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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for the ‘Linux’ Category

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Getting your public IP address from the command-line when http and https are blocked: use DNS

Posted by jpluimers on 2022/12/28

Years ago, I wrote Getting your public IP address from the command-line. All methods were http based, so were very easy to execute using cURL.

But then in autumn 2021, Chris Bensen wrote this cool little blog-post [Wayback/Archive] Chris Bensen: How do I find my router’s public IP Address from the command line?:

dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com

At first sight, I thought it was uncool, as the command was quite long and there was no explanation of the dig command trick.

But then, knowing that dig is a DNS client, it occurred to me: this perfectly works when http and https are disabled by your firewall, but the DNS protocol works and gives the correct result:

# dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com
"80.100.143.119"

This added the below commands and aliases to my tool chest for *nix based environments like Linux and MacOS (not sure yet about Windows yet :), but that still doesn’t explain why it worked. So I did some digging…

IPv4

  • command:
    dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com
  • command removing outer double quotes:
    dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com | xargs
  • alias:
    alias "whatismyipv4_dns=dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com | xargs"

IPv6

  • command:
    dig -6 TXT +short o-o.myaddr.l.google.com @ns1.google.com
  • command removing outer double quotes:
    dig -6 TXT +short o-o.myaddr.l.google.com @ns1.google.com | xargs
  • alias:
    alias "whatismyipv6_dns=dig -6 TXT +short o-o.myaddr.l.google.com @ns1.google.com | xargs"

How it works

Let’s stick to dig and IPv4 as that not having IPv6 (regrettably still) is the most common situation today:

# dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com
"80.100.143.119"

What it does is request the DNS TXT record of o-o.myaddr.l.google.com from the Google DNS server ns1.google.com and returns the WAN IPv4 address used in the DNS request, which is for instance explained in [Wayback/Archive] What is the mechanics behind “dig TXT o-o.myaddr.l.google.com @ns1.google.com” : linuxadmin.

Since these are TXT records, dig will automatically double quote them, which xargs can remove (see below how and why):

# dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com | xargs
80.100.143.119

The DNS query will fail when requesting the Google Public DNS servers 8.8.8.8 or 8.8.4.4:

# dig -4 TXT +short o-o.myaddr.l.google.com @8.8.8.8
"2a00:1450:4013:c1a::103"
"edns0-client-subnet 80.101.239.0/24"

Or, with quotes removed (the -L 1 ensures that xargs performs the quote-pair removal action on each line):

# dig -4 TXT +short o-o.myaddr.l.google.com @8.8.8.8 | xargs -L 1
2a00:1450:4013:c1a::103
edns0-client-subnet 80.101.239.0/24

This request is both slower than requesting the ns1.google.com server and wrong.

The reason is that only ns1.google.com understands the special o-o.myaddr.l.google.com hostname which instructs it to return the IP address of the requesting dig DNS client.

That 8.8.8.8 returns a different IP address and an additional edns0-client-subnet with less accurate information is explained in an answer to [Wayback/Archive] linux – Getting the WAN IP: difference between HTTP and DNS – Stack Overflow by [Wayback/Archive] argaz referring to this cool post: [Wayback/Archive] Which CDNs support edns-client-subnet? – CDN Planet.

Not just ns1.google.com: any DNS server serving the google.com domain

Since o-o.myaddr.l.google.com is part of the google.com domain, the above works for any DNS server serving the google.com domain (more on that domain: [Wayback/Archive] General DNS overview  |  Google Cloud).

Getting the list of DNS servers is similar to getting the list of MX servers which I explained in Getting the IP addresses of gmail MX servers, replacing MX record type (main exchange) with the NS record type (name server) and the gmail.com domain with the google.com domain:

# dig @8.8.8.8 +short NS google.com
ns3.google.com.
ns1.google.com.
ns2.google.com.
ns4.google.com.

The ns1.google.com DNS server is a special one of the NS servers: it is the start of authority server, which you can query using the SOA record type that also gives slightly more details for this server:

# dig @8.8.8.8 +short SOA google.com
ns1.google.com. dns-admin.google.com. 410477869 900 900 1800 60

The difference between using NS and SOA records with dig are explained in the [Wayback] dns – How do I find the authoritative name-server for a domain name? – Stack Overflow answer by [Wayback/Archive] bortzmeyer who also explains how to help figuring out SOA and NS discrepancies (note to self: check out the check_soa tool originally by Michael Fuhr (I could not find recent content of him, so he might have passed away) of which source code is now at [Wayback/Archive] Net-DNS/check_soa at master · NLnetLabs/Net-DNS).

So this works splendid as well using ns4.google.com on my test system:

# dig -4 TXT +short o-o.myaddr.l.google.com @ns4.google.com | xargs
80.100.143.119

The xargs removes outer quotes removal trick

[Wayback/Archive] string – Shell script – remove first and last quote (“) from a variable – Stack Overflow (thanks quite anonymous [Wayback/Archive] user1587520):

> echo '"quoted"' | xargs
quoted

xargs uses echo as the default command if no command is provided and strips quotes from the input.

More on https versus DNS requests

Some notes are in [Wayback/Archive] How to get public IP address from Linux shell, but note the telnet trick now fails as myip.gelma.net is gone (latest live version was archived in the Wayback Machine in august 2019).

Via

–jeroen

Posted in *nix, *nix-tools, Apple, bash, bash, Batch-Files, Communications Development, Development, DNS, Internet protocol suite, Linux, Mac, Mac OS X / OS X / MacOS, Power User, Scripting, Software Development, TCP | Leave a Comment »

On my reading list: Windows Console and PTY

Posted by jpluimers on 2022/10/25

With the rise of *nix tools and infrastructure on Windows (including, but certainly not limited to Visual Studio Code and Windows Subsystem for Linux), I need to get acquainted to the new ways these interface to the Windows Console.

Since Windows Console is from the (now obsolete) UCS-2 days, so it is not even fully Unicode aware, and has trouble with UTF-8, UTF-16.

So here are some links for my reading list:

–jeroen

Read the rest of this entry »

Posted in *nix, *nix-tools, CommandLine, ConPTY, Console (command prompt window), Development, Linux, Power User, Software Development, Windows, Windows 10, Windows 11, Windows Development, Windows Terminal, WSL Windows Subsystem for Linux | Leave a Comment »

Zypper: list info on all patterns, so you can find out which pattern provides a package

Posted by jpluimers on 2022/05/11

I wanted to know which pattern provides [WayBack] etckeeper which is in the [WayBack] openSUSE Software package etckeeper.

It seems no built-in search query can do that, so I built one my own.

Since the result takes quite a while to produce, the output is a pattern.txt that you can manually search.

This is the command:

zypper search -t pattern | grep "|" | tail -n +2 | perl -pe 's/^.*? \| //' | perl -pe 's/ *\| .*$//' | xargs -I {} sh -c "zypper info -t pattern {}" > patterns.txt

The content is like this (the 2017 date shows I wrote this a long time ago):

Read the rest of this entry »

Posted in *nix, *nix-tools, bash, bash, Development, etckeeper, Linux, Perl, Power User, Scripting, sed, Software Development | Leave a Comment »

Bash functions to encode and decode the ‘Basic’ HTTP Authentication Scheme

Posted by jpluimers on 2022/02/24

IoT devices still often use the ‘Basic’ HTTP Authentication Scheme for authorisation, see [Wayback] RFC7617: The ‘Basic’ HTTP Authentication Scheme (RFC ) and [Wayback] RFC2617: HTTP Authentication: Basic and Digest Access Authentication (RFC ).

Often this authentication is used even over http instead of over https, for instance the Egardia/Woonveilig alarm devices I wrote about yesterday at  Egardia/Woonveilig: some notes about logging on a local gateway to see more detailed information on the security system. This is contrary to guidance in:

  • RFC7617:
       This scheme is not considered to be a secure method of user
   authentication unless used in conjunction with some external secure
   system such as TLS (Transport Layer Security, [RFC5246]), as the
   user-id and password are passed over the network as cleartext.
  • RFC2617:
       "HTTP/1.0", includes the specification for a Basic Access
   Authentication scheme. This scheme is not considered to be a secure
   method of user authentication (unless used in conjunction with some
   external secure system such as SSL [5]), as the user name and
   password are passed over the network as cleartext.

Fiddling with those alarm devices, I wrote these two little bash functions (with a few notes) that work both on MacOS and in Linux:

# `base64 --decode` is platform neutral (as MacOS uses `-D` and Linux uses `-d`)
# `$1` is the encoded username:password
function decode_http_Basic_Authorization(){
  echo $1 | base64 --decode
  echo
}

# `base64` without parameters encodes
# `echo -n` does not output a new-line
# `$1` is the username; `$2` is the password
function encode_http_Basic_Authorization(){
  echo $1:$2 | base64
}

The first decodes the <credentials> from a Authorization: Basic <credentials> header into a username:password clean text followed by a newline.

The second one encodes a pair of username and password parameters into such a <credentials> string.

They are based on these initial posts that were not cross platform or explanatory:

  1. [Wayback] Decode HTTP Basic Access Authentication – Stack Pointer
  2. [Wayback] Create Authorization Basic Header | MJ’s Web Log

–jeroen

Posted in *nix, *nix-tools, Apple, Authentication, bash, bash, Communications Development, Development, HTTP, Internet protocol suite, Linux, Mac OS X / OS X / MacOS, Power User, Scripting, Security, Software Development, TCP, Web Development | Leave a Comment »

Viewing the last lines of the postfix log with journalctl (with help from Unix & Linux Stack Exchange)

Posted by jpluimers on 2022/02/24

Two command-lines I use to view my Postfix logs:

  1. journalctl --unit postfix --since "2 days ago"
  2. journalctl --unit postfix --pager-end

Note that neither of these work well with the --follow (or equivalent -f) option, as this will effectively disable the pager (which by default is less).

The second is via [Wayback] systemd – How to see the latest x lines from systemctl service log – Unix & Linux Stack Exchange (which got the--pagerend bit wrong, as it misses a dash and should be --pager-end, but still thanks [Wayback] Daniel Kmak):

Just:

journalctl -u SERVICE_NAME -e

Parameter -e stands for:

-e –pagerend

…

That’s the one ! Other answers will go through the whole log to get to its end, which can be veeeeery long for large syslogs.

The last bit (by [Wayback] Léo Germond, thanks!) is why I like it most.

Similarly, specifying --since in the first example will not go through the whole log.

Some background information:

Read the rest of this entry »

Posted in *nix, *nix-tools, bash, Development, journalctl and journald, Linux, postfix, Power User, Scripting, Software Development, systemd | Leave a Comment »

Creating a bootable USB installer for ESXi on other operating systems than Windows

Posted by jpluimers on 2022/02/17

I wrote about Creating a bootable USB installer for ESXi and use it to create a bootable ESXi installation.

Just in case I ever need to do this on a non-Windows system, some links:

–jeroen

Posted in *nix, Apple, ESXi6, ESXi6.5, ESXi6.7, ESXi7, Linux, Mac OS X / OS X / MacOS, Power User, Virtualization, VMware, VMware ESXi, Windows | Leave a Comment »

rsync backup of your ESXi box: How to make a statically linked rsync binary

Posted by jpluimers on 2022/02/09

As promised mid last year in “fixing” ESXi “rsync error: error allocating core memory buffers (code 22) at util2.c(106) [sender=3.1.2]”, I would follow up on building a static rsync for ESXi one day.

So below a few links on how to do this, roughly in the order I found them (most via [Wayback] vmware rsync “3.1.2” static – Google Search):

Especially the last link has a great set of steps on how to build manually.

Boy I forgot how long ago CentOS 3.9 was: [Wayback] [CentOS-announce] CentOS 3.9 is released for i386 and x86_64 Read the rest of this entry »

Posted in *nix, *nix-tools, CentOS, Development, Linux, Power User, RedHat, Software Development | 2 Comments »

Overriding some DNS entries for internal networks

Posted by jpluimers on 2022/01/27

Based on [Wayback] domain name system – Overriding some DNS entries in BIND for internal networks – Server Fault and some further reading, there seem to be two ways used in these scenarios:

I wonder how that would interact best with Pi-Hole based solutions. Would it be best to have your local network use the Pi-Hole server, then have the Pi-Hole server obtain the DNS information it cannot resolve through one of the above solutions? Or would other solutions work better?

So here are a few links:

Pi-Hole seems not interested in RPZ: [Wayback] Implement Response Zone Policies (NXDOMAIN) for end-user performance increase – Feature Requests / Implemented – Pi-hole Userspace

Pi-Hole default blacklist is mentioned in [Wayback/Archive.is] pi-hole/basic-install.sh at master · pi-hole/pi-hole (look for adlistFile which defaults to [Wayback/Archive.is] StevenBlack/hosts: 🔒 Consolidating and extending hosts files from several well-curated sources. Optionally pick extensions for porn, social media, and other categories.).

Since I need this for ESXi: [Wayback/Archive.is] Let’s Encrypt SSL for ESXi

–jeroen

Posted in *nix, *nix-tools, bind-named, DNS, Internet, Linux, Power User | Leave a Comment »

How to change system hostname in SUSE

Posted by jpluimers on 2022/01/21

The proper way is not manually changing /etc/hostname, but running this::

hostnamectl set-hostname host

[Wayback] How to change system hostname in SUSE

Background information in [Wayback] linux – What’s the point of the hostnamectl command? – Unix & Linux Stack Exchange (with a great answer by [Wayback] slm, edited by me for Wayback machine links):

Read the rest of this entry »

Posted in *nix, *nix-tools, Linux, openSuSE, Power User, SuSE Linux, Tumbleweed | Leave a Comment »

Kristian Köhntopp on Twitter: “Playing with a Ceph Storage Volume in a VM: The new openstack backend provisions an all-flash Ceph volume, which after tuning delivers a commit latency of around 1.1ms or so”

Posted by jpluimers on 2021/12/07

Not on an average VM (8 threads and 16gb memory) or network (100gbit), but ceph isn’t average solution.

For my link archive this long Twitter thread:

Archive.is Kristian Köhntopp on Twitter: “Playing with a Ceph Storage Volume in a VM: The new openstack backend provisions an all-flash Ceph volume, which after tuning delivers a commit latency of around 1.1ms or so. My dev VM has 8 Threads and 16 GB of memory, and mounts the Ceph Volume with XFS in /a.”

Hopefully this one day makes into a blog post at [Wayback] Die wunderbare Welt von Isotopp | Something old, something new, something borrowed, something blue.

–jeroen

Posted in *nix, *nix-tools, Linux, Power User, Storage | Leave a Comment »

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