Display SSH Warning Message to Users

One of the easiest way to alert unauthorized people that they are trespassing when they try to access the SSH of your server (maybe by mistake) is to add a warning message before and/or after login. Of course, this does not mean that your server is secure when you add it, but at least they […]

How to disable the firewall in CentOS

The Linux Firewall can be a powerful tool if it is used correctly. However, in some cases you may want to disable it. Here is a nice tutorial if you wish to learn more about the firewall. Here are the commands you need to run in order to stop it and to prevent it from […]

How to compute the MD5 hash of a file

MD5 is one of the most common types of hash used to verify the integrity of a file after a transfer (and not only). You may even find some files with .md5sum extension which contain the MD5 checksum of some existing files. The MD5 hash is commonly expressed as a 32 digit hexadecimal number, e.g.: 1bc29b36f623ba82aaf6724fd3b16718 […]

How to view all the open ports

One of the first thing you learn as a system administrator is that programs (applications, scripts) need TCP connections to communicate with other devices. This can sometimes also be a problem. Some exploits open a new port and can cause some serious problems. However, there is a very simple way to find out which programs […]

Identifying Email Spam From PHP

One of the biggest concerns when you manage a web server is security. Sure, you need to make sure no one hacks your machine to gain access to SSH, FTP, but how do you know if you have a security problem with one of your PHP scripts and it starts sending tons of email spam […]

What is the IP address of my server?

One of the most common questions that comes from newbies is “What is my server’s IP address?”. This is actually a pretty good question when it comes for VPS servers because the IP addresses are generally allocated by the service provider – you can have 1 IP address, maybe more, it depends on how generous […]

Chmod Files as 664 And Directories as 775

There are some times when the permissions for some files and directories are screwed: 755, 640 .. maybe something even more weird. Of course it would take a lot of time to change the permissions using chmod manually. The first mistake many people make is to  do a recursive chmod with 664 .. only to […]

How to install ffmpeg on CentOS

One of the most useful tools for multimedia conversions (audio/video) is ffmpeg. This tool has a long tradition: started in 2000, it is used by many Linux programs (both command line and with visual interface). In order to install it, you will need to setup first RPMforge and Epel repositories. You can find here the […]