Filesystem Repair & Recovery

# Check filesystem (dry run)
sudo fsck -n /dev/sda1
# e2fsck 1.46.5 (15-Mar-2021)
# /dev/sda1: clean, 234567/6553600 files, 12345678/52428800 blocks

# Repair automatically
sudo fsck -y /dev/sda1

# Repair with backup
sudo fsck -b 8192 /dev/sda1
# -b uses a backup superblock

# Check specific filesystem type
sudo fsck.ext4 /dev/sda1

# Force check (even if clean)
sudo fsck -f /dev/sda1

# Full ext4 check with options
sudo e2fsck -f -v /dev/sda1
# Pass 1: Checking inodes, blocks, and sizes
# Pass 2: Checking directory structure
# Pass 3: Checking directory connectivity
# Pass 4: Checking reference counts
# Pass 5: Checking group summary information

# Common errors fixed:
# - Duplicate blocks
# - Orphaned inodes
# - Directory entry pointing to wrong inode
# - Missing blocks in use map

# If root filesystem, force at boot
sudo tune2fs -C 50 /dev/sda1   # Set mount count to force check
sudo tune2fs -I 30 /dev/sda1   # Set interval to 30 days

# Check XFS filesystem (dry run)
sudo xfs_repair -n /dev/sda1
# Phase 1 - find and verify superblock
# Phase 2 - using primary superblock
# Phase 3 - checking free space
# Phase 4 - checking contents (sounds like the scariest phase)

# Repair XFS filesystem
sudo xfs_repair /dev/sda1

# Repair with log clear (if log is corrupt)
sudo xfs_repair -L /dev/sda1
# WARNING: This clears the journal, may lose recent data

# Check with log replay
sudo xfs_repair /dev/sda1   # Automatically replays log

# Repair from live CD
sudo xfs_repair /dev/sda1

# ext4: force journal replay
sudo tune2fs -O has_journal /dev/sda1
sudo mount /dev/sda1 /mnt  # Journal replays automatically

# Check journal status
sudo tune2fs -l /dev/sda1 | grep journal
# Journal inode:            8
# Journal backup:          blocks

# XFS: journal is internal by default
# Replay happens automatically at mount

# If mount fails due to journal corruption:
# ext4: sudo e2fsck -y /dev/sda1
# XFS: sudo xfs_repair -L /dev/sda1

# Btrfs: restore from snapshot
sudo btrfs subvolume delete /mnt/corrupted_data
sudo btrfs subvolume snapshot /mnt/.snapshots/good_copy /mnt/corrupted_data

# ZFS: rollback to snapshot
sudo zpool import mypool
sudo zfs rollback mypool/data@last_known_good

# LVM: restore from snapshot
sudo lvmerge /dev/myvg/data_snap /dev/myvg/data

# For databases, prefer point-in-time recovery
# Use the database's WAL/binlog for consistency

# Boot from Ubuntu/Debian live USB
# Select "Try Ubuntu"

# Find the root partition
lsblk
# /dev/sda2 is the root partition

# Run fsck
sudo fsck -y /dev/sda2

# For XFS
sudo xfs_repair /dev/sda2

# If GRUB is broken
sudo mount /dev/sda2 /mnt
sudo mount /dev/sda1 /mnt/boot
for i in /dev /proc /sys /run; do sudo mount --bind $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sda
update-grub
exit
sudo umount -R /mnt