שאטצ'יט Linux — דף עזר לפקודות

Files, search, processes, permissions, archives, network, shortcuts, Vim and cron — command and example.

A quick reference for the whole Linux track: command, what it does and an example. Technical terms stay in English, as at work.

General command pattern

command [-argument] [--long-argument] file

text

Command	What it does
Command `cd dir; ls`	What it does; — run in sequence, even if the previous one failed
Command `mkdir proj && cd proj`	What it does&& — runs only if the previous one succeeded
Command `ping -c1 host \|\| echo "down"`	What it does\|\| — runs only if the previous one failed
Command `long-task &`	What it does& — run in the background
Command `cmd1 \| cmd2`	What it does\| — output of one becomes input of the next
Command `TAB`	What it doesAuto-complete commands, files and paths
Command `history / !100`	What it doesCommand history; !100 re-runs line 100
Command `ls -la`	What it doesShows hidden files too (names starting with a dot)

📁 Files and directories

Command	What it does
Command `ls -la`	What it doesList directory contents with details and hidden files
Command `cd /var/log · cd ~ · cd -`	What it doesChange directory; ~ home, - back to previous
Command `pwd`	What it doesCurrent path
Command `mkdir -p a/b/c`	What it doesCreate a directory including parents
Command `rm -r dir · rm -f file`	What it doesDelete — there is no recycle bin!
Command `cp -r src/ dst/`	What it doesCopy
Command `mv old.txt new.txt`	What it doesMove or rename
Command `ln -s target link`	What it doesCreate a symbolic link
Command `touch file.txt`	What it doesCreate a file or update its timestamp

🔍 Searching

Command	What it does
Command `grep -r "error" /var/log`	What it doesSearch text inside files
Command `find / -name "*.conf" 2>/dev/null`	What it doesFind files by attributes
Command `locate passwd`	What it doesFast search from a database (needs updatedb)
Command `which python3`	What it doesWhere a command lives
Command `grep Failed auth.log \| cut -d' ' -f11 \| sort \| uniq -c \| sort -rn \| head`	What it doesTypical log chain: who failed to log in most often

⚙️ Processes

Command	What it does
Command `ps aux · ps aux \| grep nginx`	What it doesRunning processes
Command `kill -9 PID`	What it doesStop a process (-9 = SIGKILL, last resort)
Command `killall firefox`	What it doesStop by name
Command `top · htop`	What it doesLive view and process management
Command `jobs · fg %1 · Ctrl+Z → bg`	What it doesMove jobs between background and foreground

🔐 Permissions

order: owner / group / world
r = read (4) · w = write (2) · x = execute (1)
chmod 755 file → rwx owner, r-x group/world
chmod 777 file → rwx for everyone (avoid!)

text

Command	What it does
Command `chmod 644 file · chmod u+x script.sh`	What it doesChange permissions
Command `sudo chown user:group file`	What it doesChange owner
Command `umask`	What it doesDefault mask: 022 = files 644
Command `id alice · groups`	What it doesWho am I and which groups

🗜️ Archives and compression

Command	What it does
Command `tar -czvf a.tar.gz dir/`	What it doesCreate a compressed archive
Command `tar -xzvf a.tar.gz -C /restore/`	What it doesExtract
Command `tar -tzvf a.tar.gz`	What it doesList contents — before extracting!
Command `gzip -k file.log · gunzip`	What it doesCompress one file (-k keeps the original)
Command `zcat log.gz \| tail`	What it doesView a compressed file

🌐 Network

Command	What it does
Command `ping -c 4 8.8.8.8`	What it doesReachability and latency
Command `ip a · ip r`	What it doesIP addresses and routing table
Command `ss -tulpn`	What it doesOpen ports and the listening process
Command `dig +short example.com · nslookup`	What it doesDNS query
Command `curl -I https://site.com`	What it doesHTTP check
Command `wget -O out.zip URL`	What it doesDownload a file
Command `ssh -p 2222 user@host`	What it doesRemote login
Command `scp file user@host:/tmp/`	What it doesCopy over SSH

💻 System info

Command	What it does
Command `uname -a`	What it doesKernel and system version
Command `cat /etc/os-release`	What it doesWhich distribution is installed
Command `df -h`	What it doesDisk usage — the most important!
Command `du -sh /var/*`	What it doesWhat takes up space
Command `free -h`	What it doesMemory (cache is not really used memory)
Command `uptime`	What it doesUptime and load average
Command `who · w`	What it doesWho is logged in
Command `journalctl -p err --since today`	What it doesToday's errors

⌨️ Terminal shortcuts

Command	What it does
Command `Ctrl+C`	What it doesStop the current command
Command `Ctrl+Z`	What it doesSuspend to background (fg to resume)
Command `Ctrl+R`	What it doesReverse history search
Command `Ctrl+L`	What it doesClear the screen (like clear)
Command `Ctrl+A · Ctrl+E`	What it doesStart / end of line
Command `Ctrl+U · Ctrl+K`	What it doesDelete line backward / forward
Command `Ctrl+D`	What it doesExit / EOF (careful as root!)
Command `!! · sudo !!`	What it doesRepeat last command; or with sudo

✏️ Vim survival

Command	What it does
Command `Esc → :wq`	What it doesSave and quit
Command `Esc → :q!`	What it doesQuit without saving
Command `i`	What it doesEnter insert mode
Command `/text + Enter · n`	What it doesSearch; n for next match
Command `dd · u · Ctrl+R`	What it doesDelete line, undo, redo
Command `o · O`	What it doesNew line below / above
Command `:N · G · gg`	What it doesJump to line N / end / start

⏰ cron and ufw

crontab -e                    # edit scheduler
crontab -l                    # list
0 3 * * * /home/u/backup.sh   # min hour day month weekday
sudo ufw allow 22/tcp && sudo ufw enable   # SSH first, then enable
sudo ufw status verbose

bash

Linux cheat sheet — commands on one page

What you will learn here