Earlier today while investigating the logs on a CentOS Linux server I noticed the btmp file had grown to over 5GB. I was curious to look into the log and when attempting to read the 5GB file using last I received an error since last will only handle files that are 2GB in size or less. So what needs to happen is to split the file into multiple pieces so they can be read via the last command. Below I describe the error in detail, how to resolve it by splitting the btmp file into multiple files, and then how to join them together if you need to read logs older than the last split file.
The rar command can be useful on Linux to not only compress a file but also split the file into multiple parts during the compression. This will make the files easier to transfer to other servers or easier for other people to download. First rar needs to be installed which can done on CentOS using the directions below. After that we describe how to easily compress and break a file into multiple chunks using one simple rar command.