The Geek Diary

The grpck command removes corrupt or duplicate entries in the /etc/group and /etc/gshadow files. It generates warnings for other errors found. grpck will prompt for a “yes” or “no” before deleting entries. If the user replies “no,” the program will exit. If run in a read-only mode, the reply to all prompts is “no.” Alternate […]

Similar to od, xxd produces a hexadecimal or binary dump of a file in several different formats. It can also do the reverse, converting from its hex dump format back into the original data. For example, here’s a hex dump of binary file /usr/bin/who: $ xxd /usr/bin/who 0000000: 7f45 4c46 0101 0100 0000 … 0000 […]

The seinfo and sesearch utilities can assist users in performing single-step analysis: they either provide immediate information about a SELinux object (which is mainly what seinfo is about) or are capable of querying direct SELinux rules (which is the scope of sesearch). These utilities are provided through the setools package. Where the seinfo application displays […]

MAC address flooding is a great way to render a network useless. Basically, through MAC flooding, you can turn the network into a large hub. MAC flooding works by essentially allowing the switch ports to learn as many MAC addresses as they see on their ports, and if no limits on in place, can fill […]

Quick Emulator (QEMU) is the main component of the QEMU/KVM virtualization technology suit. It provides hardware virtualization and processor emulation. QEMU runs in userspace and, without the need for kernel, drivers can still provide fast system emulation. QEMU supports two operating modes: Full system emulation, where QEMU emulates an entire computer system, including the CPU […]

A new command that was introduced in systemd-based distributions that enables you to manage many aspects of time is timedatectl. When used without any arguments, this command shows detailed information about the current time and date. It also displays the time zone your system is in, in addition to information about the use of NTP […]

MPI is not a programming language. MPI defines a set of library routines that can be called from C and Fortran programs. MPI programs typically employ a single-program, multiple-data approach. Multiple instances, or MPI ranks, of the same program run concurrently. Each rank computes a different part of the larger problem and uses MPI to […]

KDE Plasma Workspaces is a popular graphical desktop environment for Linux-based systems. Once you have installed the “KDE Plasma Workspaces package group”, you can start the desktop environment using startkde. When you’re done using KDE and log out of the desktop, you’ll be returned to the console: # startkde To configure the system to automatically […]

The Windows Volume Shadow Copy Service (VSS) allows for backups of files, even protected system files, to be made while the operating system is running. Windows uses VSS to make periodic differential backups of the blocks of data on NTFS volumes. These backups are called volume shadow copies and are stored in the System Volume […]

Using ifrename is the easiest way to make sure your network cards keep the correct configurations on Linux systems. Usually, interfaces will come up in the same order, and the kernel will assign them the same names, but sometimes this can change (e.g., after a kernel upgrade or adding another network card). Your nice Linux […]