I presume you checked the logs see the oh shit when you ran these commands
```text
[traefikprg@nixos-traefik:~]$ df -H
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        818M     0  818M   0% /dev
tmpfs           8,2G     0  8,2G   0% /dev/shm
tmpfs           4,1G  4,6M  4,1G   1% /run
/dev/sda1        20G   19G     0 100% /
tmpfs           1,1M     0  1,1M   0% /run/credentials/systemd-journald.service
tmpfs           8,2G  1,4M  8,2G   1% /run/wrappers
tmpfs           1,7G   13k  1,7G   1% /run/user/995
tmpfs           1,7G   13k  1,7G   1% /run/user/1000

[traefikprg@nixos-traefik:~]$ lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   83G  0 disk 
└─sda1   8:1    0   19G  0 part /nix/store
                                /
sr0     11:0    1  3,4G  0 rom  
zram0  253:0    0  7,6G  0 disk [SWAP]

[traefikprg@nixos-traefik:~]$ sudo fdisk -l
[sudo] password for traefikprg: 
Sorry, try again.
[sudo] password for traefikprg: 
Disk /dev/sda: 83 GiB, 89120571392 bytes, 174063616 sectors
Disk model: QEMU HARDDISK   
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: dos
Disk identifier: 0x44a3447a

Device     Boot Start      End  Sectors Size Id Type
/dev/sda1  *     2048 39845887 39843840  19G 83 Linux


Disk /dev/zram0: 7,62 GiB, 8176795648 bytes, 1996288 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

```

Well, panic and then you look up how to increase disk space size.

![img.png](img.png)

I presume you have already tried to naively increase the disk size through the
proxmox' increase disk space but after reboot still not increasing? Yeah, I learned that the
hard way that ISO based solution does not implicitly change it.

Try to change to boot order to boot into ISO and Gparted and pray

![img_1.png](img_1.png)

> [!WARNING]
> NOTE THAT REBOOT DOES NOT CHANGE THE BOOT ORDER... APPARENTLY, SHUTDOWN, WAIT AND THEN START AGAIN

Use gparted to just resize the partition and hopefully ends up fine.

![img_2.png](img_2.png) 

Remember to change the boot order back, SHUTDOWN and **then** start again.

Hopefully it worked out fine for you.