Git and Linux Daily Workflow for Backend Engineers

# Inspect the object graph directly
git cat-file -p HEAD              # show the commit object
git cat-file -p HEAD^{tree}       # show the tree it points to
git log --oneline --graph --all   # visualize the commit graph

# Short-lived branch, rebased daily onto main
git checkout -b feat/rate-limit-header
# ... work, commit small increments ...
git fetch origin
git rebase origin/main          # stay current, avoid a giant merge later
git push --force-with-lease     # safe force-push after rebase

# Keep your feature branch current — rebase onto latest main
git checkout feat/rate-limit-header
git fetch origin
git rebase origin/main
 
# Squash messy WIP commits before opening a PR
git rebase -i HEAD~5
# In the editor: mark commits as 'squash' or 'fixup', keep one clean commit
 
# Merging a finished feature into main (typical PR merge)
git checkout main
git merge --no-ff feat/rate-limit-header   # explicit merge commit, preserves branch context

$ git merge origin/main
Auto-merging src/main/java/com/acme/order/OrderService.java
CONFLICT (content): Merge conflict in src/main/java/com/acme/order/OrderService.java
Automatic merge failed; fix conflicts and then commit the result.

public void cancelOrder(String orderId) {
<<<<<<< HEAD
    Order order = repository.findById(orderId)
        .orElseThrow(() -> new OrderNotFoundException(orderId));
    order.markCancelled();
=======
    Order order = repository.findByIdOrThrow(orderId);
    order.transitionTo(OrderStatus.CANCELLED);
    auditLog.record(orderId, "CANCELLED");
>>>>>>> origin/main
    repository.save(order);
}

git add src/main/java/com/acme/order/OrderService.java
git rebase --continue     # if resolving during a rebase
# or
git commit                # if resolving during a merge

git merge --abort      # bail out of a merge, return to pre-merge state
git rebase --abort     # bail out of a rebase, return to pre-rebase state

# The escape hatch: reflog remembers everything, even after a bad reset --hard
git reflog
# a1b2c3d HEAD@{0}: reset: moving to HEAD~1
# f4e5d6c HEAD@{1}: commit: add idempotency key to payment endpoint  ← I want this back
git reset --hard f4e5d6c

# grep: search file contents
grep -rn "OrderNotFoundException" src/                # recursive, show line numbers
grep -rn --include="*.java" "TODO" src/                # only .java files
grep -A 3 -B 1 "ERROR" application.log                 # 3 lines after, 1 before match
grep -c "GET /health" access.log                        # count matches
grep -v "DEBUG" app.log | grep "payment-service"         # exclude, then filter
 
# find: search the filesystem
find . -name "*.yml" -mtime -1                          # yaml files modified in last 24h
find . -type f -size +100M                               # files over 100MB (log bloat)
find /var/log -name "*.log" -mtime +30 -delete            # cleanup old logs (careful!)
find . -name "*.class" -exec rm {} \;                     # delete build artifacts

ps aux | grep java                    # find the running JVM process
ps -ef --forest                       # process tree view
top                                   # live CPU/memory (or htop if installed)
lsof -i :8080                         # what's holding port 8080
lsof -p <pid>                         # open files/sockets for a process
kill -15 <pid>                        # SIGTERM — graceful shutdown
kill -9 <pid>                         # SIGKILL — force kill (last resort)
df -h                                 # disk space by filesystem
du -sh */ | sort -rh | head -10       # largest directories
free -h                               # memory usage

tail -f /var/log/app/service.log                 # follow a log file live
tail -f service.log | grep --line-buffered ERROR   # live-filter for errors
journalctl -u myapp.service -f                      # follow systemd-managed service logs
journalctl -u myapp.service --since "10 min ago"    # recent logs for a unit
less +F application.log                              # tail-like mode inside less (Ctrl+C, then F to resume)

curl -s https://api.internal/health | jq .           # hit an endpoint, pretty-print JSON
curl -i -X POST https://api.internal/orders \
  -H "Content-Type: application/json" \
  -d '{"customerId":"c1","items":[]}'                 # inspect headers + body
curl -w "@curl-format.txt" -o /dev/null -s https://api.internal/orders  # timing breakdown
ss -tulnp                                             # listening ports (modern replacement for netstat)
dig api.internal +short                               # DNS resolution
nc -zv db.internal 3306                                # test TCP connectivity to a port

chmod 640 application-secrets.yml     # owner rw, group r, others nothing
chmod +x deploy.sh                    # make a script executable
chown appuser:appgroup /var/app       # change owner and group
umask 027                             # default permissions for newly created files

systemctl status myapp.service         # is it running? recent log tail included
systemctl start myapp.service
systemctl stop myapp.service
systemctl restart myapp.service
systemctl enable myapp.service         # start automatically on boot
sudo systemctl daemon-reload           # reload unit files after editing them
journalctl -u myapp.service -n 100 --no-pager  # last 100 log lines

# /etc/systemd/system/myapp.service — a minimal Spring Boot service unit
[Unit]
Description=Order Service
After=network.target
 
[Service]
User=appuser
WorkingDirectory=/opt/order-service
ExecStart=/usr/bin/java -jar /opt/order-service/app.jar
SuccessExitStatus=143
Restart=on-failure
RestartSec=5
Environment=SPRING_PROFILES_ACTIVE=production
 
[Install]
WantedBy=multi-user.target