Find What Is Using a Local Dev Port
Your dev server says port 3000 is busy. Ask macOS who is holding it.
lsof -nP -iTCP:3000 -sTCP:LISTEN
problem area
Apple Terminal
macOS and Apple-adjacent terminal workflows for developers and power users.
10 checked fixes
One-liners in this area
Stop the Process Blocking a Dev Port
Free a stuck dev port without hunting through Activity Monitor.
lsof -ti tcp:3000 | xargs kill
Show Your PATH One Entry Per Line
Wrong Node, Python, or FFmpeg? Start by reading your PATH clearly.
echo "$PATH" | tr ':' '\n' | nl -ba
See Exactly Which Command macOS Will Run
Before blaming npm, Python, or Git, check the binary your shell actually found.
command -v node && node -v
Find Large Files Inside a Project
Before committing, check whether a huge video, build artifact, or export slipped into your repo.
find . -type f -size +100M -print
Find Which Folder Is Eating Disk Space
When your Mac is full, start with the biggest folders in the current directory.
du -sh ./* 2>/dev/null | sort -h
Flush macOS DNS Cache
Changed DNS but your Mac still visits the old place? Flush the resolver cache.
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
Watch a Log or Build File Update
Need to see whether a file is still changing? Let tail follow it live.
tail -f ./app.log
Search a Log for Errors With Context
A wall of logs is useless until you pull the error and the lines around it.
grep -n -C 2 'ERROR' ./app.log
Check a URL Without Downloading the Page
Before opening a broken page in five browsers, ask the server for headers.
curl -I https://example.com