Linux commands

Make a short name for a longer command (alias), or remove it (unalias).

RHCSA exam2 options, 11 examples

Search the short descriptions of the man pages (apropos), or show the description of one page (whatis).

RHCSA exam15 options, 11 examples

The Bourne Again Shell: the default command shell of RHEL, and the program that runs shell scripts.

RHCSA exam20 options, 10 examples

Switch the screen of the machine to another virtual terminal (tty1 … tty12).

Everyday Linux# Yes3 options, 10 examples

Clean the terminal screen (and, by default, the scrollback buffer).

Everyday Linux3 options, 11 examples

Print text or the value of variables to the screen (or to a file with redirection).

RHCSA exam13 options, 12 examples

Show the environment variables, or run a program with a changed environment.

RHCSA exam13 options, 11 examples

End the shell or script with an exit status (0 = success, 1–255 = error); return does the same for a function.

Everyday Linux1 options, 10 examples

Make a shell variable available to the programs you start (export), or remove a variable (unset).

RHCSA exam6 options, 11 examples

Show, search, repeat and clear the commands you typed before.

RHCSA exam22 options, 12 examples

Read the longer GNU documentation (Texinfo manuals) with chapters and links.

RHCSA exam13 options, 11 examples

Read the manual page of a command, a configuration file or a system call.

RHCSA exam39 options, 12 examples

Build or update the search database of the man pages (used by man -k, apropos and whatis).

RHCSA exam# Yes12 options, 11 examples

Print the value of environment variables (all, or the ones you name).

Everyday Linux4 options, 11 examples

Print formatted text: columns, numbers, padding — more exact than echo.

Everyday Linux2 options, 10 examples

Read one line of input (from the keyboard, a file or a pipe) into variables.

RHCSA exam11 options, 10 examples

Print a list of numbers — for loops and test data.

Everyday Linux5 options, 10 examples

Turn shell options on or off (like -x trace, -e stop on error), set the positional parameters, or list all variables.

Everyday Linux23 options, 10 examples

Wait for a given time.

Everyday Linux3 options, 10 examples

Run the commands of a file in the current shell, so its variables, aliases and functions stay.

RHCSA exam2 options, 10 examples

Check a condition (file exists, strings equal, number greater …) and return 0 (true) or 1 (false). Also written as [ … ].

RHCSA exam0 options, 11 examples

Print the name of the terminal device you are using (like /dev/tty3 or /dev/pts/0).

Everyday Linux3 options, 11 examples

Show what a command name really is: an alias, a shell keyword, a function, a built-in or a program file.

RHCSA exam5 options, 11 examples

Show the full path of the program that runs for a command name.

Everyday Linux12 options, 11 examples

Change the current folder of your shell.

RHCSA exam6 options, 11 examples

Copy files and folders.

RHCSA exam35 options, 12 examples

Find out what kind of data a file contains (text, script, program, image, archive …), whatever its name.

Everyday Linux30 options, 11 examples

Search a folder tree for files that match tests (name, owner, size, time, permissions …) and act on them.

RHCSA exam68 options, 17 examples

Make links: hard links (a second name for the same data) or symbolic links (a pointer to a path).

RHCSA exam16 options, 11 examples

List the files in a folder, with details like permissions, owner, size and time.

RHCSA exam60 options, 13 examples

Create new folders (directories), also with all missing parent folders.

RHCSA exam7 options, 11 examples

Move files and folders, or rename them.

RHCSA exam17 options, 11 examples

Print the full path of the folder you are in (print working directory).

Everyday Linux4 options, 11 examples

Delete files, and with -r folders with all their content.

RHCSA exam12 options, 11 examples

Remove empty folders (and refuse to remove folders that still have files).

RHCSA exam5 options, 11 examples

Show all details of a file: size, blocks, inode, links, permissions, owner, SELinux context and all its times.

Everyday Linux26 options, 11 examples

Create an empty file, or change the access and modification times of a file.

RHCSA exam11 options, 11 examples

Process text line by line as fields: print columns, filter by conditions, count and sum.

RHCSA exam28 options, 13 examples

Print files to the screen, join files together (cat), or print them last line first (tac).

RHCSA exam15 options, 12 examples

Take parts of each line: fields split by a separator, or character positions.

RHCSA exam15 options, 11 examples

Search files or command output for lines that match a pattern (text or regular expression).

RHCSA exam48 options, 14 examples

Show the first lines (or bytes) of files or command output.

RHCSA exam8 options, 11 examples

Read a file or command output one screen at a time, with scrolling and searching.

RHCSA exam40 options, 12 examples

Show text one screen at a time (the simple, older pager).

Everyday Linux14 options, 11 examples

Edit text files with a simple terminal editor that shows its keys on the screen.

RHCSA exam56 options, 11 examples

Change text as it flows through: replace words, delete or print lines — and edit files in place with -i.

RHCSA exam35 options, 13 examples

Put lines in order: alphabetical, by numbers, by sizes, by versions, by a chosen column.

RHCSA exam31 options, 12 examples

Show the last lines of files, and follow a log file live while it grows.

RHCSA exam13 options, 11 examples

Copy the input to the screen (or the next command) and to one or more files at the same time.

Everyday Linux6 options, 11 examples

Replace, delete or squeeze single characters in a text stream.

Everyday Linux12 options, 11 examples

Remove or count repeated lines that are next to each other (use it after sort).

Everyday Linux13 options, 11 examples

Edit text files in the terminal with the vi/vim editor (keys and commands, no mouse needed).

RHCSA exam28 options, 12 examples

Count lines, words, characters and bytes.

RHCSA exam9 options, 11 examples

Compress files to .bz2 (bzip2), unpack them (bunzip2), or read them without unpacking (bzcat).

RHCSA exam14 options, 12 examples

Compress files to .gz (gzip), unpack them (gunzip), or read them without unpacking (zcat).

RHCSA exam19 options, 12 examples

Pack files and folders into one archive file (and unpack it), with optional compression.

RHCSA exam128 options, 13 examples

Compress files to .xz with very good compression (xz), unpack them (unxz), or read them (xzcat).

Everyday Linux21 options, 11 examples

Pack files into a .zip archive (zip) and unpack it (unzip) — the format that Windows and macOS open directly.

Everyday Linux50 options, 12 examples

Show and change the password aging and the expire date of an account.

RHCSA exam# For changes11 options, 12 examples

Look up entries in the system databases (users, groups, hosts, services …) the same way programs do.

RHCSA exam6 options, 12 examples

Add or remove members of a group, set group admins, or set a group password.

RHCSA exam# For changes8 options, 10 examples

Create a group (groupadd), change it (groupmod) or delete it (groupdel).

RHCSA exam# Yes17 options, 11 examples

Show the names of the groups a user is in.

Everyday Linux3 options, 10 examples

Show the UID, primary group and all groups of a user (or of yourself).

RHCSA exam10 options, 11 examples

Print the name of the user who logged in to this session (also after su or sudo).

Extra2 options, 10 examples

Start a new shell with another primary group — useful right after you were added to a group.

Everyday Linux2 options, 10 examples

Set or change a password, and lock, unlock, expire or show the password of an account.

RHCSA exam# For changes17 options, 12 examples

Run a program as another user (by default root) when polkit allows it.

Extra# For changes5 options, 10 examples

Start a shell (or one command) as another user. You type the password of that user.

RHCSA exam# For changes12 options, 11 examples

Run a command as root (or another user) with your own password, if the sudo rules allow it.

RHCSA exam# For changes31 options, 12 examples

Create a new user account (and by default its private group and home folder).

RHCSA exam# Yes26 options, 11 examples

Delete a user account, and with -r also its home folder and mail.

RHCSA exam# Yes6 options, 11 examples

Change an existing user: groups, shell, home folder, name, UID, expire date, lock.

RHCSA exam# Yes25 options, 12 examples

Edit /etc/passwd (vipw) or /etc/group (vigr) safely by hand, with a lock.

Everyday Linux# Yes6 options, 11 examples

Edit the sudo rules safely: visudo locks the file and checks the syntax before it saves.

RHCSA exam# Yes9 options, 11 examples

Show who is logged in and what each user is doing now, plus the uptime and load of the system.

Everyday Linux10 options, 11 examples

Show who is logged in now, on which terminal, since when and from where.

Everyday Linux16 options, 11 examples

Print the user name you are working as right now (the effective user).

Everyday Linux2 options, 11 examples

Set or remove file attributes, like immutable (no change at all) and append only.

Everyday Linux# Yes5 options, 10 examples

Change the group of files and directories.

RHCSA exam# For changes14 options, 10 examples

Change the permissions (mode) of files and directories, with numbers or letters.

RHCSA exam# For changes9 options, 12 examples

Change the owner and/or the group of files and directories.

RHCSA exam# Yes15 options, 11 examples

Show the access control lists (ACLs) of files and directories.

Everyday Linux14 options, 10 examples

List the file attributes (like i = immutable, a = append only).

Everyday Linux# For changes7 options, 10 examples

Follow a path step by step and show every directory and link on the way, with owner and permissions.

Everyday Linux9 options, 10 examples

Add, change or remove ACL entries: rights for extra users and groups on files and directories.

Everyday Linux# For changes18 options, 11 examples

Show or set the mask that decides the permissions of new files and directories.

RHCSA exam3 options, 11 examples

Show the use of memory (RAM) and swap.

Everyday Linux17 options, 10 examples

List the jobs of your shell, and move them between foreground (fg) and background (bg).

RHCSA exam8 options, 10 examples

Send a signal to processes by PID (or job number) — by default SIGTERM, a polite request to stop.

RHCSA exam# For changes8 options, 11 examples

Send a signal to all processes with a given name.

Everyday Linux# For changes16 options, 10 examples

Start a command with a changed CPU priority (nice value from -20 to 19).

RHCSA exam# For changes3 options, 10 examples

Run a command that keeps running after you log out (it ignores the hang-up signal).

Everyday Linux2 options, 10 examples

Print the PIDs of a running program, by its exact name.

Everyday Linux13 options, 10 examples

Find processes by name or other attributes (pgrep), signal them (pkill), or wait for them to end (pidwait).

RHCSA exam# For changes32 options, 11 examples

Show a snapshot of running processes: PID, user, CPU and memory use, state and command.

RHCSA exam51 options, 12 examples

Show the running processes as a tree: who started whom.

Everyday Linux20 options, 10 examples

Change the nice value (CPU priority) of running processes, by PID, process group or user.

RHCSA exam# For changes7 options, 10 examples

Show the control groups (cgroups) as a tree with their processes (systemd-cgls), or their live resource use (systemd-cgtop).

Everyday Linux26 options, 10 examples

Watch the processes live, sorted by CPU, with load, CPU and memory totals — and kill or renice from it.

RHCSA exam19 options, 10 examples

Choose and check the tuned performance profile (a set of kernel, CPU, disk and power settings).

RHCSA exam# For changes7 options, 10 examples

Show how long the system runs, how many users are logged in and the load average.

Everyday Linux4 options, 10 examples

Stop, restart or switch off the system cleanly — now or at a planned time, with a warning to users.

RHCSA exam# Yes19 options, 11 examples

Control systemd: start, stop, enable and check services and other units, change targets, reboot and power off.

RHCSA exam# For changes57 options, 15 examples

Analyze systemd: boot time, slow units, unit file errors, timer expressions and the security of services.

Everyday Linux27 options, 10 examples

Run commands once at a later time (at), list (atq) or remove (atrm) those jobs, or run them when the load is low (batch).

RHCSA exam14 options, 11 examples

Edit, list or remove the cron job list (crontab) of a user.

RHCSA exam# For changes11 options, 12 examples

Run a command as a temporary (transient) systemd service or scope — now, later with a timer, or with resource limits.

Everyday Linux# For changes35 options, 10 examples

Read and search the systemd journal: by service, time, priority, boot, user and any field.

RHCSA exam# For changes53 options, 15 examples

Write a message to the system log (journal and rsyslog) — from the command line or a script.

RHCSA exam24 options, 10 examples

Rotate, compress and delete old log files by the rules in /etc/logrotate.conf and /etc/logrotate.d/.

RHCSA exam# Yes11 options, 10 examples

Create the index (repodata) for a folder of RPM files, so dnf can use it as a repository.

Everyday Linux# For changes21 options, 10 examples

Install, update, remove and search RPM packages from repositories, with all dependencies.

RHCSA exam# For changes50 options, 15 examples

Install, update and run (mostly graphical) applications in a sandbox, from Flatpak remotes like Flathub.

RHCSA exam# For changes19 options, 11 examples

Query, verify, install and remove RPM packages directly — mostly used to ask what is installed and which files a package has.

RHCSA exam# For changes62 options, 13 examples

Register a RHEL system with Red Hat, and turn Red Hat repositories on or off.

RHCSA exam# Yes23 options, 12 examples

The autofs daemon: mounts file systems (mostly NFS) when they are used and unmounts them when idle. Managed with systemctl; the command helps debugging.

RHCSA exam# Yes18 options, 10 examples

Show the UUID, label and type of file systems and swap spaces — the values you need for /etc/fstab.

RHCSA exam# For changes20 options, 10 examples

Copy data block by block: make disk images, write ISO files to USB, create files of a fixed size, wipe or test disks.

Everyday Linux# For changes15 options, 11 examples

Show how much space is used and free on each mounted file system.

RHCSA exam18 options, 11 examples

Show how much disk space files and folders use.

Everyday Linux27 options, 12 examples

Show the superblock and block group details of an ext2/ext3/ext4 file system.

Everyday Linux# Yes10 options, 10 examples

Manage the NFS export table: apply changes of /etc/exports, show the active exports, or export a folder for a moment.

RHCSA exam# Yes9 options, 10 examples

Reserve disk space for a file at once (no data is written), or punch holes into a file.

Everyday Linux12 options, 10 examples

Create, delete and change partitions on MBR and GPT disks with a menu.

RHCSA exam# Yes17 options, 10 examples

Show mounted file systems as a tree, find one mount, or check /etc/fstab for errors.

RHCSA exam43 options, 11 examples

Check and repair file systems — the front end fsck, and e2fsck (= fsck.ext4) for ext2/3/4.

RHCSA exam# Yes31 options, 10 examples

Edit GPT partition tables with a menu (like fdisk, made for GPT).

Extra# Yes1 options, 10 examples

List disks, partitions, LVM volumes and other block devices as a tree, with size, type and mount point.

RHCSA exam33 options, 11 examples

Create a file system on a partition or volume (front end for mkfs.xfs, mkfs.ext4, mkfs.vfat …).

RHCSA exam# Yes5 options, 10 examples

Create an ext4 (or ext3/ext2) file system.

RHCSA exam# Yes30 options, 10 examples

Create a FAT file system (FAT12/16/32) — for USB sticks, SD cards and the EFI system partition.

Everyday Linux# Yes27 options, 10 examples

Create an XFS file system — the default file system of RHEL.

RHCSA exam# Yes16 options, 10 examples

Prepare a partition, logical volume or file to be used as swap space.

RHCSA exam# Yes14 options, 10 examples

Attach a file system (disk, partition, ISO, network share) to a folder, or show what is mounted.

RHCSA exam# For changes29 options, 12 examples

Create, delete, resize and list partitions — in a menu or with one command line (good for scripts).

RHCSA exam# Yes8 options, 10 examples

Tell the kernel to read the partition table of a disk again.

RHCSA exam# Yes5 options, 10 examples

Grow or shrink an ext2/ext3/ext4 file system.

RHCSA exam# Yes10 options, 10 examples

Show the exports of an NFS server (and which clients mounted them).

RHCSA exam6 options, 10 examples

Switch swap spaces on (swapon) or off (swapoff), and show which are active.

RHCSA exam# For changes18 options, 10 examples

Show and change the settings of an ext2/ext3/ext4 file system (label, reserved blocks, default mount options, checks, UUID).

RHCSA exam# Yes21 options, 10 examples

Detach a mounted file system from the folder tree.

RHCSA exam# For changes18 options, 10 examples

List or remove file system, RAID, LVM and partition table signatures from a device (fast, without wiping the data).

Everyday Linux# Yes14 options, 10 examples

Show or change the label, UUID and some features of an XFS file system (unmounted).

RHCSA exam# Yes12 options, 10 examples

Grow a mounted XFS file system to fill its (bigger) device.

RHCSA exam# Yes11 options, 10 examples

Show the geometry and features of an XFS file system (block size, allocation groups, log, features).

Everyday Linux# For changes3 options, 10 examples

Check and repair a damaged XFS file system (it must be unmounted).

RHCSA exam# Yes14 options, 10 examples

Create a logical volume from the free space of a volume group (lvcreate), or delete one (lvremove).

RHCSA exam# Yes46 options, 10 examples

Make a logical volume bigger — with -r also its file system, while it stays mounted.

RHCSA exam# Yes28 options, 10 examples

Make a logical volume smaller — with -r the file system is shrunk first (ext4 only; XFS cannot shrink).

RHCSA exam# Yes21 options, 10 examples

Show logical volumes: short table (lvs), full details (lvdisplay), or list all (lvscan).

RHCSA exam# Yes28 options, 10 examples

Turn a disk or partition into an LVM physical volume (pvcreate), or remove the LVM label again (pvremove).

RHCSA exam# Yes27 options, 10 examples

Move the data of a physical volume to other PVs in the same VG — while the LVs stay in use.

Everyday Linux# Yes20 options, 10 examples

Show physical volumes: short table (pvs), full details (pvdisplay), or scan for PVs (pvscan).

RHCSA exam# Yes34 options, 10 examples

Create a volume group from one or more physical volumes (vgcreate), or delete a volume group (vgremove).

RHCSA exam# Yes28 options, 10 examples

Add physical volumes to a volume group (vgextend), or remove them (vgreduce).

RHCSA exam# Yes20 options, 10 examples

Show volume groups: short table (vgs), full details (vgdisplay), or scan for VGs (vgscan).

RHCSA exam# Yes28 options, 10 examples

Ask DNS servers for records (A, AAAA, MX, TXT, NS …) and show the full answer — the main DNS test tool.

Everyday Linux42 options, 12 examples

Simple DNS lookups with short, readable output.

Everyday Linux20 options, 10 examples

Show the host name (and its FQDN, domain or IP addresses), or set it until the next reboot.

RHCSA exam# For changes12 options, 10 examples

Show and change network cards, addresses, routes and neighbours (the live kernel settings).

RHCSA exam# For changes34 options, 15 examples

Set up, change and check network connections with NetworkManager.

RHCSA exam# For changes45 options, 16 examples

A menu in the terminal to edit NetworkManager connections, activate them and set the host name.

RHCSA exam# Yes2 options, 10 examples

Ask a DNS server for the address of a name, or for other DNS records (mail, text, name servers).

Everyday Linux20 options, 14 examples

Send ICMP echo requests to a host to test if it is reachable and how fast it answers.

RHCSA exam38 options, 11 examples

Show network sockets: which ports are listening, which connections are open, and which process owns them.

RHCSA exam# For changes39 options, 11 examples

Show the routers (hops) on the way to a host and the MTU of the path. Needs no root.

Everyday Linux8 options, 10 examples

Copy and synchronize files and folders (locally or over SSH), sending only what changed.

RHCSA exam102 options, 14 examples

Copy files between systems over SSH (secure copy).

RHCSA exam22 options, 12 examples

Transfer files interactively over SSH, like a secure FTP client.

RHCSA exam24 options, 11 examples

Log in to another system over an encrypted connection, run remote commands, and make secure tunnels.

RHCSA exam43 options, 14 examples

Keep unlocked SSH keys in memory (ssh-agent) and load or remove keys there (ssh-add), so you type a passphrase only once.

RHCSA exam30 options, 12 examples

Install your public SSH key on a server, so you can log in with the key instead of a password.

RHCSA exam9 options, 11 examples

Create SSH key pairs, change their passphrase, show fingerprints and clean the known_hosts file.

RHCSA exam42 options, 12 examples

The OpenSSH server. Mostly used through systemctl; the command itself tests the configuration (-t, -T) and helps debugging.

RHCSA exam# Yes19 options, 10 examples

Explain SELinux denials (audit2why) or build a policy module that allows them (audit2allow) — the last resort.

Extra# Yes17 options, 10 examples

Search the audit log (/var/log/audit/audit.log): SELinux denials, logins, commands and other kernel audit events.

RHCSA exam# Yes38 options, 10 examples

Change the SELinux context of files directly — only for a quick test, because restorecon or a relabel undoes it.

RHCSA exam# Yes13 options, 10 examples

Show the SELinux mode (getenforce), or switch between enforcing and permissive until the next reboot (setenforce).

RHCSA exam# For changes2 options, 10 examples

Show SELinux booleans (getsebool) or switch them on and off (setsebool; with -P permanently).

RHCSA exam# For changes4 options, 10 examples

Set the SELinux labels of files back to what the policy (and your semanage fcontext rules) say.

RHCSA exam# Yes17 options, 10 examples

Explain SELinux denials in plain text, with the likely cause and the commands that fix it.

Everyday Linux# Yes9 options, 10 examples

Change the SELinux policy settings that admins need: file context rules, port types, booleans, permissive domains, user mappings.

RHCSA exam# Yes18 options, 11 examples

Show the full SELinux status: on or off, current and config mode, policy name and version.

RHCSA exam2 options, 10 examples

Configure firewalld: zones, services, ports, sources, rich rules, forwarding — at run time or permanently.

RHCSA exam# For changes43 options, 12 examples

Show and manage nftables rules: tables, chains, rules and sets — the kernel firewall below firewalld.

Extra# Yes18 options, 10 examples

Show the kernel messages (the kernel ring buffer): hardware found, drivers loaded, disk and memory errors.

RHCSA exam# For changes30 options, 11 examples

Create (or rebuild) the initramfs: the small root file system in RAM that finds and mounts the real root at boot.

RHCSA exam# Yes38 options, 10 examples

Install the GRUB 2 boot loader to a disk (BIOS systems) — used to repair a system that does not find its boot loader.

Everyday Linux# Yes20 options, 10 examples

Generate the GRUB 2 configuration file from /etc/default/grub and the scripts in /etc/grub.d/.

RHCSA exam# Yes4 options, 10 examples

Show and change the boot entries of GRUB 2: kernel arguments, the default kernel, and entry details.

RHCSA exam# Yes25 options, 10 examples

Load one module file into the kernel (insmod) or remove a loaded module (rmmod) — without dependency handling.

Everyday Linux# Yes7 options, 10 examples

Show the content of an initramfs image: dracut modules, files, kernel modules, and the content of single files.

Everyday Linux# For changes8 options, 10 examples

List the kernel modules that are loaded now.

RHCSA exam0 options, 10 examples

List the PCI devices (network cards, disk controllers, GPUs …) and the drivers that handle them.

Everyday Linux# For changes22 options, 10 examples

List USB buses and the USB devices connected to them.

Everyday Linux# For changes7 options, 10 examples

Show information about a kernel module: file, description, license, dependencies, aliases and parameters.

RHCSA exam11 options, 10 examples

Load or unload kernel modules, with their dependencies and the settings from /etc/modprobe.d/.

RHCSA exam# Yes20 options, 10 examples

Read and change kernel parameters at run time (the files under /proc/sys), and load them from config files.

RHCSA exam# For changes14 options, 10 examples

Control and query udev, the service that creates device files and runs rules when hardware appears.

Everyday Linux# For changes38 options, 10 examples

Talk to the chrony NTP daemon: show time sources, sync state and statistics, or make the clock step.

RHCSA exam# For changes13 options, 10 examples

Show the date and time in any format, calculate other dates, or set the system clock.

RHCSA exam# For changes12 options, 11 examples

Read or set the hardware clock (RTC), and copy the time between the hardware clock and the system clock.

RHCSA exam# Yes22 options, 10 examples

Show and change the system time, the time zone, the RTC mode and whether NTP sync is on.

RHCSA exam# For changes11 options, 10 examples

Find the name of a time zone by answering questions (it does not change the system).

Everyday Linux4 options, 10 examples

Control and test the Apache web server: check the config syntax, list virtual hosts and modules. (Start and stop with systemctl.)

RHCSA exam# Yes16 options, 10 examples

Send requests to URLs (HTTP, HTTPS, FTP …): test web servers, call APIs, download files, check TLS.

Everyday Linux57 options, 12 examples

Run a command (default: a shell) with another folder as the root / — the key step to repair an installed system from a rescue shell.

RHCSA exam# Yes6 options, 10 examples

Show and change the hostname of the system, and see the OS, kernel and hardware facts.

RHCSA exam# For changes10 options, 11 examples

Show the CPU: architecture, model, sockets, cores, threads, caches, flags, virtualization and CPU security bugs.

Everyday Linux15 options, 10 examples

Print the number of CPUs (cores/threads) that the current process can use.

Everyday Linux4 options, 10 examples

Show the name and version of the kernel, the machine type and the hostname.

Everyday Linux11 options, 11 examples