Terminal Commands

A cheat sheet for working in a UNIX terminal.

Common Commands

Bash Functions

Change prompt to “username@hostname:cwd $”

export PS1="\[\033[36m\]\u\[\033[m\]@\[\033[32m\]\h:\[\033[33;1m\]\w\[\033[m\]\$ "

Enable command line colors

export CLICOLOR=1

Define colors for the ‘ls’

export LSCOLORS=ExFxBxDxCxegedabagacad

Short-cut

  • G: colorizes output
  • h: makes sizes human readable
  • F: throws a / after a directory
alias ls='ls -GFh'

Terminal windows

Update packages: sudo apt update sudo apt upgrade

Freeze windows ctrl+s and release it ctrl+q

turn off scroll through history: tput rmcup

New windows:

Ctrl+Shift+N

Set up initial environment: https://www.ibm.com/developerworks/linux/library/l-tip-prompt/

Run a script containing “cd”

. name.sh

To download new fonts:sudo apt-get install ttf-mscorefonts-installer Fix the download failed problem: 1.Alt+F2. 2.Type “software-properties.gtk” 3.Click in and select the “Download from” option as “Main server”.

To change user password into anything:sudo passwd user:

delete passwd: passwd -d username

Drop to a console:

Ctrl+Alt+F1; Crtl+Alt+F7 to go back.

Adjust username:

usermod

Process management:top;

Ctrl+L to search;

End a process:

xkill; 
killall process_name

End a process precisely:

  1. Locate PID#:

     ps u

  2. Kill:

    kill PID#
kill -9 PID# (kill a process immediately)

  3. Kill in the top:

     top, k, PID#, 9 (kill a process in top)

Open the current folder and select the file:

	nautilus file_name

Open a file A under current directory in a new window:

gnome-open A (Tab to fill the name)
xdg-open A

Folder Navigation:

cd A (Change to a directory named A); 
cd .. (move up one folder); 
cd - (get back);
ls         (list files); 
ls -d -- */ (list all the directories in current directory)
ls -lrth (show dates of diles)
ls -al (show all link)

Link a file (shortcut)

 ln -s <target> <file for calling the target>

We can see where the symbolic is linked to using ls -la

Open setting:

unity-control-center

Shutdown the system via any of the followings:

poweroff;
shutdown --help (Information of shutdown); 
shutdown 5 (shutdown after 5 minutes); 
reboot (restart)

Search a pattern in a file: grep pattern file_name

search a tab: grep -P '\t' ./*

view running processes:

gnome-system-monitor Show installed apps:

apt list --installed Download Website:

wget --mirror -p --convert-links -P ~/Desktop/C/Books/ http://www.ee.surrey.ac.uk/Teaching/Unix/

--no-parent - do not download files form folders below given root folder (folder1/folder/ in our example; files from /folder1 are not going to be transferred).

Intallation Global vs. local

  • Global directory: /usr/local/bin/
  • local directory: $HOME/

Deal with text

cat <text_file> Concatenates files And print on the stand output

Print output (https://askubuntu.com/questions/420981/how-do-i-save-terminal-output-to-a-file)

<executable> > <.txt> //rediret output
<executable> 2> <.txt> //rediret stdeer
<executable> &> <.txt> //redirect stdeer & output
<executable> >> <.txt> //append output
<executable> &>> <.txt> //append stdeer & output
<executable> 2>&1 <.txt> //append stdeer & output and display them

Desktop icons

Remove trash can desktop icon in ubuntu 20.04 link:

gsettings set org.gnome.shell.extensions.desktop-icons show-trash false

Get connected

ssh -X account@server Copy file to the school:

ssh-copy-id -i ~/.ssh/id_rsa.pub account@server Copy file again:

scp <file> <username>@<IP address or hostname>:<Destination>

File operation

ls -alF shows detail of files in the current folder.

du -a -h checks the size of files in terminal:

rm <file> deletes a file (permanently):

Delete an empty folder

rmdir folder

Delete a non-empty folder:

rm -rf folder

Copy a file (-b means backup):

cp -b [file name] [location]

Rename a file:

mv [old name] [new name]

Move a file:

mv file_name location

Create and edit a text file (in nano):

sudo nano /location

Use chmod to chnage permission of a file with a permission code:

0777: read & write & execute to everyone
755: read & execute to the owner

Apps

App Management

A not reliable way

Install ZOOM via sudo snap install zoom-client Remove it via sudo snap remove zoom-client

should do it via:

sudo apt-get remove zoom
wget http://zoom.us/client/latest/zoom_amd64.deb
sudo apt install ./zoom_amd64.deb
rm zoom_amd64.deb

Installed Tools

ipython/ idle3/ otave/ jupyter notebook/ putty/ dconf/ gnome-tweaks/pdftk/lutris

echo

Apply / in the printout

echo -e "\na will produce


a

pdftk

Get all pdf in one:

pdftk * pdf cat output ALL.pdf

Two slide in one page:

pdfjam Page1.pdf Page2.pdf --nup 2x1 --landscape --outfile Page1+2.pdf

Rearrange Pdf layout (column x row)

pdfnup --nup 2x1 mypdf.pdf

tmux

Console

Call up special command throuh Ctrl+b + <command>:

enable scrolling: <command> = [ next windows: <command> = )

Session Management

tmux list-sessions shows sessions.

tmux a attaches the last session tmux a -t <session #/name> attaches the session in the list.

tmux kill-session -t <name of sessions> to end one session.

tmux kill-server or pkill -f tmux to kill all tmux sessions

Tar

Extract a a .tar.gz file

tar -zxvf file.tar.gz
tar -xvf file.tar

Make

etc/Makefile.arch has some alias that can be directly used that vary according to operation system.

  • *.so is a dynamic library

Some grammar for Makefile:

For given input A:B, $@ calls A and $^ calls B.

Jupyter Notebook

Install Jupyter at Ubuntu 22.04.1 LTS, sovling problem of Access to the file was denied:

Modify ~/.jupyter/jupyter_notebook_config.py created by jupyter notebook --generate-config

Jekyll

Activate webpage in the local computer:

bundle exec jekyll serve

Go to http://localhost:4000 to visit it from the browser:

Netcat

A tool to check network connection nc -c <url> <port> gives the connection infomation

nethogs

A tool to check network usage sudo nethogs $device

Dig

A tool for network trouble shooting

Run a general diagnosis: dig smtp.office365.com

Brew

See what homebrew has installed in your computer brew list

xmllint

See what’s wrong with your xml file: xmllint --noout <*.xml>

Projects

Formating a flash drive

Remove bad blocks:

	Ooohu@Ooohu:~$ lsblk
	NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
	sda      8:0    0 111.8G  0 disk 
	├─sda1   8:1    0 107.8G  0 part /
	└─sda2   8:2    0     4G  0 part [SWAP]
	sdb      8:16   1  28.9G  0 disk 
	└─sdb1   8:17   1  28.9G  0 part 
	Ooohu@Ooohu:~$ sudo fsck /dev/sdb1

Change it to the NTFS:

	sudo mkfs.ntfs -f /dev/name

To be a Wlan server

Install Samba:

	sudo apt-get install samba

Set up password for yourself (Ooohu) for log in.

	sudo smbpasswd -a Ooohu

Configurate

	sudo vim /etc/samba/smb.conf

Add the following lines:

	[NAME]
	comment = A Ubuntu server
	path = ~/Public/ 
	read only = no
	guest ok = yes

AND manually right click the ~/Public/ file, and open it to guest user in “Local Network Share”

Check local ip for connection (in the wlan0 section):

	ifconfig

To be a VPN server

Tutorial from https://linuxconfig.org/openvpn-setup-on-ubuntu-18-04-bionic-beaver-linux

  • Install OpenVPN in phone; install easy-rsa and openvpn in Ubuntu.

      $sudo apt-get update && sudo apt-get install openvpn easy-rsa

- Create a working directory (via easy-rsa package) and move in to this directory:

$ make-cadir certificates && cd certificates

  1. Adjust variables in the certificate/vas file. From

     export KEY_CONFIG=`$EASY_RSA/whichopensslcnf $EASY_RSA`
	
 export KEY_COUNTRY="US"
 export KEY_PROVINCE="CA"
 export KEY_CITY="SanFrancisco"
 export KEY_ORG="Fort-Funston"
 export KEY_EMAIL="me@myhost.mydomain"
 export KEY_OU="MyOrganizationalUnit"  to

 export KEY_CONFIG=`$EASY_RSA/openssl-1.0.0.cnf`
	
 export KEY_COUNTRY="US"
 export KEY_PROVINCE="NY"
 export KEY_CITY="NYC"
 export KEY_ORG="CHN"
 export KEY_EMAIL="1@2.com"
 export KEY_OU="ME"

    then “source” the variables after finished editing:

     $ source vars

  2. Generate the CA (certificate authority) (ca.crt). Follow the instruction and use “enters” to answer questions.

     $ ./clean-all && ./build-ca

  3. Generate the certificate (serve.crt) and key (server.key).
    Follow the instruction and use “enters” to answer questions.

     $ ./build-key-server server

  4. Generate Diffie-Hellman parameters (dh2048.pem).

     $ ./build-dh

  5. Generate a random key for sharing (ta.key)

    $ openvpn –genkey –secret keys/ta.key

  6. Copy the files to the OpenVPN folder (in Ubuntu):

     $ sudo cp keys/{server.crt,server.key,ca.crt,dh2048.pem,ta.key} /etc/openvpn

–

  • Configurate OpenVPN by extracting an example file:

      $ gzip -d -c /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz | sudo tee /etc/openvpn/server.conf > /dev/null

Check that the /etc/openvpn/server.conf file contains the following

	ca ca.crt
	cert server.crt
	key server.key  # This file should be kept secret
	dh dh2048.pem

  • Setup firewall (Ubuntu FireWall). Enable it manually:

      sudo vim /etc/ufw/ufw.conf

    Change the following

      ENABLED=no   to
  ENABLED=yes

    The following command allows incoming traffic from port 1194/udp (default port and protocol):

      $ sudo ufw allow openvpn

    Edit the server configuration file (/etc/openvpn/server.conf): uncomment the following line:

      push "redirect-gateway def1 bypass-dhcp"

    Set up iptable rule (eth0 is adjustable here) to NAT the VPN client.

      $ sudo iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

    Edit rules for ufw (Ubuntu FireWall); insert the following lines at the beginning of the file “/etc/ufw/before.rules” (use sudo vim command) :

      *nat
  :POSTROUTING ACCEPT [0:0] 
  -A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE
  COMMIT

    uncomment the line 28 of the file /etc/sysctl.conf, so it becomes:

      # Uncomment the next line to enable packet forwarding for IPv4
  net.ipv4.ip_forward=1

    reload the configuration:

      $ sudo sysctl -p /etc/sysctl.conf

    Allow packet through the ufw; change the following section to ACCEPT in /etc/default/ufw:

      # Set the default forward policy to ACCEPT, DROP or REJECT.  Please note that
  # if you change this you will most likely want to adjust your rules
  DEFAULT_FORWARD_POLICY="ACCEPT"

    Reload firewall (it should say “firewall reloaded”):

      $ sudo ufw reload

  • Start (stop) the service

      $ sudo systemctl start openvpn@server

    Use the following command to check the status:

      $ sudo systemctl is-active openvpn@server

  • Prepare documents for clients (still in the certificate folder):

      $ source vars && ./build-key client

    Extract the example document:

      $ mkdir clients && cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf clients/client.ovpn

    The rest of steps are done in the clients/client.ovpn file:

    Edit line 42:

      remote my-server-1 1194

    replace my-server-1 with ip address (wlan0 ip works):

      remote ip 1194

    uncomment lines 61,62:

      # Downgrade privileges after initialization (non-Windows only)
  ;user nobody
  ;group nogroup

    comment lines 88-90 and 108:

      #ca ca.crt
  #cert client.crt
  #key client.key
  #tls-auth ta.key 1

    Lookup certificate/key folder, copy contents in ca.crt, client.crt, client.key, ta.key into clients/client.ovpn:

      <ca>
  # Here goes the content of the ca.crt file
  </ca>
	
  <cert>
  # Here goes the content of the client.crt file
  </cert>
	
  <key>
  # Here goes the content of the client.key file
  </key>
	
  key-direction 1
  <tls-auth>
  # The content of the ta.key file
  </tls-auth>

  • Last step! Let the phone use OpenVPN to import this .ovpn file to build connection!

Trouble shooting:

  • Search for NDS: adjust ip address in the .ovpn file.

  • waiting for server, activiate server via

      $ sudo systemctl start openvpn@server

Set up SSH keypairs (auto log in)

  1. Generate a SSH Key:

see gitHub:

https://help.github.com/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent/

One key for each server, and the name of id_rsa can be changed; just remember to add it after rename it.

  1. Intro:

id_rsa: private key that NEVER share. id_rsa.pub: public key that stores in the remote server.

  1. Paste public key to remote server.

Paste the id_rsa.pub to the following location of the remote server:

~/.ssh/

the file needs to be named as authorized_keys.

change permission:

chmod 600 authorized_keys
For mac, edit config file in the local ~/.ssh/
Host *
 AddKeysToAgent yes
 UseKeychain yes
 IdentityFile ~/.ssh/id_rsa

id_rsa is the name of the key to be verified.

Shortcut for the log in:

For example, I want to use $ssh k$ to log in:

Host k
    User account
    IdentityFile .ssh/id_rsa
    HostName server

Got a Problem?

Mac Issue

Incorrect directory for an app? Try:

export PATH="/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin"

Error: unrecognized command-line option ‘-stdlib=libc++’

I think I mess up gcc..

C++ compiler

error: ld returned 1 exit status

Function is not defined, try a dummy definition.