During bootup process, kernel gets loaded into the system memory and it controls the entire system.
During the bootup process , kernel displays number of messages and hardware divice information.
These messages will keep in a ring buffer. You can use these messages for sytem Troubleshooting. You can see these messages by using dmesg command.
1. open a terminal and type
$ dmesg |more
2. To see the status of Network
$ dmesg | grep eth
3. To see the memory status
$ dmesg | grep Memory
4. for clearing dmesg buffer
$ dmesg -c