Category: Linux

Install Xfce VNC remote desktop on CentOS 7
Xfce is a lightweight linux desktop environment. You can install Xfce on a remote server or virtual machine, connect to it using VNC to use it as a desktop.

To install Xfce, enable EPEL repo
```
yum install -y epel-release
```
Install Xfce
```
yum groupinstall Xfce
```
You can see other groups available with command “yum grouplist”.

Insall vnc server
```
yum install -y tigervnc-server
```
Creating User

We need to create a normal linux user to use with Xfce. Using it as root is not recommended.

To create user, run
```
useradd -m --shell /bin/bash serverok
```
Replace “serverok” with whatever username you want to use.

Configure VNC server

Change to the user we created before
```
su - serverok
```
To create initial vnc config files and set password, run
```
vncserver -fg
```
We used -fg option to keep vncserver in forground. vcnserver will ask you to set password, this will be used to connect to VNC server.

When i run “vncserver -fg” on CentOS, it exited with error. If it keep running, press CTRL+C to stop vnc server.

If you run with out -fg option, you can stop vnc server with command
```
vncserver -kill :1
```
Edit file
```
vi /home/serverok/.vnc/xstartup
```
Replace contents of this file with following
```
#!/bin/sh

unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
/etc/X11/xinit/xinitrc
/bin/startxfce4
```
Now you can start vncserver manually with command
```
vncserver -fg
```
You will be able to connect to VNC server with YOUR_SERVER_IP:1

Auto start VNC server

Following need to be done as user root.

Edit file
```
vi /usr/lib/systemd/system/[email protected]
```
Find
```
ExecStart=/usr/bin/vncserver_wrapper  %i
```
Replaced with
```
ExecStart=/usr/bin/vncserver_wrapper serverok %i
```
reload systemctl
```
systemctl daemon-reload
```
Enable vncserver to start on boot
```
systemctl enable vncserver@:1.service
```
Start vncserver
```
systemctl start vncserver@:1.service
```
Open port in firewall

You need to open VNC port in firewall. vnc ports start at 5900, for :1, it will be 5901.
```
[root@centos7 ~]# netstat -lntp | grep vnc
tcp        0      0 0.0.0.0:5901            0.0.0.0:*               LISTEN      1951/Xvnc           
tcp        0      0 0.0.0.0:6001            0.0.0.0:*               LISTEN      1951/Xvnc           
tcp6       0      0 :::5901                 :::*                    LISTEN      1951/Xvnc           
tcp6       0      0 :::6001                 :::*                    LISTEN      1951/Xvnc           
[root@centos7 ~]# 
```
If you are using firewalld, you can open port 5901 with
```
firewall-cmd --zone=public --add-port=5901/tcp
firewall-cmd --zone=public --add-port=5901/tcp --permanent
```
firewall-cmd command is run 2 times as first command only make changes in current session. second command with –permanent option make changes permanent, but that only happens after you reload firewalld or reboot server. Running command 2 times make the changes permanent and apply changes to current session.

See VNC, Remote Desktop
December 6, 2020

Firewalld list rules

To list rules use command

firewall-cmd --list-all --zone=public

To list all open ports

firewall-cmd --list-ports

Example

[root@centos7 zones]# firewall-cmd --zone=public --add-rich-rule='rule family="ipv4" source address="10.1.1.2/32" port protocol="tcp" port="1-65535" accept'
success
[root@centos7 zones]# firewall-cmd --list-all --zone=public
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: eth0 eth1
  sources: 
  services: dhcpv6-client ssh
  ports: 25/tcp 9090/tcp
  protocols: 
  masquerade: no
  forward-ports: 
  source-ports: 
  icmp-blocks: 
  rich rules: 
        rule family="ipv4" source address="10.1.1.2/32" port port="1-65535" protocol="tcp" accept
[root@centos7 zones]# firewall-cmd --zone=public --remove-rich-rule='rule family="ipv4" source address="10.1.1.2/32" port protocol="tcp" port="1-65535" accept'                                            
success
[root@centos7 zones]# firewall-cmd --list-all --zone=public
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: eth0 eth1
  sources: 
  services: dhcpv6-client ssh
  ports: 25/tcp 9090/tcp
  protocols: 
  masquerade: no
  forward-ports: 
  source-ports: 
  icmp-blocks: 
  rich rules: 

[root@centos7 zones]#

See firewall-cmd

December 5, 2020

Install Monit on CentOS
Monit allow you to monitor process. It can restart failed process or alert when server is overloaded.

On CentOS server, you need to enable EPEL repo to install monit.
```
yum install epel-release -y
```
Install monit with
```
yum install monit -y
```
Enable monit to auto start on boot
```
systemctl enable monit
```
Start monit service
```
systemctl start monit
```
On CentOS, monit configuration file located at
```
vi  /etc/monitrc
```
See monit
December 4, 2020
ls
ls command is used to list files in linux. It is same as dir on windows.

List all files in long format (l), a is to show hidden files
```
ls -la
```
Show only file names
```
ls -b
```
Show only file names. One file per line
```
ls -1
```
December 4, 2020
Ubuntu 20.04/22.04 settings won’t open
On Ubuntu 20.04/22.04 settings won’t open. This may be caused by some software install/update.

I tried to run
```
gnome-control-center
```
From the terminal, I get the error
```
boby@sok-01:~$ gnome-control-center

Command 'gnome-control-center' not found, but can be installed with:

sudo apt install gnome-control-center

boby@sok-01:~$ 
```
To fix the error, I installed gnome-control-center package as the error suggests.
```
sudo apt install gnome-control-center
```
See Ubuntu
December 4, 2020
Sent maldet scan report to email
After running a scan, maldet will give you command to see result like
```
maldet --report SCAN_ID
```
If you need this email sent to your email, use command
```
maldet --report SCAN_ID EMAIL_ADDR
```
Example

See maldet
December 1, 2020
gsettings

Ubuntu Screen Recorder

December 1, 2020

Install Preview Generator in Nextcloud

To enable preview for files in nextcloud, you need to install “Preview Generator” from next cloud app store

https://apps.nextcloud.com/apps/previewgenerator

To install login to nextcloud as admin. From right drop down menu, click + Apps link.

Once on Apps page, you can use the search button on right side to search for “Preview Generator” and install it.

You need to install some additional software, on ubuntu/debian install it with

sudo apt install libreoffice ffmpeg imagemagick ghostscript

Now edit config/config.php file of your nextcloud installation, add following code

'enable_previews' => true,
'preview_libreoffice_path' => '/usr/bin/libreoffice',
'enabledPreviewProviders' =>
 array (
    0 => 'OC\\Preview\\TXT',
    1 => 'OC\\Preview\\MarkDown',
    2 => 'OC\\Preview\\OpenDocument',
    3 => 'OC\\Preview\\PDF',
    4 => 'OC\\Preview\\MSOffice2003',
    5 => 'OC\\Preview\\MSOfficeDoc',
    6 => 'OC\\Preview\\PDF',
    7 => 'OC\\Preview\\Image',
    8 => 'OC\\Preview\\Photoshop',
    9 => 'OC\\Preview\\TIFF',
   10 => 'OC\\Preview\\SVG',
   11 => 'OC\\Preview\\Font',
   12 => 'OC\\Preview\\MP3',
   13 => 'OC\\Preview\\Movie',
   14 => 'OC\\Preview\\MKV',
   15 => 'OC\\Preview\\MP4',
   16 => 'OC\\Preview\\AVI',
 ),

Generate Preview for existing files

Let’s generate thumbnail for existing files, for this, I enabled shell access for www-data so preview files have proper file ownership (not owned by root).

chsh --shell /bin/bash www-data

Now change to www-data user

su - www-data

Now run

/usr/bin/php /var/www/nextcloud/occ preview:generate-all -vvv

Autogenerate Previews for new files

set a cronjob as user www-data

crontab -e -u www-data

*/5 * * * * /usr/bin/php /var/www/nextcloud/occ preview:pre-generate > /dev/null 2>&1

See Nextcloud

November 30, 2020

Enable SEO url in nextcloud
To enable SEO url in next cloud, first make sure your web server have mod_rewrite module enabled.

Edit config.php file
```
vi config/config.php
```
add following
```
'overwrite.cli.url' => 'https://yourdomain.com/',
'htaccess.RewriteBase' => '/',
```
overwrite.cli.url may already there, in that case, don’t add it again.

Now run
```
sudo -u www-data php /var/www/nextcloud/occ maintenance:update:htaccess
```
See NextCloud
November 30, 2020

csf error path to iptables is either not set or incorrect

Whem install csf firewall on Ubuntu 20.04, i get following error

root@ok:~# csf
*Error* The path to iptables is either not set or incorrect for IPTABLES [/usr/sbin/ip6tables] in /etc/csf/csf.conf at /usr/local/csf/lib/ConfigServer/URLGet.pm line 26.
Compilation failed in require at /usr/sbin/csf line 21.
BEGIN failed--compilation aborted at /usr/sbin/csf line 21.
root@ok:~#

This is because path for iptables is changed in Ubuntu 20.04. To fix the error edit csf.conf

vi /etc/csf/csf.conf

Find

IPTABLES = "/sbin/iptables"
IPTABLES_SAVE = "/sbin/iptables-save"
IPTABLES_RESTORE = "/sbin/iptables-restore"
IP6TABLES = "/sbin/ip6tables"
IP6TABLES_SAVE = "/sbin/ip6tables-save"
IP6TABLES_RESTORE = "/sbin/ip6tables-restore"

Replace with

IPTABLES = "/usr/sbin/iptables"
IPTABLES_SAVE = "/usr/sbin/iptables-save"
IPTABLES_RESTORE = "/usr/sbin/iptables-restore"
IP6TABLES = "/usr/sbin/ip6tables"
IP6TABLES_SAVE = "/usr/sbin/ip6tables-save"
IP6TABLES_RESTORE = "/usr/sbin/ip6tables-restore"

Now restart csf with csf -r, it will work.

csf -r
systemctl restart lfd

See csf

November 30, 2020

Linux User
November 27, 2020
Disable systemd-resolved on Ubuntu/Deb/CentOS
systemd-resolved provide DNS resolver facility in newer version of Linux servers running systemd.

I prefer manually editing /etc/resolv.conf and add resolvers. If you are running your own DNS server, then you need to disable systemd-resolved as it listen on port 53, with out disabling the service, you can’t start your DNS server.

To disable systemd-resolved, run
```
wget https://raw.githubusercontent.com/serverok/server-setup/master/tools/disable-systemd-resolved.sh
bash disable-systemd-resolved.sh
```
Or do the following.
```
systemctl disable systemd-resolved.service
systemctl stop systemd-resolved
```
Now create /etc/resolv.conf file
```
rm -f /etc/resolv.conf
tee /etc/resolv.conf << END
nameserver 8.8.8.8
nameserver 1.1.1.1
END
```
See resolv.conf, dns
November 27, 2020

Category: Linux

Creating User

Configure VNC server

Auto start VNC server

Open port in firewall

Generate Preview for existing files

Autogenerate Previews for new files