What command is used to set file permissions using octal numbers?

The command to set file permissions using octal numbers is indeed the one that includes 'chmod'. The 'chmod' command stands for "change mode," which is specifically used to define who can read, write, or execute a file. The '755' in this context represents the octal number that specifies the permissions.

In the octal permission system, the number is composed of three digits, each representing the permissions for the user, group, and others, respectively. In the case of '755', it indicates that the owner of the file has read (4), write (2), and execute (1) permissions, while the group and others have read and execute permissions but no write permissions. Therefore, 'chmod 755 filename' accurately modifies the file permissions according to this octal notation.

Understanding the components of the command is critical in UNIX-like systems, as it allows for precise control over security and access rights for files and directories.