How to change the Hostname on CentOS 7

The easiest way to change the hostname on CentOS 7 is to use the hostnamectl command.

First I will check the current hostname by running "hostnamectl status" on the shell of my server:

hostnamectl status

The output on my system is:

[root@server1 ~]# hostnamectl status
   Static hostname: server1.example.com
         Icon name: computer-vm
           Chassis: vm
        Machine ID: d89865d34b5a4637a9a4ff0ce0f6da02
           Boot ID: 56d1685056d743b39e57a7b9cbfe467c
    Virtualization: vmware
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
            Kernel: Linux 3.10.0-123.el7.x86_64
      Architecture: x86_64

Then I change the hostname with the set-hostname option of the hostnamectl command to server2.example.com

hostnamectl set-hostname server2.example.com

Afterward, I check with the command hostname and hostname -f if the hostname change has succeeded.

hostname
hostname -f

The result should be:

[root@server1 ~]# hostname
server2.example.com
[root@server1 ~]# hostname -f
server2.example.com

Instead of the hostname command you could also use the "hostnamectl status" command again to check if the new hostname has been set:

[root@server1 ~]# hostnamectl status
   Static hostname: server2.example.com
         Icon name: computer-vm
           Chassis: vm
        Machine ID: d89865d34b5a4637a9a4ff0ce0f6da02
           Boot ID: 56d1685056d743b39e57a7b9cbfe467c
    Virtualization: vmware
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
            Kernel: Linux 3.10.0-123.el7.x86_64
      Architecture: x86_64

How to set a VNC password

The Linux VNC server provides a command to set a new password. The command is "vncpasswd", the password is stored in encrypted form into the file ~/.vnc/passwd of the home directory of te user. Run:

vncpasswd

to set a new password for the currently logged in user. The command will then prompt for the new password. If you like to set a new VNC password for a different user, then append the password file name to the command. Example for the user "jane":

vncpasswd /home/jane/.vnc/passwd

The above command to set a new password for jane requires it that you are logged in as root user. On Ubuntu systems you can use sudo instead:

sudo vncpasswd /home/jane/.vnc/passwd

Which ports are used on a ISPConfig 3 server and shall be open in the firewall?

Here is a list of ports that are used commonly on ISPConfig 3 servers. If you don't have all services installed or if you e.g. don't want to connect to MySQL from external servers, then close the unused or unwanted ports.

TCP ports

20 - FTP Data
21 - FTP Command
22 - SSH
25 - Email
53 - DNS
80 - HTTP (Webserver)
110 - POP3 (Email)
143 -Imap (Email)
443 - HTTPS (Secure web server)
993 - IMAPS (Secure Imap)
995 - POP3S (Secure POP3)
3306 - MySQL Database server
8080 - ISPConfig web interface
8081- ISPConfig apps vhost

UDP ports

53 - DNS
3306 - MySQL

How To Check And Repair All MySQL Databases on Debian And Ubuntu Linux

The Following command can be used to check and repair all MySQL databases on a Ubuntu or Debian Linux System.

Ubuntu Linux

sudo mysqlcheck --defaults-file=/etc/mysql/debian.cnf --auto-repair --optimize --all-databases

Debian Linux

mysqlcheck --defaults-file=/etc/mysql/debian.cnf --auto-repair --optimize --all-databases

The benefit of the above command is that it uses the debian-sys-maint login to MySQL which is available on every Debian and Ubuntu System, so you don't have to provide the MySQL root login details.

How to Copy Files with SCP between Linux Servers

1.1 SCP Command Line-An Overview

 

The SCP command line is commonly used to copy files over SSH, and between popular Operating systems like Linux, Mac and Windows in a secure fashion. SCP is used to copy files to/from a remote server. It also allows you to copy files from one remote server to another remote server, without passing traffic through your PC.

Continue reading How to Copy Files with SCP between Linux Servers

Solution for: fatal: open database /var/lib/postfix/smtpd_scache.db: File exists

If your mail server stops working (neither incoming nor outgoing email works) and you find the following error message in the mail.log file:

fatal: open database /var/lib/postfix/smtpd_scache.db: File exists

then the smtpd_scache.db might got corrupted. Postfix will recreate this file if it does not exist. So it can be removed to solve the issue:

/etc/init.d/postfix stop
rm -f /var/lib/postfix/smtpd_scache.db
/etc/init.d/postfix start

Thanks to Alexander Fox for sending me this FAQ.

Enable virtualization on Gigabyte Z77X-UDH3 motherboard BIOS

To enable virtualization on a machine with a Z77X-UDH3 motherboard run the BIOS by hitting Del while booting the computer.

Once inside click on the BIOS Features tab and look for the Intel Virtualization Technology entry. If it's set on Disabled, set it on Enabled. Afterwards save the changes made to your settings and quit the BIOS using the last tab from the main tab-line.

Virtualbox: VT-X is not available

In some cases when you try to get a virtual machine running with Virtualbox or similar virtualization software you will get an error stating that 'VT-X is not available'. This relates to BIOS settings which, depending on your processor, determine whether your computer is able to virtualize stuff. These settings are not set automatically however, so it's worth a look into your BIOS whether you can actually change the setting and if your processor allows it.

The keyword to look for in the settings is 'Virtualization', it's probably placed in some advanced tab if there are some of those in your BIOS.

To see how it's done with a Z77X-UDH3 motherboard by Gigabyte see this post: Gigabyte Z77X-UDH3