Category: Ubuntu

kex_exchange_identification: read: Connection reset by peer

When connecting to Ubuntu 20.04 server using SSH from a Mac computer, get an error

kex_exchange_identification: read: Connection reset by peer

On checking the servers log file (/var/log/auth.log), found the following error message

Jul 23 06:53:34 server sshd[24147]: Unable to negotiate with 17.19.44.24 port 47280: no matching key exchange method found. Their offer: diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1 [preauth]

To fix this, on the server, edit sshd_config

vi /etc/ssh/sshd_config

At end of the file, add

KexAlgorithms +diffie-hellman-group1-sha1

Restart ssh

systemctl restart ssh

See SSH

July 23, 2020

Ubuntu Screen Recorder

Ubuntu come with screen recorder, this can be activated with shortcut

CTRL + ALT + SHIFT + R

By default, it will record for 30 seconds. Video get saved in your home directory (/home/USERNAME) in webm format.

If you want to increase time, you can run following command

gsettings set org.gnome.settings-daemon.plugins.media-keys max-screencast-length  TIME_IN_SECONDS_HERE

It is better to set this to 0, this way record never auto stop. You need to manually stop recording with CTRL + ALT + SHIFT + R key combination.

gsettings set org.gnome.settings-daemon.plugins.media-keys max-screencast-length 0

Default value on Ubuntu 20.04 is “uint32 30”

gsettings

boby@sok-01:~$ gsettings get org.gnome.settings-daemon.plugins.media-keys max-screencast-length
uint32 30
boby@sok-01:~$ gsettings set org.gnome.settings-daemon.plugins.media-keys max-screencast-length 0
boby@sok-01:~$ gsettings get org.gnome.settings-daemon.plugins.media-keys max-screencast-length
uint32 0
boby@sok-01:~$

See Ubuntu

May 27, 2020

Install LAMP Server on Ubuntu/Debian
To install LAMP (Apache, MySQL, PHP) on Ubuntu/Debian web server, run
```
apt-get install lamp-server^
```
This use meta package install LAMP. If you want to remove, don’t remove the meta package as it will remove many other required packages. You need to remove packages one by one.

Related Posts

Apache

MySQL
April 12, 2020

Uninstall Time Doctor on Ubuntu

Time Doctor is an application to track time. To uninstall Time Doctor on Ubuntu, run

sudo /bin/bash -c 'apt purge sfproc; /bin/bash /opt/sfproc/uninstall'

Time doctor run following process

root@pc8:~# ps aux | grep sfp
root      7884  0.0  0.1  72848  4316 pts/1    S    09:53   0:00 sudo -H -u training /bin/bash -l -c export DISPLAY=:0; export XAUTHORITY=/run/user/1004/gdm/Xauthority; export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1004/bus,guid=be774defc4c97a1711ff06305e2fb38d; export TD_DEVELOPER=; export XDG_CURRENT_DESKTOP=ubuntu:GNOME; export XDG_SESSION_DESKTOP=ubuntu; export XDG_SESSION_ID=2; cd /home/training; /opt/sfproc/SF/sfproc/3.0.64/sfproc &> /dev/null
training  7889  0.0  0.0  19992  3148 pts/1    S    09:53   0:00 /bin/bash -l -c export DISPLAY=:0; export XAUTHORITY=/run/user/1004/gdm/Xauthority; export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1004/bus,guid=be774defc4c97a1711ff06305e2fb38d; export TD_DEVELOPER=; export XDG_CURRENT_DESKTOP=ubuntu:GNOME; export XDG_SESSION_DESKTOP=ubuntu; export XDG_SESSION_ID=2; cd /home/training; /opt/sfproc/SF/sfproc/3.0.64/sfproc &> /dev/null
training  7893  4.4  1.2 1407988 51724 pts/1   SLl  09:53   0:00 /opt/sfproc/SF/sfproc/3.0.64/sfproc
root      7947  0.0  0.0  21536   976 pts/1    S+   09:54   0:00 grep --color=auto sfp
root@pc8:~#

January 27, 2020

netplan

Ubuntu Server 20.04 set static IP with netplan
Ubuntu Server 20.04 configure OVH failover IP
Configure KVM Bridge Network using netplan
Configure VPS IP address in OneProvider Server

January 15, 2020

Ubuntu 18.04 MariaDB 10.2 Too many open files

On my computer running Ubuntu 18.04, MriaDB stopped working. PHP application i run on my computer failed with error

SQLSTATE[42S02]: Base table or view not found: 1146 Table 'ok_test.feeds' doesn't exist (SQL: select * from `feeds` where `processed` = 0)

Application can’t find the table. So i tried to login to MySQL and see if table is there or not. But i get error

boby@sok-01:~$ mysql
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 2504
Server version: 10.2.30-MariaDB-1:10.2.30+maria~bionic-log mariadb.org binary distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> show databases;
ERROR 1018 (HY000): Can't read dir of '.' (errno: 24 "Too many open files")
MariaDB [(none)]>

Next i checked if this is due to any MySQL upgrade. I found MySQL got updated today

root@sok-01:~# grep mariadb /var/log/dpkg.log
2019-12-13 08:02:46 status triggers-pending mariadb-server-10.2:amd64 1:10.2.29+maria~bionic
2019-12-13 08:02:46 upgrade mariadb-common:all 1:10.2.29+maria~bionic 1:10.2.30+maria~bionic
2019-12-13 08:02:46 status half-configured mariadb-common:all 1:10.2.29+maria~bionic
2019-12-13 08:02:46 status unpacked mariadb-common:all 1:10.2.29+maria~bionic
2019-12-13 08:02:46 status half-installed mariadb-common:all 1:10.2.29+maria~bionic

To fix this error, run

systemctl edit mysql

This wil open a text editor. Add following

[Service]
LimitNOFILE=8192

Save and quit the editor. Restart MaraDB with

systemctl restart mysql

MySQL will work properly now. systemctl edit mysql will create file /etc/systemd/system/mysql.service.d/override.conf

root@sok-01:~# cat /etc/systemd/system/mysql.service.d/override.conf 
[Service]
LimitNOFILE=8192

root@sok-01:~#

December 13, 2019

Disable Native Notification on Google Chrome Ubuntu
On Ubuntu, Google chrome had a disable native notification option. On Chrome 78, this option is removed. But you still can manually enable it.

To enbale chrome notification, edit file
```
gedit ~/.config/google-chrome/Local\ State
```
Find
```
"tab-hover-cards@4"
```
Replace with
```
"enable-native-notifications@2","tab-hover-cards@4"
```
Save and exit the file. Now restart google chrome.

Related Posts

Google Chrome
November 8, 2019
Install NextCloud Desktop client on Ubuntu
To install NextCloud desktop client on Ubuntu, add PPA
```
sudo add-apt-repository ppa:nextcloud-devs/client
sudo apt-get update
```
Now run
```
sudo apt install nextcloud-client
```
After install, start nextcloud client, you will be able to login with nextcloud server URL, user and password.
September 28, 2019

Linux KVM Bridge network on Ubuntu

On Ubuntu 18.04 server, first i get Ubuntu to use /etc/network/interface, by default Ubuntu 18.04 and newer use netplan.

First install ifdown

apt install ifupdown -y

Install bridge utils and resolvconf.

apt install bridge-utils resolvconf

Now you can configure your network interface by editing file

vi  /etc/network/interface

Here is my network configuration on an OVH server.

root@ns3048991:~# cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

auto eno3
iface eno3 inet static
    address 149.202.199.137
    netmask 255.255.255.255
    broadcast 149.202.199.137
    gateway 149.202.199.254
    dns-nameservers 8.8.8.8 8.8.4.4
root@ns3048991:~#

To convert this interface to bridge network, do the following

1) Replace all occurance of “eno3” with “br0”

2) Add following lines

    bridge_ports eno3
    bridge_stp off
    bridge_maxwait 5

In above, replace “eno3” with name of your physical interface.

Here is my final network configuration.

root@ns3048991:~# cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

auto br0
iface br0 inet static
    address 149.202.199.137
    netmask 255.255.255.255
    broadcast 149.202.199.137
    gateway 149.202.199.254
    bridge_ports eno3
    bridge_stp off
    bridge_maxwait 5
    dns-nameservers 8.8.8.8 8.8.4.4
root@ns3048991:~#

See Linux KVM, Networking @ linux-kvm.org

September 17, 2019

Install Xfce VNC remote desktop on Ubuntu
XFCE is a lightweight Desktop Environment for Linux. XFCE + vnc allows you to set up a remote desktop on a VPS or dedicated server located in a remote data center or cloud. You can connect to remote desktop using a VNC client and work like it is a local computer, similar to Windows Remote Desktop (RDP).

To install XFCE run
```
apt update
apt install -y xfce4 xfce4-goodies dbus-x11
```
You will be asked to select Default Display Manager. You can select any of the options.

Next install vncserver
```
apt install tightvncserver autocutsel
```
It is a bad idea to use root user for logging into the desktop. Create a normal user with sudo privileges to be used as desktop user.
```
useradd -m -s /bin/bash USERNAME
```
It will be good to make this user an admin, so the user can install software or update the system.
```
usermod -aG sudo USERNAME
```
Set a password for the user
```
passwd USERNAME
```
Now login as the user
```
su - USERNAME_HERE
```
Create a vnc password for this user.
```
vncpasswd
```
Create vnc startup file
```
vi ~/.vnc/xstartup
```
Add
```
#!/bin/bash

xrdb $HOME/.Xresources
autocutsel -fork
startxfce4 &
```
Make it executable
```
chmod 755 ~/.vnc/xstartup
```
Auto start VNC Server

To autostart vncserver on boot, you need to create a service file. You need to do the following as user root.
```
vi /etc/systemd/system/vncserver@.service
```
Add
```
[Unit]
Description=Start VNC server at startup
After=syslog.target network.target

[Service]
Type=forking
User=USERNAME
Group=USERNAME
WorkingDirectory=/home/USERNAME

PIDFile=/home/USERNAME/.vnc/%H:%i.pid
ExecStartPre=-/usr/bin/vncserver -kill :%i > /dev/null 2>&1
ExecStart=/usr/bin/vncserver -depth 24 -geometry 1920x1080  :%i
ExecStop=/usr/bin/vncserver -kill :%i

[Install]
WantedBy=multi-user.target
```
In the above, replace USERNAME with the actual user name you created above.

Enable the service with
```
systemctl enable vncserver@1
```
Start the VNC server
```
systemctl start vncserver@1
```
Now reboot the server. You should be able to connect to VNC server using SERVER_IP:1

Common Errors and Solutions

When starting vncserver, i get error
```
xfce4-session-CRITICAL **: 20:18:42.985: dbus-launch not found, the desktop will not work properly!
```
To fix it, install
```
apt install dbus-x11
```
OPTIONAL: Using RDP instead of VNC

If you want to use RDP (Windows Remote Desktop) to connect instead of VNC, install xrdp
```
apt install -y xrdp
```
Edit
```
vi /etc/xrdp/xrdp.ini
```
Set value of new_cursors to false.
```
new_cursors=false
```
Change to desktop user
```
su - USERNAME
```
Create file
```
vi ~/.xsession
```
Add following content
```
xfce4-session
export XDG_SESSION_DESKTOP=xubuntu
export XDG_DATA_DIRS=/usr/share/xfce4:/usr/local/share:/usr/share:/var/lib/snapd/USERNAME:/usr/share
export XDG_CONFIG_DIRS=/etc/xdg/xfce4:/etc/xdg:/etc/xdg
```
Enable and restart XRDP
```
systemctl enable xrdp
systemctl restart xrdp
```
See VNC Server
September 17, 2019
Install HandBrake on Ubuntu 18.04
HandBreak is an OpenSource Video transcoder available from https://handbrake.fr. It can convert video to various format.

Latest version of Handbreak available in Ubuntu PPA. To install, enable Handbreak PPA
```
add-apt-repository ppa:stebbins/handbrake-releases
```
Install handbreak with
```
apt install handbrake-gtk handbrake-cli
```
September 17, 2019
Install Linux KVM on Ubuntu
Linux KVM is virtualisation software that allow you to create virtual machine under linux. To install on Ubuntu, run
```
apt install -y qemu-kvm qemu-utils
```
Install libvirtd, this allow you to easily create KVM virtual machines and allow remote connection from virt-manager GUI application.

For Ubuntu 20.04
```
apt install -y libvirt-daemon libvirt-daemon-system
```
For Ubuntu 18.04
```
apt install -y libvirt-bin
```
Enable and start libvirt
```
systemctl enable libvirtd
systemctl start libvirtd
systemctl is-active libvirtd
systemctl status libvirtd
```
At this stage, you should be able to connect to KVM server form your computer using virt-manager.

You need to create a bridge network interface (“br0”), for this, follow instructions at Linux KVM Bridge network on Ubuntu.

Downloading ISO

Before you can setup any VM, you need to download ISO image for the OS. Here i downloaded ISO image for Ubuntu 19.04
```
cd /var/lib/libvirt/images
wget http://mirrors.piconets.webwerks.in/ubuntu-mirror/ubuntu-releases/19.04/ubuntu-19.04-live-server-amd64.iso
```
Once downloaded, you should be able to select this ISO image in virt-manager when creating a VM.

See Linux KVM
September 17, 2019

Category: Ubuntu

Auto start VNC Server

Common Errors and Solutions

OPTIONAL: Using RDP instead of VNC

Downloading ISO