$devvkit resources --cheatsheet linux-command-line

Linux Command Line

[terminal]

Every essential Linux CLI command: navigation, files, permissions, processes, text processing, archives, and disk, with syntax and real use cases.150 commands · 8 sections

The Linux command line is the developer's home base. This cheatsheet covers the commands you use daily: navigating and inspecting files, creating and moving files, permissions and ownership, managing processes, text processing with grep/sed/awk, archives, and disk usage.

Every command shows its real syntax followed by the use case: when and why you reach for it.

Navigation & File Info20

$pwd

Use case: Print the current working directory: where am I?Example: pwd

$ls

Use case: List files in the current directory.Example: ls

$ls -la

Use case: List ALL files with details: hidden files, permissions, sizes, dates.Example: ls -la

$ls -lh

Use case: List files with human-readable sizes (KB, MB, GB).Example: ls -lh

$ls -lt

Use case: Sort by modification time, newest first: what did I just touch?Example: ls -lt

$ls -R

Use case: List recursively: see the whole tree.Example: ls -R src

$cd <dir>

Use case: Change directory.Example: cd ~/projects

$cd ..

Use case: Go up one level.Example: cd ..

$cd -

Use case: Go to the previous directory: toggle between two folders.Example: cd -

$cd ~

Use case: Go to your home directory.Example: cd ~

$find . -name "*.ts"

Use case: Find files by name pattern: recursive search.Example: find . -name "*.ts"

$find . -type d -name "node_modules"

Use case: Find directories by name: locate all node_modules.Example: find . -type d -name "node_modules"

$find . -mtime -7

Use case: Files modified in the last 7 days: what changed this week?Example: find . -mtime -7

$find . -size +100M

Use case: Files larger than 100MB: disk hogs.Example: find . -size +100M

$find . -name "*.log" -delete

Use case: Find and delete in one shot: clean up log files.Example: find . -name "*.log" -delete

$tree -L 2

Use case: Show the directory tree 2 levels deep (install with apt install tree).Example: tree -L 2

$file <file>

Use case: Identify a file's type: what is this mystery file?Example: file report.pdf

$stat <file>

Use case: Full metadata: permissions, timestamps, size, inode.Example: stat package.json

$which <cmd>

Use case: Where is this command installed?Example: which node

$type <cmd>

Use case: Is it a binary, alias, or shell builtin?Example: type cd

File Operations22

$touch <file>

Use case: Create an empty file or update its timestamp.Example: touch .env.local

$mkdir <dir>

Use case: Create a directory.Example: mkdir src

$mkdir -p a/b/c

Use case: Create nested directories: no error if they exist.Example: mkdir -p src/components/ui

$cp <src> <dst>

Use case: Copy a file.Example: cp .env.example .env

$cp -r <src> <dst>

Use case: Copy a directory recursively.Example: cp -r dist backup-dist

$cp -a <src> <dst>

Use case: Copy preserving permissions, ownership, and timestamps: full fidelity.Example: cp -a public public-backup

$mv <src> <dst>

Use case: Move or rename a file.Example: mv index.js main.js

$rm <file>

Use case: Delete a file. No trash, no undo.Example: rm old-report.txt

$rm -r <dir>

Use case: Delete a directory and everything inside it.Example: rm -r node_modules

$rm -rf <dir>

Use case: Force recursive delete: the nuclear option. Double-check the path.Example: rm -rf build

$rm -i <file>

Use case: Interactive delete: confirm each file.Example: rm -i *.tmp

$ln -s <target> <link>

Use case: Create a symlink: point to a file or dir from elsewhere.Example: ln -s ../shared-config.json config.json

$cat <file>

Use case: Print a file's contents.Example: cat package.json

$cat file1 file2 > merged

Use case: Concatenate files into one.Example: cat a.txt b.txt > merged.txt

$less <file>

Use case: View a file page by page: q to quit, / to search.Example: less app.log

$head -20 <file>

Use case: First 20 lines: peek at a log or config.Example: head -20 app.log

$tail -20 <file>

Use case: Last 20 lines: see the newest entries.Example: tail -20 app.log

$tail -f <file>

Use case: Follow a file as it grows: live log viewing.Example: tail -f app.log

$wc -l <file>

Use case: Count lines: how big is this file?Example: wc -l app.log

$wc -w <file>

Use case: Count words.Example: wc -w README.md

$diff file1 file2

Use case: Compare two files line by line.Example: diff local.env prod.env

$diff -r dir1 dir2

Use case: Compare two directories recursively.Example: diff -r src-backup src

Permissions & Ownership9

$chmod 755 <file>

Use case: Owner rwx, group and others r-x: standard for executables and directories.Example: chmod 755 deploy.sh

$chmod +x <file>

Use case: Make a script executable.Example: chmod +x deploy.sh

$chmod 600 <file>

Use case: Owner read/write only: private files like SSH keys and .env.Example: chmod 600 ~/.ssh/id_rsa

$chmod -R 755 <dir>

Use case: Apply recursively to a directory tree.Example: chmod -R 755 public

$chown user:group <file>

Use case: Change file owner and group.Example: sudo chown www-data:www-data index.html

$chown -R user:group <dir>

Use case: Change ownership recursively: fix permission messes.Example: sudo chown -R $USER:$USER ~/projects

$umask 022

Use case: Set default permissions for new files: 022 = 644 for files, 755 for dirs.Example: umask 022

$getfacl <file>

Use case: Show extended ACLs: finer-grained permissions.Example: getfacl config.json

$setfacl -m u:deploy:rwx <dir>

Use case: Grant a user specific rights via ACL: no chown needed.Example: setfacl -m u:deploy:rwx /var/www

Process Management22

$ps aux

Use case: List ALL processes with CPU/memory: find what is eating the machine.Example: ps aux

$ps aux | grep node

Use case: Filter processes by name: all node processes.Example: ps aux | grep node

$top

Use case: Live process monitor: refresh every second.Example: top

$htop

Use case: Nicer interactive process monitor with tree view.Example: htop

$kill <pid>

Use case: Send SIGTERM: ask the process to stop gracefully.Example: kill 1234

$kill -9 <pid>

Use case: Send SIGKILL: force kill. Last resort, skips cleanup.Example: kill -9 1234

$killall <name>

Use case: Kill every process with that name.Example: killall node

$pkill -f <pattern>

Use case: Kill processes matching a full command-line pattern.Example: pkill -f "next dev"

$pgrep -a <name>

Use case: Find process IDs with their command lines.Example: pgrep -a node

$jobs

Use case: List background jobs in the current shell.Example: jobs

$fg

Use case: Bring the most recent background job to the foreground.Example: fg

$bg

Use case: Resume a stopped job in the background.Example: bg

$command &

Use case: Run a command in the background: get your prompt back.Example: npm run dev &

$nohup <cmd> &

Use case: Run a command immune to hangup: keep it alive after logout.Example: nohup node server.js &

$nice -n 10 <cmd>

Use case: Lower a process's priority: run heavy jobs politely.Example: nice -n 10 make build

$renice 5 -p <pid>

Use case: Change priority of a running process.Example: renice 5 -p 1234

$crontab -e

Use case: Edit your cron jobs: schedule recurring tasks.Example: crontab -e

$crontab -l

Use case: List your scheduled jobs.Example: crontab -l

$systemctl status <service>

Use case: Check a systemd service's status: is nginx running?Example: systemctl status nginx

$systemctl start/stop/restart <service>

Use case: Manage a service: systemctl restart nginx.Example: systemctl restart nginx

$systemctl enable --now <service>

Use case: Start a service and enable it on boot.Example: systemctl enable --now docker

$journalctl -u <service> -f

Use case: Follow a service's logs: systemd logging.Example: journalctl -u nginx -f

Text Processing & Pipes27

$grep "error" app.log

Use case: Find lines containing "error".Example: grep "error" app.log

$grep -i "error" app.log

Use case: Case-insensitive search.Example: grep -i "error" app.log

$grep -r "apiKey" src/

Use case: Recursive search across a directory.Example: grep -r "apiKey" src/

$grep -l "error" *.log

Use case: List filenames only: which logs contain errors?Example: grep -l "error" *.log

$grep -c "error" app.log

Use case: Count matching lines.Example: grep -c "error" app.log

$grep -v "debug" app.log

Use case: Invert: lines WITHOUT "debug".Example: grep -v "debug" app.log

$grep -E "error|fatal" app.log

Use case: Extended regex: match multiple patterns.Example: grep -E "error|fatal" app.log

$grep -n "error" app.log

Use case: Show line numbers: jump straight to the problem.Example: grep -n "error" app.log

$grep -r --include="*.js" "TODO" src/

Use case: Search only certain file types.Example: grep -r --include="*.js" "TODO" src/

$sed -i 's/old/new/g' <file>

Use case: Replace all occurrences in place: edit files from the terminal.Example: sed -i 's/localhost:3000/www.devvkit.com/g' config.js

$sed -n '1,20p' <file>

Use case: Print lines 1-20: a precise slice.Example: sed -n '1,20p' app.log

$sed -i '/^#/d' <file>

Use case: Delete comment lines in place.Example: sed -i '/^#/d' .env

$awk '{print $1}' <file>

Use case: Print the first column of each line.Example: awk '{print $1}' access.log

$awk -F, '{print $2}' data.csv

Use case: Split by comma and print column 2: CSV work.Example: awk -F, '{print $2}' users.csv

$awk '{sum += $1} END {print sum}' nums.txt

Use case: Sum a column of numbers.Example: awk '{sum += $1} END {print sum}' sales.txt

$cut -d, -f1-3 data.csv

Use case: Extract fields 1-3 by delimiter.Example: cut -d, -f1-3 users.csv

$cut -c1-10 <file>

Use case: Extract the first 10 characters of each line.Example: cut -c1-10 app.log

$sort <file>

Use case: Sort lines alphabetically.Example: sort names.txt

$sort -n <file>

Use case: Sort numerically: sizes, counts, scores.Example: sort -n scores.txt

$sort -r <file>

Use case: Sort in reverse: biggest first.Example: sort -rn scores.txt

$sort -u <file>

Use case: Sort and remove duplicates.Example: sort -u emails.txt

$uniq -c <file>

Use case: Count consecutive duplicates: pair with sort first.Example: sort access.log | uniq -c | sort -rn

$wc -l access.log | awk '{print $1}'

Use case: Count lines and strip the filename: script-friendly.Example: wc -l access.log | awk '{print $1}'

$cat *.log | grep -E "ERROR" | wc -l

Use case: Count errors across all logs: the pipeline pattern.Example: cat *.log | grep -E "ERROR" | wc -l

$tee <file>

Use case: Write output to a file AND keep printing it: capture while watching.Example: npm run build | tee build.log

$xargs -n1 <cmd>

Use case: Run a command for each input line: batch operations.Example: find . -name "*.tmp" | xargs rm

$tr '[:lower:]' '[:upper:]' < <file>

Use case: Translate characters: uppercase conversion.Example: echo "hello" | tr '[:lower:]' '[:upper:]'

Archives & Disk17

$tar -czf archive.tar.gz <dir>

Use case: Create a compressed archive.Example: tar -czf backup.tar.gz src

$tar -xzf archive.tar.gz

Use case: Extract a .tar.gz archive.Example: tar -xzf backup.tar.gz

$tar -tzf archive.tar.gz

Use case: List contents without extracting.Example: tar -tzf backup.tar.gz

$tar -xzf archive.tar.gz -C <dir>

Use case: Extract into a specific directory.Example: tar -xzf node.tar.gz -C /opt

$tar -czf - <dir> | ssh server "tar -xzf - -C /target"

Use case: Stream a directory to a remote machine without a temp file.Example: tar -czf - src | ssh server "tar -xzf - -C /var/www"

$zip -r archive.zip <dir>

Use case: Create a zip archive.Example: zip -r release.zip dist

$unzip archive.zip

Use case: Extract a zip.Example: unzip release.zip

$unzip -l archive.zip

Use case: List zip contents.Example: unzip -l release.zip

$gzip <file>

Use case: Compress a single file: creates file.gz.Example: gzip app.log

$gunzip <file>.gz

Use case: Decompress a .gz file.Example: gunzip app.log.gz

$df -h

Use case: Disk space per filesystem, human-readable.Example: df -h

$du -sh <dir>

Use case: Total size of a directory.Example: du -sh node_modules

$du -sh * | sort -rh | head -10

Use case: The 10 largest items in the current directory: disk cleanup.Example: du -sh * | sort -rh | head -10

$du -sh --max-depth=1 . | sort -rh

Use case: Size of each immediate subdirectory.Example: du -sh --max-depth=1 . | sort -rh

$fsck /dev/sda1

Use case: Check and repair a filesystem (run from recovery mode).Example: sudo fsck /dev/sda1

$mount /dev/sdb1 /mnt/data

Use case: Mount a partition.Example: sudo mount /dev/sdb1 /mnt/data

$umount /mnt/data

Use case: Unmount a filesystem.Example: sudo umount /mnt/data

Users & Network20

$whoami

Use case: Print the current user.Example: whoami

$id

Use case: Show user and group IDs.Example: id

$sudo -i

Use case: Open a root shell.Example: sudo -i

$sudo -u <user> <cmd>

Use case: Run a command as another user.Example: sudo -u www-data ls /var/www

$useradd -m -s /bin/bash <name>

Use case: Create a user with home directory and shell.Example: sudo useradd -m -s /bin/bash deploy

$passwd <name>

Use case: Set a user's password.Example: sudo passwd deploy

$usermod -aG sudo <name>

Use case: Add a user to the sudo group: grant admin rights.Example: sudo usermod -aG sudo deploy

$userdel -r <name>

Use case: Delete a user and their home directory.Example: sudo userdel -r olduser

$groups

Use case: List groups the current user belongs to.Example: groups

$ip addr

Use case: Show all network interfaces and IPs.Example: ip addr

$ip route

Use case: Show the routing table.Example: ip route

$ping <host>

Use case: Check network reachability.Example: ping -c 4 google.com

$curl -I https://www.www.devvkit.com

Use case: Fetch HTTP headers only: is the site up?Example: curl -I https://www.www.devvkit.com

$curl -s https://api.github.com/repos/nodejs/node | jq .stargazers_count

Use case: Fetch JSON and extract a field with jq.Example: curl -s https://api.github.com/repos/nodejs/node | jq .stargazers_count

$wget -O file.zip https://example.com/file.zip

Use case: Download a file to a specific name.Example: wget -O node.tar.gz https://nodejs.org/dist/latest/node.tar.gz

$ss -tulpn

Use case: List listening ports and owning processes: what is running on port 3000?Example: ss -tulpn | grep 3000

$nc -zv <host> <port>

Use case: Test if a port is open.Example: nc -zv www.devvkit.com 443

$ssh <user>@<host>

Use case: Connect to a remote server.Example: ssh deploy@192.168.1.10

$scp <file> <user>@<host>:<path>

Use case: Copy a file to a remote server.Example: scp build.zip deploy@192.168.1.10:/var/www

$rsync -avz <src> <user>@<host>:<dst>

Use case: Sync directories to a remote: incremental, resume-friendly.Example: rsync -avz dist/ deploy@server:/var/www/

System & Shell13

$uname -a

Use case: Kernel and system info.Example: uname -a

$cat /etc/os-release

Use case: Which Linux distribution and version?Example: cat /etc/os-release

$uptime

Use case: How long has the system been up, and load average.Example: uptime

$free -h

Use case: Memory usage, human-readable.Example: free -h

$history

Use case: Show your command history.Example: history | grep docker

$!!

Use case: Re-run the previous command.Example: sudo !!

$!<n>

Use case: Re-run command number n from history.Example: !123

$alias ll='ls -la'

Use case: Create a permanent shortcut (add to ~/.bashrc).Example: alias ll='ls -la'

$export VAR=value

Use case: Set an environment variable for this session.Example: export NODE_ENV=production

$echo $PATH

Use case: Show the executable search path.Example: echo $PATH

$env

Use case: List all environment variables.Example: env | grep -i proxy

$shutdown -h now

Use case: Shut down the system.Example: sudo shutdown -h now

$reboot

Use case: Restart the system.Example: sudo reboot

Linux Command Line

Every essential Linux CLI command: navigation, files, permissions, processes, text processing, archives, and disk, with syntax and real use cases.

Every command shows its real syntax followed by the use case: when and why you reach for it.

Navigation & File Info

pwd: Print the current working directory: where am I?

Example: pwd

ls: List files in the current directory.

Example: ls

ls -la: List ALL files with details: hidden files, permissions, sizes, dates.

Example: ls -la

ls -lh: List files with human-readable sizes (KB, MB, GB).

Example: ls -lh

ls -lt: Sort by modification time, newest first: what did I just touch?

Example: ls -lt

ls -R: List recursively: see the whole tree.

Example: ls -R src

cd <dir>: Change directory.

Example: cd ~/projects

cd ..: Go up one level.

Example: cd ..

cd -: Go to the previous directory: toggle between two folders.

Example: cd -

cd ~: Go to your home directory.

Example: cd ~

find . -name "*.ts": Find files by name pattern: recursive search.

Example: find . -name "*.ts"

find . -type d -name "node_modules": Find directories by name: locate all node_modules.

Example: find . -type d -name "node_modules"

find . -mtime -7: Files modified in the last 7 days: what changed this week?

Example: find . -mtime -7

find . -size +100M: Files larger than 100MB: disk hogs.

Example: find . -size +100M

find . -name "*.log" -delete: Find and delete in one shot: clean up log files.

Example: find . -name "*.log" -delete

tree -L 2: Show the directory tree 2 levels deep (install with apt install tree).

Example: tree -L 2

file <file>: Identify a file's type: what is this mystery file?

Example: file report.pdf

stat <file>: Full metadata: permissions, timestamps, size, inode.

Example: stat package.json

which <cmd>: Where is this command installed?

Example: which node

type <cmd>: Is it a binary, alias, or shell builtin?

Example: type cd

File Operations

touch <file>: Create an empty file or update its timestamp.

Example: touch .env.local

mkdir <dir>: Create a directory.

Example: mkdir src

mkdir -p a/b/c: Create nested directories: no error if they exist.

Example: mkdir -p src/components/ui

cp <src> <dst>: Copy a file.

Example: cp .env.example .env

cp -r <src> <dst>: Copy a directory recursively.

Example: cp -r dist backup-dist

cp -a <src> <dst>: Copy preserving permissions, ownership, and timestamps: full fidelity.

Example: cp -a public public-backup

mv <src> <dst>: Move or rename a file.

Example: mv index.js main.js

rm <file>: Delete a file. No trash, no undo.

Example: rm old-report.txt

rm -r <dir>: Delete a directory and everything inside it.

Example: rm -r node_modules

rm -rf <dir>: Force recursive delete: the nuclear option. Double-check the path.

Example: rm -rf build

rm -i <file>: Interactive delete: confirm each file.

Example: rm -i *.tmp

ln -s <target> <link>: Create a symlink: point to a file or dir from elsewhere.

Example: ln -s ../shared-config.json config.json

cat <file>: Print a file's contents.

Example: cat package.json

cat file1 file2 > merged: Concatenate files into one.

Example: cat a.txt b.txt > merged.txt

less <file>: View a file page by page: q to quit, / to search.

Example: less app.log

head -20 <file>: First 20 lines: peek at a log or config.

Example: head -20 app.log

tail -20 <file>: Last 20 lines: see the newest entries.

Example: tail -20 app.log

tail -f <file>: Follow a file as it grows: live log viewing.

Example: tail -f app.log

wc -l <file>: Count lines: how big is this file?

Example: wc -l app.log

wc -w <file>: Count words.

Example: wc -w README.md

diff file1 file2: Compare two files line by line.

Example: diff local.env prod.env

diff -r dir1 dir2: Compare two directories recursively.

Example: diff -r src-backup src

Permissions & Ownership

chmod 755 <file>: Owner rwx, group and others r-x: standard for executables and directories.

Example: chmod 755 deploy.sh

chmod +x <file>: Make a script executable.

Example: chmod +x deploy.sh

chmod 600 <file>: Owner read/write only: private files like SSH keys and .env.

Example: chmod 600 ~/.ssh/id_rsa

chmod -R 755 <dir>: Apply recursively to a directory tree.

Example: chmod -R 755 public

chown user:group <file>: Change file owner and group.

Example: sudo chown www-data:www-data index.html

chown -R user:group <dir>: Change ownership recursively: fix permission messes.

Example: sudo chown -R $USER:$USER ~/projects

umask 022: Set default permissions for new files: 022 = 644 for files, 755 for dirs.

Example: umask 022

getfacl <file>: Show extended ACLs: finer-grained permissions.

Example: getfacl config.json

setfacl -m u:deploy:rwx <dir>: Grant a user specific rights via ACL: no chown needed.

Example: setfacl -m u:deploy:rwx /var/www

Process Management

ps aux: List ALL processes with CPU/memory: find what is eating the machine.

Example: ps aux

ps aux | grep node: Filter processes by name: all node processes.

Example: ps aux | grep node

top: Live process monitor: refresh every second.

Example: top

htop: Nicer interactive process monitor with tree view.

Example: htop

kill <pid>: Send SIGTERM: ask the process to stop gracefully.

Example: kill 1234

kill -9 <pid>: Send SIGKILL: force kill. Last resort, skips cleanup.

Example: kill -9 1234

killall <name>: Kill every process with that name.

Example: killall node

pkill -f <pattern>: Kill processes matching a full command-line pattern.

Example: pkill -f "next dev"

pgrep -a <name>: Find process IDs with their command lines.

Example: pgrep -a node

jobs: List background jobs in the current shell.

Example: jobs

fg: Bring the most recent background job to the foreground.

Example: fg

bg: Resume a stopped job in the background.

Example: bg

command &: Run a command in the background: get your prompt back.

Example: npm run dev &

nohup <cmd> &: Run a command immune to hangup: keep it alive after logout.

Example: nohup node server.js &

nice -n 10 <cmd>: Lower a process's priority: run heavy jobs politely.

Example: nice -n 10 make build

renice 5 -p <pid>: Change priority of a running process.

Example: renice 5 -p 1234

crontab -e: Edit your cron jobs: schedule recurring tasks.

Example: crontab -e

crontab -l: List your scheduled jobs.

Example: crontab -l

systemctl status <service>: Check a systemd service's status: is nginx running?

Example: systemctl status nginx

systemctl start/stop/restart <service>: Manage a service: systemctl restart nginx.

Example: systemctl restart nginx

systemctl enable --now <service>: Start a service and enable it on boot.

Example: systemctl enable --now docker

journalctl -u <service> -f: Follow a service's logs: systemd logging.

Example: journalctl -u nginx -f

Text Processing & Pipes

grep "error" app.log: Find lines containing "error".

Example: grep "error" app.log

grep -i "error" app.log: Case-insensitive search.

Example: grep -i "error" app.log

grep -r "apiKey" src/: Recursive search across a directory.

Example: grep -r "apiKey" src/

grep -l "error" *.log: List filenames only: which logs contain errors?

Example: grep -l "error" *.log

grep -c "error" app.log: Count matching lines.

Example: grep -c "error" app.log

grep -v "debug" app.log: Invert: lines WITHOUT "debug".

Example: grep -v "debug" app.log

grep -E "error|fatal" app.log: Extended regex: match multiple patterns.

Example: grep -E "error|fatal" app.log

grep -n "error" app.log: Show line numbers: jump straight to the problem.

Example: grep -n "error" app.log

grep -r --include="*.js" "TODO" src/: Search only certain file types.

Example: grep -r --include="*.js" "TODO" src/

sed -i 's/old/new/g' <file>: Replace all occurrences in place: edit files from the terminal.

Example: sed -i 's/localhost:3000/www.devvkit.com/g' config.js

sed -n '1,20p' <file>: Print lines 1-20: a precise slice.

Example: sed -n '1,20p' app.log

sed -i '/^#/d' <file>: Delete comment lines in place.

Example: sed -i '/^#/d' .env

awk '{print $1}' <file>: Print the first column of each line.

Example: awk '{print $1}' access.log

awk -F, '{print $2}' data.csv: Split by comma and print column 2: CSV work.

Example: awk -F, '{print $2}' users.csv

awk '{sum += $1} END {print sum}' nums.txt: Sum a column of numbers.

Example: awk '{sum += $1} END {print sum}' sales.txt

cut -d, -f1-3 data.csv: Extract fields 1-3 by delimiter.

Example: cut -d, -f1-3 users.csv

cut -c1-10 <file>: Extract the first 10 characters of each line.

Example: cut -c1-10 app.log

sort <file>: Sort lines alphabetically.

Example: sort names.txt

sort -n <file>: Sort numerically: sizes, counts, scores.

Example: sort -n scores.txt

sort -r <file>: Sort in reverse: biggest first.

Example: sort -rn scores.txt

sort -u <file>: Sort and remove duplicates.

Example: sort -u emails.txt

uniq -c <file>: Count consecutive duplicates: pair with sort first.

Example: sort access.log | uniq -c | sort -rn

wc -l access.log | awk '{print $1}': Count lines and strip the filename: script-friendly.

Example: wc -l access.log | awk '{print $1}'

cat *.log | grep -E "ERROR" | wc -l: Count errors across all logs: the pipeline pattern.

Example: cat *.log | grep -E "ERROR" | wc -l

tee <file>: Write output to a file AND keep printing it: capture while watching.

Example: npm run build | tee build.log

xargs -n1 <cmd>: Run a command for each input line: batch operations.

Example: find . -name "*.tmp" | xargs rm

tr '[:lower:]' '[:upper:]' < <file>: Translate characters: uppercase conversion.

Example: echo "hello" | tr '[:lower:]' '[:upper:]'

Archives & Disk

tar -czf archive.tar.gz <dir>: Create a compressed archive.

Example: tar -czf backup.tar.gz src

tar -xzf archive.tar.gz: Extract a .tar.gz archive.

Example: tar -xzf backup.tar.gz

tar -tzf archive.tar.gz: List contents without extracting.

Example: tar -tzf backup.tar.gz

tar -xzf archive.tar.gz -C <dir>: Extract into a specific directory.

Example: tar -xzf node.tar.gz -C /opt

tar -czf - <dir> | ssh server "tar -xzf - -C /target": Stream a directory to a remote machine without a temp file.

Example: tar -czf - src | ssh server "tar -xzf - -C /var/www"

zip -r archive.zip <dir>: Create a zip archive.

Example: zip -r release.zip dist

unzip archive.zip: Extract a zip.

Example: unzip release.zip

unzip -l archive.zip: List zip contents.

Example: unzip -l release.zip

gzip <file>: Compress a single file: creates file.gz.

Example: gzip app.log

gunzip <file>.gz: Decompress a .gz file.

Example: gunzip app.log.gz

df -h: Disk space per filesystem, human-readable.

Example: df -h

du -sh <dir>: Total size of a directory.

Example: du -sh node_modules

du -sh * | sort -rh | head -10: The 10 largest items in the current directory: disk cleanup.

Example: du -sh * | sort -rh | head -10

du -sh --max-depth=1 . | sort -rh: Size of each immediate subdirectory.

Example: du -sh --max-depth=1 . | sort -rh

fsck /dev/sda1: Check and repair a filesystem (run from recovery mode).

Example: sudo fsck /dev/sda1

mount /dev/sdb1 /mnt/data: Mount a partition.

Example: sudo mount /dev/sdb1 /mnt/data

umount /mnt/data: Unmount a filesystem.

Example: sudo umount /mnt/data

Users & Network

whoami: Print the current user.

Example: whoami

id: Show user and group IDs.

Example: id

sudo -i: Open a root shell.

Example: sudo -i

sudo -u <user> <cmd>: Run a command as another user.

Example: sudo -u www-data ls /var/www

useradd -m -s /bin/bash <name>: Create a user with home directory and shell.

Example: sudo useradd -m -s /bin/bash deploy

passwd <name>: Set a user's password.

Example: sudo passwd deploy

usermod -aG sudo <name>: Add a user to the sudo group: grant admin rights.

Example: sudo usermod -aG sudo deploy

userdel -r <name>: Delete a user and their home directory.

Example: sudo userdel -r olduser

groups: List groups the current user belongs to.

Example: groups

ip addr: Show all network interfaces and IPs.

Example: ip addr

ip route: Show the routing table.

Example: ip route

ping <host>: Check network reachability.

Example: ping -c 4 google.com

curl -I https://www.www.devvkit.com: Fetch HTTP headers only: is the site up?

Example: curl -I https://www.www.devvkit.com

curl -s https://api.github.com/repos/nodejs/node | jq .stargazers_count: Fetch JSON and extract a field with jq.

Example: curl -s https://api.github.com/repos/nodejs/node | jq .stargazers_count

wget -O file.zip https://example.com/file.zip: Download a file to a specific name.

Example: wget -O node.tar.gz https://nodejs.org/dist/latest/node.tar.gz

ss -tulpn: List listening ports and owning processes: what is running on port 3000?

Example: ss -tulpn | grep 3000

nc -zv <host> <port>: Test if a port is open.

Example: nc -zv www.devvkit.com 443

ssh <user>@<host>: Connect to a remote server.

Example: ssh deploy@192.168.1.10

scp <file> <user>@<host>:<path>: Copy a file to a remote server.

Example: scp build.zip deploy@192.168.1.10:/var/www

rsync -avz <src> <user>@<host>:<dst>: Sync directories to a remote: incremental, resume-friendly.

Example: rsync -avz dist/ deploy@server:/var/www/

System & Shell

uname -a: Kernel and system info.

Example: uname -a

cat /etc/os-release: Which Linux distribution and version?

Example: cat /etc/os-release

uptime: How long has the system been up, and load average.

Example: uptime

free -h: Memory usage, human-readable.

Example: free -h

history: Show your command history.

Example: history | grep docker

!!: Re-run the previous command.

Example: sudo !!

!<n>: Re-run command number n from history.

Example: !123

alias ll='ls -la': Create a permanent shortcut (add to ~/.bashrc).

Example: alias ll='ls -la'

export VAR=value: Set an environment variable for this session.

Example: export NODE_ENV=production

echo $PATH: Show the executable search path.

Example: echo $PATH

env: List all environment variables.

Example: env | grep -i proxy

shutdown -h now: Shut down the system.

Example: sudo shutdown -h now

reboot: Restart the system.

Example: sudo reboot

Frequently asked questions

How do I view disk and file size usage?

Use df -h for disk space per filesystem, du -sh <dir> for the total size of a directory, and du -sh * | sort -rh to rank the largest items in the current directory.

What does chmod 755 mean?

The three digits set permissions for owner, group, and others: 7 (rwx) for the owner, 5 (r-x) for the group, and 5 (r-x) for everyone else. Directories commonly use 755 so they remain traversable.

How do I find and kill a process?

Find it with ps aux | grep <name> or pgrep -a <name>, then terminate with kill <pid>. Use kill -9 <pid> only as a last resort, since it skips cleanup. pkill <name> kills by name pattern.

How do I search inside file contents?

Use grep -r "pattern" /path for recursive search, grep -ril for case-insensitive file listing, and combine with --include="*.js" to filter by file type. For speed, ripgrep (rg) is a modern alternative.