My Cheatsheets

Getting Help in Linux

MAN Pages

man ls

Navigation inside man (uses less):

• h: Help
• q: Quit
• space: Next screen
• /string: Search forward
• ?string: Search backward
• n/N: Next/previous search

Command Type

type rm   # shows if rm is builtin or executable
type cd   # cd is a shell builtin

Help for Commands

help cd         # shell built-in help
rm --help       # executable help
command --help  # general help

Search Man Pages

man -k uname
apropos passwd

Keyboard Shortcuts

• TAB TAB: autocomplete
• CTRL+L: clear
• CTRL+D: close shell
• CTRL+U: cut current line
• CTRL+A: move cursor to start
• CTRL+E: move cursor to end
• CTRL+C: stop command
• CTRL+Z: suspend command
• CTRL+R: reverse search history

Bash History

history            # show history
history -d 100     # delete entry
!!                 # rerun last command
!20                # run command #20
!abc               # run last command starting with abc

Root Access

sudo command       # run as root
sudo su            # become root
sudo passwd root   # set root password
passwd username    # change user password
su                 # switch to root (if password set)

Linux Paths

• Absolute: starts with /
• Relative: relative to current
• .: current dir
• ..: parent dir
• ~: home dir

Changing Directories

cd        # home
d cd ~    # home
cd -      # last dir
cd /path  # go to path
pwd       # print working dir

Listing and Tree

ls          # list
ls -l       # long list
ls -a       # include hidden
ls -lh      # human readable
ls -t       # sort by time
tree .      # tree

Disk Usage

du -sh ~    # size of home

File Timestamps

ls -lu      # access time
ls -lt      # modification time
ls -lc      # change time
stat file   # all timestamps

Touch

touch file.txt

Date and Calendar

date
cal
cal 2021
cal -3  # prev, current, next

Viewing Files

cat file
cat -n file      # with line numbers
less file
head -n 15 file
tail -f file     # follow

Creating and Managing Files

touch file
mkdir dir
mkdir -p a/b/c

Copy

cp file1 file2
cp -r dir1 dir2

Move/Rename

mv file1 file2
mv file1 dir/

Remove

rm file
rm -r dir
rm -rf dir   # force

Secure Delete

shred -vu -n 100 file

Piping and Redirection

ls -lSh /etc/ | head
ps -ef | grep sshd
ps aux > processes.txt
id >> users.txt
tail -n 10 /var/log/*.log > out.txt 2> err.txt

Finding Files

locate filename
find ~ -type f -size +1M
grep -n pattern file

VIM Basics

Modes: Command, Insert, Last Line

vim file
:wq     # save & quit
:q!     # quit without saving

User Management

useradd user
usermod user
userdel -r user
groupadd group
groupdel group

File Permissions

ls -l file
chmod 755 file
chmod u+x file
chown user file
chgrp group file

Special: SUID (u+s), SGID (g+s), Sticky Bit (o+t)

Processes

ps -ef
ps aux | less
top
htop
kill pid
killall name

Background/Foreground:

command &
jobs
fg %1
bg %1

Networking

ifconfig
ip addr
route -n
ping host
netstat -tupan
ss -tupan
lsof -iTCP -sTCP:LISTEN
nmap -sS 192.168.0.1

SSH

ssh user@host
ssh -p 2222 user@host
scp file user@host:~
rsync -av /src /dest

Software Management (Debian)

dpkg -i pkg.deb
apt update
apt install package
apt remove package
apt autoremove

Cron Scheduling

crontab -e
* * * * * cmd       # every min
30 18 * * * cmd     # daily 18:30
@reboot cmd         # on boot

System Hardware Info

lscpu
lsusb
lsblk
uname -a
free -m

Services

systemctl status nginx
systemctl start nginx
systemctl stop nginx
systemctl enable nginx

Bash Scripting Basics

Aliases

alias c='clear'
unalias name

Variables

var=value
echo $var

Flow Control

if [ cond ]; then cmd; fi
for i in {1..5}; do echo $i; done
while [ cond ]; do cmd; done

Functions

function name() { cmd; }