Device Management

# lsblk - Recommended for overview
lsblk
lsblk -f                     # Filesystem info
lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINT,UUID
lsblk -p                     # Full device paths
lsblk --json                 # JSON output

# Example output
# NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
# sda           8:0    0   500G  0 disk
# ├─sda1        8:1    0   512M  0 part /boot/efi
# ├─sda2        8:2    0   100G  0 part /
# └─sda3        8:3    0 399.5G  0 part /home
# nvme0n1     259:0    0   1.8T  0 disk
# └─nvme0n1p1 259:1    0   1.8T  0 part /data

# blkid - Show UUIDs and labels
blkid
blkid /dev/sda1
blkid -o list

# Device paths
ls -la /dev/disk/by-id/
ls -la /dev/disk/by-uuid/
ls -la /dev/disk/by-path/
ls -la /dev/disk/by-label/

# Use stable identifiers in fstab
# UUID=abc123-def456 /mount ext4 defaults 0 2
# LABEL=data /data xfs defaults 0 2

# Find device by UUID
findfs UUID=abc123-def456

# fdisk - Partition info
fdisk -l
fdisk -l /dev/sda

# Detailed device info
hdparm -I /dev/sda           # SATA/IDE drives
smartctl -a /dev/sda         # SMART data
nvme list                    # NVMe devices
nvme smart-log /dev/nvme0n1  # NVMe SMART

# udevadm - Device attributes
udevadm info /dev/sda
udevadm info --query=all --name=/dev/sda
udevadm info --attribute-walk /dev/sda

# Start fdisk
fdisk /dev/sda

# Common commands:
# m - help
# p - print partition table
# n - new partition
# d - delete partition
# t - change partition type
# a - toggle bootable flag
# w - write changes and exit
# q - quit without saving

# Non-interactive (scripted)
echo -e "n\np\n1\n\n+10G\nw" | fdisk /dev/sda

# Using sfdisk (scriptable)
sfdisk /dev/sda << EOF
, 10G, L
, 20G, L
, , L
EOF

# Start gdisk
gdisk /dev/sda

# Common commands (similar to fdisk):
# ? - help
# p - print partition table
# n - new partition
# d - delete partition
# c - change partition name
# t - change type code
# w - write changes
# q - quit

# Convert MBR to GPT (backup first!)
gdisk /dev/sda
# Then use 'w' to write GPT

# Common partition type codes:
# 8300 - Linux filesystem
# 8200 - Linux swap
# ef00 - EFI System
# fd00 - Linux RAID
# 8e00 - Linux LVM

# Interactive mode
parted /dev/sda

# Commands:
# print - show partitions
# mklabel gpt - create GPT table
# mklabel msdos - create MBR table
# mkpart primary ext4 1MiB 100GiB
# rm 1 - delete partition 1
# resizepart 1 200GiB
# name 1 mydata
# quit

# Non-interactive
parted -s /dev/sda mklabel gpt
parted -s /dev/sda mkpart primary ext4 1MiB 100GiB
parted -s /dev/sda mkpart primary ext4 100GiB 200GiB
parted -s /dev/sda set 1 boot on

# Align partitions (important for SSDs)
parted -s /dev/sda align-check optimal 1

# Print in machine-readable format
parted -m /dev/sda print

# Check alignment
parted /dev/sda align-check optimal 1

# Modern drives need 1MiB alignment
# Start first partition at 1MiB (2048 sectors for 512-byte)

# fdisk automatically aligns on recent versions
# For parted, always use MiB/GiB units

# Check current alignment
parted /dev/sda unit s print  # Sectors
# First partition should start at 2048s or higher (multiple of 2048)

# ext4 (most common)
mkfs.ext4 /dev/sda1
mkfs.ext4 -L mylabel /dev/sda1        # With label
mkfs.ext4 -b 4096 /dev/sda1           # Block size
mkfs.ext4 -m 1 /dev/sda1              # 1% reserved (default 5%)

# XFS (good for large files)
mkfs.xfs /dev/sda1
mkfs.xfs -L mylabel /dev/sda1
mkfs.xfs -f /dev/sda1                 # Force overwrite

# Btrfs (CoW, snapshots)
mkfs.btrfs /dev/sda1
mkfs.btrfs -L mylabel /dev/sda1
mkfs.btrfs -d raid1 -m raid1 /dev/sda1 /dev/sdb1  # RAID1

# FAT32 (USB drives, EFI)
mkfs.vfat -F 32 /dev/sda1
mkfs.vfat -F 32 -n LABEL /dev/sda1

# exFAT (large files, cross-platform)
mkfs.exfat /dev/sda1

# Swap
mkswap /dev/sda2
swapon /dev/sda2

# Set label (ext4)
e2label /dev/sda1 mylabel
tune2fs -L mylabel /dev/sda1

# Set label (XFS)
xfs_admin -L mylabel /dev/sda1

# Set label (Btrfs)
btrfs filesystem label /dev/sda1 mylabel

# Change UUID (ext4)
tune2fs -U random /dev/sda1
tune2fs -U $(uuidgen) /dev/sda1

# Change UUID (XFS)
xfs_admin -U generate /dev/sda1

# View labels and UUIDs
blkid
lsblk -f

# Check filesystem (UNMOUNT FIRST!)
fsck /dev/sda1
fsck -y /dev/sda1             # Auto-fix
e2fsck -f /dev/sda1           # Force ext check
xfs_repair /dev/sda1          # XFS repair

# Resize filesystem
# ext4 (can grow online)
resize2fs /dev/sda1
resize2fs /dev/sda1 50G       # Specific size

# XFS (can only grow, must be mounted)
xfs_growfs /mnt

# Btrfs (can grow and shrink online)
btrfs filesystem resize max /mnt
btrfs filesystem resize -10G /mnt

# Check filesystem usage
df -h
df -i                         # Inode usage

# Check for errors
dmesg | grep -i "filesystem\|ext4\|xfs"

# Basic mount
mount /dev/sda1 /mnt

# With options
mount -o rw,noatime /dev/sda1 /mnt
mount -o ro /dev/sda1 /mnt    # Read-only
mount -o remount,rw /mnt      # Remount with different options

# By UUID
mount UUID=abc123-def456 /mnt

# By label
mount LABEL=data /mnt

# Specific filesystem type
mount -t ext4 /dev/sda1 /mnt
mount -t ntfs-3g /dev/sda1 /mnt

# Unmount
umount /mnt
umount /dev/sda1
umount -l /mnt                # Lazy unmount (when busy)
umount -f /mnt                # Force unmount (NFS)

# Check what's using mount point
fuser -m /mnt
lsof +f -- /mnt

# Common mount options
defaults        # rw,suid,dev,exec,auto,nouser,async
rw              # Read-write
ro              # Read-only
noatime         # Don't update access times (performance)
nodiratime      # Don't update directory access times
relatime        # Update atime relative to mtime (default)
discard         # Enable TRIM for SSDs
noexec          # No execution of binaries
nosuid          # Ignore setuid bits
nodev           # No device files
sync            # Synchronous I/O
async           # Asynchronous I/O (default)

# Security options
noexec,nosuid,nodev    # Common for /tmp, /var/tmp

# Example
mount -o rw,noatime,discard /dev/sda1 /mnt

# /etc/fstab format:
# <device>  <mountpoint>  <type>  <options>  <dump>  <pass>

# By UUID (recommended)
UUID=abc123-def456  /           ext4    defaults,noatime     0  1
UUID=def789-ghi012  /home       ext4    defaults,noatime     0  2
UUID=jkl345-mno678  /boot/efi   vfat    umask=0077           0  1

# By label
LABEL=data          /data       xfs     defaults,noatime     0  2

# Swap
UUID=pqr901-stu234  none        swap    sw                   0  0

# Temporary filesystems
tmpfs               /tmp        tmpfs   defaults,noatime,mode=1777  0  0

# NFS mount
server:/export      /nfs        nfs     defaults,_netdev     0  0

# Mount options explained:
# dump (5th field): 0=no backup, 1=backup
# pass (6th field): 0=no fsck, 1=root, 2=other filesystems

# Test fstab entry without mounting
mount -fav

# Mount all fstab entries
mount -a

# Check current mounts
mount
findmnt
findmnt --fstab              # Show fstab entries
findmnt -t ext4              # Filter by type

# Reload systemd after fstab changes
systemctl daemon-reload

Physical Volume (PV) → Volume Group (VG) → Logical Volume (LV)
    /dev/sda1              vg0                 /dev/vg0/root
    /dev/sdb1                                  /dev/vg0/home
                                              /dev/vg0/data

# Create physical volume
pvcreate /dev/sda1
pvcreate /dev/sdb1

# List physical volumes
pvs
pvdisplay
pvdisplay /dev/sda1

# Remove physical volume
pvremove /dev/sda1

# Move data from one PV to another
pvmove /dev/sda1 /dev/sdb1
pvmove /dev/sda1            # Move to any available PV in VG

# Create volume group
vgcreate vg0 /dev/sda1
vgcreate vg0 /dev/sda1 /dev/sdb1    # Multiple PVs

# List volume groups
vgs
vgdisplay
vgdisplay vg0

# Extend volume group
vgextend vg0 /dev/sdc1

# Reduce volume group (after moving data)
vgreduce vg0 /dev/sda1

# Rename volume group
vgrename vg0 newvg

# Remove volume group
vgremove vg0

# Create logical volume
lvcreate -L 10G -n root vg0           # Fixed size
lvcreate -l 100%FREE -n data vg0      # All remaining space
lvcreate -l 50%VG -n home vg0         # 50% of VG
lvcreate -l 100%PVS -n lv0 vg0 /dev/sda1  # All of specific PV

# List logical volumes
lvs
lvdisplay
lvdisplay /dev/vg0/root

# Extend logical volume
lvextend -L +5G /dev/vg0/root         # Add 5G
lvextend -l +100%FREE /dev/vg0/root   # All free space
lvextend -L 20G /dev/vg0/root         # Set to 20G

# Resize filesystem after extend
resize2fs /dev/vg0/root               # ext4
xfs_growfs /mount/point               # XFS (must be mounted)

# Extend LV and resize filesystem in one command
lvextend -r -L +5G /dev/vg0/root

# Reduce logical volume (BACKUP FIRST!)
umount /dev/vg0/root
e2fsck -f /dev/vg0/root
resize2fs /dev/vg0/root 10G
lvreduce -L 10G /dev/vg0/root
mount /dev/vg0/root /mnt

# Remove logical volume
lvremove /dev/vg0/root

# Rename logical volume
lvrename vg0 oldname newname

# Create snapshot
lvcreate -L 5G -s -n root-snap /dev/vg0/root

# List snapshots
lvs -a
lvs -o +snap_percent

# Mount snapshot (read-only by default)
mount -o ro /dev/vg0/root-snap /mnt/snap

# Restore from snapshot
lvconvert --merge /dev/vg0/root-snap
# Reboot for root volume or remount for others

# Remove snapshot
lvremove /dev/vg0/root-snap

# Create thin pool
lvcreate -L 100G --thinpool thin-pool vg0

# Create thin volumes
lvcreate -V 50G --thin -n thin-vol1 vg0/thin-pool
lvcreate -V 50G --thin -n thin-vol2 vg0/thin-pool

# Thin volumes can overcommit
# Total thin volumes > pool size (careful!)

# Monitor usage
lvs -o +data_percent,snap_percent

# Create RAID arrays
# RAID 0 (stripe)
mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda1 /dev/sdb1

# RAID 1 (mirror)
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1

# RAID 5 (stripe with parity)
mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1

# RAID 6 (stripe with double parity)
mdadm --create /dev/md0 --level=6 --raid-devices=4 /dev/sd[a-d]1

# RAID 10 (stripe of mirrors)
mdadm --create /dev/md0 --level=10 --raid-devices=4 /dev/sd[a-d]1

# Check status
cat /proc/mdstat
mdadm --detail /dev/md0
mdadm --examine /dev/sda1

# Save configuration
mdadm --detail --scan >> /etc/mdadm.conf

# Add spare disk
mdadm --add /dev/md0 /dev/sdc1

# Remove disk
mdadm --fail /dev/md0 /dev/sda1
mdadm --remove /dev/md0 /dev/sda1

# Replace failed disk
mdadm --fail /dev/md0 /dev/sda1
mdadm --remove /dev/md0 /dev/sda1
# Replace physical disk
mdadm --add /dev/md0 /dev/sdd1

# Stop and remove array
mdadm --stop /dev/md0
mdadm --zero-superblock /dev/sd[ab]1

# Watch rebuild progress
watch cat /proc/mdstat

# Email alerts
# /etc/mdadm.conf
MAILADDR admin@example.com

# Start monitoring daemon
systemctl enable mdmonitor
systemctl start mdmonitor

# udev handles device events
# Rules in /etc/udev/rules.d/ and /lib/udev/rules.d/

# Get device attributes for rules
udevadm info --query=all --name=/dev/sda
udevadm info --attribute-walk /dev/sda

# Monitor device events
udevadm monitor
udevadm monitor --property

# /etc/udev/rules.d/99-custom.rules

# Match by attribute, assign name/symlink
# Give USB drive a persistent name by serial
SUBSYSTEM=="block", ENV{ID_SERIAL}=="WD-ABC123", SYMLINK+="myusb"

# Run script when device added
ACTION=="add", SUBSYSTEM=="block", ENV{ID_SERIAL}=="WD-ABC123", RUN+="/usr/local/bin/backup.sh"

# Set I/O scheduler for SSDs
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="none"

# Set permissions
SUBSYSTEM=="tty", ATTRS{idVendor}=="1234", ATTRS{idProduct}=="5678", MODE="0666"

# Reload rules
udevadm control --reload-rules

# Trigger rules for existing devices
udevadm trigger

# Test rule without applying
udevadm test /sys/block/sda

# Create LUKS container
cryptsetup luksFormat /dev/sda1

# With specific options
cryptsetup luksFormat --type luks2 --cipher aes-xts-plain64 --key-size 512 /dev/sda1

# Open encrypted volume
cryptsetup luksOpen /dev/sda1 cryptdata
# Creates /dev/mapper/cryptdata

# Create filesystem
mkfs.ext4 /dev/mapper/cryptdata

# Mount
mount /dev/mapper/cryptdata /mnt

# Close
umount /mnt
cryptsetup luksClose cryptdata

# View key slots
cryptsetup luksDump /dev/sda1

# Add key
cryptsetup luksAddKey /dev/sda1

# Add key from file
cryptsetup luksAddKey /dev/sda1 /path/to/keyfile

# Remove key
cryptsetup luksRemoveKey /dev/sda1

# Change passphrase
cryptsetup luksChangeKey /dev/sda1

# /etc/crypttab
# name    device                                  key         options
cryptdata UUID=abc123-def456-ghi789               none        luks

# With keyfile
cryptdata UUID=abc123-def456-ghi789               /root/keyfile  luks

# /etc/fstab
/dev/mapper/cryptdata  /data  ext4  defaults  0  2

# Rescan SCSI bus
echo "- - -" > /sys/class/scsi_host/host0/scan

# Rescan all hosts
for host in /sys/class/scsi_host/host*; do
    echo "- - -" > $host/scan
done

# Force kernel to reread partitions
partprobe /dev/sda
blockdev --rereadpt /dev/sda

# Check dmesg for errors
dmesg | tail -50
dmesg | grep -i "sd\|nvme\|error"

# Check SMART status
smartctl -H /dev/sda
smartctl -a /dev/sda

# Run SMART tests
smartctl -t short /dev/sda
smartctl -t long /dev/sda

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

# NVMe health
nvme smart-log /dev/nvme0n1

# Force fsck at boot
touch /forcefsck

# Or via tune2fs
tune2fs -C 100 /dev/sda1    # Force fsck in 100 mounts

# Repair XFS
xfs_repair /dev/sda1
xfs_repair -L /dev/sda1     # Zero log (data loss risk)

# Recover ext4 superblock
mke2fs -n /dev/sda1         # Find backup superblock locations
e2fsck -b 32768 /dev/sda1   # Use backup superblock