Linux command manual

Prints the full path of the folder you are in. It is your reference when you get lost.

Lists the content of a folder. With no arguments, the current one.

Changes folder. It is the command you will use most in your whole terminal life.

Draws the tree of folders and files, like a diagram.

Creates an empty file or updates its modification date.

Creates folders. With -p it also creates any missing parents.

Copies files. For whole folders it needs -r.

Moves files or folders. It also renames.

Deletes files. With -r, whole folders. There is no recycle bin.

Deletes folders, but only if they are empty. It is the safe option.

Creates links: a shortcut to another file on the system.

Shows the full technical record of a file: size, permissions, dates and owner.

Shows the whole content of a file. It also joins several on screen.

Opens the file page by page: you can move, search and quit whenever you want.

Shows the first lines of a file (10 by default).

Shows the last lines of a file. The log watcher's command.

Counts lines, words and characters. With pipes it is a result counter.

Searches a pattern inside files and shows only the matching lines.

Finds files and folders by name, type or size inside a tree.

Tells the path of the program that runs when you type a command.

Sorts the lines of a file or of the input. Alphabetical by default.

Removes consecutive repeated lines and, with -c, counts them.

Cuts columns or fields from each line. Ideal for separated listings.

Changes or deletes characters. Very useful to uppercase or clean text.

Edits text as a stream: above all, replaces words inside lines.

Processes text by columns and lets you filter and compute in one line.

Prints text on screen. With redirection, it writes to files.

Changes the permissions of a file or folder. The basis of Linux security.

Changes the owner of a file. It needs administrator privileges.

Changes the group a file belongs to.

Defines which permissions are REMOVED from new files you create.

Tells which user you are working as right now.

Shows your user number, your main group and the groups you belong to.

Switches user inside the same session. It asks for the other user's password.

Creates a new user account. It requires administrator privileges.

Deletes a user account. With -r it also deletes their home folder.

Changes a user's password. With no arguments, your own.

Shows the processes running on the system.

Shows the free and used space of mounted disks.

Measures how much a folder or file takes. The space detective.

Shows the available RAM and swap area.

Shows system information: kernel, architecture and host name.

Tells how long the machine has been on and the system load average.

Checks whether a host responds and how long it takes.

Shows the path a packet travels to its destination, hop by hop.

Inspects and configures the network: addresses, routes and interfaces.

The classic to see network configuration. Today ip is preferred.

Lists the connections and ports listening on your machine.

Opens a session on another machine, encrypted. The gateway to servers.

Copies files between your machine and another over the ssh connection.

Requests a URL and shows the response. The command to talk to web services.

Downloads files from the internet with a single command.

The Debian and Ubuntu package manager: installs, searches and updates software.

Packs files and folders into a single file, with or without compression.

Shows the commands you have typed in this session, numbered.

Creates custom shortcuts for long commands.

Defines environment variables: named values your programs use.

Shows all current environment variables.

Opens the official manual of a command: Linux's source of truth.

Sends a signal to a process to ask it to finish, pause it or resume it. It is how you tell a program to stop.

Finds processes by name and returns their PIDs. It is pkill's sibling without killing anything.

Kills processes by name, without looking up the PID first.

Pauses execution for a while. Very useful in scripts to wait between steps.

Shows a snapshot of every process sorted by usage, with the load and memory summary on top.

A more visual alternative to top, with CPU and memory bars and colours. Many people's favourite.

Runs a command with lower priority so it does not hog the CPU. It goes from -20 (highest) to 19 (lowest).

Changes the priority of a process that is already running.

Lists the jobs launched in the background from this terminal, with their number and state.

Brings a background or stopped job back to the foreground.

Resumes a stopped job in the background, so it keeps going without occupying the terminal.

Runs a command so it keeps working even if you close the terminal. Output is saved to nohup.out.

Repeats a command every few seconds to watch for a change: memory, space, connections...

Runs a command and stops it if it takes longer than allowed. Ideal for scripts and tests.

Manages the system's services (units): start, stop, check whether they are active and decide whether they start with the machine.

Reads the system log, where the messages from services and the kernel end up.

Shows the kernel messages since boot: detected hardware, disks, network and errors.

The old (SysV) way of managing services. It still works, but systemctl is used today.

Shows the current date and time. With +FORMAT you can extract just the part you need for file names or reports.

Lists the users with a session open right now, with their terminal and where they connected from.

Shows the history of logins and logouts. Useful to know when the machine was used and to spot unusual access.

Manages your scheduled tasks: commands the system runs on its own at certain times or days.

Prints formatted text. Unlike echo, it reliably interprets sequences such as \n (newline) or \t (tab).

Shows the output on screen and saves it to a file at the same time. It is the 'T' of a pipeline: it writes to two places.

Turns one command's output into arguments for another. Used when a command does not accept piped input.

Compares two files line by line and shows the differences. It is the basis of patches and version control.

Processes and formats JSON from the terminal: extracts fields, filters and shows API data readably.

Locates the binary, the source code and the manual pages of a command.

Shows processes as a tree: who launched whom. It is the best way to see the process hierarchy.

Returns the PID of a program by name. Handy for scripts that need the exact number.

Sends a signal to every process sharing a name. Useful to close at once a program opened many times.

Summarises the processor: architecture, cores, threads, frequency and cache. All without opening the machine.

Shows and changes the machine name and machine data (operating system, kernel, architecture).

Shows and adjusts the time, the time zone and network synchronisation (NTP).

Shows a calendar of the month or the year in the terminal.

Shows who is logged in and what they are doing, plus the system load average.

Reports the state of memory, swap, disk I/O and CPU usage in a single table.

Shows the locale configuration: language, number format, dates and alphabetical sorting.

Lists disks and their partitions as a tree, with sizes and mount points.

Shows the UUID and filesystem type of each device. Key to mounting by UUID.

Shows mounted filesystems as a tree, indicating which device is at each mount point.

Mounts a device into a folder so you can access its contents, or lists what is already mounted.

Unmounts a device or a folder that was mounted, leaving it ready to be safely removed.

Views and edits a disk's partitions. With -l it shows the table without entering interactive mode.

Formats a partition with the ext4 filesystem, the Linux standard.

Formats a partition as FAT32, the format compatible with Windows, cameras and almost any device.

Copies data at a low level, block by block. Used to clone disks, create images and fill files.

Prepares a partition or file to be used as swap memory.

Enables swap memory and shows which one is in use.

Disables swap memory, returning its contents to RAM.

Checks and repairs the integrity of a filesystem. It is Linux's 'chkdsk'.

Grants fine-grained permissions to specific users or groups without changing the owner or the basic mode.

Shows the access control list (ACL) of a file or folder.

Changes special file attributes, such as making it immutable so not even root can delete it.

Lists the special attributes of files (such as immutable).

Creates a new group in the system.

Deletes a group from the system.

Modifies an existing group, for example renaming it.

Shows which groups a user belongs to. With no arguments, the current user.

Modifies a user account: groups, shell, home directory, account lock, and more.

Views and changes a password's expiry: when it expires and how often it must be changed.

Changes a user's default shell.

Queries the system databases (users, groups, hosts). It is the right way to check whether an account or group exists.

Changes the effective group of the current session without logging out.

Ubuntu's simple firewall. Enables protection and decides which ports are allowed or blocked.

Linux's low-level firewall: chains of rules that filter network traffic.

Generates an SSH key pair (public and private) to connect to servers without a password.

Copies your public key to the remote server so you can log in over SSH without a password.

The network 'Swiss army knife': checks whether a port is open, transfers data or listens.

Lists the files opened by processes. With -i, it shows which processes use the network and which ports listen.

Queries DNS servers and shows the full answer: IP address, servers and timings.

Resolves domain names to IP addresses and back, with short output.

Queries DNS interactively or directly. Classic and also available on Windows.

Controls network connections from the terminal: device status, wifi networks and connection profiles.

Shows the ARP table: the mapping between local IP addresses and network MAC addresses.

Shows the routing table: where traffic leaves for each network and what the gateway is.

Shows and adjusts a network card's parameters: speed, duplex and whether the cable is connected.

Captures the network traffic passing through an interface, to troubleshoot or study protocols.

Scans hosts and ports to discover which services are exposed. A basic auditing tool.

Generates a sequence of numbers. Perfect for loops, tests and generating data.

Numbers the lines of a file. It is like cat -n but with fine control of the format.

Reverses the character order of each line. Fun and useful for some text tricks.

Shows a file with the lines in reverse order: the last first. It is 'cat' backwards.

Wraps long lines into chunks of a given width. Useful to fit text to a screen or page.

Reformats paragraphs: joins the lines and splits them again to fill a uniform width.

Organises text into aligned columns. With -t it turns messy output into a clean table.

Joins lines from several files into one, sticking them side by side separated by a tab.

Splits a large file into smaller chunks. Very useful to upload or move files in parts.

Compares two sorted files and shows in columns which lines are only in the first, only in the second or shared.

Combines two files by a common field, like a database query but with text.

Compares two files byte by byte and says exactly at which byte and line they differ.

Encodes data into safe text (only letters, numbers, + and /) and decodes it back. Useful to embed binaries in text.

Shows a file in hexadecimal and its text equivalent, byte by byte. Essential to inspect binary data.

Dumps a file in octal (or other formats) showing its bytes, useful to inspect raw data.

Converts text between character encodings, for example from UTF-8 to ASCII or Latin-1.

Converts a file from Windows line endings (CRLF) to Unix (LF). Fixes the classic ^M error.

Converts a file from Unix line endings (LF) to Windows (CRLF).

Compresses a file with the gzip algorithm and adds the .gz extension. It is the de facto standard on Linux.

Decompresses .gz files and recovers the original.

Shows the contents of a .gz file without decompressing it to disk. It is cat + gunzip.

Compresses files with the bzip2 algorithm (.bz2), which usually packs more than gzip at the cost of speed.

Decompresses .bz2 files.

Shows the contents of a .bz2 file without decompressing it to disk.

Compresses files with the xz algorithm (.xz), the best compressor of the three classics.

Decompresses .xz files.

Shows the contents of a .xz file without decompressing it to disk.

Creates .zip compressed archives, the format most compatible with Windows, macOS and almost any program.

Extracts .zip files and can list their contents without extracting.

Guesses a file's real type by looking at its content, not its extension. Very useful when you do not know what it is.

Does nothing and exits successfully (code 0). Its use is in scripts, for infinite loops or default values.

Does nothing and exits with an error (code 1). The complement of true.

Says what a name is: a binary, a shell builtin or an alias. It answers 'why does this command behave like this'.

Runs a command file in the current shell, so the variables and functions it defines stay in your session.

With no arguments, shows every shell variable. It also changes shell behaviour options.

Deletes a variable or function from the shell.

Marks a variable as read-only: it cannot be changed or deleted during the session.

Performs arithmetic and stores the result in variables, right on the command line.

Evaluates simple arithmetic and logical expressions from the command line.

Arbitrary-precision calculator. Unlike the shell, it handles decimals without losing precision.

Creates a temporary file or folder with a unique, safe name, so it does not clash with others.

Shows or limits the resources your session can consume: open files, processes, memory, etc.

Manages .deb packages directly: install them, list them or check which package a file belongs to.

Queries the package catalogue without installing anything: search, view details or check the available version.

Manages snap packages: applications bundled with all their dependencies that update themselves.

Shuts down or restarts the machine in an orderly way, warning users and closing programs.

Restarts the machine immediately.

Powers off the machine immediately, in an orderly way.

Stops the system without necessarily cutting the power. Classic way to halt the machine.

Schedules a command to run once at a specific time.

Lists the pending tasks scheduled with at.

Deletes a task scheduled with at, by its number.

Runs a program showing the system calls it makes. It is the magnifying glass to understand what it really touches.

Says which processes are using a file, a folder or a port. Very useful before unmounting a USB stick.

Reads a line from the input and stores it in a variable. It is how you ask the user for data in a script.

Computes the MD5 hash (128 bits) of one or more files. Used to check that a file has not changed.

Computes the SHA-1 hash (160 bits) of a file. Stronger than MD5, though SHA-256 is preferred today.

Computes the SHA-256 hash (256 bits) of a file. The standard to verify downloads and integrity.

Computes the SHA-512 hash (512 bits) of a file. The longest of the SHA-2 family.

Like grep but treating the pattern as an extended regular expression. Equivalent to grep -E.

Like grep but searching the text literally, without special characters. Equivalent to grep -F.

From a full path, shows only the final name of the file or folder.

From a full path, shows the folder that contains it (removes the last segment).

Shows where a symbolic link points. With -f it gives the resolved absolute path.

Gives the absolute, real path of a file, resolving links and dots.

Changes a file size: shrinks it or pads it up to the size you ask.

Overwrites a file content before deleting it, so it cannot be recovered.

Creates a named pipe (FIFO): a special file through which two programs exchange data.

Randomly shuffles lines, values or a range of numbers. Handy for draws and tests.

Converts numbers to human-readable form (1M, 2G) or back. Very useful when reading sizes.

Extracts the readable text inside a file, even if it is binary.

Repeats a word endlessly (the letter y by default). Used to answer questions automatically.

Lists the kernel modules currently loaded, with their size and who uses them.

Loads a kernel module (or unloads it with -r), resolving dependencies.

Inserts a specific module from its .ko file, without resolving dependencies.

Unloads a kernel module. With -f it forces even if in use.

Shows information about a module: file, description, license and dependencies.

Reads or changes kernel parameters live. With -w it applies them and saves to /etc/sysctl.conf.

Shows and manages user sessions and who is logged in (systemd-logind).

Shows and tests name resolution from systemd-resolved. With query it resolves a name.

Shows or changes the system language and keyboard layout.

Measures how long boot takes and which services slow it down. With blame it sorts by time.

Writes a message to the system log (journal), with an optional tag.

Manages the nftables firewall: creates modern rules (replaces iptables).

Controls firewalld (the Red Hat/Fedora firewall): ports, services and zones.

Shows the current SELinux mode: Enforcing, Permissive or Disabled.

Switches SELinux between Enforcing (1) and Permissive (0) live.

Manages SELinux settings: ports and file contexts.

Restores files to their correct SELinux context according to the rules.

Changes the SELinux context of a specific file (temporary).

Cryptography Swiss army knife: hashes, random numbers, certificates and passwords.

Encrypts and decrypts files or messages with GPG. With -c it uses symmetric encryption.

Searches which package a file belongs to, even if it is not installed.

Adds a repository (PPA) to the APT sources so you can install from it.

Reconfigures an already installed package (language, timezone, etc.).

Saves the current folder on a stack and moves to another. Perfect to go and come back.

Removes the last folder from the stack and moves to it.

Shows the directory stack you have been saving with pushd.

Runs a command and tells you how long it took (real, user and system).

Re-interprets the text you pass it as if you had typed it.

Declares or shows variables (and arrays) with their attributes.

Declares a local variable inside a function: it does not leak out.

Shifts a script arguments left: $1 becomes the old $2.

Walks through a script options (-a, -b value) one at a time.

Schedules an action for when the script exits or receives a signal.

Prepares a disk or partition as a physical volume (PV) to use with LVM.

Summarizes the physical volumes (PV), their group and size.

Shows the details of each physical volume: size, extent and group.

Removes the LVM label from a physical volume to reuse the disk.

Creates a volume group (VG) grouping one or more PVs.

Extends a volume group by adding more physical disks.

Summary of volume groups: PVs, LVs and size.

Details of each volume group: size, PE and layout.

Creates a logical volume (LV) inside a group, like a flexible partition.

Extends a logical volume without unmounting it or losing data.

Shrinks a logical volume. Careful: it can cut data if the filesystem is not adjusted.

Removes a logical volume and frees its space in the group.

Summary of logical volumes: group, attributes and size.

Details of each logical volume: path, name, group and size.

Creates and manages software RAID: mirror (raid1), parity (raid5), etc.

Creates and examines partitions and partition tables (GPT/MBR).

Checks and repairs ext2/ext3/ext4 filesystems.

Tunes parameters of an ext filesystem and shows its information.

DHCP server: hands out IP addresses automatically to the machines on a network. With -t it only validates the config.

DHCP client: asks the server for an address and configures the interface with it.

Lists the leases handed out by the DHCP server: MAC, IP and hostname.

Checks that the BIND configuration (named.conf and its includes) is correct. Prints nothing if OK.

Validates a DNS zone file: checks that it has SOA and NS and that the syntax is correct.

Controls and checks Apache. With configtest it validates the config and with -S it lists the virtual hosts.

Nginx web server. With -t it checks the config and with -s reload it reloads without downtime.

Enables an Apache site (virtual host) by creating the link in sites-enabled.

Disables an Apache site (virtual host) by removing the link from sites-enabled.

Checks that the Samba configuration (smb.conf) is valid and shows the shared resources.

Manages Samba user passwords (with -a it adds one).

Samba client: lists shares (-L) or connects to a shared folder.

Shows or reloads the directories NFS shares (defined in /etc/exports).

Shows which directories an NFS server is exporting (-e to list them).

Mail transfer agent (MTA). With check it validates the config and with status it tells if running.

Sends an email from the command line (with -s the subject).

Shows the system mail queue (messages pending delivery).

SSH server. With -t it checks the configuration file (/etc/ssh/sshd_config).

Shows the status of CUPS printers (the default printer with -d).

Sends a document to the printer (with -d you choose which one).

Administers printers in CUPS: with -p and -v you add a printer and its destination.

Simple text editor in the terminal. Ideal to edit config files without hassle.

Powerful, fast text editor. It has several modes; you learn it with practice.

The classic Unix editor. Almost always vim is its modern version.

Shows a file page by page, without scrolling through the text.

Clears the terminal screen leaving the prompt at the top.

Closes the terminal session (or the script you are in).

Shows help for the shell built-in commands.

Evaluates a condition and returns success or failure. Used in scripts and with [ ].

Shows or changes the machine name on the network.

Lists the devices on the PCI bus (cards, controllers...).

Lists the devices connected over USB.

Shows the Linux distribution and its version. With -a, all the data.

Shows disk and CPU input/output statistics.

Shows network connections, open ports and routing tables (classic).

Sends a message to every terminal of the logged-in users.

Classic Debian/Ubuntu tool to install and upgrade packages.

Debian version of apachectl: checks and controls the Apache server.

Removes an alias you had defined earlier.

Like declare: declares variables and their attributes (same as declare).

Creates a filesystem on a device (format). With -t you choose the type.

Creates a new user account. With -m it builds the home folder and copies the base files; it prompts for the rest interactively.

Netcat, the network Swiss army knife: opens TCP/UDP connections, listens on a port and checks whether a port is open. It is invoked as nc or netcat.