Gfilui

After booting from Live USB (16.04):

ubuntu@ubuntu:~$ sudo fdisk -l
[...]
Disk /dev/nvme0n1: 953.9 GiB, 1024209543168 bytes, 2000409264 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: C5CE78D6-06C1-4528-BF0F-098BAEE04CC0

Device Start End Sectors Size Type
/dev/nvme0n1p1 2048 1050623 1048576 512M EFI System
/dev/nvme0n1p2 1050624 2050047 999424 488M Linux filesystem
/dev/nvme0n1p3 2050048 2000408575 1998358528 952.9G Linux filesystem

[...]

# Later, de-crypting nvme0n1p3 and looking inside it:

ubuntu@ubuntu:~$ sudo cryptsetup luksOpen /dev/nvme0n1p3 n1p3
Enter passphrase for /dev/nvme0n1p3:
ubuntu@ubuntu:~$ sudo vgscan
 Reading all physical volumes. This may take a while...
 Found volume group "ubuntu-vg" using metadata type lvm2
ubuntu@ubuntu:~$ sudo lvs
 LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
 root ubuntu-vg -wi-a----- 867.47g
 swap_1 ubuntu-vg -wi-a----- 63.85g
ubuntu@ubuntu:~$ sudo vgchange -ay ubuntu-vg
 2 logical volume(s) in volume group "ubuntu-vg" now active
ubuntu@ubuntu:~$ sudo lvs
 LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
 root ubuntu-vg -wi-a----- 867.47g
 swap_1 ubuntu-vg -wi-a----- 63.85g
ubuntu@ubuntu:~$ mkdir /tmp/n1p3
ubuntu@ubuntu:~$ sudo mount /dev/ubuntu-vg/root /tmp/n1p3
ubuntu@ubuntu:~$ ls /tmp/n1p3
bin cdrom data etc initrd.img lhome lib32 libx32 measurements mnt proc run snap sys usr vmlinuz
boot core dev home initrd.img.old lib lib64 lost+found media opt root sbin srv tmp var vmlinuz.old
ubuntu@ubuntu:~$

Questions:

1. What is in the first 2048 sectors of /dev/nvme0n1?


2. What is in /dev/nvme0n1p1?


3. What is in /dev/nvme0n1p2?


4. What is in swap_1?

1. Out of the initial 2048 sectors at the start of the disk, the very first 34 sectors of a GPT-partitioned drive contain the partition table, the rest of the (2048 - 34 =) 2014 sectors are not used. Partitions need to start on a certain sector for optimal disk-performance, a common practice is to align partitions to 1 MiB (512 B (sector size) x 2048 (number of sectors) = 1 MiB), that's why you see this gap at the start of the disk.




2. /dev/nvme0n1p1 is the ESP (EFI System Partition), it is the place where boot-loaders are stored. This partition is a must, it is required by UEFI specifications, without this partition you would not be able to boot the machine. This partition will be mounted at /boot/efi in your system.




3. /dev/nvme0n1p2is your boot-partition and will be mounted at /boot in your system. This partition is not encrypted. You need this extra partition because you use LVM and encryption. The boot-loader can not read from a partition which is encrypted, so the need for this extra partition. This partition holds the kernel(s) and the boot-loader-configuration.




4. swap_1 is the swap-space. Swap acts as virtual memory. The system will use this space to move contents which are in RAM to the swap-space to free some RAM when necessary (this may happen if an application uses a lot of RAM, it will definitely happen if an application needs to use more RAM than installed, if you don't have swap-space in that case, the application would crash).