Why Lastlog files are getting bigger

The Lastlog file is the information that records the last login for all users.

The algorithm for this file is this:

Log user logon Information size = UID * 256byte

For example, a nfsnobody user on a 64-bit system with a UID of 4294967294 or 2^32-2, which is also the last UID on the system.

So the above algorithm can explain how the file displays the 1.2TB size:

4294967294 * 256 = 1099511627264 bytes from the above algorithm can also see that 256 is the amount of space each UID occupies in the Lostlog file. So this file is called a sparse (sparse) file: A sparse file is a lot of space left in the file to keep the data inserted for future use. These free spaces are occupied by the null characters of the ASCII code, and the space is quite large, which is called a sparse file, but does not allocate the appropriate disk block. That is, the file system space is not really occupied. So you don't have to worry about it. This file takes up 1.2TB of space. You can use Du-h/var/log/lastlog to find out what he sees that really takes up disk space.