Linux Commands Useful

Average size of files


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CAM_DIR="/dev/shm/streams/OSK_CAM_1"
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files=("${CAM_DIR}"/*)
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if [ ${#files[@]} -eq 0 ]; then
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  echo "NaN"
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else
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  total_size=$(du -cb "${CAM_DIR}"/* | grep 'total' | awk '{print $1}')
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  file_count=${#files[@]}
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  average_size_mb=$(awk "BEGIN {printf \"%.2f\", ($total_size / $file_count) / 1048576}")
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  echo "${average_size_mb} MB"
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fi

Count files in directory


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ls -1 /dev/shm/streams/WOW_CAM_1 | wc -l


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ssh user@127.127.127.127
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ssh -i /path/private.key user@127.127.127.127

Remove host from ssh known hosts (when server changes, but IP stays the same)


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ssh-keygen -R "hostname"

Key must have read only rights


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chmod 600 /path/private.key

Controling console

Exit any program in console using CTRL+C command

move to directory


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cd /path/to/some/dir

Tab button gives you auto-complete

Move back one dir


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cd ..

Your home directory


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cd ~/

Make directory


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mkdir ~/some_dir

Delete directory


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rm -rf ~/some_dir

Get my public IP address


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curl ifconfig.me

Installing programs

Install programs in Debian/Ubuntu using apt / apt-get package manager (replace PACKAGE_NAME)


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sudo apt install PACKAGE_NAME

If program not available in package managers download using wget and install manually.

chmod gives execution rights, sudo means - execute as administrator


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cd ~/downloads
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wget https://repo.anaconda.com/archive/Anaconda3-2021.11-Linux-x86_64.sh
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sudo chomd +x ./Anaconda3-2021.11-Linux-x86_64.sh
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sudo ./Anaconda3-2021.11-Linux-x86_64.sh

Making bash scripts executable / readable

Rxecutable


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chmod +x ./file.sh

Readable by all users


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chomd a+wr ./file.sh

get chomd settings from file


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ls -l myfile.txt

Process management

htop - Activity monitor, also can kill programs with F9 , then 9

Which process use most CPU


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ps auxh --sort=-pcpu | head -n 10

Which processes use most Memory


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ps auxh --sort=-rss | head -n 10

Find parent Process ID (to find correct screen)


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ps -o ppid= -p 1289173

CPU temperature


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sudo apt install lm-sensors

then


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sensors

htop for network net monitor firewall linux


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sudo apt-get install jnettop
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sudo jnettop

GPU usage

nvidia-smi shows GPU usage and memory usage

Firewall


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sudo apt install firewalld firewall-config ufw
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sudo firewall-cmd --zone=public --add-port=10090/tcp --permanent 
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sudo firewall-cmd --zone=public --add-port=10090-10200/tcp --permanent 
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sudo firewall-cmd --reload
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sudo firewall-cmd --zone=public --add-port=8080/tcp --permanent 
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sudo firewall-cmd --zone=public --add-port=80/tcp --permanent 
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sudo firewall-cmd --reload
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sudo firewall-cmd --zone=public --add-port=443/tcp --permanent 
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sudo firewall-cmd --reload
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sudo ufw allow 8080
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sudo ufw allow 443
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sudo ufw allow from any to any proto tcp port 10090:10210

See all open ports and which programs are using


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sudo lsof -i -P -n
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sudo lsof -i -P -n | grep LISTEN

Checking what ports are listnening


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sudo apt install net-tools
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netstat -nlt

Test specific port


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telnet ADDRESS PORT

Debug incoming requests HTTP netcat


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nc -l PORT

Test open ports


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for i in {1..255}; do
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  (
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    ping -c 1 -t 1 192.168.82.$i &> /dev/null && echo "192.168.82.$i is alive"
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  ) &
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done
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wait

Speedtest


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sudo apt install speedtest-cli
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speedtest-cli

crontab - automation

Edit tasks


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crontab -e

Format


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@reboot /media/hdd/automation_cron/startup_automations_evalds_1.sh
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*/5 * * * * /media/hdd/automation_cron/run_automations_evalds_1.sh

Log output to file


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59 23 * * * /home/john/bin/backup.sh > /media/hdd/automation_cron/run_automations_evalds_1.log 2>&1

Global crontab (with user names admin )


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sudo vim /etc/crontab

Restart


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sudo service cron restart

Logs


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sudo grep CRON /var/log/syslog

List all services


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sudo service --status-all

Chmod


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0: No permission
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1: Execute
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2: Write
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3: Write and execute
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4: Read
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5: Read and execute
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6: Read and write
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7: Read, write, and execute


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The owner can read, write, and execute the file.
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The group can read, write, and execute the file.
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Anyone else can read, write, and execute the file.


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sudo chmod 660 /shome/file

Alternative way!

plus means add rights

minus means remove rights

Add folder write/read rights for all users


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sudo chmod -R a+wr /some/folder

Remove folder write/read rights for all users


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sudo chmod -R a-wr /some/folder

Make SH file executable


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sudo chmod +x /some/folder

List files in directory


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ls -l #as list
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ls -t # sort by time ASC
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ls -tr # sort by time DESC


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ls -ltr /path/dir
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ls -ltr /path/dir | grep "filter-text"
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https://www.tecmint.com/sort-ls-output-by-last-modified-date-and-time/

List current directory


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pwd

Find file


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find /dir -name "*Something*"

https://www.geeksforgeeks.org/find-command-in-linux-with-examples/

Find text in files


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grep -i -A 5 -B 5 "string" FILE_PATTERN

https://www.thegeekstuff.com/2009/03/15-practical-unix-grep-command-examples/

Kill process


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kill -9 PROCES_ID
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kill -9 $(ps aux | grep 'SOME TEXT IN PROCESS' | awk '{print $2}')

Zip a folder

Compression level 0-9


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zip -X -9 -r <output_file> <folder_1>

Find location of some app in global path


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whereis app_name

Find location of binary


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which docker
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# gives /snap/bin/docker

Symlinks

Create


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ln -s /path/source/folder_or_file /path/destination

Will result in /path/destination/folder_or_file

Find source


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readlink -f /path/to/syslink
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readlink -f which command

Linux Screen

create with name screen -S newname

List screens: screen -ls

Attach to existing screen -rd newname

Detach from screen ctrl+a => d

Kill screen ctrl+a => k

Rename screen

screen -S <session-id> -X sessionname <new-name>

Kill screen by name


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screen -X -S sttlt6.asya.ai_app kill
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Alias command in .bashrc


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alias killscreen="screen -X -S $1 kill"


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killscreen session_name

Scroll mode

Screen shortcuts

Send commands to screen:


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screen -dmS server
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screen -r server -X stuff "/media/hdd/Document/server.sh\n"

Alternative to Linux screens - tmux https://superuser.com/questions/236158/tmux-vs-screen

Format file system


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sudo fdisk -l
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sudo mkfs.ext4 /dev/sde1

Unarchive tar.gz format tar gz


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tar –xvzf file.tar.gz
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unzip latest.zip

Count files ls in directory


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cd /dir/
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ls -1 | wc -l

List of running services


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systemctl list-units --type=service

Current directory


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pwd

http://share.yellowrobot.xyz/quick/2022-9-5-DF70FF8D-C119-4746-BC69-17E78082B14F.html

Bash extract JSON values

Disk space analyzers (Space Sniffer)

ncdu

Linux distribution identify


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cat /etc/os-release
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lsb_release -a

tmux screen manager

ctrl+b then : activates commands

https://tmuxcheatsheet.com

:kill-session

Common services


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sudo service postgresql status
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sudo service postgresql start 
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sudo service nginx start 
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sudo service nginx status

Adding user with directory


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sudo useradd -m -d /home/username -s /bin/bash username

Setting password


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sudo passwd username

🔴 Even accounts that you login only using key must have password

Remove user from group


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sudo gpasswd -d username groupname

Folder to specific group


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sudo chown :groupname file_or_directory

Adding to user group


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sudo usermod -a -G www-data username

Generate key


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sudo mkdir -p /home/username/.ssh
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ssh-keygen -t rsa -b 4096 -C "username"


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sudo chown -R username:username /home/username/.ssh
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sudo chmod -R 770 /home/username/.ssh
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sudo chmod 770 /home/username/.ssh
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sudo touch /home/username/.ssh/authorized_keys 
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sudo vim /home/username/.ssh/authorized_keys 
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sudo chmod 770 /home/username/.ssh/authorized_keys 
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sudo chmod 600 /home/username/.ssh/authorized_keys 
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Adding new users Creating new user

linux create new user group and add user to group


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sudo groupadd faradai
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sudo usermod -aG new_group username

list users in group


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cat /etc/group | grep groupname

linux folder owned by group


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sudo chown :group_name /path/to/folder