Cheat sheet

• 1. Basics
  • 1.1. Signal codes
• 2. System and service management
  • 2.1. systemctl
  • 2.2. systemd-analyze
• 3. Account administration
  • 3.1. Root privileges
  • 3.2. Users and groups
• 4. Container management
  • 4.1. podman
• 5. Network configuration
  • 5.1. ip
  • 5.2. IPv4
    • 5.2.1. Address classes
    • 5.2.2. Private addresses
• 6. Manual pages

1. Basics

Command	Meaning
cat	Concatenate files and print on the stdout
cd	Change working directory
chmod	Change file permission bits
chown	Change file owner and group
cp	Copy files
du	Estimate file space usage
echo	Display a line of text
file	Determine file type
find	Search for files in a directory hierarchy
grep	Print lines that match patterns
head	Output the first part of files
id	Print real and effective user and group IDs
kill	Send a signal to a process
less	Display file contents one screen at a time
ln	Make links between files
ls	List directory contents
man	Show manual pages
mkdir	Make directories
mv	Move (rename) files
nano	Text editor
ps	Report a snapshot of the current processes
pwd	Print name of current working directory
python3	CPython, version 3
readlink	Print resolved symbolic links or canonical file names
rm	Remove files
sleep	Delay for a specified amount of time
tail	Output the last part of files
top	Provide a dynamic real-time view of a running system
vim	Text editor
which	Locate a command
whoami	Print effective user name

1.1. Signal codes

#	Name	Description	Default	Dump	Catch	Block
1	HUP	Hangup	Terminate	No	Yes	Yes
2	INT	Interrupt	Terminate	No	Yes	Yes
3	QUIT	Quit	Terminate	Yes	Yes	Yes
7	BUS	Bus error	Terminate	Yes	Yes	Yes
9	KILL	Kill	Terminate	No	No	No
10	USR1	User-defined 1	Terminate	No	Yes	Yes
11	SEGV	Segm. fault	Terminate	Yes	Yes	Yes
12	USR2	User-defined 2	Terminate	No	Yes	Yes
15	TERM	Software term.	Terminate	No	Yes	Yes
18	CONT	Cont. after stop	Ignore	No	Yes	No
19	STOP	Stop	Stop	No	No	No
20	TSTP	Keyboard stop	Stop	No	Yes	Yes

2. System and service management

Command	Meaning
journalctl	Print log entries from the systemd journal
systemctl	Control systemd
systemd-analyze	Analyze and debug systemd

2.1. systemctl

Subcommand	Argument	Meaning
daemon-reload	n/a	Reload unit files and systemd config
disable	unit	Prevent unit from activating at boot
enable	unit	Enable unit to activate at boot
get-default	n/a	Show the default target
isolate	target	Change operating mode to target
kill	pattern	Send a signal to units matching pattern
list-timers	pattern	List the timer units matching pattern currently in memory
list-unit-files	pattern	List the unit files matching pattern installed in the system
list-units	pattern	List the units matching pattern currently in memory
reboot	n/a	Reboot the computer
restart	unit	Restart unit immediately
start	unit	Activate unit immediately
status	unit	Show the status of unit and recent logs
stop	unit	Deactivate unit immediately

2.2. systemd-analyze

Subcommand	Argument	Meaning
calendar	expression	Parse a calendar repetitive event expression, output the normalized form, and calculate when next occurrences
timespan	expression	Parse a time span expression and output the normalized form and the equivalent value in microseconds

3. Account administration

3.1. Root privileges

Command	Meaning
su	Allows commands to be run with a substitute user and group ID
sudo	Execute a command as another user
visudo	Edit the sudoers file with syntax validation

3.2. Users and groups

Command	Meaning
chage	Change user password-aging metadata
groupadd	Create a new group
groupdel	Remove a group
passwd	Change user password
useradd	Create a new user account
userdel	Remove a user account
usermod	Modify an existing user account
vipw	Edit the password file with locking

4. Container management

Command	Meaning
podman	Manage containers and images

4.1. podman

Subcommand	Argument	Meaning
build	n/a	Build an image from a Containerfile
exec	container	Run a command in running container
image prune	n/a	Discard images not referenced by any container
images	n/a	List locally stored images
ps	n/a	Show running containers
pull	image	Pull image from a registry
push	image	Push image to a registry
rm	container	Remove stopped container
rmi	image	Remove image
run	image	Create and start a container from image
start	container	Start stopped container
stop	container	Stop running container
tag	image	Add a name and tag to image

5. Network configuration

Command	Meaning
ip	Show and manipulate routing, network devices, interfaces, and tunnels
iptables	Administer IPv4 packet filtering and NAT
nc	Open arbitrary TCP or UDP connections
ping	Send ICMP echo request to network hosts
ss	Dump socket statistics
sysctl	Configure kernel parameters at runtime
tcpdump	Dump traffic on a network
traceroute	Print the route packets trace to network host

5.1. ip

Subcommand	Argument	Meaning
address	n/a	Show network interface addresses
neigh	n/a	Show ARP cache entries
route	n/a	Show routing table

5.2. IPv4

5.2.1. Address classes

Class	1st byte	Implicit netmask	Use case
A	0 - 127	255.0.0.0 (/8)	Large networks
B	128 - 191	255.255.0.0 (/16)	Medium networks
C	192 - 223	255.255.255.0 (/24)	Small networks
D	224 - 239	n/a	Multicasting
E	240 - 255	n/a	Experimental addresses

5.2.2. Private addresses

IP class	From	To	CIDR range
A	10.0.0.0	10.255.255.255	10.0.0.0/8
B	172.16.0.0	172.31.255.255	172.16.0.0/12
C	192.168.0.0	192.168.255.255	192.168.0.0/16

6. Manual pages

Page	Topic
man:systemd.unit(5)	[Unit] and [Install] section directives
man:systemd.service(5)	[Service] section directives
man:systemd.timer(5)	[Timer] directives and calendar expressions
man:sudoers(5)	Sudoers file syntax
man:iptables(8)	iptables command-line syntax
man:iptables-extensions(8)	iptables match modules (e.g., conntrack)

Licenses

Content	License
Code	MIT License
Text	Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International