Posts on Network

Network-related posts.

How to Change Linux Account Password Through SSH: A Beginners’ Tutorial

By Eric Z Ma,
People are sometimes given access to Linux/Unix and asked to change their initial passwords. But for beginners, changing a Linux/Unix password is not an easy task, especially when there is only SSH log on allowed to the Linux/Unix server. This post introduces how to change password of user USER on host HOST remotely using SSH. linux-passwd.png Steps are as follows. Note: you will need to replace HOST and USER with the actual username and hostname you are using. » Read more

How to Set the Static IP Address Using CLI in Fedora/CentOS Linux

By Eric Z Ma,
How to set the static IP address for CentOS 7/Fedora 22+ is introduced in this post. Here, we assume the Linux is using NetworkManager to manage the network. All steps are done as root. Find the interface you want to set the address ∞ Command ifconfig -a lists all interfaces. Find the interface name to set, such as enp2s0. datacenter-servers.jpg Edit the interface’s configuration file ∞ For interface NAME, the configuration file is stored in /etc/sysconfig/network-scripts/ifcfg-NAME. » Read more

How to Keep Linux SSH Session Alive from Disconnecting – Server and Client Side Fixes

By Eric Z Ma,
SSH is a very common tool for Linux/Unix platforms. One annoying problem when using SSH is that the connection may get disconnected if the SSH connection is idle for some time under common configurations. Users may run an infinite loop like while true; do uptime; sleep 30; done when there is no work to be done in a SSH session. There are better ways as SSH servers and clients already provide such support and we will discuss these methods in this post. » Read more

Blocking JavaScripts from a Site in Chrome in 2 Easy Steps

By Eric Z Ma,
You may be aware of the GitHub’s largest DDoS attack in history on Mar. 27, 2015 (some context, technical details, and discussions):We've been under continuous DDoS attack for 24+ hours. The attack is evolving, and we're all hands on deck mitigating. — GitHub Status (@githubstatus) March 27, 2015 One important technique when facing this kind of problems is blocking certain sites’ JavaScripts in your browser. » Read more

Free VPNs for iPhone Users: OpenVPN + Ovpn Spider

By Eric Z Ma,
VPNs are useful for testing viewing webpages from a remote location or visiting blocked websites. In this post, I will introduce a method for finding and using free VPNs on iPhone. Note that the VPNs are free and the providers are not identified. Hence, only use this method for visiting public webpages or keeping visiting https sites. If security or privacy are important concerns, find a reliable VPN service or set up your own. » Read more

iPhone Connecting to Internet Using Windows PC’s Network through USB Cable

By Eric Z Ma,
Note that this was only tested on certain combinations like this (Windows 7 with iOS 8), this (Windows 7 with iOS 7), this and this (Windows 7 with iOS 9.3.2 (iphone 6s)). Windows 7 seems a possible Windows OS that can work. Recently, I tested it on Windows 8 and iOS 9. Unfortunately, it did not work. It seems iOS or Windows has changed its way configuring the network. » Read more

Lazy Linux Admins Going to Server Rooms Less: Forced Reboot, Auto Reboot after Kernel Panic and Email Notification after Reboot

By Eric Z Ma,
Having to go the the server room to reset servers is the most headache thing for admins managing a cluster of Linux servers in a remote site. Either you can ping the server but can not ssh to it, or you even can not ping it. There are various reasons that may cause a Linux server crash or fail to be connected to by SSH. » Read more

MPlayer over SSH to Play Movie from Remote Host

By Eric Z Ma,
MPlayer is a great movie player. SSH is a great tool to connect and transfer data over the network securely. Combining these 2 great tools together will be greater. You may already has a small server storing some movies or videos or music and playing them on your laptop will be convenient. In this post, we will introduce three methods to play movie using MPlayer over SSH. » Read more

Git through SSH Tunnel as Proxy

By Eric Z Ma,
git is a great tool and it is common to have a git server over SSH possibly managed by gitolite. However, there are situations that we can not directly connect to the git server but be able to SSH to another node that can connect to the git server. The git server may allow only internal connections because of security. With the node that we can SSH to, we can still use the git server “directly” by setting up a SSH tunnel as a proxy for the git connection. » Read more

Improving ssh/scp Performance by Choosing Suitable Ciphers

By Eric Z Ma,
Update on Oct. 9, 2014: You should be aware of the possible security problems of blowfish and it is suggested not to be used. Instead, you may consider ChaCha20 as suggested by Tony Arcieri. To use this with OpenSSH, you need to specify the Ciphers in your *.ssh/config* files as chacha20-poly1305@openssh.com possibly with another default one since only newer vesion of OpenSSH supports it. » Read more

How to Set Up A Gitolite Git Server – A Ten-Minute Tutorial

By Eric Z Ma,
I ever introduced seting up git server using SSH or gitosis. However, gitolite is the way to go for managing git servers if you want an lightweight authentication layer. gitolite provides many very usefull features which can control each user’s right on each branch. I set up one gitolite git server and am very happy with it. In this post, let’s look at how to set up one gitolite git server. » Read more

Connecting to Remote Servers by VNC on Windows

By Weiwei Jia,
Software you will need 1, Putty 2, Real VNC viewer 3, twm (lightweight desktop). On fedora (centos, redhat): sudo yum install twm (on other distros, you may need other commands, or download source code and install it). Specific steps ∞ 1, Enter your Host name and port in putty. 1_9.jpg 2, Set port forwarding in putty Tunnels. 1_7.jpg 3, Start vncserver in the server side. » Read more

How to Configure iOS to Use Socks Proxy over SSH with a Linux/Unix Host

By Eric Z Ma,
The socks proxy I created following Proxy Using SSH Tunnel works very well on both Linux and Windows. However, when I try to configure my iPhone and iPad with iOS, I find iOS does not support socks proxy in its settings interface. I don’t know why it is not added while socks proxy is indeed supported by the iOS operating system. » Read more

Flushing iptables on Fedora

By Eric Z Ma,
iptables is a mechanism in Linux kernel for port forwarding, NAT, firewalls etc. In Linux distros, such as Fedora, the iptables is configured to be as a “strict” firewall that opens a limited know ports, such as 22 for SSH. However, in some network environment, such as a private cluster, the nodes are trusted and firewalls are usually not needed. We may flush the default iptables to make it accept all connections and add rules as needed. » Read more

Disabling IPv6 on Fedora 17 Linux

By Eric Z Ma,
IPv6 is enabled by default on most Linux distros. However, IPv6 is not used most of time (at least in my case). This post introduces how to disable IPv6 support on Linux (newer Kernel versions, such as in Fedora 17). IPv6 on Linux can be easily configured via sysctrl. Add these lines to /etc/sysctl.conf: net.ipv6.conf.all.disable_ipv6=1 net.ipv6.conf.default.disable_ipv6=1 Note that you will need to restart Linux to make it take effect. » Read more

Changing Hostname of Fedora Linux

By Eric Z Ma,
Different Linux distros have different method to set the hostname. On Fedora Linux, it is quite simple. On newer Fedora releases ∞ At least from Fedora 19 (sorry, no sure the exact earliest version): You need to edit the file /etc/hostname which just contains the hostname. On older Fedora releases ∞ Sorry, I do not know the exact version till which you need to use the above method. » Read more

Installing ns-2 and ns-3 on Fedora Linux

By Eric Z Ma,
ns is a discrete-event network simulator targeted primarily for research and educational use. There are two version of ns, ns-2 and ns-3, which are quite different with each other in the implementation and method to use them. In this post, we introduce how to install ns-2 and ns-3 on Fedora Linux 15. Install ns-2.34 on Fedora Download the allinone package $ wget http://downloads.sourceforge.net/project/nsnam/allinone/ns-allinone-2.34/ns-allinone-2.34.tar.gz Uncompress the pacakge $ tar xf ns-allinone-2.34.tar.gz Install needed pacakges # yum install gcc make libX11-devel libXt-devel libXmu-devel Ns-2 requires older version of gcc. » Read more

Disable IPv6 on Linux

By Eric Z Ma,
Update: this only works on older Linux kernels (e.g. Fedora 12). For newer kernels, please see Disabling IPv6 on Fedora 17 Linux IPv6 is enabled by default on most Linux distros. However, IPv4 is still the mostly used network and IPv6 is not used in many environment. This post introduces how to disable IPv6 support on Linux. The method is simple: # echo "options ipv6 disable=1" >> /etc/modprobe.d/disable-ipv6.conf “option ipv6 disable=1” tells Linux not to enable the ipv6 module. » Read more