# Debian disk and filesystems

Manage storage: partitions, formatting, mounting, and monitoring disk usage.

## Listing disks and partitions

```bash
lsblk
lsblk -f           # show filesystems
```

Show device details:

```bash
fdisk -l
parted -l
```

## Partitioning

Interactive partition editor:

```bash
sudo cfdisk /dev/sda
```

Or `fdisk` (older, text-based):

```bash
sudo fdisk /dev/sda
```

Or `parted` (supports GPT):

```bash
sudo parted /dev/sda
```

After partitioning, reread partition table:

```bash
sudo partprobe /dev/sda
```

## Formatting filesystems

Create ext4 filesystem (most common):

```bash
sudo mkfs.ext4 /dev/sda1
```

Other options:
- `mkfs.ext3`: older, journaled
- `mkfs.xfs`: high-performance
- `mkfs.btrfs`: modern with snapshots
- `mkfs.vfat`: FAT32 (USB drives)

## Mounting

Mount filesystem (temporary):

```bash
sudo mount /dev/sda1 /mnt
sudo umount /mnt
```

List mounted filesystems:

```bash
mount
df -h
```

## Persistent mounts

Edit `/etc/fstab`:

```
/dev/sda1  /home  ext4  defaults  0  2
```

Format: `device mount-point filesystem options dump fsck-order`

- `options`: usually `defaults`, or comma-separated: `noatime`, `nodiratime`, `noexec`
- `dump`: 0 to skip, 1 to include in dumps
- `fsck-order`: 0 to skip, 1 for root, 2 for others

Test before applying:

```bash
sudo mount -a
```

## Disk usage

Show usage per filesystem:

```bash
df -h
```

Show directory size:

```bash
du -sh /path/to/dir
du -sh /path/to/dir/*
```

Find large files:

```bash
find / -type f -size +1G
```

## Filesystem types

- **ext4**: reliable, default on Debian
- **xfs**: high-performance, used on servers
- **btrfs**: modern, supports snapshots and RAID
- **vfat**: FAT32, USB drives, Windows-compatible
- **ntfs**: Windows filesystems (limited support)

## Checking filesystems

Check for errors (unmounted only):

```bash
sudo fsck /dev/sda1
sudo e2fsck -n /dev/sda1    # read-only check
```

During boot, systemd runs fsck on damaged filesystems automatically.

## Disk space issues

If disk is full:

```bash
sudo apt autoremove
sudo apt clean
sudo journalctl --vacuum=size=100M
```

Monitor space regularly to avoid emergency cleanup.