Generate SSH key
ssh-keygen -t ed25519 -C "[email protected]"
# when no support for Ed25519 present
ssh-keygen -t rsa -b 4096 -C "[email protected]"
Note: By default SSH keys get stored to /home/<username>/.ssh/ folder.
Login to host via SSH
# connect to host as your local username
ssh host
# connect to host as user
ssh <user>@<host>
# connect to host using port
ssh -p <port> <user>@<host>
Execute command on a server through SSH
# execute one command
ssh [email protected] "ls /root"
# execute many commands
ssh [email protected] "cd /root;touch file.txt"
Displays currently logged in users in the system
w
Displays Linux system information
uname
Displays kernel release information
uname -r
Shows the system hostname
hostname
Shows system reboot history
last reboot
Displays information about the user
sudo apt install finger
finger <username>
Displays IP addresses and all the network interfaces
ip addr show
Downloads a file from an online source
wget https://example.com/example.tgz
Note: If URL contains ?, & enclose the URL in double quotes.
Compress a file with gzip
# will not keep the original file
gzip file.txt
# will keep the original file
gzip --keep file.txt
Interactive disk usage analyzer
sudo apt install ncdu
ncdu
ncdu <path/to/directory>
Install Node.js using the Node Version Manager
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.35.3/install.sh | bash
source ~/.bashrc
nvm install v13
Too long; didn't read
npm install -g tldr
tldr tar
Combine all Nginx access logs to one big log file
zcat -f /var/log/nginx/access.log* > /var/log/nginx/access-all.log
Set up Redis server
sudo apt install redis-server redis-tools
# check if server is running
sudo service redis status
# set and get a key value
redis-cli set mykey myvalue
redis-cli get mykey
# interactive shell
redis-cli
Generate statistics of your webserver
sudo apt install goaccess
# check if installed
goaccess -v
# combine logs
zcat -f /var/log/nginx/access.log* > /var/log/nginx/access-all.log
# export to single html
goaccess \
--log-file=/var/log/nginx/access-all.log \
--log-format=COMBINED \
--exclude-ip=0.0.0.0 \
--ignore-crawlers \
--real-os \
--output=/var/www/html/stats.html
# cleanup afterwards
rm /var/log/nginx/access-all.log
Search for a given pattern in files
grep -r ‘pattern’ files
Find proccess ID for a specific program
pgrep nginx
Print name of current/working directory
pwd
Creates a blank new file
touch newfile.txt
Displays first lines in a file
# -n <x> presents the number of lines (10 by default)
head -n 20 somefile.txt
Displays last lines in a file
# -n <x> presents the number of lines (10 by default)
tail -n 20 somefile.txt
# -f follows the changes in file (doesn't closes)
tail -f somefile.txt
Count lines in a file
wc -l somefile.txt
Find all instances of the file
sudo apt install mlocate
locate somefile.txt
Find file names that begin with ‘index’ in /home folder
find /home/ -name "index"
Find files larger than 100MB in the home folder
find /home -size +100M
Displays block devices related information
lsblk
Displays free space on mounted systems
df -h
Displays free and used memory in the system
free -h
Displays all active listening ports
sudo apt install net-tools
netstat -pnltu
Kill a process violently
kill -9 <pid>
List files opened by user
lsof -u <user>
Execute "df -h", showing periodic updates
# -n 1 means every second
watch -n 1 df -h