Linux Commands Useful

Login using SSH

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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

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

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 ufw allow 8080
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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

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 

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 -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

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

Unarchive tar.gz format

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

Archive

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zip -r <output_file> <folder_1>

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