How to Recursively Change File Permissions in Linux

• This article explains how to recursively change file permissions in Linux using the chmod command.

If you want to change the permissions of multiple files and directories in Linux, you can use the chmod command with the -R option. This option allows you to recursively apply the same permissions to all files and directories within a given path. In this article, you will learn how to use the chmod command with the -R option, what are the advantages and disadvantages of this method, and some common use cases and scenarios.

What is the chmod command?

The chmod command is a Linux command that allows you to change the access permissions of files and directories. The permissions control who can read, write, or execute the files and directories, as well as some special flags such as setuid, setgid, and sticky bit.

The syntax of the chmod command is:

chmod [options] mode file

Where:

• options are optional flags that modify the behavior of the command. For example, -v for verbose output, -c for changes only, or -f for silent mode.
• mode is a combination of symbols or numbers that specify the new permissions. For example, u+rwx for adding read, write, and execute permissions to the owner (user), or 755 for setting read, write, and execute permissions for the owner, and read and execute permissions for the group and others.
• file is the name of the file or directory whose permissions you want to change. You can also use wildcards (*) or multiple names separated by spaces.

How to use the -R option with chmod?

The -R option stands for recursive. It means that the chmod command will apply the same mode to all files and directories within the specified path. For example, if you want to change the permissions of all files and directories in your home directory to 644 (read and write for owner, read for group and others), you can use this command:

chmod -R 644 /home/username

This command will change the permissions of your home directory and all its subdirectories and files. However, this may not be what you want. For example, you may want to keep some directories or files with different permissions, such as executable scripts or hidden files. Also, changing all directories to 644 will make them inaccessible, as directories need execute permission to be entered.

Therefore, using the -R option with chmod requires caution and attention. You should always check what files and directories are affected by your command before executing it. You can use the find command or the ls -lR command to list all files and directories within a path and their current permissions.

How to change permissions of only files or only directories?

One way to avoid changing permissions of unwanted files or directories is to use the find command with the -type option. This option allows you to filter files by their type: regular file (-type f) or directory (-type d). For example, if you want to change the permissions of only regular files in your home directory to 644, you can use this command:

find /home/username -type f -exec chmod 644 {} \;

This command will find all regular files in your home directory and execute the chmod 644 command on each of them. The {} represents the name of each file found, and the \; terminates the command.

Similarly, if you want to change the permissions of only directories in your home directory to 755 (read, write, and execute for owner, read and execute for group and others), you can use this command:

find /home/username -type d -exec chmod 755 {} \;

This command will find all directories in your home directory and execute the chmod 755 command on each of them.

How to exclude some files or directories from changing permissions?

Another way to avoid changing permissions of unwanted files or directories is to use the -not option with the find command. This option allows you to negate a condition. For example, if you want to change the permissions of all files and directories in your home directory except those that start with a dot (.), which are usually hidden or configuration files, you can use this command:

find /home/username -not -name ".*" -exec chmod 644 {} \;

This command will find all files and directories in your home directory that do not match the pattern .*, which means any name that starts with a dot, and execute the chmod 644 command on each of them.

You can also combine multiple conditions with -and or -or options. For example, if you want to change the permissions of all files and directories in your home directory except those that are executable or have a .txt extension, you can use this command:

find /home/username -not -perm /a+x -and -not -name "*.txt" -exec chmod 644 {} \;

This command will find all files and directories in your home directory that do not have any execute permission (-perm /a+x) and do not match the pattern *.txt, which means any name that ends with .txt, and execute the chmod 644 command on each of them.

Frequently Asked Questions (FAQs)

Question: What is the difference between chmod and chown?

Answer: chmod stands for change mode, and it is used to change the permissions of files and directories. chown stands for change owner, and it is used to change the owner and group of files and directories. For example, if you want to change the owner of a file to alice and the group to users, you can use this command:

chown alice:users file

Question: How can I undo a chmod command?

Answer: There is no direct way to undo a chmod command, as Linux does not keep track of the previous permissions of files and directories. However, you can try to restore the original permissions by using backup tools, such as rsync or tar, that preserve the permissions of files and directories when copying or archiving them. Alternatively, you can manually change the permissions back to what they were before using the chmod command.

Question: How can I make a file or directory immutable?

Answer: Immutable means that a file or directory cannot be modified, deleted, or renamed, even by the root user. To make a file or directory immutable, you can use the chattr command with the +i option. This command will set the immutable flag on the file or directory, which means that it cannot be changed by any user or process. To remove the immutable flag, you can use the `-i` option instead of `+i`.

Question: What are the advantages and disadvantages of using the -R option with chmod?

Answer: Using the -R option with chmod can be useful in some situations, such as:

• When you want to quickly change the permissions of a large number of files and directories with the same mode.
• When you want to apply a consistent permission policy to a directory tree.
• When you want to fix incorrect or inconsistent permissions that may cause errors or security issues.

However, using the -R option with chmod can also have some drawbacks, such as:

• It can overwrite the existing permissions of files and directories that may have different purposes or requirements.
• It can affect hidden or special files and directories that may not be intended to be modified.
• It can cause unintended consequences, such as making directories inaccessible, breaking symbolic links, or changing executable scripts.

Therefore, using the -R option with chmod requires careful planning and testing before applying it to a production environment.

Summary

In this article, you learned how to use the chmod command in Linux to recursively change the permissions of files and directories. You also learned how to use the find command to filter files by type or name, and how to use the chattr command to make files or directories immutable. You also learned about the advantages and disadvantages of using the -R option with chmod, and some common use cases and scenarios.

Disclaimer: This article is for informational purposes only and does not constitute professional advice. The author is not responsible for any damages or losses caused by following the instructions or suggestions in this article. Always backup your data and test your commands before applying them to your system.