Troubleshooting Guide

Solutions to common problems you may encounter while learning Linux.

Permission Errors

"Permission denied"

Symptom:

$ touch /etc/test.txt
touch: cannot touch '/etc/test.txt': Permission denied

Solutions:

1. Use sudo for system operations:

   sudo touch /etc/test.txt
   

2. Check if you need to own the file:

   sudo chown $USER /etc/test.txt
   

3. Check file permissions:

   ls -l /etc/test.txt
   

Command Not Found

"command not found"

Symptom:

$ git
git: command not found

Solutions:

1. Check spelling:

   # Common typos
   cd /hme/user      # Wrong
   cd /home/user     # Correct
   

2. Install missing package:

   Fedora:

   sudo dnf install git
   

   Debian:

   sudo apt install git
   

3. Check PATH:

   echo $PATH
   which git
   

File System Issues

"No such file or directory"

Symptom:

$ cd documents
bash: cd: documents: No such file or directory

Solutions:

1. List current directory contents:

   ls -la
   

2. Check your location:

   pwd
   

3. Use tab completion to avoid typos:

   cd doc<Tab>    # Completes to documents/
   

4. Search for the file:

   find ~ -name "documents" -type d
   

"Directory not empty"

Symptom:

$ rm directory/
rm: cannot remove 'directory/': Is a directory

Solutions:

1. Use recursive remove:

   rm -r directory/
   

2. Remove with confirmation:

   rm -ri directory/
   

Package Management Issues

"Could not get lock /var/lib/dpkg/lock"

Symptom (Debian):

E: Could not get lock /var/lib/dpkg/lock-frontend

Solutions:

1. Wait for another package manager to finish

2. Check for running processes:

   ps aux | grep apt
   

3. Remove lock (if stuck):

   sudo rm /var/lib/dpkg/lock-frontend
   sudo rm /var/lib/dpkg/lock
   

"Cannot update repository metadata"

Symptom (Fedora):

Error: Cannot update repository metadata

Solutions:

1. Clean metadata cache:

   sudo dnf clean all
   sudo dnf makecache
   

2. Check network connection:

   ping -c 3 fedoraproject.org
   

3. Refresh repositories:

   sudo dnf refresh
   

Process Issues

Process won't stop

Symptom: Application freezes and won't close.

Solutions:

1. Find the process ID:

   ps aux | grep application_name
   

2. Try graceful termination:

   kill <PID>
   

3. Force kill if needed:

   kill -9 <PID>
   

4. Kill by name:

   pkill application_name
   killall application_name
   

Service won't start

Symptom:

$ sudo systemctl start nginx
Job for nginx.service failed.

Solutions:

1. Check service status:

   systemctl status nginx
   

2. View service logs:

   journalctl -u nginx -n 50
   

3. Check configuration:

   sudo nginx -t    # Test nginx config
   

4. Check for port conflicts:

   sudo ss -tulpn | grep :80
   

Network Issues

Cannot connect to WiFi

Solutions:

1. Check network interface:

   ip link show
   

2. Bring interface up:

   sudo ip link set wlan0 up
   

3. Use NetworkManager (GUI or CLI):

   nmcli dev wifi list
   nmcli dev wifi connect "SSID" password "password"
   

4. Restart network service:

   sudo systemctl restart NetworkManager
   

SSH connection refused

Symptom:

$ ssh user@host
ssh: connect to host port 22: Connection refused

Solutions:

1. Check if SSH server is running:

   systemctl status sshd       # Fedora
   systemctl status ssh        # Debian
   

2. Start SSH server:

   sudo systemctl start sshd
   sudo systemctl enable sshd
   

3. Check firewall:

   sudo firewall-cmd --list-all    # Fedora
   sudo ufw status                 # Debian
   

4. Check if port 22 is open:

   sudo ss -tulpn | grep :22
   

Disk Space Issues

"No space left on device"

Symptom:

$ touch file.txt
touch: cannot touch 'file.txt': No space left on device

Solutions:

1. Check disk usage:

   df -h
   

2. Find large files:

   du -h ~ | sort -hr | head -20
   

3. Clean package cache:

   Fedora:

   sudo dnf clean all
   

   Debian:

   sudo apt clean
   sudo apt autoremove
   

4. Empty trash:

   rm -rf ~/.local/share/Trash/*
   

5. Clean old logs:

   sudo journalctl --vacuum-time=7d
   

Git Issues

"fatal: not a git repository"

Symptom:

$ git status
fatal: not a git repository (or any of the parent directories)

Solutions:

1. Initialize repository:

   git init
   

2. Clone existing repository:

   git clone <url>
   

Merge conflicts

Symptom:

$ git merge feature
Auto-merging file.txt
CONFLICT (content): Merge conflict in file.txt

Solutions:

1. Edit the file and resolve conflicts manually

2. Mark as resolved:

   git add file.txt
   git commit
   

3. Abort merge if needed:

   git merge --abort
   

Docker Issues

"Permission denied while trying to connect to the Docker daemon"

Symptom:

$ docker ps
permission denied while trying to connect to the Docker daemon socket

Solutions:

1. Use sudo:

   sudo docker ps
   

2. Add user to docker group:

   sudo usermod -aG docker $USER
   

3. Log out and back in for changes to take effect.

Container exits immediately

Symptom:

$ docker run nginx
$ docker ps -a
CONTAINER ID   STATUS
abc123         Exited (0) 5 seconds ago

Solutions:

1. Container may have no foreground process

2. Use -d for detached mode:

   docker run -d nginx
   

3. Check logs:

   docker logs <container_id>
   

Getting Help

Built-in Help

Man pages (manual):

man <command>      # e.g., man ls
man -k <keyword>   # Search man pages

Help flag:

<command> --help   # e.g., ls --help

Info pages:

info <command>

Online Resources

• Fedora Documentation: https://docs.fedoraproject.org/
• Debian Documentation: https://www.debian.org/doc/
• Arch Wiki (excellent general reference): https://wiki.archlinux.org/
• Linux Command Library: https://linux.die.net/
• Stack Overflow: https://stackoverflow.com/questions/tagged/linux

Community Forums

• Fedora Discussion: https://discussion.fedoraproject.org/
• Debian Forums: https://forums.debian.net/
• Reddit r/linux4noobs: https://reddit.com/r/linux4noobs

Debugging Commands