chattr is a not-well known command, but it can do very useful things with files attributes. In this post I will show you some examples.

Table of Contents

Installation

chattr is part of the e2fsprogs package, which is usually already installed on most Linux systems.

Usage

The basic syntax of chattr is:

chattr [options] [mode] <files>

To list the attributes of a file, use lsattr:

lsattr <files>
  • -R to do recursive listing.

Options

The most relevant option is -R to recursively change attributes of directories and their contents.

Mode (attributes)

The format of a mode consist of:

  • +, - or =: add attributes (+), remove them (-) or set only the specified ones (=).
  • One or more of the following letters: aAcCdDeFijmPsStTux. Check chattr man page for a full explanation of all available attributes.

For example:

# Add an attribute
chattr +i some_file

# Remove an attribute
chattr -i some_file

Now, I am going to explain some of the available attributes:

  • a: the file can only be opened in append mode. Only a superuser can set or clear this attribute. 
    $ echo "Hola" > test1
$ sudo chattr +a test1
$ echo "Adios" > test1
bash: test1: Operation not permitted
$ echo "Adios" >> test1
$ cat test1
Hola
Adios
  • A: don’t change access time when the file is accessed.
  • i: the file cannot be modified, deleted or renamed, and no link can be created using this file. The file cannot be opened in write mode. Only a superuser can set or clear this attribute. 
    $ sudo chattr +i test1
$ echo "Hasta luego" >> test1
bash: test1: Operation not permitted

Some attributes such as c (compress), s (overwrite with zeros when deleted) and u (save contents when deleted) don’t work on ext2/3/4 filesystems.

If you have any suggestion, feel free to contact me via social media or email.