# Linux

## Finding out which Linux Version running

```sh
cat /etc/issues
cat /etc/os-release  
hostnamectl
cat /etc/upstream-release/lsb-release
```

* `/etc/issues`: Linux Mint 21.1 Vera \n \l
* `/etc/os-release`: more mint details
* `/etc/upstream-release/lsb-release`: Ubuntu info
* `lsb-release`: Here I will collect my general Tips on Linux\`

## Directories and permissions

place additional package managers and executables in and config files.

```bash
~/.local/
~/.config/
```

Pretty Printing Path with each entry in new line as alias `ep`

```bash
alias ep='echo $PATH | tr ":" "\n"'
```

## Generate Random strings

thanks to [How-to-Geek](https://www.howtogeek.com/howto/30184/10-ways-to-generate-a-random-password-from-the-command-line/) Generating 20 character long random strings.

```bash
openssl rand -base64 20
```

or

```sh
< /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c20
```

On Mac prepend it with `LC_CTYPE=C`, like

```bash
< /dev/urandom | LC_CTYPE=C tr -dc _A-Z-a-z-0-9 | head -c24
```

## Setup ssh Key connectivity

Install openssh\_server

```sh
sudo apt install openssh-server
sudo systemctl is-enabled ssh
```

Generate a new ssh key pair

```sh
ssh-keygen -t rsa -b 2048 -C "comments etc" -f ~/.ssh/outfile -N ""
ssh-add ~/outfile
```

preferably store it in `/home/<user>/.ssh/<keyname>` and append it into the `authorized_keys` File. Use the `-N ""` to avoid being prompted for a passphrase if desired.

```sh
cat ~/.ssh/<keyname>.pub >> ~/.ssh/authorized_keys
```

Update the sshd configuration to allow key based authorization. My preffered configuration checks the users .ssh directory for and `authorized_keys` File and also checks for a file per user like `/etc/ssh/authorized_keys/<user>` Depending on the Firewall settings I sometimes have to run the openssh-server on a different port than 22

```sh
Port <port_of_choice>
PubkeyAuthentication yes
PasswordAuthentication no
AuthorizedKeysFile %h/.ssh/authorized_keys /etc/ssh/authorized_keys/%u
```

Lastly copy the **private** `keyname` file to the machine you want to use to connect from. **The private keyfile is the key to access your host use caution and encryption when to save or share it.**

```sh
scp ~/.ssh/keyname user@host:~/.ssh/
```

## Setting up Debian

I used the debian-9.8.0-amd64-netinst.iso image. First I highlighted the *Install* option to avoid using the graphical installer. This is because I had issues in an earlier install when I was monitoring the log output and then switching back to the first console. Then I hit tab to add and additional boot parameter *netcfg/disable\_autoconfig=true*. This was because when I used automated Network Configuration, it defaulted to IPv6 and then froze when it tried to copy the apt mirrors because it didn't fell back to IPv4. I also used the following Partioning Table setup.

![Partioning Table](https://media.404founders.com/Partioning.jpg)

To see the log output press `Ctrl+Alt+4` to switch back press `1` instead or use `2`or`3` to start a console terminal\
See also\
[Debian-Installer 5.1.7. The Boot Screen](https://www.debian.org/releases/stable/amd64/ch05s01.html.en#boot-screen)\
[Debian-Installer 5.3.2. Debian Installer Parameters](https://www.debian.org/releases/stable/amd64/ch05s03.html.en#ftn.idm1345)\
[Debian-Installer 6.1. How the Installer Works](https://www.debian.org/releases/stable/amd64/ch06s01.html.en)

## LVM

LVM stands for **Logical Volume Management** and is used to create, display and manage **Physical Volumes(pv)**, **Volume Groups (vg)**, and **Logical Volumes (lv)**

## Installing Xen

As described in [Xen Getting started](https://wiki.xenproject.org/wiki/Xen_Project_Beginners_Guide)

```sh
apt-get install xen-system-amd64 lvm2
pvcreate /dev/sda7
vgcreate vg0 /dev/sda7
```

`/dev/sda7` differs from the turorial due to my different partion tables I re-installed Linux-Mint on a setup with existing LVM settings. I mounted a data volume in `/etc/fstab` with `lvdisplay` revealed the `$` **LV Path** as `/dev/vg-01/data01`

```sh
/dev/vg-01/data01       /data   ext4    defaults        0       0
<nas_ip>:/volume1/<nas_folder> /mnt/<mount_dir> nfs  _netdev,nofail,x-systemd.automount,x-systemd.idle-timeout=600,timeo=50,retrans=2  0  0
```

see `man mount` for more settings

| option                     | description |
| -------------------------- | ----------- |
| \_netdev                   |             |
| nofail                     |             |
| x-systemd.idle-timeout=600 |             |
| timeo=50                   |             |
| retrans=2                  |             |

## NFS Issues

Make sure the `/etc/exports` file on the nfs server has the right ip addresses. They did not get updated when the ip address of the server changed due to a change of my ISP. The shared folder on the NasDrive needs to have nfs Permissions:

| Setting                 | Value                  |
| ----------------------- | ---------------------- |
| - Client:               | 10.0.0.\*              |
| + Privilege:            | Read/Write             |
| \* Squash:              | Map all users to admin |
| \* Asynchronous:        | No                     |
| \* Non-privileged port: | Denied                 |
| \* Cross-mount:         | Allowed                |

Install **nfs-common** to mount nfs

```sh
sudo apt-get install nfs-common
```

In `/etc/fstab` mount it with, make sure to ues **tabs** for separation (no spaces!)

```sh
192.168.1.152:/volume1/pullovas /home/wolle/nasghoul    nfs     defaults        0       0
```

## Mount Usb stick

Find device location with `fdisk` and look for the flash drive, use the `exfat-fuse` if the stick is *exfat* formatted. To find out about the filsystem run `blkid`, then make the mount point and mount the drive.

```sh
sudo fdisk -l
sudo apt install exfat-fuse 
sudo blkid 
sudo mkdir /media/<user>/usbreb 
sudo mount /dev/sdc1 /media/<user>/usbreb -o uid=1000
```

## rsync

Copying folders recursively with rsync\
`rsync --recursive --progress -v source/path destination/path`

## Mountpoint android phone

The phone is mounted to the Computer through `mtp` and the SD-Card is in the phone\
`ls -lah /var/run/user/1000/gvfs/mtp:host=%5Busb%3A002%2C003%5D/SD\ card`

## Change screen brightness

Install xbacklight and set screen brightness to 60%

```
sudo apt-get install xbacklight
xbacklight -get display 60
```

## Install deb package

run `sudo dpkg -i <deb-File>.deb`

### Check installed Ubuntu Version

For Linux Mint

```bash
optiplex in Library on  master [$!]
➜ cat /etc/upstream-release/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu Jammy Jellyfish"

optiplex in Library on  master [$!]
➜ cat /usr/lib/os-release
NAME="Linux Mint"
VERSION="21.1 (Vera)"
ID=linuxmint
ID_LIKE="ubuntu debian"
PRETTY_NAME="Linux Mint 21.1"
VERSION_ID="21.1"
HOME_URL="https://www.linuxmint.com/"
SUPPORT_URL="https://forums.linuxmint.com/"
BUG_REPORT_URL="http://linuxmint-troubleshooting-guide.readthedocs.io/en/latest/"
PRIVACY_POLICY_URL="https://www.linuxmint.com/"
VERSION_CODENAME=vera
UBUNTU_CODENAME=jammy
```

## Printing from the commandline

```
~/Documents pyenv 🐍 system 
➜ lpstat -p -d
printer HP_LaserJet_M15w_0725E9_ is idle.  enabled since Sun 22 Dec 2019 09:37:15 AM EST
printer HP_LaserJet_M15w_0725E9_@NPI0725E9.local is idle.  enabled since Sun 22 Dec 2019 09:39:27 AM EST
no system default destination

~/Documents pyenv 🐍 system 
➜ lpoptions -d HP_LaserJet_M15w_0725E9_
device-uri=ipps://HP%20LaserJet%20M15w%20(0725E9)._ipps._tcp.local/ printer-info='HP LaserJet M15w (0725E9)' printer-location printer-make-and-model='HP HP LaserJet M14-M17' printer-type=16781316

~/Documents pyenv 🐍 system 
➜ lp D\&B-E-card.pdf                   
request id is HP_LaserJet_M15w_0725E9_-2 (1 file(s))

~/Documents pyenv 🐍 system 
➜ 
```

## Firewall

Use `ufw` to allow firewall request for port and protocol.

```
sudo ufw allow 53
sudo ufw allow 53/tcp
sudo ufw allow 53/udp
```

## Pseudo stresstest forkbomb

```bash
t(){for ((i=1; i<=100; i++ )) { (curl www.URL.com > /dev/null  ; echo $i );next} & ; t }
```

Only blows your system without putting real stress on a server, but might get you banned or blocked.


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