📌 Table of Contents

• 1. Linux Boot & GRUB Errors
• 2. Package Manager & Update Errors
• 3. Wi-Fi & Network Issues
• 4. Audio & Sound Problems
• 5. Graphics & Display Driver Issues
• 6. Laptop Battery & Power Management
• 7. Permission Denied & File System Errors
• 8. Storage & Disk Space Errors
• 9. Bluetooth & Peripheral Issues
• 10. Flatpak & Snap App Issues
• 11. SSH & Docker Connectivity Errors
• 12. Advanced Troubleshooting
• 13. Quick Reference Tables
• 14. Frequently Asked Questions
• 15. Conclusion

🔍 Quick Problem Finder

• GRUB rescue or boot loop? → Boot & GRUB Errors
• apt-get update failed? → Package Manager & Update Errors
• Wi-Fi keeps disconnecting? → Wi-Fi & Network Issues
• No sound or crackling audio? → Audio & Sound Problems
• NVIDIA black screen? → Graphics & Display Driver Issues
• Permission denied? → Permission Denied & File System Errors
• No space left on device? → Storage & Disk Space Errors
• SSH connection refused? → SSH & Docker Connectivity Errors

Is your Linux system not booting, Wi-Fi dropping, sound crackling, or showing permission denied errors? Linux is powerful and stable, but issues do arise – especially after updates, driver changes, or hardware upgrades. Whether you use Ubuntu, Arch Linux, Fedora, or Linux Mint, this ultimate Linux troubleshooting hub brings together fixes for the most common problems, organized by category. Based on real user reports and tested fixes, most Linux issues can be resolved without reinstalling your system.

🐧 Before you start: Many Linux problems can be fixed from the command line. Keep a live USB of your distribution handy – it’s your best friend for recovery. Also, note that some fixes require root privileges (sudo). Always back up important data before making major system changes.

1. Linux Boot & GRUB Errors

Boot problems are among the most stressful Linux issues. Here’s how to recover when your system won’t start.

GRUB Rescue Error (Unknown Filesystem)

You see a grub rescue> prompt after deleting a Linux partition or after a failed update. This happens because GRUB’s files are on a partition that no longer exists or is corrupted.

Why it happens: GRUB (the bootloader) stores its core files in the /boot directory. When that partition is deleted, moved, or corrupted, GRUB cannot find its configuration and drops to the rescue shell.

How to fix it:

1. Find your Linux partition: At the grub rescue> prompt, type ls to list partitions. You’ll see something like (hd0) (hd0,msdos1) (hd0,msdos2). Try each: ls (hd0,msdos2)/ until you find one with a /boot directory.
2. Set the root and prefix: set root=(hd0,msdos2) and set prefix=(hd0,msdos2)/boot/grub.
3. Load normal module: insmod normal then normal. The GRUB menu should appear.
4. Boot into your system and run sudo update-grub (Debian/Ubuntu) or sudo grub-mkconfig -o /boot/grub/grub.cfg (Arch/Fedora).
5. Reinstall GRUB if needed: sudo grub-install /dev/sda (replace sda with your main disk).

📖 Read the complete GRUB rescue fix guide →

Ubuntu Stuck on Splash Screen (Boot Freeze)

Your Ubuntu system gets stuck on the purple splash screen with the dots animating endlessly.

Why it happens: This is often caused by graphics driver issues (especially NVIDIA), a full /boot partition, or a filesystem check that got stuck.

How to fix it:

1. Boot into recovery mode: Hold Shift during boot to enter GRUB, select “Advanced options for Ubuntu”, then choose a kernel with “(recovery mode)”.
2. Add nomodeset parameter: In GRUB, press ‘e’ to edit, find the line starting with “linux”, add nomodeset before quiet splash, then press Ctrl+X to boot.
3. Purge and reinstall graphics drivers: In recovery mode root shell, run apt purge nvidia* then ubuntu-drivers autoinstall.
4. Free up /boot space: df -h /boot – if full, remove old kernels with apt autoremove.
5. Run fsck from recovery: fsck -fy /dev/sdaX (replace with your root partition).

📖 Read the complete boot freeze fix guide →

Arch Linux PGP Signature Unknown Trust Error

When running pacman -Syu, you see “PGP signature is unknown trust” or “invalid or corrupted package”.

Why it happens: The pacman keyring is outdated or not initialized. GPG keys have expiration dates, and Arch updates the keyring frequently.

How to fix it:

1. Reinitialize the keyring: sudo rm -rf /etc/pacman.d/gnupg then sudo pacman-key --init and sudo pacman-key --populate archlinux.
2. Update the keyring package: sudo pacman -S archlinux-keyring.
3. Refresh keys: sudo pacman-key --refresh-keys. If the default keyserver is slow, try sudo pacman-key --keyserver keyserver.ubuntu.com --refresh-keys.
4. Check your system date: GPG signatures are time-sensitive. Run date to verify; if incorrect, use timedatectl set-ntp true.

📖 Read the complete Arch PGP fix guide →

2. Package Manager & Update Errors

Package managers (apt, dnf, pacman) are the heart of Linux. Here’s how to fix common update and installation errors.

Ubuntu “Failed to Fetch” Apt-Get Update Error

Running sudo apt update shows red “Failed to fetch” lines with repository URLs.

Why it happens: DNS resolution issues, outdated repository URLs, problematic PPAs, or server outages.

How to fix it:

1. Check your internet connection: ping -c 4 google.com. If it fails, fix DNS first (edit /etc/resolv.conf and add nameserver 8.8.8.8).
2. Change Ubuntu mirror: In Software & Updates > Ubuntu Software > “Download from” > “Other” > “Select Best Server”.
3. Remove problematic PPAs: sudo add-apt-repository --remove ppa:name or delete files in /etc/apt/sources.list.d/.
4. Clear apt cache: sudo apt clean and sudo rm -rf /var/lib/apt/lists/*, then sudo apt update.
5. Check your system date: date – if wrong, run sudo timedatectl set-ntp true.

📖 Read the complete apt update fix guide →

GPG Key Error Ubuntu (NO_PUBKEY)

When running sudo apt update, you see “NO_PUBKEY XXXXXXXXXXXXXXXX”. This means a repository’s GPG key is missing or expired.

Why it happens: The repository maintainer updated their key, or the key was never imported. This is common after adding third-party PPAs or when a distribution version reaches end-of-life.

How to fix it:

1. Add the missing key using apt-key (older Ubuntu): sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys XXXXXXXXXXXXXXXX.
2. For newer Ubuntu (22.04+), use gpg: sudo gpg --homedir /tmp --no-default-keyring --keyring /usr/share/keyrings/archive-keyring.gpg --keyserver keyserver.ubuntu.com --recv-keys XXXXXXXXXXXXXXXX
3. Update the repository’s .list file to use signed-by (for newer Ubuntu versions).
4. If the key is expired, update the keyring package: sudo apt install --reinstall ubuntu-keyring.

3. Wi-Fi & Network Issues

Wireless problems are common on Linux, especially with certain Wi-Fi chips (Realtek, Broadcom).

Fedora Wi-Fi Keeps Disconnecting

Your Wi-Fi drops every few minutes, then reconnects automatically.

Why it happens: Wi-Fi power management is too aggressive, or there’s interference with the 2.4 GHz band.

How to fix it:

1. Disable Wi-Fi power management: Check status with iwconfig. To disable permanently, create a systemd service or run sudo sed -i 's/iwconfig wlp2s0 power on/iwconfig wlp2s0 power off/g' /etc/NetworkManager/dispatcher.d/99-wifi-powersave (adjust interface name).
2. Adjust NetworkManager roaming: nmcli connection modify "YourSSID" 802-11-wireless.bgscan "100:0" to disable background scanning.
3. Disable IPv6: nmcli connection modify "YourSSID" ipv6.method "disabled".
4. Update kernel and firmware: sudo dnf upgrade --refresh and sudo dnf install linux-firmware.
5. For Realtek/Broadcom chips: Install proprietary drivers from RPM Fusion non-free: sudo dnf install akmod-rtw88 or broadcom-wl.

📖 Read the complete Fedora Wi-Fi fix guide →

Linux Wi-Fi Not Working (No Networks Found)

Your Wi-Fi adapter is not detected, or no networks appear in the list.

Why it happens: Missing firmware, driver not loaded, or hardware switch disabled.

How to fix it:

1. Check if the adapter is detected: lspci -knn | grep -i net (PCIe) or lsusb (USB).
2. Load the driver manually: sudo modprobe <driver_name> (e.g., iwlwifi for Intel, rtw88 for Realtek).
3. Install firmware: sudo apt install firmware-iwlwifi (Debian/Ubuntu) or sudo dnf install iwlwifi-dvm-firmware (Fedora).
4. Check hardware switch: Some laptops have a physical or Fn key Wi-Fi switch. Toggle it.
5. Disable secure boot (if driver fails to load): Secure boot can block unsigned kernel modules.

4. Audio & Sound Problems

Sound issues on Linux are often related to PulseAudio, PipeWire, or ALSA configuration.

Linux Mint Sound Crackling or Distorted

Audio pops, crackles, or distorts, especially during playback or system sounds.

Why it happens: PulseAudio buffer underruns, sample rate mismatches, or power saving on the audio device.

How to fix it:

1. Increase PulseAudio buffer size: Edit /etc/pulse/daemon.conf, uncomment and set default-fragments = 8 and default-fragment-size-msec = 25. Then restart PulseAudio with pulseaudio -k.
2. Set default sample rate to 48000 Hz: In the same file, default-sample-rate = 48000 and alternate-sample-rate = 48000.
3. Disable timer-based scheduling (tsched): Edit /etc/pulse/default.pa and change load-module module-udev-detect to load-module module-udev-detect tsched=0.
4. Switch to PipeWire: sudo apt install pipewire pipewire-pulse wireplumber (Mint/Ubuntu), then systemctl --user --now disable pulseaudio.service && systemctl --user --now enable pipewire pipewire-pulse.
5. Disable audio power saving: echo 'options snd-hda-intel power_save=0' | sudo tee /etc/modprobe.d/alsa.conf.

📖 Read the complete audio crackling fix guide →

PipeWire No Sound After Upgrade

After switching to PipeWire, you have no audio output.

Why it happens: PipeWire configuration conflicts or missing ALSA plugins.

How to fix it:

1. Check PipeWire status: systemctl --user status pipewire pipewire-pulse.
2. Restart PipeWire: systemctl --user restart pipewire pipewire-pulse.
3. Reinstall PipeWire: sudo apt install --reinstall pipewire pipewire-pulse wireplumber.
4. Check ALSA device: aplay -l. If no devices, run sudo alsa force-reload.

5. Graphics & Display Driver Issues

NVIDIA drivers are a common source of problems on Linux, but AMD and Intel have their own issues too.

NVIDIA Driver Black Screen on Ubuntu

After installing NVIDIA drivers, you boot to a black screen (no login screen, just black).

Why it happens: Nouveau (open-source driver) conflicts with the proprietary NVIDIA driver, or Secure Boot is blocking the driver.

How to fix it:

1. Boot into recovery mode or TTY: Press Ctrl+Alt+F2 to get a terminal. Log in with your username and password.
2. Disable Nouveau: Create /etc/modprobe.d/blacklist-nouveau.conf with: blacklist nouveau options nouveau modeset=0 Then sudo update-initramfs -u.
3. Add nomodeset kernel parameter: Edit /etc/default/grub, change GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to add nomodeset, then sudo update-grub.
4. Purge old NVIDIA drivers and reinstall: sudo apt purge nvidia*, then sudo ubuntu-drivers autoinstall.
5. Disable Secure Boot in BIOS or sign the driver with sudo update-secureboot-policy --enroll-key.

📖 Read the complete NVIDIA black screen fix guide →

6. Laptop Battery & Power Management

Linux laptop battery drain is a common complaint. Here’s how to optimize power consumption.

Linux Laptop High Battery Drain (TLP Optimization)

Your Linux laptop battery drains faster than on Windows.

Why it happens: Default Linux power management is not aggressive enough, especially for Intel CPUs.

How to fix it:

1. Install TLP: sudo apt install tlp tlp-rdw (Ubuntu/Debian) or sudo dnf install tlp (Fedora). Enable it: sudo systemctl enable tlp && sudo systemctl start tlp.
2. Run powertop –auto-tune: sudo apt install powertop, then sudo powertop --auto-tune. To make it permanent, add to systemd.
3. Install auto-cpufreq: git clone https://github.com/AdnanHodzic/auto-cpufreq.git && cd auto-cpufreq && sudo ./auto-cpufreq-installer. Then sudo auto-cpufreq --install.
4. Add kernel parameters for better power saving: In /etc/default/grub, add pcie_aspm=force i915.enable_dc=4, then sudo update-grub.
5. Disable discrete GPU on battery: For NVIDIA, sudo prime-select intel.

📖 Read the complete battery drain fix guide →

7. Permission Denied & File System Errors

“Permission denied” is one of the most common Linux errors, especially for new users.

Linux “Permission Denied” Error (Chmod & Chown Guide)

You cannot execute a script, edit a file, or enter a directory because of permission restrictions.

Why it happens: Every file in Linux has three permission sets (owner, group, others) for read (r), write (w), and execute (x). If your user lacks the required permission, you get “Permission denied.”

How to fix it:

1. Add execute permission to a script: chmod +x script.sh (adds execute for owner). For all users: chmod a+x script.sh.
2. Change file ownership: sudo chown yourusername:yourgroup filename. To change recursively: sudo chown -R yourusername:yourgroup directory/.
3. Fix directory execute permission: To enter a directory, you need execute (x) permission: chmod +x directory/.
4. Use numeric permissions: chmod 755 script.sh (owner: rwx, group: r-x, others: r-x) is common for scripts. chmod 644 file.txt for text files.
5. Check filesystem mount options: mount | grep " / " – if it says noexec, you cannot execute anything; remount with sudo mount -o remount,exec /.

📖 Read the complete permission fix guide →

Filesystem Mounted as Read-Only (Remount RW)

You cannot write files because the filesystem is read-only.

Why it happens: This can occur after a crash, disk error, or improper shutdown. The kernel remounts the partition as read-only to prevent further damage.

How to fix it:

1. Remount as read-write: sudo mount -o remount,rw /.
2. Check filesystem errors: sudo fsck -f /dev/sdaX (unmount the partition first if possible).
3. Check the logs: dmesg | grep -i "remount" to see why it became read-only.
4. If the system consistently becomes read-only, your disk may be failing. Check SMART status: sudo smartctl -a /dev/sda.

Docker Permission Denied (Cannot connect to Docker daemon)

Running docker ps shows “permission denied” or “Cannot connect to the Docker daemon”.

Why it happens: Your user is not in the docker group, or the Docker service is not running.

How to fix it:

1. Add your user to the docker group: sudo usermod -aG docker $USER.
2. Log out and log back in (or run newgrp docker).
3. Restart Docker service: sudo systemctl restart docker.
4. If the docker group does not exist: sudo groupadd docker.
5. Check Docker socket permissions: ls -l /var/run/docker.sock. It should be owned by root:docker with permissions 660.

8. Storage & Disk Space Errors

Full disks and “No space left on device” errors are common, especially on systems with small root partitions.

No Space Left on Device (Disk Full)

You try to write a file, and you see “No space left on device” even though you thought you had space.

Why it happens: The partition is full, or inodes are exhausted (too many small files).

How to fix it:

1. Check disk usage: df -h (space) and df -i (inodes).
2. Find large files: sudo du -sh /* | sort -rh | head -20.
3. Clean apt cache: sudo apt clean && sudo apt autoclean (Ubuntu/Debian).
4. Remove old kernels: sudo apt autoremove --purge (Ubuntu) or sudo pacman -Sc (Arch).
5. Clear journal logs: sudo journalctl --vacuum-size=100M.
6. Find and delete old Docker images/containers: docker system prune -a.
7. If inodes are exhausted, find directories with many small files: find / -xdev -type f | cut -d "/" -f 2 | sort | uniq -c | sort -nr | head -20.

9. Bluetooth & Peripheral Issues

Bluetooth on Linux can be hit-or-miss, especially with newer hardware.

Linux Bluetooth Not Working (No Adapter Found)

Bluetooth settings show “No adapter found” or the Bluetooth service fails to start.

Why it happens: Missing firmware, kernel module not loaded, or USB device not recognized.

How to fix it:

1. Check if the adapter is detected: lsusb | grep -i bluetooth or lspci -knn | grep -i bluetooth. If nothing appears, the hardware may be disabled in BIOS or faulty.
2. Install Bluetooth firmware: sudo apt install firmware-b43-installer (Broadcom) or sudo dnf install btusb-firmware (Fedora).
3. Load the btusb module: sudo modprobe btusb. To make it permanent: echo 'btusb' | sudo tee /etc/modules-load.d/btusb.conf.
4. Restart Bluetooth service: sudo systemctl restart bluetooth.
5. Unblock Bluetooth: rfkill unblock bluetooth.

Bluetooth No Adapter Found (Chipset not recognized)

Your Bluetooth chipset is not recognized at all. This is common with newer Realtek and Intel chips.

How to fix it:

1. Check chipset: lsusb for USB dongles, lspci for integrated.
2. Update kernel to latest version: Newer kernels have better Bluetooth support.
3. Install proprietary firmware: For Intel: sudo apt install firmware-iwlwifi. For Realtek: sudo apt install rtl8821ce-dkms (for specific chips).
4. If still not working, use a USB Bluetooth dongle (Linux-compatible like CSR 4.0).

10. Flatpak & Snap App Issues

Containerized apps have their own troubleshooting needs. For Flatpak, see the detailed section in Package Manager & Update Errors above.

Snap Apps Not Opening or Stuck

Snap applications (especially from the Snap Store) fail to launch.

Why it happens: Snap daemon issues, permission problems, or missing dependencies.

How to fix it:

1. Check snap service status: systemctl status snapd. If not running, sudo systemctl enable --now snapd.
2. Refresh all snaps: sudo snap refresh.
3. Reinstall the problematic snap: sudo snap remove appname && sudo snap install appname.
4. Check for permission issues: snap connections appname to see which interfaces are connected. sudo snap connect appname:home for home directory access.

11. SSH & Docker Connectivity Errors

Remote access and containerization tools have their own error patterns.

SSH Connection Refused (or Permission Denied)

You cannot connect to a remote server via SSH, with errors like “Connection refused” or “Permission denied (publickey)”.

Why it happens: SSH service not running, firewall blocking port 22, or incorrect key permissions.

How to fix it (client-side):

1. Check if SSH is running on the server: systemctl status ssh. If not, start it: sudo systemctl start ssh.
2. Check firewall: sudo ufw status (if using ufw). Allow SSH: sudo ufw allow 22.
3. Fix key permissions: chmod 600 ~/.ssh/id_rsa and chmod 644 ~/.ssh/id_rsa.pub.
4. Test connection with verbosity: ssh -vvv user@host to see where it fails.
5. Ensure the SSH agent has your key: ssh-add -l; if empty, run ssh-add ~/.ssh/id_rsa.

Docker: Cannot connect to the Docker daemon

Running docker ps shows “Cannot connect to the Docker daemon”.

Why it happens: Docker service not running, or user not in docker group.

How to fix it:

1. Start Docker service: sudo systemctl start docker and enable it: sudo systemctl enable docker.
2. Add your user to the docker group: sudo usermod -aG docker $USER. Log out and back in.
3. Check Docker socket permissions: ls -l /var/run/docker.sock. It should be owned by root:docker with permissions 660.

12. Advanced Troubleshooting

• Use a live USB to chroot and repair: Boot from a live USB, mount your root partition to /mnt, then sudo chroot /mnt. This lets you run repairs as if you were booted into your system.
• Check system logs: journalctl -xb | grep -i error (since last boot). dmesg | grep -i fail (kernel messages).
• Use boot parameters to bypass issues: nomodeset (graphics), acpi=off (power, last resort), pci=noacpi, irqpoll.
• Roll back a kernel update: In GRUB, select “Advanced options” and choose an older kernel. Once booted, remove the problematic kernel with sudo apt remove linux-image-X.X.X.
• Recover deleted files with testdisk/photorec: sudo apt install testdisk, then run sudo photorec to recover deleted files from any partition.

13. Quick Reference Tables

Table 1: Common Linux Errors & Quick Fixes

Table 2: Package Manager Commands by Distribution

14. Frequently Asked Questions

Q1: How do I fix GRUB rescue error?

At the grub rescue> prompt, type ls to list partitions. Test each with ls (hdX,msdosY)/ until you find your /boot directory. Then set root=(hdX,msdosY), set prefix=(hdX,msdosY)/boot/grub, insmod normal, normal. Once booted, run sudo update-grub and sudo grub-install /dev/sda.

Q2: Ubuntu is stuck on the purple splash screen – what do I do?

Boot into recovery mode (hold Shift, select Advanced options > recovery mode). Then, either add nomodeset in GRUB or purge/reinstall graphics drivers from the root shell. This is almost always a graphics driver issue.

Q3: Why does apt-get update show “Failed to fetch”?

This is usually a network issue or a problem with a PPA. First, check your internet connection (ping google.com). If that works, remove problematic PPAs (sudo add-apt-repository --remove ppa:name) or change your mirror in Software & Updates.

Q4: How do I fix “Permission denied” when running a script?

Add execute permission: chmod +x script.sh. Then run it with ./script.sh (not just the filename). If you still get errors, check the file’s owner with ls -l and use sudo if needed.

Q5: NVIDIA driver gives a black screen after install – how to recover?

Press Ctrl+Alt+F2 to get a terminal. Then disable Nouveau (sudo nano /etc/modprobe.d/blacklist-nouveau.conf with content blacklist nouveau and options nouveau modeset=0), update initramfs (sudo update-initramfs -u), and reinstall the NVIDIA driver. Also add nomodeset to GRUB.

Q6: Wi-Fi keeps disconnecting on Fedora – what can I do?

Disable Wi-Fi power management: iwconfig to see your interface, then disable with sudo iw dev wlp2s0 set power_save off. Also adjust NetworkManager’s background scan: nmcli connection modify "YourSSID" 802-11-wireless.bgscan "100:0".

Q7: How do I increase battery life on Linux?

Install TLP (sudo apt install tlp) and enable it. Also run sudo powertop --auto-tune. For Intel CPUs, install auto-cpufreq. Disable your discrete GPU on battery (sudo prime-select intel for NVIDIA).

Q8: Arch Linux pacman shows “PGP signature is unknown trust” – fix?

Reinitialize the keyring: sudo rm -rf /etc/pacman.d/gnupg, then sudo pacman-key --init, sudo pacman-key --populate archlinux, and sudo pacman -S archlinux-keyring. Also ensure your system date is correct.

Q9: No space left on device – how to find what’s taking space?

Use df -h to see which partition is full, then sudo du -sh /* | sort -rh | head -20 to find large directories. Common culprits: /var/log, /var/cache/apt, Docker images, and old kernels.

Q10: SSH connection refused – how to debug?

On the server: systemctl status ssh, sudo ufw status, ss -tlnp | grep 22. On the client: ssh -vvv user@host for verbose output. Check /var/log/auth.log on the server for denied attempts.

15. Conclusion: Find Your Problem, Apply the Fix

Linux is a robust operating system, but issues do arise. The good news is that most problems have straightforward solutions:

• Boot/GRUB issues → recover from rescue mode or live USB, reinstall GRUB.
• Package manager errors → check mirrors, clear cache, update keyrings.
• Wi-Fi problems → disable power management, update firmware, install proprietary drivers.
• Audio crackling → increase PulseAudio buffer, disable tsched, switch to PipeWire.
• NVIDIA black screen → disable Nouveau, add nomodeset, reinstall drivers.
• Battery drain → install TLP, powertop, auto-cpufreq.
• Permission denied → use chmod/chown, understand file permissions.
• No space left → clean apt cache, remove old kernels, clear logs.
• SSH connection refused → check service status, firewall, key permissions.

If you have tried everything and your system still does not work, consider these final options:

• Boot from a live USB – backup your data before attempting major repairs.
• Reinstall your distribution – sometimes the fastest solution, especially if the system is heavily corrupted.
• Ask for help on community forums – Ubuntu Forums, Arch Linux Wiki, Reddit’s r/linuxquestions are excellent resources. Include your distribution, version, hardware, and exact error messages.

🔗 This Linux troubleshooting hub is part of our Linux Fixes category. For detailed step-by-step instructions, use the linked guides throughout this page. Each guide includes tested commands and explanations. If you cannot find your specific error, use the search function or leave a comment below.

HowToFixPro Team – a technology-focused editorial team publishing accurate, tested troubleshooting guides for Windows, Android, AI tools, and Linux systems.

Last updated: June 2026 — Includes fixes for Ubuntu 24.04, Fedora 40, Arch Linux, and Linux Mint 21.3. Expanded with storage, SSH, Docker, and GPG troubleshooting.