LinuxGuide.it > Linux Man Page: "chattr"

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man page(1) manual page Table of Contents

Name

chattr - change file attributes on a Linux second extended file system

Synopsis

chattr [ -RV ] [ -v version ] [ mode ] files...

Description

chattr changes the file attributes on a Linux second extended file system.

The format of a symbolic mode is +-=[ASacDdIijsTtu].

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 ‘acdijsuADST’ select the new attributes for the files: append only (a), compressed (c), no dump (d), immutable (i), data journalling (j), secure deletion (s), no tail-merging (t), undeletable (u), no atime updates (A), synchronous directory updates (D), synchronous updates (S), and top of directory hierarchy (T).

Options

-R: Recursively change attributes of directories and their contents. Symbolic links encountered during recursive directory traversals are ignored.
-V: Be verbose with chattr’s output and print the program version.
-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.

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 ’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 ‘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 (which is used in on systems with Linux 2.5.46 or later).

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 tailmerging.

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) .

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 and ext3 filesystems as implemented in the current mainline Linux kernels. These attributes may be implemented in future versions of the ext2 and ext3 filesystems.

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.

Availability

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