chattr Man page

Resume Wikipedia de Chattr

chattr est une commande Linux qui permet à un utilisateur de définir certains attributs sur un fichier présent dans divers systèmes de fichiers. Le pendant BSD de cette commande est chflags. La commande est similaire à attrib sous DOS, OS/2 ou Microsoft Windows. Les commandes chatr sur HP-UX et chattr sur AIX n’ont rien à voir avec la commande de cet article.
Les commandes chattr et lsattr sous Linux et les attributs manipulés étaient, à l’origine, propres à la deuxième génération de l’Extended File System (ext2, ext3 et ext4), et sont disponibles à travers le package e2fsprogs. Depuis sa création, le support d’autres systèmes de fichier a été ajouté, notamment pour XFS, ReiserFS, JFS, bien que tous les attributs ne sont pas encore gérés.
Cette commande peut être utilisée pour protéger des fichiers de la suppression (notamment pendant des mises à jour système) grâce au bit d’immutabilité.

Resume Wikipedia de Chattr

chattr est une commande Linux qui permet à un utilisateur de définir certains attributs sur un fichier présent dans divers systèmes de fichiers. Le pendant BSD de cette commande est chflags. La commande est similaire à attrib sous DOS, OS/2 ou Microsoft Windows. Les commandes chatr sur HP-UX et chattr sur AIX n’ont rien à voir avec la commande de cet article.
Les commandes chattr et lsattr sous Linux et les attributs manipulés étaient, à l’origine, propres à la deuxième génération de l’Extended File System (ext2, ext3 et ext4), et sont disponibles à travers le package e2fsprogs. Depuis sa création, le support d’autres systèmes de fichier a été ajouté, notamment pour XFS, ReiserFS, JFS, bien que tous les attributs ne sont pas encore gérés.
Cette commande peut être utilisée pour protéger des fichiers de la suppression (notamment pendant des mises à jour système) grâce au bit d’immutabilité.

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
‘=’ causes them to be the only attributes that the files have.

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
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 sys‐
tems.

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; this is equivalent to the
‘dirsync’ mount option applied to a subset of the files.

The ‘e’ attribute indicates that the file is using extents for mapping
the blocks on disk. It may not be removed using chattr.

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, although it can be displayed by
lsattr.

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, although it can be displayed by lsattr.

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 direc‐
tory is being indexed using hashed trees. It may not be set or reset
using chattr, although it can be displayed by lsattr.

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 capa‐
bility 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, although it can be displayed by lsattr.

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 filesys‐
tems 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
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.

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 compressed file can be accessed
directly. It currently may not be set or reset using chattr,
although it can be displayed by lsattr.

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, although it can be displayed by lsattr.

AUTHOR

chattr was written by Remy Card . It is currently
being maintained by Theodore Ts’o .

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 ker‐
nels.

The ‘j’ option is only useful if the filesystem is mounted as ext3 or
ext4.

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

E2fsprogs version 1.42.13 May 2015 CHATTR(1)