Linux

Links

SSH

Download to local:

scp -[r]P <port> <user>@<ip>:<path/to/folder> <path/to/local>

Upload to server:

scp -[r]P <port> <source file> <username>@<destination server>:<destination directory>

Generate ssh key:
```
ssh-keygen -t rsa
ssh-add
```
List of private keys:
```
ssh-add -l
```
Access to public ssh key:
```
cat ~/.ssh/id_rsa.pub
```

Prevent SSH from disconnecting:

# /etc/ssh/ssh_config or ~/.ssh/config
ServerAliveInterval 60

Compress & Extract

.tgz:

# Compress
tar -czvf <file_name.tgz> </path/to/directory>
tar -czvf <file_name.tgz> </path/to/directory>/.  # include hidden files
tar -czvf <file_name.tgz> </path/to/file>

# Extract
tar -xzvf <file_name.tgz>
tar -xzvf <file_name.tgz> -C </path/to/directory>

# Split into multiple files
split --bytes=<split_size: 10m> --suffix-length=4 --numeric-suffix <source_file.tgz> <destination_file.tgz.>

# Extract from splitted files (tgz)
cat <destination_file.tgz.*> | tar -xzvf -

.zip:

# Compress
zip <filename.zip> <file>

# Extract (`sudo apt install unzip`)
unzip <file_name.zip>
unzip '*.zip'

.rar:

# Extract (sudo apt-get install unrar)
unrar x -r </path/to/file.rar>

Cron

Create a bash file that starts with #!/bin/bash and without the .sh filename suffix
Change the file to runnable mode with the sudo chmod +x command
ceate a soft link in the /etc/cron.daily/ or add it to the /etc/crontab
Test for correct run: run-parts --test /etc/cron.daily

Xmodmap

Remove a key from a mod:
```
xmodmap -e 'remove Mod1 = Alt_R'
```
Add a key to a mod:
```
xmodmap -e 'add Mod3 = Alt_R'
```

Firewall

Enable and disable firewall:
```
sudo ufw enable/disable
```
Get status of firewall and all available ports:
```
sudo ufw status verbose
```
Get list of apps that wanna firewall access:
```
sudo ufw app list
```

Set or get firewall access for port:

sudo ufw allow <port>
sudo ufw delete allow <port>

Set or get firewall access for app:

sudo ufw allow in "<app name>"
sudo ufw delete allow in "<app name>"

Add Proxy To Apt-Get

Go to https://free-proxy-list.net/ and find an free proxy address

Add below code to /etc/apt/apt.conf:

# If your proxy has not password
Acquire::http::Proxy "http://<yourproxyaddress>:<proxyport>";

# If your proxy has password
Acquire::http::Proxy "http://<username>:<password>@<proxyaddress>:<proxyport>";

Remove Launcher Entry

Go to ~/.local/share/applications/ or /usr/share/applications/
Remove <your application name: jetbrains-pycharm.desktop>

Networkmanager

List of connections:
```
nmcli connection
```

Change DNS:

nmcli connection modify <connection name> ipv4.dns "<dns one:8.8.8.8> <dns two:8.8.4.4>"

Connection down (need to restart):

nmcli connection down <connection name>

Connection up (need to restart):
```
nmcli connection up <connection name>
```

Tmux

Create new terminal:
```
tmux
```
Split current terminal vertically:
```
ctrl+b %
```
Split current terminal horizontally:
```
ctrl+b "
```
New window (tab):
```
ctrl+b c
```
Maximize and minimize terminal:
```
ctrl+b z
```
Switch between terminals:
```
ctrl+b o
```
Create new session:
```
tmux new -s <session_name>
```
Connect to session:
```
tmux attach-session -t <session_name>
```
Disconnect from session:
```
ctrl+b + d
```
Destroy session:
```
ctrl+d
```

Grub

Edit configs:

sudo vim /etc/default/grub
sudo update-grub

Grub Problem:
1. To install and fix grub, you need Live CD or Live USB of Ubuntu
2. Once you load Live Ubuntu, Open Terminal and fire following commands to install boot-repair and let it fix the Grub
```
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair
```
3. After installation, boot-repair will get automatically launched
4. Make sure to select "recommended repair" option to repair grub. Reboot
5. You will now have a Grub menu on boot, where you can choose from Ubuntu, and Windows
Add Windows to boot loader:
```
sudo os-prober
sudo update-grub
```

Disable Sudo Password

Run:
```
sudo EDITOR=vim visudo
```

And add below line after the %sudo line:

# For specific user
<username> ALL=(ALL) NOPASSWD: <command: /bin/systemctl>

# For all users
ALL ALL=(ALL) NOPASSWD: <command: /bin/systemctl>

Machine

Version:
```
cat /etc/*-release
```
CPU:
```
lscpu
```
Memory:
```
free -h
```
Disk space:
```
# Simple
df -h

# Advanced
ncdu
```

Install package:

# .dev
sudo dpkg -i path/to/file.deb
sudo apt-get install -f

# .rpm
sudo alien -i path/to/file.rpm

Boot type:

cat /etc/fstab

# If there is a line like `UUID=xxx /boot/efi ntfs defaults 0 1`, it means the system boot mode is UEFI, otherwise, it is Legacy BIOS

Kernel logs:
```
dmesg -l err
```

Nvidia Driver

First we will install the proper driver:

sudo apt install nvidia-detect
nvidia-detect
sudo apt install <suggested_package_from_previous_step>

After restarting the system driver should work properly, if not we will install the below packages:
```
sudo apt-get install bumblebee bumblebee-nvidia linux-headers-generic
```
Now each time that we want to use the NVIDIA GPU should run the following command! (While the following command is runnuing we can run every program that we want to use NVIDIA GPU)
```
sudo optirun nvidia-settings -c :8
```

Gnome

Reset an extension configs:

dconf reset -f /org/gnome/shell/extensions/<extension_name>

Mount & Partition

See disk usage:
```
sudo lsblk
```

Create primary partition:

sudo fdisk /dev/sda

... Command (m for help): n
... Select (default p): p
... Partition number (1-4, default 1):
... First sector (46483456-62914559, default 46483456):
... Last sector, +/- sectors or +/-size{K,M,G,T,P} (46483456-62914559, default 62914559):

... Command (m for help): w

Create file system:
```
sudo mkfs.ext4 /dev/sda1
```

Mount partition:

sudo mkdir /sample_dir

sudo mount /dev/sda1 /sample_dir  # for mount
sudo umount /sample_dir  # for unmount

Mount directory:

sudo mkdir /source_dir
sudo mkdir /destination_dir

sudo mount --bind /source_dir /destination_dir

Determine the file system type:
```
sudo fsck -N /dev/sda1
```

Alt+Shift+any_other_key Doesn't Work

The problem is related to the change-layout shortcut, by default it is set to Alt+Shift, for this reason, the system intercepts it for itself and doesn't let it reach some programs like Pycharm or VSCode.

To solve, update /etc/default/keyboard and replace

XKBOPTIONS="grp:alt_shift_toggle,grp_led:scroll"

with

XKBOPTIONS="grp:super_space_toggle,grp_led:scroll"

Other

Minimal Curl:

curl -i -H "Accept: text/html" 127.0.0.1:31001 -v

Vim replace all:
```
:%s/foo/bar/g
```
Open shell without login:
```
ctrl + alt + f5
```