What is the chattr command in Linux? How to use (code example)

We know that Linux is a multi-user operating system, and users can delete files that another user cares about very much, such as an administrator. To avoid this situation, Linux provides the "chattr" command. Next, we will introduce the chattr command in detail, so that everyone can briefly understand how to use the chattr command.

What is the chattr command in Linux?

The chattr command in Linux is a file system command used to change the attributes of files in a directory. The main use of this command is to make multiple files unable to be changed by users other than superuser.

To put it simply, the 'chattr' command can make the file immutable, non-deletable, only appendable, etc.!

The syntax of chattr

#chattr [operator] [flags] [filename]

At the beginning of the flags string of the chattr command, one of the following operators must appear:

1. ' ': Add the selected attributes to the existing attributes of the file.

2. ' - ': Delete the selected attribute.

3. ' = ': Make the selected attribute the only attribute of the file.

The following is a list of common properties and associated flags (flags strings) that can be set or unset using the chattr command:

A: The atime record was not updated.

S: Changes are updated synchronously on disk.

a: Files can only be opened for writing in append mode.

i: File cannot be modified (immutable), only superuser can unset attributes.

j: All file information is updated to the ext3 log before updating to the file itself.

t: Tail merging is not allowed.

d: There are no more backup candidates when running the dump process.

u: When such a file is deleted, its data is saved, allowing the user to ask it to cancel the deletion.

However, all the above commands are not eligible for files and can be used on directories (folders) to protect the directories from deletion or any other similar mishaps. However, when protecting directories, it is recommended to use the flag -R' to recursively protect everything in the specified directory.

The following are the different options for the chattr command:

-R: Used to recursively display list properties of directories and their contents.

-V: It will show the version of the program.

-a: Used to list all files in a directory, including directories whose names begin with a period ('.').

-d: This option lists the directory as a regular file instead of listing its contents.

-v: Used to display the version/generation number of the file, etc.

How to use the Chattr command?

#1. Add attributes to the file

Create a new file to test it. For example, a new file tecadmin.txt was created using the touch command and 777 permissions were assigned to the file.

# touch tecadmin.txt
# chmod 777 tecadmin.txt
# ls -l tecadmin.txt
-rwxrwxrwx 1 root root 0 Apr 10 13:10 tecadmin.txt

Now enable i file attributes

# chattr +i tecadmin.txt

Since we have enabled i file attributes, let us try to delete this file, we will receive the following error prompted by rm, even though the file has 777 permissions.

# rm -f tecadmin.txt
rm: cannot remove `tecadmin.txt': Operation not permitted

2. Delete the attributes of the file

To clear the attributes of the file, just use the (-) symbol of the attached attribute. For example in tecadmin.txt.

# chattr -i tecadmin.txt
# lsattr tecadmin.txt
------------- tecadmin.txt

3. Protect the directory

The flag i' can be used on the directory (as shown below) to make the directory immutable; the flag -R' is used so that the call is Recursive so that all subfiles and directories are also immutable. This protects the entire directory and its files. Example: folder folder

#chattr -R + i  folder/

Now delete/delete the folder and its files, you will receive the following error prompted by rm

#rm -rf folder / 
rm: cannot remove ‘ folder/’ : Operation not permitted

Use the '-R' switch again, '-i' flag and the full path to the folder to unset permissions.

# chattr -R -i folder/
# rm -rf folder/

The folder directory is successfully deleted.

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