Making files immutable

Files on extended type filesystems, which are common in Linux (for example, ext2, ext3, ext4, and so on) can be made immutable using a certain type of file attributes. When a file is made immutable, any user or super user cannot remove the file until the immutable attribute is removed from the file. We can easily find out the filesystem type of any mounted partition by looking at the /etc/mtab file. The first column of the file specifies the partition device path (for example, /dev/sda5) and the third column specifies the file system type (for example, ext3).

Making a file immutable is one of the methods for securing files from modification. An example would be to use it for the /etc/resolv.conf file which stores a list of DNS servers. A DNS server is used to convert domain names (such as packtpub.com) to IP addresses. Usually, the DNS server will be set to your ISP's DNS server. However, some people prefer to use a third-party server and they can modify /etc/resolv...