1. Computing
Linux / Unix Command: chattr
Command Library

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

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 pessessing 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.

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 behind 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 pessessing 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=journalled" 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.

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 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 who don't understand tail-merged files.

When a file with the `u' attribute set is deleted, its contents are saved. This allows the user to ask for its undeletion.

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).

SEE ALSO

lsattr(1)


Important: Use the man command (% man) to see how a command is used on your particular computer.

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