Linux Commands Useful

Testing if user can access directory

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sudo -u www-data ls -l /home/ubuntu/moodledata
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Current IP address

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hostname -I

See running ubuntu services

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service --status-all | grep '\[ + \]'  

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

Make folder write/read 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

Delete old files

older than 30 days

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find /opt/backup -type f -mtime +30 -delete 
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find /var/log -name "*.log" -type f -mtime +30 -delete 

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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ls -a # shows also hidden files

https://www.tecmint.com/sort-ls-output-by-last-modified-date-and-time/

Count files

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cd ~/documents/api_asya_ai/requests_files/unprocessed
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ls | wc -l#
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List File systems

Available HDDs

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sudo fdisk -l

Disk UUIDs

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sudo lsblk -f 

Mounting disk

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sudo mount /dev/sdX /media/hdd

Automatic mounting

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sudo vim /etc/fstab
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LABEL=cloudimg-rootfs   /        ext4   defaults        0 1
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LABEL=UEFI      /boot/efi       vfat    umask=0077      0 1
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UUID="69d4002e-a45a-483e-a13b-a3a1ffb255fb" /media/hdd1 ext4 defaults,noatime,_netdev 0 2
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/swapfile swap swap defaults 0 0

Mount points to these HDDs

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cat /proc/mounts

List current directory

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pwd

Find file

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find /dir -name "*Something*
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  find /dir -iname "*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

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zip -r <output_file> <folder_1>
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unzip <zip_file>

Find location of some app in global path

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whereis app_name

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

Move betwween folders:

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cd..   (move directory up)
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cd-    (move to previous directory)
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cd ...(exact path)...   (move to some concrete folder)

Debug incoming requests HTTP netcat

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nc -l PORT

Test if port is accepting something

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netstat -a | grep PORT

Opening firewall ports

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sudo apt install firewalld firewall-config
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sudo firewall-cmd --zone=public --add-port=5432/tcp --permanent 
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sudo firewall-cmd --reload
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sudo ufw allow 5432
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sudo firewall-cmd --zone=public --add-port=8080/tcp --permanent 
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sudo firewall-cmd --reload
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sudo firewall-cmd --zone=public --add-port=80/tcp --permanent 
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sudo firewall-cmd --reload

Recover non-bootable linux using HDD

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grep -i -A 5 -B 5 "error" ./var/log/dmesg
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sudo tail ./var/log/syslog
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sudo tail ./var/log/kern.log
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grep -i -A 5 -B 5 "error" ./var/log/kern.log
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cat ./etc/ssh/sshd_config
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cat ./etc/iptables/rules.v4
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sudo cat ./etc/ufw/user.rules
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sudo rm -rf ./etc/firewalld/zones/

HPC:

Started tasks:

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showq -r
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qstat

Videocard memory usage:

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ssh wn56   (choose wn... from showq -r)
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logout   (iziet no wn)
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watch nvidia-smi   (ctrl+C lai izietu)
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htop

Starting/killing tasks:

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qsub -N reinis_freibergs -A ditf_ldi start_hpc.sh   (Example for start)
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qdel ...(task name from qstat)...   (Kill a task)

Screens:

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screen -ls     (List all of the screen sessions for a user)
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screen -rd ...(name of screen to log into)...
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screen -S ...(new screen name)...

Console management:

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Ctrl+A D   (exit screen, program will continue to  run)
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Ctrl+A K   (kill a screen)

Installing lates NodeJS

https://github.com/nodesource/distributions#debinstall

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curl -fsSL https://deb.nodesource.com/setup_19.x | sudo -E bash - &&\
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sudo apt-get install -y nodejs

Append files through command line

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echo "user_allow_other" | sudo tee -a /etc/fuse.conf
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Set hostname

Set and store

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sudo hostnamectl set-hostname www.something.com

Stored here

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vim /etc/hostname

Users

List users

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getent passwd

DHCP reset / renew

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sudo dhclient

Installing DEB packages from URL

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TEMP_DEB="$(mktemp)" && wget -O "$TEMP_DEB" 'http://packages.ros.org/ros/ubuntu/pool/main/r/ros-kinetic-gazebo-dev/ros-kinetic-gazebo-dev_2.5.21-1xenial-20210405-102417-0800_amd64.deb' && sudo dpkg -i "$TEMP_DEB" && rm -f "$TEMP_DEB"

ngrok

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wget https://bin.equinox.io/c/bNyj1mQVY4c/ngrok-v3-stable-linux-amd64.tgz
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tar -xvzf ./ngrok-v3-stable-linux-amd64.tgz
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chmod +x ./ngrok
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./ngrok config add-authtoken 5y6UbNYvFYS9nvyby8HA4_5SKcfhGhnApPF8aEDJstj
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./ngrok tcp 8000

List All IP addresses in network and Mac Addresses

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arp -a

Hack to disable sshd clear text password access

Lock user

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 passwd -l username

Unlock user

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 passwd -u username

Ubuntu server static IP address

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sudo vim  /etc/netplan/00-installer-config.yaml

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network:
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  version: 2
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  ethernets:
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    eno1:
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      dhcp4: no
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      addresses: [192.168.1.10/24]
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      gateway4: 192.168.1.1
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      nameservers:
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          addresses: [8.8.8.8,1.1.1.1]

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sudo netplan apply

Verify IP

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ip addr show eno1