The Helpdesk For I.T. Administrators
Changing the port number that your SSH server listens on is a simple way to prevent random brute force login attacks against your server. While people can still perform attacks against SSH running on a different port number, most automated tools will default to port 22, and not actually do a full port scan. Any …
Most Linux distributions allow the root user to connect in via SSH, and CentOS is no exception. It is recommended that root logins are never used, and you should use either su or sudo to elevate the permissions of a normal user account. As such, the best option is to disable root logins in the …
Most Linux distributions allow the root user to connect in via SSH, however if you try to connect into Ubuntu as root after a default install, you will find that you wont be able to get in. While it may look like the root account is not permitted to login, it is just because that …
A default install of CentOS will enable IPv6 connectivity. If you don’t need IPv6, there is no need to have it enabled. Follow the steps below to disable IPv6 on a CentOS install. Note: Run these commands as a user with root privileges. Check to see if you’re installation is currently set up for IPv6: …
A default install of Ubuntu will enable IPv6 connectivity. If you don’t need IPv6, there is no need to have it enabled. Follow the steps below to disable IPv6 on a Ubuntu install. Check to see if you’re installation is currently set up for IPv6: $ cat /proc/sys/net/ipv6/conf/all/disable_ipv6 If the output is 0, IPv6 is …
An important aspect of any firewall are the log files. Iptables on Linux provides logging functionality, however by default, it will get outputted to the /var/log/messages log file. This can clutter things up, and make it hard to check the logs. If you want to change the file that IPTables logs to, you need to …
The Linux DD command allows you to read and write directly to block devices. If you are playing around with boot loaders, dual booting, etc, its a good idea to take a copy of your master boot record just in case things go astray and you need to restore it. To backup the master boot …
The default port for SMTP is port 25, but there may be some scenarios where you may need Postfix to listen on another port as well (or instead of). For example, if you want to send emails via your own mail server, from your work computer, but the work network may be blocking all port …
On a default install of Postfix, it will listen on all interfaces/IP addresses on your machine. Sometimes this is not what you want. For example, the computer may be connected directly to the internet on one network interface, and connected to a lan on another interface, however you may not want to allow access to …
Having a computer that replies to ping requests allows for simple network connectivity tests, however there may be circumstances where you need to disable ping replies coming from your computer. This can be done using firewall rules, however Linux provides an easy way to change the kernel parameters at run time to disable ping replies. …