Command reference

Use this as a reminder after completing the chapters. Replace file paths and service names with actual lab values.

Task	Command
Current directory	`pwd`
Detailed file listing	`ls -lah`
Create a directory	`mkdir practice`
Move a file	`mv notes.txt practice/`
Read a file	`cat practice/notes.txt`
Search with line numbers, ignoring case	`grep -in 'word' practice/notes.txt`
Current identity	`id`
Username	`id -un`
Addresses	`ip -br addr`
Routes	`ip route`
Neighbor cache	`ip neigh`
Resolver file	`cat /etc/resolv.conf`
DNS lookup	`dig example.com`
Four bounded ping probes	`ping -c 4 -W 2 example.com`
HTTP headers	`curl -I --connect-timeout 3 --max-time 10 https://example.com`
Listening TCP sockets	`ss -ltn`
Listening UDP sockets	`ss -lun`
SSH service state	`systemctl status ssh --no-pager`
Recent nginx journal entries	`journalctl -u nginx -n 30 --no-pager`
Filesystem space	`df -h`
Filesystem inodes	`df -i`
Directory disk usage	`du -sh ~/interview-practice`
Last ten file lines	`tail practice/notes.txt`
Command help	`man ip`

Remember: > truncates, >> appends, and | sends one command's standard output to another command's standard input.