Linux

Many of my scripts work with temporary files, usually relative to the scripts directory¹, while at the same time using set -e to exit as soon as something fails.

In this scenario the script leaves behind these temporary files by default, which is not desireable.

We can however do a proper cleanup using the trap concept.

By default HAProxy resolves all DNS names in it’s config on startup and then never again.

This might cause issues down the road if DNS records, for example the ones for backends, change.

This section of the documentation is a good starting point as it describes IP address resolution using DNS in HAProy really well: https://docs.haproxy.org/3.0/configuration.html#5.3

Additionally this guide can also be helpful: https://www.haproxy.com/documentation/haproxy-configuration-tutorials/dns-resolution/

Often times we need the current date (and time) when scripting inside bash or other shells. For example when creating a backup file or writing to a log.

Often times when writing scripts I want to reference files in the same directory, but keep the script portable in case it is part of a git repository being checked out somewhere else or just the folder getting moved.

I often whish to search through large bodies of text, like my knowledge base or source code repositories, from the command line.

I use fuz for this and I’m quite happy with it.

I also have it aliased to my knowledge base folder for even easier searching.

alias search="fuz -p /path/to/knowledge-base/"

The problem

If you use ssh-agent with an encrypted ssh key it does not persist when you open a new terminal window.

The solution

Use keychain instead.

1. Install

   sudo apt install keychain
   

2. Add to your shells rc file, eg. .bashrc or .zshrc

   # Repeat this line for all keys you want to unlock and use this way
   /usr/bin/keychain -q --nogui $HOME/.ssh/id_rsa
   source $HOME/.keychain/wsl-sh
   

3. Unlock your keys on shell startup and enjoy

When using netplan it is easy to force .local DNS requests to go to you nameservers instead of being only resolved locally (the default and standard).

This also works with all other strange .WHATEVER domains you may have lying around in your organization.

Snippet from netplan configuration:

 nameservers:
        addresses:
          - X
          - Y
        search:
          - local
          - myotherstupiddomain

Debian/Ubuntu

grep -vH "#" /var/spool/cron/crontabs/*

RedHat/Centos/Rocky

grep -vH "#" /var/spool/cron/*

SELinux by default prohibits certain things from working through VMware tools (Ansible connection or plain API).

This can be solved two ways:

• Disabling SELinux: BAD, but easy
• Writing a custom SELinux policy: complicated but more secure

Note: Adding/Changing this policy through a VMware tools connection is thankfully possible

Example policy

This policy is the base for a VMware tools policy and allows entering the rpm context (yum).

module custom-vmtools 1.0;

require {
        type rpm_script_t;
        type vmtools_unconfined_t;
        class process transition;
}

#============= vmtools_unconfined_t ==============

allow vmtools_unconfined_t rpm_script_t:process transition