How to Use Rescue Mode for Troubleshooting

# List all available disks and partitions
lsblk

# You will see something like:
# NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
# vda      254:0    0   50G  0 disk
# ├─vda1   254:1    0   49G  0 part
# └─vda2   254:2    0    1G  0 part

# Mount the main partition
mount /dev/vda1 /mnt

# Verify it worked — you should see your server's files
ls /mnt
# bin  boot  dev  etc  home  lib  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

# IMPORTANT: The partition must NOT be mounted for fsck to work safely
# If you already mounted it, unmount first: umount /mnt

# Check and repair the filesystem (-y automatically answers "yes" to repair prompts)
fsck -y /dev/vda1

# For ext4 filesystems specifically
e2fsck -fy /dev/vda1

# Mount your server's disk
mount /dev/vda1 /mnt

# Look at the current fstab
cat /mnt/etc/fstab

# Edit the file and fix or comment out the broken entry
nano /mnt/etc/fstab

# To comment out a problematic line, add a # at the beginning:
# # /dev/sdb1  /data  ext4  defaults  0  2

# Save and exit (Ctrl+O, Enter, Ctrl+X in nano)

# Unmount cleanly
umount /mnt

# Mount your server's disk
mount /dev/vda1 /mnt

# Browse and identify what you need
ls /mnt/home/
ls /mnt/var/www/
ls /mnt/etc/

# Option A: Copy files to a remote server via SCP
scp -r /mnt/var/www/html user@backup-server:/backups/

# Option B: Create a compressed archive and transfer it
tar czf /tmp/backup.tar.gz -C /mnt/var/www html
scp /tmp/backup.tar.gz user@backup-server:/backups/

# Option C: Copy database files
cp /mnt/var/lib/mysql /tmp/mysql-backup -r
scp -r /tmp/mysql-backup user@backup-server:/backups/

# Unmount when done
umount /mnt

# Mount your server's disk
mount /dev/vda1 /mnt

# Chroot into your server's filesystem
# This makes the rescue system "pretend" it is your server's OS
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
chroot /mnt

# Now you are "inside" your server's OS — change the password
passwd root
# Enter and confirm your new password

# Exit the chroot
exit

# Clean up mounts
umount /mnt/sys
umount /mnt/proc
umount /mnt/dev
umount /mnt

# Mount your server's disk
mount /dev/vda1 /mnt

# Check the SSH config for syntax errors
# Common mistakes: typos, duplicate directives, setting PermitRootLogin to "no" without another user
cat /mnt/etc/ssh/sshd_config

# Fix the configuration
nano /mnt/etc/ssh/sshd_config

# If you are not sure what is wrong, you can restore the default config:
# cp /mnt/etc/ssh/sshd_config /mnt/etc/ssh/sshd_config.broken
# apt-get download openssh-server  (to get a fresh default config)

# Unmount
umount /mnt

# Mount your server's disk and set up chroot
mount /dev/vda1 /mnt
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
chroot /mnt

# Reinstall GRUB (for BIOS/MBR systems)
grub-install /dev/vda
update-grub

# For UEFI systems, you may also need to mount the EFI partition first:
# mount /dev/vda15 /boot/efi  (partition number may vary)
# grub-install --target=x86_64-efi /dev/vda
# update-grub

# Exit chroot and clean up
exit
umount /mnt/sys
umount /mnt/proc
umount /mnt/dev
umount /mnt