Tag: linux

Adding disk space to a Linux VM can be a lot more complex than expected. Please find below an explanation on how to extend the size of the root partition of a Photon OS VM running on vSphere. The resize is done without unmounting the partition (but there is a reboot done initially). This is made possible in part because the filesystem is Ext4. The VM does need to be rebooted after changing the disk size in vSphere however. Otherwise it won’t realize it now has a larger disk.

Process

• Increase size of disk in vSphere
• Reboot the VM so it recognizes the new disk size
• Use fdisk to delete and re-create the root partition
• Use resize2fs to expand the partition size
• Update fstab and grub with the new partition ID (or the VM won’t boot)

For Photon OS this process is extra easy as the root partition is at the end of the filesystem table and it doesn’t use an “Extended” partition. It’s possible to resize partitions with an Extended partition as well, but it takes a bit more work.

Note: These commands can easily break your system. Don’t try it on a machine where you value the data unless you have a solid backup of everything before attempting a resize.

Video covering the steps shown below

Step one is to change the disk size in vCenter

Reboot

In order for the Linux VM to recognize that it has a larger disk it needs to be rebooted.

root@stress-vm-01 [ ~ ]# reboot

Prior to modifying the partitions, verify which disk to modify

After rebooting, log back into the VM. We want to modify the root “/” partition and with “lsblk” we can verify that it is labeled “sda3”

root@stress-vm-01 [ ~ ]# lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0  375G  0 disk 
├─sda1   8:1    0    4M  0 part 
├─sda2   8:2    0   10M  0 part /boot/efi
└─sda3   8:3    0   80G  0 part /

Launch fdisk

We use “fdisk” to modify the partitions and tell it to look at “/dev/sda” rather than “/dev/sda3”. This is because we want to see the entire disk, not just the partition we will modify

root@stress-vm-01 [ ~ ]# fdisk /dev/sda

Welcome to fdisk (util-linux 2.36).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

GPT PMBR size mismatch (167772159 != 786431999) will be corrected by write.

Command (m for help):

Print partition information

We can see that the partition we want to modify (“/dev/sda3”) is at the end of the partition table. This makes it easy as we don’t have to shift any other partitions around to make space for the new, larger partition.

Command (m for help): p

Disk /dev/sda: 375 GiB, 402653184000 bytes, 786432000 sectors
Disk model: Virtual disk    
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: 2C13B474-2D24-4FE6-9905-D3A52DB28C9E

Device     Start       End   Sectors Size Type
/dev/sda1   2048     10239      8192   4M BIOS boot
/dev/sda2  10240     30719     20480  10M EFI System
/dev/sda3  30720 167772126 167741407  80G Linux filesystem

Command (m for help):

Delete the last partition (number 3)

Command (m for help): d
Partition number (1-3, default 3): 

Partition 3 has been deleted.

Command (m for help):

Recreate the partition

Here we use “n” to create a new partition, starting it at the exact same place as the old partition: “307020”. Fdisk will automatically suggest we end the new partition at the end of the disk: “786431966”. Pressing enter will accept this value and create the partition.

We can also see that the partition contains an ext4 signature – this is why we can resize the partition while it still is mounted.

Command (m for help): n
Partition number (3-128, default 3): 
First sector (30720-786431966, default 30720): 
Last sector, +/-sectors or +/-size{K,M,G,T,P} (30720-786431966, default 786431966): 

Created a new partition 3 of type 'Linux filesystem' and of size 375 GiB.
Partition #3 contains a ext4 signature.

Do you want to remove the signature? [Y]es/[N]o: N

Command (m for help):

Print the updated partition table

Note that it is not yet written to disk, this is just a preview

Command (m for help): p

Disk /dev/sda: 375 GiB, 402653184000 bytes, 786432000 sectors
Disk model: Virtual disk    
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: 2C13B474-2D24-4FE6-9905-D3A52DB28C9E

Device     Start       End   Sectors  Size Type
/dev/sda1   2048     10239      8192    4M BIOS boot
/dev/sda2  10240     30719     20480   10M EFI System
/dev/sda3  30720 786431966 786401247  375G Linux filesystem

Command (m for help):

Writing the partition table to disk

Command (m for help): w
The partition table has been altered.
Syncing disks.

Verifying the current size of the root “/” partition

root@stress-vm-01 [ ~ ]# df -h .
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3        79G  1.1G   74G   2% /
root@stress-vm-01 [ ~ ]# 

Resizing on the fly (without unmounting)

root@stress-vm-01 [ ~ ]# resize2fs /dev/sda3
resize2fs 1.45.6 (20-Mar-2020)
Filesystem at /dev/sda3 is mounted on /; on-line resizing required
old_desc_blocks = 10, new_desc_blocks = 47
The filesystem on /dev/sda3 is now 98300155 (4k) blocks long.

Verifying the new partition size

root@stress-vm-01 [ ~ ]# df -h .
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3       369G  1.1G  352G   1% /

Verify the new partition ID (“PARTUUID”)

root@stress-vm-01 [ ~ ]# blkid
/dev/sda2: SEC_TYPE="msdos" UUID="53EC-9755" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="0a2847cf-9e9d-4d1a-9393-490e1b2459bf"
/dev/sda3: UUID="9cb30e86-d563-478d-8eeb-16f2449cb608" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="5e0b1089-595c-4f42-8d4b-4b06220cd6c7"
/dev/sda1: PARTUUID="d2bf275a-1df1-4aa6-adbf-8b5f6c4cac3a"

Update /etc/fstab and /boot/grub/grub.conf

Use your favorite editor (vi / vim / nano). Look for the partition UUID and update to match the new partition ID. Note that grub.conf may have a slightly different name or location if you aren’t using Photon OS.

root@stress-vm-01 [ ~ ]# vi /etc/fstab 

• 

root@stress-vm-01 [ ~ ]# vi /boot/grub/grub.cfg 

• 

All done!