Modest Destiny (Posts about Linux)

Linux Change Username, UID (userid) and GID (groupid)

Adam Basfop Cavendish — Mon, 10 Aug 2020 12:41:33 GMT

Assume we would like to change a user's username, uid and gid into some random number.

Limiting Fan Speed in Dell Poweredge Series

Adam Basfop Cavendish — Sun, 31 May 2020 14:22:40 GMT

Sometimes we need to limit the fan speed in Dell PowerEdge server series maybe for the noise. The followings are the ipmi raw commands to setup the manual fan control which are very much undocumented.

Function	`ipmitool raw` command
Enable manual fan control	`ipmitool raw 0x30 0x30 0x01 0x00`
Disable manual fan control	`ipmitool raw 0x30 0x30 0x01 0x01`
Set manual fan speed step	`ipmitool raw 0x30 0x30 0x02 0xff 0x??`

I'm using Dell r720xd and setting 0x?? to 0x26 effectively limits the fan speed to around 8000 RPM. It is a somewhat safe value before you slowly set down the value to limit further down the fan speed.

Run Linux GUI Applications within Docker Containers

Adam Basfop Cavendish — Mon, 25 May 2020 01:32:54 GMT

Introduction

Running GUI applications inside docker might be useful when sandbox mechanism is needed or debugging complex and tricky container networking related issues.

Generally there are 3 major ideas when trying to run GUI applications in docker, which are:

Penetrate in the host X11 sockets (most straight forward but not fully secure)
Expose SSH connection and use X11Forwarding configuration
Run VNC server inside the container and use VNC client to access the GUI application inside

Linux Pre-shutdown and Post-bootup Task Automation

Adam Basfop Cavendish — Fri, 28 Feb 2020 20:50:57 GMT

There are always plenty to do before a machine is shutdown and after a machine is startup. With systemd adopted by most linux distributions, it is possible to automate these tasks in parallel.

We can write various shell scripts to automate the tasks and specify them with different systemd units.

PDF Compression with Ghostscript

Adam Basfop Cavendish — Fri, 13 Dec 2019 06:47:18 GMT

PDF do preserve the original information especially image when exported. The feature makes it very attractive for archive but it might be too large to spread.

We can use ghostscript command to compress (actually rewrite) a PDF file with a lot of images embedded.

Enabling Linux OOM Killer

Adam Basfop Cavendish — Sun, 13 Oct 2019 18:31:23 GMT

Sometimes we do want to have some process killed to save the overall other works left not saved on Linux.

Add Ceph RBD Storage Pool to KVM/QEMU/Libvirt

Adam Basfop Cavendish — Mon, 07 Oct 2019 03:03:46 GMT

If you have a ceph cluster and you would like to add a rbd pool to your kvm, qemu or libvirt, you can follow the steps listed as below.

Multi-boot from ISO on USB with Grub 2

Adam Basfop Cavendish — Wed, 12 Jun 2019 14:36:17 GMT

Last time we've talked about how to Manually UEFI Boot Linux and Windows 10 USB from Grub, today we'd like to talk about creating a multi-boot usb stick with grub 2.

Sometimes we need to create multiple linux distribution installation media or bootable usb stick. However, it is always so annoying to re-flush the usb stick again and again.

However, grub actually enables us to boot most of the linux distributions through loop format or iso image files. The iso image format is known for its original design for CD disks or DVD disks so that the distributions are bootable through your CD-ROM drivers. If the distribution is bootable through the CD-ROM drivers and the CD or DVD media is not writable, which it effectively means that we can actually boot from the non-writable iso image file as well.

Linux Device Tree Pinctrl Tutorial

Adam Basfop Cavendish — Thu, 09 Aug 2018 12:09:17 GMT

When porting drivers on a specific board for a comparatively new linux kernel, it is common to edit the linux device tree files to put together all the device configurations with register values, working modes and pin control offsets set to expected values.

Here in this post we focus on the exact steps one needs to find the correct pin control offset for specific devices. Here we'd take TI's AM4379 (AM437x) chip as an example for this tutorial.

Manually UEFI Boot Linux and Windows 10 USB from Grub

Adam Basfop Cavendish — Fri, 28 Apr 2017 04:01:13 GMT

Introduction

Dead boot of Linux or Windows needs a lot of labor when sometimes it just does not work.

Legacy boot mode does not support hard drives that provides more than 2TB disk space, and mostly you would like to use UEFI mode for better Windows 10 support.

With this tutorial you may:

Learn how to boot from a blank computer into grub via changing BIOS options
- You need a working computer with Linux
- Note: it may differ from BIOS to BIOS, but the basic idea does not change
Learn how to boot from multiple different Linux distribution ISO images from a UEFI compatible USB device
Learn how to boot Windows 10 USB in grub