Disk Management¶

# List all block devices (disks, partitions, loop devices)
lsblk

# Detailed view with filesystem type and mount points
lsblk -f

# List disks with partition table info
sudo fdisk -l

# Show disk UUIDs (use these in fstab, not /dev/sdX)
blkid

# Specific device
blkid /dev/sda1

# Disk usage — how full are your filesystems?
df -h               # human-readable sizes
df -hT              # includes filesystem type

# Directory disk usage
du -sh /path/       # total size of directory
du -sh /*           # size of each top-level directory
du -h --max-depth=1 /var    # one level deep

# Open a disk for editing (destructive — be careful)
sudo fdisk /dev/sda

# fdisk interactive commands:
# p — print partition table
# n — new partition
# d — delete partition
# t — change partition type
# w — write changes and exit
# q — quit without saving

# Open disk
sudo parted /dev/sda

# parted commands:
# print           — show partition table
# mklabel gpt     — create GPT partition table
# mkpart primary ext4 0% 100%   — create partition using full disk
# quit

# Create ext4 filesystem on a partition
sudo mkfs.ext4 /dev/sdb1

# Create with a label
sudo mkfs.ext4 -L mydrive /dev/sdb1

# XFS (what my NAS uses for the big data/parity disks; needs xfsprogs)
sudo apt install xfsprogs
sudo mkfs.xfs /dev/sdb1

# Check and repair a filesystem (must be unmounted)
sudo fsck /dev/sdb1
sudo fsck -y /dev/sdb1    # auto-fix errors

# Resize ext4 filesystem (after expanding partition)
sudo resize2fs /dev/sdb1

# Mount a partition
sudo mount /dev/sdb1 /mnt/data

# Mount with specific filesystem type
sudo mount -t ext4 /dev/sdb1 /mnt/data

# Mount an ISO
sudo mount -o loop image.iso /mnt/iso

# Unmount
sudo umount /mnt/data
sudo umount /dev/sdb1    # either works

# View currently mounted filesystems
mount | column -t
findmnt                  # tree view

# Format:
# <device>   <mountpoint>   <fstype>   <options>   <dump>  <pass>

# View current fstab
cat /etc/fstab

# Mount by UUID (always prefer UUID over /dev/sdX — device names can change)
UUID=abc123-def456  /mnt/data  ext4  defaults  0  2

# NFS share
192.168.1.20:/volume1/media  /mnt/media  nfs  defaults,_netdev  0  0

# tmpfs (RAM-based temp filesystem)
tmpfs  /tmp  tmpfs  defaults,size=1G  0  0

# Bind mount (make a directory appear at another path)
/source/path  /target/path  none  bind  0  0

# Test fstab without rebooting
sudo mount -a      # mounts everything in fstab not yet mounted

# Verify fstab syntax
sudo findmnt --verify

# Install smartmontools
sudo apt install smartmontools

# Quick health check
sudo smartctl -H /dev/sda

# Full SMART info
sudo smartctl -a /dev/sda

# Run short self-test (~2 min)
sudo smartctl -t short /dev/sda

# Run long self-test (~hours, do overnight)
sudo smartctl -t long /dev/sda

# Check test results
sudo smartctl -l selftest /dev/sda

# -a                health, attributes, error log and self-test log
# -o on -S on       automatic offline data collection + attribute autosave (ATA)
# -n standby,24,q   don't spin up sleeping disks for a check, but check at least every 24 polls
# -s (...)          short self-test daily at 01:00; long self-test on the 2nd of each month at 06:00
#                   (after the nightly SnapRAID run; a 12 TB long test takes most of a day)
# -W 4,50,60        log temperature changes >= 4 C and >= 50 C; alert at >= 60 C
# -m <nomailer> -M exec   no mail; run the hook instead. -M daily repeats an unresolved problem once a day
DEVICESCAN -a -o on -S on -n standby,24,q -s (S/../.././01|L/../02/./06) -W 4,50,60 -m <nomailer> -M daily -M exec /usr/local/sbin/smartd-notify

#!/bin/sh
# smartd sets SMARTD_DEVICE, SMARTD_FAILTYPE, SMARTD_MESSAGE, SMARTD_FULLMESSAGE, ...
case "$SMARTD_FAILTYPE" in
  EmailTest) prio=2 ;;
  Health|FailedHealthCheck|CurrentPendingSector|OfflineUncorrectableSector|SelfTest) prio=5 ;;
  *) prio=4 ;;
esac
printf '%s\n\n%s\n' "$SMARTD_MESSAGE" "$SMARTD_FULLMESSAGE" | head -c 3500 |
  curl -fsS -H "Authorization: Bearer $(cat /etc/smartd-ntfy-token)" \
       -H "Title: Disk ${SMARTD_FAILTYPE}: ${SMARTD_DEVICE}" -H "Priority: $prio" \
       --data-binary @- https://ntfy.<YOUR_DOMAIN>/alerts

sudo chmod 755 /usr/local/sbin/smartd-notify
sudo systemctl restart smartmontools     # the service is called smartmontools on Debian (alias: smartd)
# Test the whole path: add "-M test" to the DEVICESCAN line, restart, and you get one EmailTest message per disk

# View swap usage
swapon --show
free -h

# Create a swapfile
sudo fallocate -l 4G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

# Make permanent — add to fstab
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

# Adjust swappiness (how aggressively kernel uses swap)
# 0 = avoid swap, 100 = use swap aggressively, 10-20 typical for servers
cat /proc/sys/vm/swappiness
sudo sysctl vm.swappiness=10

# Persist swappiness across reboots
# (Debian 13+ no longer reads /etc/sysctl.conf — use a file in /etc/sysctl.d/)
echo 'vm.swappiness=10' | sudo tee /etc/sysctl.d/99-swappiness.conf

# Show physical volumes
sudo pvs
sudo pvdisplay

# Show volume groups
sudo vgs
sudo vgdisplay

# Show logical volumes
sudo lvs
sudo lvdisplay

# Extend a logical volume by 10GB
sudo lvextend -L +10G /dev/vgname/lvname

# Resize the filesystem after extending LV
sudo resize2fs /dev/vgname/lvname    # ext4
sudo xfs_growfs /mountpoint          # xfs