chattr
change file attributes on a Linux file system
see also :
lsattr
Synopsis
chattr [
-RVf ] [ -v version ] [
mode ] files...
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description
chattr
changes the file attributes on a Linux file system.
The format of a
symbolic mode is +-=[acdeijstuACDST].
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
’acdeijstuACDST’ select the new attributes for
the files: append only (a), compressed (c), no dump (d),
extent format (e), immutable (i), data journalling (j),
secure deletion (s), no tail-merging (t), undeletable (u),
no atime updates (A), no copy on write (C), synchronous
directory updates (D), synchronous updates (S), and top of
directory hierarchy (T).
The following
attributes are read-only, and may be listed by
lsattr(1) but not modified by chattr: huge file (h),
compression error (E), indexed directory (I), compression
raw access (X), and compressed dirty file (Z).
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
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 ’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.
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.)
When a directory with the ’D’ attribute set is modified, the
changes are written synchronously on the disk; this is equivalent
to the ’dirsync’ mount option applied to a subset of the files.
A file with the ’d’ attribute set is not candidate for backup
when the dump(8) program is run.
The ’E’ attribute is used by the experimental compression patches
to indicate that a compressed file has a compression error. It
may not be set or reset using chattr(1), although it can
be displayed by lsattr(1).
The ’e’ attribute indicates that the file is using extents for
mapping the blocks on disk. It may not be removed using
chattr(1).
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).
The ’h’ attribute indicates the file is storing its blocks in
units of the filesystem blocksize instead of in units of sectors,
and means that the file is (or at one time was) larger than 2TB.
It may not be set or reset using chattr(1), although it
can be displayed by lsattr(1).
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.
A file with the ’j’ attribute has all of its data written to the
ext3 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.
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 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.
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.
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 a raw contents of a compressed 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).
availability
chattr is part of the e2fsprogs package and is available
from http://e2fsprogs.sourceforge.net.
bugs and limitations
The ’c’, ’s’, and ’u’ attributes are not honored by the ext2 and
ext3 filesystems as implemented in the current mainline Linux
kernels.
The ’j’ option is only useful if the filesystem is mounted as
ext3.
The ’D’ option is only useful on Linux kernel 2.5.19 and later.
see also
lsattr
author
chattr
was written by Remy Card <Remy.Card[:at:]linux[:dot:]org>. It is
currently being maintained by Theodore Ts’o
<tytso[:at:]alum.mit[:dot:]edu>.