Linux - Ubuntu Server Essential Commands

Basic Git Operations

• You can get help on a specific git command using git help commit or alternatively view the Git User Manual and git-scm Documentation
• -s option with each commit adds a Signed-off-by: entry required when using DCO to document code contributions.
• git gui provides a graphical interface to git.

Git Commands

• Create a local git repository - the version control information is stored in the .git subdirectory:

  mkdir gitdir
  cd gitdir
  git init
  ls -l .git
  

• Add new files to staging area ready to commit:

echo "This is testfile1" > testfile1.txt
echo "This is testfile2" > testfile2.txt
git add .
git status

• Set who is responsible for the repository:

  git config --global user.name "Richard Hudson"
  git config --global user.email "richard.b.j.hudson@gmail.com"
  

  Note: You may omit the --global option to set on a per repository basis.

• Commit changes to files:

echo "Line2" >> testfile1.txt
cat testfile1.txt
git diff testfile1.txt
git add testfile1.txt
git status
git commit -m "Initial commit"
git status

Note: You may sign off a git commit using git commit -m "Initial commit" -s.

• View git commit history using git log.
• Create and switch to a main branch to replace master:

git checkout -b main
git branch
git branch -d master
git branch

• Rename master branch to main:

git checkout master
git branch -m master main
git push -u origin main
git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main
git branch -a

Note: You could simply create a new main branch and then ignore the master branch.

Create, configure, and troubleshoot services

• Systemd configures the environment and starts processes ready for user login. It replaces shell scripts with programs and provides on-demand daemon starting and can track processes using cgroups.
• systemctl displays everything that systemd controls.
• You can list units of type service using systemctl list-units -t service.
• systemctl status apache2 is used to display the status of a service.
• You can change the state of a service with sudo systemctl [start/stop/restart] apache2 and reload its configuration using sudo systemctl reload apache2.
• systemctl [enable/ disable] apache2 is used to set a service to start at boot time.

Monitor and troubleshoot system performance and services

System Monitoring

Process Monitoring

Memory Monitoring

Determine application and service specific constraints

• How to troubleshoot services
• How to troubleshoot system performance issues
• How to troubleshoot a SELinux label issue
• Most applications will have their own log file located in /var/log.
• help ulimit may be used to provide control over the resources available to the shell and processes.
  • To make changes effective for all logged-in users amend /etc/security/limits.conf.

Troubleshoot diskspace issues

• df -Th displays filesystem usage with its type and human readable size.
• Once you have identified a filesystem that is running out of space, you may examine disk usage for the current directory using du -hsc *.
• df -i displays the number of inodes (metadata describing stored data) in use. A filesystem may report as full if an inode limit is hit. You would need to delete files to reclaim inodes.
• ncdu -x /var provides a tree view of your filesystem and D allows you to delete the selected file or directory.

Work with SSL certificates

• How to Setup an Apache Web Server