How to fix dpkg: error: unable to make backup link of './path' before installing new version in APT

Use lsattr to check for the immutable flag on the problematic file:

# If error shows file path like ./usr/bin/sshd
lsattr /usr/bin/sshd

# Output with immutable flag looks like: ----i---------

If you see an 'i' in the output, the file has the immutable flag. Remove it:

sudo chattr -i /usr/bin/sshd

Try the upgrade again. This resolves the issue in most cases.

List your mounted filesystems to check for /boot on FAT32:

mount | grep -E '(^/dev|/boot)'

If /boot shows 'vfat' (FAT32), dpkg cannot create hardlinks. Check if a /boot/efi directory exists:

ls -ld /boot/efi

Modern Debian/Ubuntu systems should have /boot/efi for EFI partition mounting, with actual boot files in /boot (on ext4/btrfs). If /boot itself is mounted on FAT32, this is the root cause.

If /boot is FAT32, you need to reorganize: mount the FAT32 EFI partition at /boot/efi instead.

# Check current fstab
cat /etc/fstab

# Look for the FAT32 partition UUID/path currently at /boot
# You may need to:
# 1. Create /boot/efi directory
# 2. Move contents from /boot to /boot/efi
# 3. Update /etc/fstab to mount EFI partition at /boot/efi
# 4. Create a regular /boot directory on the main filesystem

This is a complex operation. Document the current fstab, then carefully update mount points. After changes:

sudo update-grub
sudo update-initramfs -u

This permanent fix allows dpkg to operate safely on /boot files.

If no immutable attributes or FAT32 issues, try reconfiguring dpkg:

# Stop package managers
sudo systemctl stop apt-daily-upgrade.service apt-daily.service

# Reconfigure packages
sudo dpkg --configure -a

# Try upgrade again
sudo apt update && sudo apt upgrade

This completes any interrupted package installations.

If you're on a system with SELinux or AppArmor:

# Check SELinux status
getenforce

# Check AppArmor status
sudo systemctl status apparmor

If either is enabled and you suspect they're blocking operations:

# For SELinux, check audit logs
sudo grep dpkg /var/log/audit/audit.log

# For AppArmor, check logs
sudo grep dpkg /var/log/syslog

Security policies are rarely the culprit, but worth checking if other steps fail.