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lvresize
Know what's annoying? I'll tell you: default Ubuntu server installs from I-don't-know-when don't actually use 100% of the disk space you allocate to them. Neat right? NOPE! Anyway, if that happens to you, this article will get you squared away, and here's the TLDR version:
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Reclaim 100% of disk space in Ubuntu server (unencrypted drive)
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Check if you can actually do the resize
sudo lvresize -tvl +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv
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Resize it for realsiez
sudo lvresize -vl +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv
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Resize the file system to match
sudo resize2fs -p /dev/mapper/ubuntu--vg-ubuntu--lv
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Reclaim 100% of disk space in Ubuntu server (ENCRYPTED drive)
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Confirm disk size
sudo fdisk -l /dev/sda
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Grow root partition to fill new space
sudo apt install -y cloud-guest-utils # if not already installed
sudo growpart /dev/sda 3
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Resize LUKS container
sudo cryptsetup resize dm_crypt-0
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Resize LVM
sudo pvresize /dev/mapper/dm_crypt-0
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Extend logical volume
sudo lvextend -l +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv
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Resize file system
sudo resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv
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Verify results
df -h /