Linux Cheatsheet

Print the full path of your current working directory.

💡 Use this before destructive commands so you know exactly where you are.

List files with permissions, owners, sizes, and hidden entries in a readable format.

💡 Add --group-directories-first on supported systems to keep folders at the top.

Change into another directory by absolute or relative path.

💡 Use cd - to jump back to your previous directory instantly.

Search recursively for files matching a name pattern.

💡 Combine find with -mtime, -size, or -exec for precise cleanup and audits.

Locate files modified within the last day.

Query the locate database for files by name almost instantly.

💡 If results look stale, refresh the database with sudo updatedb.

Display directory contents as a tree up to a chosen depth.

Show the total size of the current directory in human-readable form.

Rank files and folders by size to find what is consuming space.

💡 Great for identifying oversized logs, caches, and build artifacts.

Show mounted filesystem capacity, usage, and free space.

💡 Use df -i too when you suspect inode exhaustion rather than disk exhaustion.

Resolve a relative path into its canonical absolute path.

Inspect detailed file metadata like size, inode, mode, and timestamps.

Extract the filename portion from a full path.

💡 Use dirname for the parent path when building scripts that split file locations.

Copy files or directories while preserving attributes and showing progress.

💡 Use -a for backups because it preserves permissions, symlinks, and timestamps.

Recursively copy a directory and everything inside it.

Rename a file or move it to another directory.

💡 Add -n to avoid overwriting an existing destination file.

Force-remove files or directories recursively.

💡 Run pwd and ls first when using rm -rf in production paths.

Create nested directories without failing if parents already exist.

Create an empty file or update its modification timestamp.

Set a file timestamp manually for testing or restore workflows.

Create a symbolic link that points to another file or directory.

💡 Symlinks are ideal for release switching because the target can change atomically.

Create a hard link that references the same inode as the original file.

Set read-write for owner and read-only for group and others.

💡 644 is common for config files that should not be executable.

Add execute permission for the file owner using symbolic mode.

Recursively apply restrictive directory and file permissions.

Change file ownership recursively to a user and group.

💡 Use chgrp -R devops shared/ when you only need to update the group.

Print a file to standard output exactly as stored.

Search for matching text and show the line numbers for each hit.

💡 Add -i for case-insensitive matching and -C 3 for nearby context.

Search recursively through a project for a string or pattern.

Split input into fields and print selected columns or computed values.

💡 AWK shines when you need lightweight reporting without opening a spreadsheet.

Print only a selected range of lines from a file.

Replace matching text in a stream using sed substitution syntax.

💡 Use sed -i.bak for in-place edits while keeping a backup copy.

Extract specific delimiter-separated fields from each input line.

Sort lines alphabetically and remove duplicates in one step.

Collapse adjacent duplicate lines and count their occurrences.

💡 Remember to sort first unless duplicate lines are already adjacent.

Count lines, words, or bytes in a file or stream.

Show the first lines of a file for quick inspection.

Follow the end of a growing log file in real time.

💡 Use tail -n 100 -f to start with recent history before following new entries.

Compare two files and show unified diff output.

Open a file in a pager for efficient scrolling, searching, and navigation.

💡 Inside less, press / to search forward and n to jump to the next match.

List every running process with CPU, memory, user, and command details.

Find process IDs and commands by pattern without scanning raw ps output manually.

💡 Pair pgrep with pkill in real life, but use pgrep first so you know what will match.

Open the built-in live process monitor for CPU and memory analysis.

Use an interactive, colorized process viewer with easier sorting and filtering.

💡 htop is ideal for quickly spotting noisy processes and sending signals interactively.

Send SIGTERM so a process can shut down gracefully.

Force-kill a stuck process using SIGKILL when graceful shutdown fails.

💡 Prefer SIGTERM first because SIGKILL skips cleanup hooks and can corrupt temp state.

Signal all processes with the same name at once.

Start a process with lower CPU scheduling priority.

Run a command immune to hangups so it keeps running after logout.

List background and stopped jobs in the current shell session.

Resume a stopped shell job and continue it in the background.

Bring a background or stopped job back into the foreground.

Check the current state, logs, and unit details for a systemd service.

💡 Use systemctl is-active service-name in scripts when you only need a health check.

Restart a service managed by systemd.

Follow logs from a specific systemd service in real time.

💡 Add -n 100 to review recent lines before following live output.

Display IP addresses and status for all network interfaces.

💡 Use ip -br addr for a concise summary on modern Linux distributions.

Inspect the kernel routing table and default gateway configuration.

Show interface configuration using the legacy net-tools command set.

💡 Prefer ip addr on newer systems because ifconfig is deprecated on many distros.

Test reachability and round-trip latency to a host.

Fetch HTTP headers to verify status codes, redirects, and server metadata.

💡 Use curl -sS for scripts so errors remain visible without a progress meter.

Download a remote resource and save it to a chosen filename.

List listening TCP and UDP sockets with associated processes.

💡 ss is the modern replacement for many netstat use cases.

Display active listening ports and bound services with the classic networking tool.

Scan a target host for open ports and detected service versions.

💡 Use nmap only on systems you are authorized to assess.

Open an encrypted remote shell session over SSH.

Securely copy files between local and remote systems over SSH.

Synchronize files efficiently while transferring only deltas.

💡 rsync is safer and faster than repeated full scp uploads for deployments.

Test whether a TCP port is reachable using netcat.

💡 Netcat is perfect for quick smoke tests when curl or ssh are too specific.

Print the effective username of the current shell session.

Show the current user ID, group ID, and supplementary groups.

List the commands the current user may run with sudo.

💡 Useful when diagnosing why a deployment user cannot run a privileged action.

Switch to another user account with a full login shell.

Change the password for the current account.

Create a new user with a home directory and default Bash shell.

Append a user to an additional supplementary group.

💡 Always include -a with -G so you do not overwrite existing group memberships.

Delete a user account and remove its home directory.

Create a new system group for shared access control.

List all groups that a user belongs to.

Set owner read-write-execute and read-execute for group and others using octal mode.

💡 755 is common for scripts that should be executable but not writable by everyone.

Restrict a sensitive file to owner read-write and group read-only using octal permissions.

Recursively set both owner and group for an application directory.

💡 Pair chown with chmod to fully correct both ownership and access mode issues.

Show disk usage with human-readable sizes and filesystem types.

Measure how much space a directory consumes.

List block devices, partitions, filesystems, and mount points.

💡 Run lsblk before mounting a new disk so you target the correct device.

Display all currently mounted filesystems in an easy-to-scan format.

Mount a filesystem at a chosen directory so it becomes accessible.

Unmount a filesystem cleanly before removing or reformatting it.

💡 Use lsof or fuser first if umount reports that the device is busy.

List disk partitions and geometry using the classic partitioning utility.

Inspect partition tables with GNU Parted, including GPT layouts.

Create an ext4 filesystem on a partition or block device.

💡 Formatting destroys data, so verify the device name carefully with lsblk first.

Create a compressed tar archive from files or directories.

Extract a gzip-compressed tar archive into the current directory.

Compress a file with gzip while keeping the original copy.

Create a ZIP archive recursively from a folder or file set.

Extract a ZIP archive into a target directory.

Use a portable shebang so the script runs with Bash from the current environment.

💡 Place the shebang on the first line of every executable Bash script.

Exit on errors, treat unset variables as failures, and catch pipe errors early.

💡 This is one of the best defaults for safer production shell scripts.

Assign a shell variable without spaces around the equals sign.

Expand a variable and transform it to uppercase using Bash string operations.

💡 Parameter expansion like ${var:-default} is cleaner than many small if statements.

Run commands conditionally when a file, string, or status test succeeds.

Dispatch different logic branches based on an input argument.

Loop over matching files and run the same command for each one.

Read input line by line from standard input or a file safely.

💡 Use -r with read so backslashes are not interpreted unexpectedly.

Define a reusable shell function that accepts positional parameters.

Create a Bash array for managing multiple related values.

Expand every array element as separate words.

Redirect standard output and standard error to different files.

💡 Use 2>/dev/null only when you deliberately want to hide expected noise.

Append both stdout and stderr to the same log file.

Pipe output through multiple commands and save a copy with tee.

💡 Pipes let each tool do one job well, which is the Unix philosophy in practice.

Install a recurring cron job that runs a command on a fixed schedule.

💡 Cron uses a minimal environment, so prefer absolute paths for commands and files.