Find the largest files in a directory
find . -type f -exec du -h {} + | sort -rh | head -n 20Run it before deleting anything. du reports space on disk, so sparse files look smaller than ls says.
Linux snippets
Shell commands for everyday Linux administration that each do one job. Copy one straight from this page — the note under each says what it changes and where it differs on macOS.
Disk
Find the largest files on the root filesystem
sudo find / -xdev -type f -exec du -h {} + | sort -rh | head -n 20-xdev keeps it off /proc and network mounts. It reads every inode, so give it minutes.
Show the size of each directory one level down
du -h -d 1 . | sort -rhTotals per folder rather than per file — the quicker way to pick which tree to dig into.
Networking
See which process is listening on a port
sudo ss -tulpnWithout sudo the process column is empty for other users' sockets, which reads as nothing listening.
See what is holding one port
sudo ss -tlpn 'sport = :8080'The answer to "address already in use". A socket on 127.0.0.1 is reachable only from this host.
See what is listening on a port, on macOS too
sudo lsof -nP -iTCP:8080 -sTCP:LISTENmacOS has no ss. lsof is the equivalent there and works on Linux as well.
Services
Follow a systemd service's logs live
journalctl -u nginx -fCtrl+C stops it. A service that writes its own log file will not appear here.
Follow a service's logs from the last 100 lines
journalctl -u nginx -f -n 100Enough history to see what happened just before you attached.
Show a service's errors from the last hour
journalctl -u nginx -p err --since "1 hour ago"-p err drops the info and debug lines; --since takes plain English like "10 min ago".
List the services that failed to start
systemctl --failedThe first command to run on a box that came up wrong.