Linux chattr Command – Change File Attributes
The chattr (change attribute) command in Linux is used to modify file attributes, which control the behavior of files in the filesystem. It is primarily used to protect files from being accidentally deleted or altered and can be particularly useful for system administrators and security-conscious users.
Syntax of chattr
OPTIONS→ Flags that define the attributes to be set or removed.FILE→ The file or directory whose attributes you want to modify.
Common File Attributes in Linux
Here are some of the most common attributes that can be set using chattr:
| Attribute | Description |
|---|---|
+i | Makes the file immutable, preventing it from being modified or deleted. |
-i | Removes the immutable attribute, allowing the file to be modified. |
+a | Makes the file append-only, meaning only append operations are allowed. |
-a | Removes the append-only attribute, allowing regular file modifications. |
+e | Makes the file exclusive-use, preventing other processes from using it while open. |
-e | Removes the exclusive-use attribute. |
+s | Makes the file secure-delete, so it is deleted securely and cannot be recovered. |
-s | Removes the secure-delete attribute. |
+u | Makes the file undeletable by ordinary users, even with root privileges. |
-u | Removes the undeletable attribute. |
+j | Enables journaled file updates, so the file is updated in the journal. |
-j | Removes the journaled file updates attribute. |
Basic Usage of chattr
1. Make a File Immutable (+i)
To prevent a file from being modified or deleted, you can set the immutable attribute:
Example:
After this, even the root cannot delete or modify important_file.txt unless the immutable attribute is removed.
2. Remove the Immutable Attribute (-i)
To allow modifications again, remove the immutable attribute:
Example:
3. Make a File Append-Only (+a)
To allow only appending data to a file, use the append-only attribute:
This ensures that the file can only be modified by appending new data, and existing data cannot be altered or deleted.
4. Make a File Securely Deleted (+s)
To ensure a file is securely deleted and cannot be recovered, use the secure-delete attribute:
When deleted, the file will be overwritten before removal to prevent recovery.
5. Check the Attributes of a File (lsattr)
To check the current attributes of a file, use the lsattr command:
Example:
Output might look like:
This shows that the file is immutable and exclusive-use.
Examples
1. Set Multiple Attributes
To make a file immutable and append-only at the same time:
2. Recursively Set Attributes for a Directory
To apply an attribute to all files in a directory:
This will make every file inside the directory immutable.
Important Notes on chattr
- Root Access: Most
chattrcommands require root (superuser) privileges to modify file attributes, especially for system files. - Filesystem Support: The
chattrcommand works only on filesystems that support extended attributes (such asext2,ext3, andext4). It will not work on other filesystems likeNTFSorFAT32. - Immutable Files: Files with the
+iattribute cannot be moved, renamed, or deleted, even by root. This is a useful protection against accidental or malicious deletion. - Append-Only Files: Files with the
+aattribute can only be appended to, not modified or truncated, making it useful for logging purposes.
Conclusion
The chattr command is a powerful tool for setting file attributes that control access and modification of files, especially for system administrators who need to protect sensitive files or logs. By using attributes like +i (immutable) or +a (append-only), you can prevent unauthorized changes or accidental deletions.
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