sysadmin

Linux rename network interface using udev rules

Sometimes it is convenient to have user assigned names to network interfaces – particularly when the MAC address of the interface remains constant but the bus on which it is attached may change because it’s a virtual machine.

All that is required to be done is create a file /etc/udev/rules.d/persistent-net.rules : This file used to exist earlier but has been phased out by most mainstream Linux distributions in favor of the consistent naming scheme or other methods like systemd-networkd.

The udev rules required in that file:

February 11, 2021|Categories: Linux|Tags: , |0 Comments

Hibernate support on Ubuntu 20.04 with encrypted swap and encrypted root filesystem

So I installed Ubuntu 20.04 on my laptop with encrypted root filesystem with bcache support since I have a NVME SSD along with the usual hard disk in it. While setting up encrypted root filesystem the installer will not allow you to have unencrypted swap – and the default encrypted swap setup is to use a random encryption key that is […]

January 26, 2021|Categories: Linux|Tags: , , |0 Comments

Speeding up PHP CLI applications using OpCache

I run a few PHP based applications which require background jobs, and I use the usual crond via crontab to run the jobs. PHP has an excellent feature – OpCache which can cache the compiled code in memory to speed up the web applications, where typically the PHP-FPM process is a long running process so the compiled code can be fetched on next request. But with CLI applications there is no shared state or memory to store the compiled code.

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April 23, 2020|Categories: Linux, Programming|Tags: , , , |0 Comments

Change username and hostname for Ubuntu instances on AWS

If you have used Ubuntu images on AWS, you might have noticed that the default username of the user on the instance is ‘ubuntu’. And the hostname is dynamically generated according to the public IP. Both of these can be changed using cloud-config supported on Ubuntu images – the config has to be provided in the User Data section in Advanced on the Configure Instance tab.

YAML configuration to change the parameters:

A lot more things are possible using the cloud-config method and it is supported on other operating […]

February 6, 2020|Categories: Linux|Tags: , , , |0 Comments

Using privileged mode (become) in Ansible without a password

So I was working on automating some stuff using Ansible when the necessity to have password less superuser access came up. A simple way would be adding the ansible management key to the root account itself and allow SSH to root, but allowing ssh to root is usually a bad idea.

I tried many things – NOPASSWD in sudo entry, requiretty, etc. And after nearly two hours of digging a spark ignited and I found a way – Linux has PAM module called pam_wheel.so which can implicitly allow root access via su when a user […]

January 20, 2020|Categories: Linux|Tags: , |0 Comments

LXD OpenVSwitch and VLANs

LXD is a fantastic container virtualization tool that comes by default with Ubuntu. In one of my applications I needed to have many containers each within it’s own VLAN network.
So I used OpenVSwitch in combination with LXD to achieve this.

There is no inherent facility in LXD to provide VLAN tag numbers to the interface. So it is necessary to use a “Fake bridge”. I managed to do it after reading this article by Scott – VLANs with […]

July 5, 2019|Categories: Linux|Tags: , , , , |2 Comments
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