Command reference

272 commands, each with the options you actually use, real examples and the gotchas that bite in production.

A

alias define or display aliases
amtool View and modify the current Alertmanager state
apropos search the manual page names and descriptions
apt package manager for Debian and Ubuntu
apt-cache query the APT package cache
apt-get package manager for Debian and Ubuntu
apt-mark mark packages held (never upgraded by apt upgrade)
argocd Argo CD command line (v3.5)
arp manipulate the system ARP cache (net-tools, deprecated)
awk pattern scanning and processing language
az Azure command-line interface

B

base64 base64 encode/decode data and print to standard output
basename strip directory and suffix from a filename
bash GNU Bourne-Again SHell
bg resume a job in the background
blkid locate/print block device attributes
break leave a loop (bash builtin)

C

capsh capability shell wrapper
cat concatenate files and print on the standard output
cd change the working directory
checkov static analysis of infrastructure as code for security and compliance misconfigurations
chgrp change group ownership
chmod change file mode bits
chown change file owner and group
clear clear the terminal screen
column columnate lists
command run a command bypassing functions and aliases
continue skip to the next iteration of a loop (bash builtin)
cp copy files and directories
crane a tool for interacting with remote images and registries (go-containerregistry)
crictl CLI for CRI-compatible container runtimes (containerd) - what the kubelet sees
curl transfer a URL
cut remove sections from each line

D

date print or set the system date and time
deactivate leave a Python virtual environment (a shell function the venv's activate script defines)
declare declare variables and give them attributes
df report filesystem disk space usage
dig DNS lookup utility
dirname strip the last component from a filename
disown remove jobs from the shell's job table (bash builtin)
dmesg print or control the kernel ring buffer
docker Docker image and container command line interface
docker-compose Define and run multi-container applications
dpkg Debian package manager, one level below apt
du estimate file space usage

E

echo display a line of text
egrep grep -E
env run a program in a modified environment, or print the environment
etcdctl etcd v3 client (etcd 3.6: talks to a live member)
etcdutl etcd offline utility: works on snapshot files and data directories
eval evaluate arguments as a shell command
exec replace the shell with a command
exit exit the shell
export set an export attribute for shell variables

F

false do nothing, unsuccessfully
fg resume a job in the foreground
fgrep grep -F
file determine file type
find search for files in a directory hierarchy
findmnt find a filesystem in the mount tree
free display amount of free and used memory
fstrim discard unused blocks on a mounted filesystem

G

gawk pattern scanning and processing language
getent get entries from Name Service Switch libraries
getopts parse option arguments in a shell script
git the stupid content tracker
gpasswd administer /etc/group
gpg OpenPGP encryption and signing tool
grep print lines matching a pattern
groupadd create a new group
groupdel delete a group
groups print the groups a user is in

H

halt power off the machine
head output the first part of files
helm The Kubernetes package manager (Helm 4)
hey HTTP load generator
history display the command history
host DNS lookup utility
hostname show or set the system host name
hostnamectl control the system hostname
htop interactive process viewer

I

id print real and effective user and group IDs
ifconfig configure a network interface (net-tools, deprecated)
iotop simple top-like I/O monitor
ip show and manipulate routing, devices and addresses
ipcalc simple IP network calculator

J

java launch a Java application
jcmd send diagnostic command requests to a running Java Virtual Machine
jinfo generate Java configuration information for a specified Java process
jmap print details of a specified process
jobs list active jobs
journalctl query the systemd journal
jps list the instrumented JVMs on the target system
jq command-line JSON processor
jstack print Java thread stack traces for a running Java process
jstat monitor JVM statistics

K

keytool manage a Java keystore of cryptographic keys, certificate chains and trusted certificates
kill send a signal to a process
killall kill processes by exact name
kubeadm bootstrap and operate a kubeadm cluster
kubectl kubectl controls the Kubernetes cluster manager
kubectl attach Attach to a running container
kubectl auth Inspect authorization
kubectl autoscale Auto-scale a deployment, replica set, stateful set, or replication controller
kubectl certificate Approve or deny certificate signing requests
kubectl cp Copy files and directories to and from containers
kubectl create Create a resource from a file or from stdin, or with a generator
kubectl create-ingress Create an ingress with the specified name
kubectl debug Create debugging sessions for troubleshooting workloads and nodes
kubectl drain Drain node in preparation for maintenance
kubectl port-forward Forward one or more local ports to a pod
kubectl proxy Run a proxy to the Kubernetes API server
kubelet the node agent (run by systemd as kubelet.service)
kubelogin client-go credential plugin for Entra ID (Azure AD) authentication to AKS
kubeseal encrypt a Kubernetes Secret into a SealedSecret only the cluster's controller can decrypt
kustomize template-free customization of Kubernetes YAML (v5.7)

L

less page through text one screen at a time
let evaluate arithmetic expressions
ln make links between files
local create a function-local variable
logcli Command-line client for Loki
logout exit a login shell
ls list directory contents
lsb_release print distribution-specific information
lsblk list block devices
lsmod show the loaded kernel modules
lsns list namespaces
lsof list open files
lspci list PCI devices
lvextend add space to an LVM logical volume

M

man an interface to the system reference manuals
mapfile read lines from stdin into an array
mawk pattern scanning and processing language
mkdir make directories
mkfs.ext4 create an ext4 filesystem
mktemp create a temporary file or directory safely
modprobe add a kernel module
more page through text one screen at a time
mount mount a filesystem, or list what is mounted
mtr a network diagnostic tool combining traceroute and ping
mv move (rename) files

N

namei follow a pathname until a terminal point is found
nano a small and friendly text editor
nc arbitrary TCP and UDP connections and listens (OpenBSD netcat)
nerdctl a docker-compatible CLI for containerd
netplan YAML network configuration abstraction for various backends
networkctl Query or modify the status of network links (systemd-networkd)
newgrp log in to a new group
nginx small, but very powerful and efficient web server
nl number lines of files
nohup run a command immune to hangups, with output to a non-tty
nproc print the number of processing units available
nsenter run program in different namespaces
nslookup query Internet name servers
nstat network statistics tool

O

oc OpenShift command-line client: kubectl plus the OpenShift APIs
oc adm Tools for managing an OpenShift cluster
oc debug Launch a new instance of a pod for debugging
oc expose Expose a replicated application as a service or route
oc login Log in to a server
oc new-app Create a new application
oc start-build Start a new build
oc status Show a high level overview of the current project
od dump files in octal and other formats
openssl OpenSSL command line program

P

parted a partition manipulation program
pgrep list process IDs matching a pattern
pidof find the process ID of a running program
ping send ICMP ECHO_REQUEST to network hosts
pip the Python package installer
pip3 the Python package installer
pipx install and run Python applications in isolated environments
pkill signal processes by name or other attribute
podman daemonless, rootless-capable container engine with a docker-compatible CLI
poweroff power off the machine
printenv print all or part of the environment
printf format and print data
prometheus The Prometheus monitoring server
promtool Tooling for the Prometheus monitoring system
ps report a snapshot of the current processes
pstree display a tree of processes
pwd print name of current working directory
pytest simple powerful testing with Python
python an interpreted, interactive, object-oriented programming language
python3 an interpreted, interactive, object-oriented programming language

R

read read a line from standard input
readarray read lines from stdin into an array (bash builtin, same as mapfile)
readlink print the target of a symbolic link
readonly mark variables as unchangeable
realpath print the resolved absolute pathname
reboot reboot the machine
resize2fs ext2/ext3/ext4 file system resizer
resolvectl resolve domain names, IPV4 and IPv6 addresses, DNS resource records, and services; introspect and reconfigure the DNS resolver
return return from a shell function
rev reverse the characters of every line
rm remove files or directories
rmdir remove empty directories

S

scp OpenSSH secure file copy
sed stream editor for filtering and transforming text
seq print a sequence of numbers
set set or unset shell options and positional parameters
setsid run a program in a new session
sh command interpreter (on Ubuntu, a link to dash; here bash in POSIX mode)
sha256sum compute SHA256 message digest
shellcheck static analysis tool for shell scripts
shift shift positional parameters
shutdown halt, power off or reboot the machine
skopeo command line utility to inspect and copy container images and image repositories, without pulling or a daemon
sleep delay for a specified time
sort sort lines of text files
source read and execute a file in the current shell
ss another utility to investigate sockets
ssh OpenSSH remote login client
ssh-keygen authentication key generation
stat display file or filesystem status
strace trace system calls and signals
su run a command with substitute user and group ID
sudo execute a command as another user
swapoff disable swap
swapon enable swap, or show what is in use
sync synchronize cached writes to persistent storage
sysctl configure kernel parameters at runtime
systemctl control the systemd system and service manager
systemd-analyze analyse system boot performance and unit files
systemd-cgls show the cgroup hierarchy
systemd-cgtop top for cgroups: CPU, memory and I/O per unit
systemd-run run a command in a transient unit or scope

T

tac concatenate and print files in reverse (last line first)
tail output the last part of files
tar an archiving utility
tcpdump dump traffic on a network
tee read stdin and write to both stdout and files
terraform build, change and destroy infrastructure as code
test evaluate an expression
tflint a pluggable linter for Terraform configurations
timeout run a command with a time limit
top display Linux processes
touch change file timestamps, creating empty files as needed
tr translate or delete characters
tracepath traces path to a network host discovering MTU along this path
traceroute print the route packets trace to network host
trap run a command when a signal is received
tree list contents of directories in a tree-like format
trivy a scanner for vulnerabilities in container images, filesystems and git repositories, and misconfigurations in IaC
true do nothing, successfully
truncate shrink or extend the size of a file
tune2fs adjust tunable filesystem parameters on ext2/3/4
type describe how a command name would be interpreted

U

ulimit modify shell resource limits
umask set the file mode creation mask
unalias remove alias definitions
uname print system information
uniq report or omit repeated adjacent lines
unset unset values and attributes of variables
update-ca-certificates update /etc/ssl/certs and ca-certificates.crt
uptime tell how long the system has been running
useradd create a new user or update default new user information
userdel delete a user account and related files
usermod modify a user account

V

vgs display information about LVM volume groups
vi Vi IMproved, a programmer's text editor
vim Vi IMproved, a programmer's text editor
vmstat Report virtual memory statistics

W

w show who is logged on and what they are doing
wait wait for a job to complete
wc print newline, word and byte counts for each file
wget the non-interactive network downloader
whereis locate the binary, source and manual page files for a command
which locate a command in $PATH
who show who is logged on
whoami print effective user name

X

xargs build and execute command lines from standard input