Resize disk on a (NixOS) VM without rebooting

resize-disk-without-reboot.md

Let's say you had a small disk on a VM and now it's full and wants to resize disk without rebooting.

(I've tested this on NixOS but it should work on other distros as well)

[root@nixos-box:~]# lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sr0     11:0    1    4M  0 rom
vda    253:0    0  3.1G  0 disk
└─vda1 253:1    0  3.1G  0 part /nix/store
                                /

Resize on a virtual hardware level:

• (on Proxmox) Choose VM > Select Disk > Disk Action > Resize Disk
• (do the equivalent for other VMM)

[root@nixos-box:~]# lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sr0     11:0    1    4M  0 rom
vda    253:0    0 23.1G  0 disk              # disk has grown
└─vda1 253:1    0  3.1G  0 part /nix/store   # but not here
                                /

[root@nixos-box:~]# nix-shell -p cloud-utils # to install growpart
[nix-shell:~]# growpart /dev/vda 1
CHANGED: partition=1 start=2048 old: size=6469632 end=6471679 new: size=48412639 end=48414686

[nix-shell:~]# lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sr0     11:0    1    4M  0 rom
vda    253:0    0 23.1G  0 disk
└─vda1 253:1    0 23.1G  0 part /nix/store   # now it's grown

But inodes are running out

[nix-shell:~]# df -ih
Filesystem               Inodes IUsed IFree IUse% Mounted on
devtmpfs                   245K   408  244K    1% /dev
tmpfs                      247K     1  247K    1% /dev/shm
tmpfs                      247K  1.2K  246K    1% /run
/dev/disk/by-label/nixos   198K  145K   54K   73% /           # see here
tmpfs                      1.0K     1  1023    1% /run/credentials/systemd-journald.service
tmpfs                      1.0K     1  1023    1% /run/credentials/systemd-resolved.service
tmpfs                      247K    18  247K    1% /run/wrappers
tmpfs                      1.0K     1  1023    1% /run/credentials/systemd-networkd.service
tmpfs                      1.0K     1  1023    1% /run/credentials/[email protected]
tmpfs                      1.0K     1  1023    1% /run/credentials/[email protected]
tmpfs                       50K    17   50K    1% /run/user/0

[nix-shell:~]# resize2fs /dev/vda1
resize2fs 1.47.2 (1-Jan-2025)
Filesystem at /dev/vda1 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 3
The filesystem on /dev/vda1 is now 6051579 (4k) blocks long.

[nix-shell:~]# df -ih
Filesystem               Inodes IUsed IFree IUse% Mounted on
devtmpfs                   245K   408  244K    1% /dev
tmpfs                      247K     1  247K    1% /dev/shm
tmpfs                      247K  1.2K  246K    1% /run
/dev/disk/by-label/nixos   1.5M  145K  1.3M   10% /           # now it's grown
tmpfs                      1.0K     1  1023    1% /run/credentials/systemd-journald.service
tmpfs                      1.0K     1  1023    1% /run/credentials/systemd-resolved.service
tmpfs                      247K    18  247K    1% /run/wrappers
tmpfs                      1.0K     1  1023    1% /run/credentials/systemd-networkd.service
tmpfs                      1.0K     1  1023    1% /run/credentials/[email protected]
tmpfs                      1.0K     1  1023    1% /run/credentials/[email protected]
tmpfs                       50K    17   50K    1% /run/user/0

All good now!