Detailed explanation of viewing and setting file permissions on Mac

Preface

To modify file permissions in the terminal of a Mac system, use the chmod command in Linux. This article will introduce you to files and permissions under Unix and Linux. Let’s take a look at the detailed introduction.

Example

# Let's create a test directory first $ mkdir test && cd test
# Create a main.txt file and write some content $ echo hello world >> text.txt
# Create another empty directory $ mkdir js
# View information$ ls -l
total 8
drwxr-xr-x 2 frank staff 64 7 12 20:03 js # This line is the information of the js directory -rw-r--r-- 1 frank staff 13 7 12 19:52 main.txt # This line is the information of main.txt

As shown above, both files and directories have the following information:

# General format of permission information:
-rwxr-xr-x number user group filesize updatetime filename

The general format is divided into 7 parts, namely:

1. File attributes, indicating the file type, read/write/executable permissions, etc., a total of 10 characters;

• The first character indicates the type, and the following 9 characters are divided into 3 groups, indicating the read/write/executable permissions of the file relative to the current user (user), the group to which the current user belongs (group), and other users (other).
• rwx: represents permissions, - represents no permissions, r represents read permissions, w represents write permissions, and x represents execute permissions.
• Take the main.txt above as an example. The first character is -, which indicates the file type. The first character of the js directory is d, which indicates the directory.
• The next three characters are rw-, which means that the file is readable and writable for the current user, but not executable.
• The next three characters are r--, which means that the file has read-only permission for members of the group to which the current user belongs, and no write or executable permission.
• The last three characters are also r--, which means that other users can only read the file but cannot write or execute it.

2. number, which indicates the number of file inodes. Inode indicates the area where the original information of the file is stored.

3. user, indicating the current user name

4. group, indicating the name of the user group to which the current user belongs

5. filesize, indicating the size of the file in bytes

6. updatetime, indicating the last modification time of the file

7. filename, indicating the file name

Modify file permissions

The permissions of main.txt are -rw-r--r-- 1 frank staff 13 7 12 19:52 main.txt, and the permissions for other users are r--, which means they can only read but not write. What if there is a requirement to allow other users to write? At this time, you need to modify the permissions of main.txt so that other users can also perform write operations.

# Command format for modifying permissions $ [sudo] chmod [<permission range><permission operation><specific permissions>] [file or directory]

1. Scope of authority

• u: user, indicating the owner of the file or directory
• g: group, indicating the group to which the file or directory belongs
• o: other, except the file or directory owner or the group to which it belongs, other users belong to this range
• a: all, that is, all users, including the owner of the file or directory, the group to which it belongs, and other users

2. Permission Operation

• + indicates adding permissions
• - means cancel the permission
• = indicates the only setting permission

3. Specific permissions

• r means readable
• w means writable
• x means executable

Having explained so much, let's now use the command to allow other users to also have write permissions to main.txt:

# Allow other users to have write permissions $ chmod o+w main.txt
# Confirm$ ls -l main.txt
-rw-r--rw- 1 frank staff 13 7 12 19:52 main.txt

# Allow all users to have executable permissions, but not to modify or read $ chmod a+xrw main.txt
# Confirm again---x--x--x 1 frank staff 13 7 12 19:52 main.txt

Summarize

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