Detailed explanation of chmod command usage in Linux

chmod Command Syntax

This is the correct syntax when using the chmod command:

chmod [options] mode [，mode] file1 [file2 ...]

Here are some common options used with chmod:

● -f, --silent, --quiet (suppress most error messages)

● -v, --verbose (output diagnostic information for each file processed)

● -c, --changes (similar to verbose but reports only when changes were made)

● -R, --recursive (recursively change files and directories)

● --help (show help and exit)

● --version (output version information and exit)

Below is a list of several numeric permissions that can be set for users, groups, and everyone else on the computer. Next to the number is the Read/Write/Execute letter equivalent.

● 7: indicates rwx, which has read, write and execute permissions

● 6: indicates rw-, which means read and write permissions

● 5: indicates rx, which has read and execute permissions

● 4: indicates r--, with read-only permission

● 3: means -wx, has write and execute permissions

● 2: means -w-, has write-only permission

● 1: indicates - x, only has execution permission

● 0: means ---, no permission

Note: If you need to list the permissions of a file, you need to use the ls command.

chmod Command Examples

If a user wants to change the permissions of the file "participants" so that everyone has full access to the file, they would enter the following command:

chmod 777 participants

Note: The first 7 sets the user's permissions, the second 7 sets the group's permissions, and the third 7 sets the permissions for other owners.

If the user wants to be the only one who can access it, he can use the following command:

chmod 700 participants

To provide full access permissions to yourself and your group members, you can use the following command:

chmod 770 participants

If a user wants to retain full access for themselves, but want to prevent others from modifying the file, they can use the following command:

chmod 755 participants

The following uses the letters above to change the permissions of the file "participants" so that the owner can read and write the file, but does not change the permissions for anyone else:

chmod u=rw participants

Setting Mode

Use the chmod command to set additional file system modes for files and directories. For example, to set the sticky bit — which means only the file owner, directory owner, or superuser can delete the file, regardless of the file's read-write group permissions — add 1 to the front of the number sequence:

chmod 1755 participants

other:

Users can also change the group ownership of existing files and folders using the chgrp command and the newgrp command to change the default group for new files and folders.

Remember that symbolic links used in the chmod command will affect the real target object.