What does the command 'chmod 755 filename' do?

The command 'chmod 755 filename' modifies the permissions of the specified file or directory, denoted by 'filename.' The numeric representation '755' specifies the permission levels for the file owner, the group, and others.

In this case, the number '7' for the owner corresponds to read (4), write (2), and execute (1) permissions combined (4 + 2 + 1 = 7). This means that the owner has full access to the file, being able to read, modify, and execute it. The second number '5' pertains to the group, which allows for read (4) and execute (1) permissions only (4 + 1 = 5). Consequently, the group members can read the file and execute it, but they cannot modify it. The final '5' applies to others, providing them with the same permissions as the group—read and execute, but no write permission.

This command is frequently used to set appropriate access levels, enabling the owner to manage the file effectively while allowing others to read and execute it as needed without compromising the integrity of the file.