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Linux desktop comes with a display manager (e.g., GDM, KDM, LightDM), which lets the desktop machine automatically boot into a GUI-based login environment. However, what if you want to disable GUI and boot straight into a text-mode console because you are troubleshooting a malfunctioning desktop manager?

Secure Shell (SSH) is a network protocol that enables remote login or remote command execution between two hosts over a cryptographically secure communication channel. SSH was designed to replace insecure clear-text protocols such as telnet, rsh or rlogin. SSH provides a number of desirable features such as authentication, encryption, data integrity, authorization, and forwarding/tunneling.

One common attack on SSH service is brute force attacks where a remote attacker indefinitely attempts to log in with different passwords. Fail2ban is an open-source intrusion prevention framework on Linux that monitors various system log files (e.g., /var/log/auth.log or /var/log/secure) and triggers various defensive actions upon detecting any suspicious activities. You can use fail2ban to defend against brute force password guessing attacks on an SSH server.

In Linux, when you want to change a file name, mv command gets the job done. However, mv cannot rename multiple files using wildcard. There are ways to deal with multiple files by using a combination of sed, awk or find in combination of xargs. However, these are rather cumbersome and not user-friendly.

phpMyAdmin is an open-source PHP application designed as a web-based MySQL/MariaDB database administration tool. Compared to lightweight database management tools such as Adminer, phpMyAdmin offers more comprehensive MySQL/MariaDB administration capabilities. It supports pretty much all MySQL databas/table related operations such as browse, create, copy, drop, rename, alter, and more.

Out of the box, enterprise Linux distributions such as CentOS or RHEL come with a powerful firewall built-in, and their default firewall rules are pretty restrictive. Thus if you install any custom services (e.g., web server, NFS, Samba), chances are their traffic will be blocked by the firewall rules.

Most consumer PCs and laptops nowadays come with a DVD writer. In Linux, optical drives such as CD/DVD drives are assigned device names by the kernel based on udev rules at the time of booting. There are several ways to detect the writer's device name and its writing speed.

Traditionally, network interfaces in Linux are enumerated as eth[0123...], but these names do not necessarily correspond to actual hardware slots, PCI geography, USB port number, etc. This introduces a unpredictable naming problem (e.g., due to undeterministic device probing behavior) which can cause various network misconfigurations.

As a de-facto packet capture tool, tcpdump provides flexible packet filtering capabilities. The libpcap packet capture engine which tcpdump is based upon supports standard packet filtering rules such as 5-tuple packet header (source/destination IP addresses/ports and IP protocol type) filtering.

In CentOS or RHEL, there are three kinds of hostnames defined: (1) static, (2) transient, and (3) pretty. The "static" hostname is also known as kernel hostname, which is initialized from /etc/hostname automatically at boot time. The "transient" hostname is a temporary hostname assigned at run time, for example, by a DHCP or mDNS server. Both static and transient hostnames follow the same character restriction rules as Internet domain names.

Revealing web server signature with server/PHP version info can be a security risk as you are essentially telling attackers known vulnerabilities of your system. Thus it is recommended you disable all web server signatures as part of server hardening process.

There are two major MySQL storage engines used: MyISAM and Innodb. MyISAM is non-transactional, and thus can be faster for reads, while InnoDB fully supports transactions (e.g., commit/rollback) with finer-grain locking. When you create a new MySQL table, you choose its type (i.e., storage engine). Without any choice, you will simply use a pre-configured default engine.

There are a variety of web server software available for Linux-based platforms including Raspbian. Using the available web server software, we can turn Raspberry Pi into a 24/7 available portable web server. In this case, however, we must remember that Raspberry Pi has hardware limitations in terms of CPU clock speed, memory, etc. As such, we want to avoid running resource-heavy software (e.g., Apache) on Raspberry Pi.

Who never procrastinated and played games instead of writing a paper, finishing a report, or looking after the kids? Absolutely no one. But when Linux users procrastinate, they procrastinate in style: while playing from the terminal! We tend to forget, but at first a graphical interface was not necessary for a good game. And thanks to open-source and the community, many arcade and other good games were ported to be played from within a terminal, without an X server running. It would be impossible to list them all, but let me present ten of these games that particularly appealed to me personally.

Any operational domain has at least two DNS servers, one being called a primary name server (ns1), and the other a secondary name server (ns2). These servers are typically operated for DNS failover: If one server goes down, the other server becomes an active DNS server. More sophisticated failover mechanisms involving load balancers, firewalls and clusters are also possible.

Conky is a light-weight system monitor for X, which displays a variety of information on your desktop. Conky is highly configurable program which can monitor various time-varying system properties such as CPU load/temperature, free memory, free disk space, battery status, network traffic, etc. Conky consumes little system resources because it renders information within a desktop theme instead of using separate widget toolkits.

As you may have already read here, LaTeX is an extremely useful document markup language. Whether it is for a research paper, a math homework, a presentation, or a fancy resume, LaTeX is pretty much the go to language. However, its syntax can be a bit confusing at first, and it is recommended, at least in the beginning, to use a LaTeX editor software.

While DNS introduces human-readable naming schemes for Internet hosts, it also brings with it extra overhead associated with resolving names to IP addresses. For end users, this overhead means additional DNS lookup latency for accessing any Internet host. For service providers, this implies the performance-critical DNS infrastructure that needs to be maintained. Minimizing these overheads has led to the extensive use of "caching" throughout DNS hierarchy. For example, there are web browser/OS's built-in DNS cache; DNS caching server of the local network; and the cache of local DNS servers operated by service providers, etc.

Domain Name System (DNS) is one of the most critical services in the Internet. Without DNS, we would not be able to access the web. Before going into the details on how DNS works, a little on the background may be helpful. When you are accessing, say, Google, your traffic originates from your computer, goes through the backbone of your ISP, and then their own upstream provider and so on; until it reaches Google's network.

One of the most important tasks in Linux administration is to check the integrity of the filesystem. The Linux filesystem can be damaged under various circumstances, e.g., system crash, power loss, disconnected disk, accidentally overwritten i-node, etc. Thus it is a good idea to check the integrity of the filesystem regularly to minimize the risk of filesystem corruption. When it comes to checking and repairing Linux filesystem, fsck is a useful tool. In this tutorial, I am going to describe how to set up automatic filesystem checks with fsck tool.