be open in append mode for writing. Only the superuser or a
process possessing the CAP_LINUX_IMMUTABLE 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 systems.
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 the No_COW attribute.)
A file with the 'd' attribute set is not 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 on the disk;
A file with the 'i' attribute cannot be modified: it cannot be deleted or renamed, no link can be created to
this file and no data can be written to the file. Only the superuser or a process possessing the
CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
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 reset 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 filesystem is mounted with the "data=ordered" or "data=writeback" options. 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 reset using chattr(1), although it can be displayed by lsattr(1).
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.
When a file with the 'S' attribute set is modified, the changes are written synchronously on 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 or ext3 filesystems do not (yet, except in very experimental patches) support tail-merging.
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 subdirecto‐
ries 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.
The 'X' attribute is used by the experimental compression patches to indicate that the raw contents of a com‐
pressed file can be accessed directly. It currently may not be set or reset using chattr(1), although it can
be displayed by lsattr(1).
The 'Z' attribute is used by the experimental compression patches to indicate a compressed file is dirty. It
may not be set or reset using chattr(1), although it can be displayed by lsattr(1).
AUTHOR
chattr was written by Remy Card <[email protected]>. It is currently being maintained by Theodore Ts'o
<[email protected]>.
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.
The 'j' option is only useful if the filesystem is mounted as ext3 or ext4.
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