Stuff I'm Up To

Technical Ramblings

apt-get Hash Sum Mismatch #2 — January 16, 2019

apt-get Hash Sum Mismatch #2

I’m still not sure why I’m getting this problem occur again. But when running apt-get upgrade the upgrades fail with a message like this:

Get:8 stretch/updates/main amd64 libudev1 amd64 232-25+deb9u8 [125 kB]
Err:8 stretch/updates/main amd64 libudev1 amd64 232-25+deb9u8
Hash Sum mismatch
Hashes of expected file:
SHA1:6590379bbc85f8d90c05a1b32cd27dac49431b7a [weak]
MD5Sum:40ace91d2e4c633f89d1571b3022dcdd [weak]
Filesize:125364 [weak]
Hashes of received file:
SHA1:7c501c7b49f4fe93d78309f5b5c635f1db487989 [weak]
MD5Sum:9b8faa999b5db9581ef0df62f697e4df [weak]
Filesize:877368 [weak]
Last modification reported: Sat, 08 Dec 2018 08:05:18 +0000

To resolve it I resorted to bypassing any caching and use apt to pull the update and upgrade:

$ sudo apt -o Acquire::https::No-Cache=True -o Acquire::http::No-Cache=True update
$ sudo apt -o Acquire::https::No-Cache=True -o Acquire::http::No-Cache=True upgrade
Laravel 5.5 HMR and Windows — January 15, 2019

Laravel 5.5 HMR and Windows

Using HMR in Chrome on Linux is faultless, but on Windows HMR fails to start in the browser.

Looking at the entries in the bowsers script tags they seem a bit goofy. There’s leading slashes and spaces before the script filename.

It seems this is a popular issue. We hunted around for quite a few pointers to resolve this.

The only thing we changed was line 90 of Entry.js to add on the extra replace(/^\//, ''); A restart of yarn hot and a browser refresh and we were good to go. HMR and WDS show in the Chrome console as expected and changes to code are now dynamic.

Public Key from Private Key — January 3, 2019

Public Key from Private Key

I fall over this every so often. I have the private key file but would either have to trawl servers for authorized_keys files to get the public password or remember how to obtain the public key from the private key.

Time to document it here so I don’t have to hunt for it with Google again.

For an RSA PEM format public key

$ openssl rsa -in private.key -pubout

-----END PUBLIC KEY-----

For an SSH putty friendly version

$ ssh-keygen -y -f private.key

php 7.0 on Debian Buster — January 2, 2019

php 7.0 on Debian Buster

Actually this is more about any version of php (5.6, 7.0, 7.1, 7.2) on buster. Php source has taken on a bit of a split and the standard repositories only deal with the one supported version for the current release of Debian you are using.

This means that on Debian 9 (buster/sid) the only version available from the Debian repository is php 7.3.

Our current production systems are Debian 9 stretch and only support php 7.0 and therefore only Laravel 5.5. In order to bring my development platform down to php 7.0 I must use a non-standard repository.

Ondřej Surý has been packaging php for Debian and Ubuntu and distributing them. To get them you need to add his key and repository into your aptitude:

$ wget -q -O- | sudo apt-key add -
$ echo "deb stretch main" | sudo tee /etc/apt/sources.list.d/php.list

Now you can add in whatever version of php you’d like even 5.6. eg.

$ sudo apt-get install php7.0-fpm php7.0-mbstring php7.0-zip php7.0-mysql php7.0-sqlite3 php7.0-dev php-pear

If you already had 7.3 installed nothing will have changed yet and when you type php from the command line you’ll see it still runs version 7.3.

$ php -v

PHP 7.3.0-2+0~20181217092659.24+stretch~1.gbp54e52f (cli) (built: Dec 17 2018 09:26:59) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.0-dev, Copyright (c) 1998-2018 Zend Technologies
with Zend OPcache v7.3.0-2+0~20181217092659.24+stretch~1.gbp54e52f, Copyright (c) 1999-2018, by Zend Technologies

To switch back to 7.0 use the following and you’ll see your php go back to 7.0. Switch back in the same way, but replace 7.0 with 7.3.

$ sudo update-alternatives --set php /usr/bin/php7.0

update-alternatives: using /usr/bin/php7.0 to provide /usr/bin/php (php) in manual mode
$ php -v

PHP 7.0.33-1+0~20181208203126.8+stretch~1.gbp2ff763 (cli) (built: Dec 8 2018 20:31:26) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
with Zend OPcache v7.0.33-1+0~20181208203126.8+stretch~1.gbp2ff763, Copyright (c) 1999-2017, by Zend Technologies

Damn that Proxy! — December 12, 2018

Damn that Proxy!

In Windows when you run into an application that doesn’t use proxy settings and doesn’t look at the environmental variable,  IE or netsh settings, then you’re kind of stuck when you must send web traffic through a proxy.

That was until we discovered proxycap.

Proxy cap is a very flexible solution that can add specific rules for various requirements. It will then intercept matching traffic and direct it to the proxy without the application even realising there is a proxy.

The example we based this on is the application Bluestacks, not being able to proxy. When we Goggled a solution we came up with posts about using proxycap. We could then add in rules only for the programs bluestacks.exe and hd-player.exe using https to be intercepted and Bluestacks would then work – even though it knew nothing about proxies.

Proxycap seems very clever in that it seems to just modify the Windows firewall to make the magic happen. It’s very flexible in that you could even set different apps to use different proxies. It also supports authentication.

It’s a commercial product, but sometimes you just have to pay the price.

Cross Origin Resource Sharing and Content Security Policy — December 4, 2018

Cross Origin Resource Sharing and Content Security Policy

Got to love having a vendor carrying out half a job… again.

Having installed a new VMWare Horizon environment for Windows 10, I thought we’d at least have Blast available via HTML  – which we don’t currently have in our Windows 7 Horizon setup.

During the install I setup a load balancer which only really handles the authentication process. This worked fine using IE or Edge, at which point I guess the vendor decided that’s enough testing and it’s considered functional. After they left I fired up my Chrome browser and found it didn’t work. So I tried Firefox with the same non-functional result.

Checking the console log in Firefox I see:

Content Security Policy: The page's settings blocked the loading of a resource at wss:// ("default-src").

A trawl of VMWare documentation results in:

Now all I have to do is translate that to Nginx so I can put that into the config.

Editing my ssl/snippets.conf file and changing the CSP header, I added the missing parts for wss: and blob: to end up with:

add_header Content-Security-Policy "default-src 'self' wss:; script-src 'self' 'unsafe-inline' 'unsafe-eval'; img-src 'self'; style-src 'self' 'unsafe-inline'; font-src 'self'; frame-src https://horizon.domain.tld blob:; object-src 'none' blob:; connect-src 'self' wss:; child-src 'self' blob:;";

A reload of Nginx and a refresh/reload on the browser and I’m into the Horizon Desktop!


VMWare Horizon Load Balancing — November 21, 2018

VMWare Horizon Load Balancing

We’re in the process of installing a new Horizon 7 infrastructure  and as part of the process the vendor added load balancers all over the place. I asked with question of why not use an Open Source solution for that?

My go to web server, proxy, load balancer is Nginx and as we already have a HA pair setup I thought we’d try to use that – even if it meant putting in a new one dedicated to the task in the longer term.

As the plan is to use a load balancer in front of the connection servers and the only tunnelling that will take place will be for external systems, our requirement will be to LB the https traffic (TCP 443) for the authentication. The PCoIP/Blast traffic will be directed straight to the ESX Host/client.

The previous document on load balancing with Nginx means I only need to add in the config needed for horizon. By using the same syncing of config it immediately becomes available on the secondary load balancer.

I created a new config file /etc/nginx/sites-available/horizon and then as standard, symbolic link it to sites-enabled to make it live.

upstream connectionservers {
server {
listen 443 ssl;
server_name horizon.domain.tld;
location ~ / {
proxy_pass https://connectionservers;

This adds our two connection servers into an upstream group called connectionservers which I then point the  proxy_pass  directive to.

The ip_hash directive ensures we have session stickiness based on the clients IP address. When a client connects they’ll stay directed to the connection server they were given until and unless the connection server becomes unavailable.


Within the nginx.conf ensure you have the reverse proxy options set in the http {} section:

enable reverse proxy
proxy_redirect off;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwared-For $proxy_add_x_forwarded_for;
client_max_body_size 10m;
client_body_buffer_size 128k;
client_header_buffer_size 64k;
proxy_connect_timeout 90;
proxy_send_timeout 90;
proxy_read_timeout 90;
proxy_buffer_size 16k;
proxy_buffers 32 16k;
proxy_busy_buffers_size 64k;

The SSL configuration on the HA pair is standard throughout all of our servers that it “proxies” for. We have a wildcard certificate and the HA proxies only services under *.domain.tld – our horizon.domain.tld fits this pattern so no changes necessary.

All the standard Nginx SSL related security settings for certificate, stapling, ciphers, HSTS are located in our /etc/nginx/snippets/ssl.conf file and is included in the nginx.conf using:

include snippets/ssl.conf


ssl_certificate /etc/ssl/certs/wildcard.pem;
ssl_certificate_key /etc/ssl/private/wildcard_key.cer;
ssl_dhparam /etc/ssl/private/dhparam.pem;

add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
ssl_session_timeout 1d;
ssl_session_cache shared:SSL:50m;
ssl_session_tickets off;

# modern configuration. tweak to your needs.
ssl_protocols TLSv1.2;
ssl_prefer_server_ciphers on;

# OCSP Stapling ---
# fetch OCSP records from URL in ssl_certificate and cache them
ssl_stapling on;
ssl_stapling_verify on;

add_header X-Content-Type-Options nosniff;
add_header Accept "*";
add_header Access-Control-Allow-Methods "GET, POST, PUT";
add_header Access-Control-Expose-Headers "Authorization";
add_header X-Frame-Options SAMEORIGIN;
add_header X-XSS-Protection "1; mode=block";

proxy_cookie_path / "/; HTTPOnly; Secure";

Note: Depending on your requirements for other system you may need to include content security policy settings to satisfy CORS (Cross Origin Resource Sharing). In fact you MUST do this to allow Chrome and Firefox to work with Blast over HTML.

In our PCoIP client we add the new server as horizon.domain.tld and we get through the authentication and on to the selection of the available pools. So clearly the load balancing is doing the job. You can check the /var/log/nginx/access.log to confirm.

If you miss out the ip_hash directive for session stickiness you’ll find you can’t get past the authentication stage.

Syncing Config Files Between Servers —

Syncing Config Files Between Servers

Having setup a pair of load balancers I wanted to ensure the Nginx configuration from one system was replicated to the secondary where changes were made on the primary.

In this instance my weapon of choice is lsyncd. It seems quite old, but stable. It’s a layer over rsync and ssh that monitors a directory for changes and copies them over ssh to a target server.

Getting it working is pretty straight forward once you crack the configuration.

Install it using:

$ sudo apt-get install lsyncd

Then you’ll need to create the config file:

$ sudo mkdir /etc/lsyncd
$ sudo mkdir /var/log/lsyncd
$ sudo vi /etc/lsyncd/lsyncd.conf.lua

This is what my final config looked like:

settings {
  logfile = "/var/log/lsyncd/lsyncd.log",
  statusFile = "/var/log/lsyncd/lsyncd.status"

sync {
  source = "/etc/nginx",
  host = "loadbal02.domain.local",
  targetdir = "/etc/nginx";

Outside of this config I needed to setup an ssh key for the root user from loadbal01 to logon to loadbal02. When you generate the key DO NOT specify a password for the key, or the process wont work.

$ sudo ssh-keygen
$ sudo cat /root/.ssh/

Then I copy the output and paste it into /root/.ssh/authorized_keys on loadbal02. Many ways of doing this scp, copy/paste, etc.

Then just to ensure it works by connecting at least once to the target host as root using ssh.

$ sudo ssh root@loadbal02.domain.local

This will ask you to trust and save the hosts id in the ~/.ssh/known_hosts file so it will be trusted in future. Make sure you connect to EXACTLY the same host name as you are putting into the config file eg. “loadbal02.domain.local” as the host id for “loadbal02″does not match the FQDN and you will get a service error like this:

recursive startup rsync: /root/sync/ -> loadbal02.domain.local:/root/sync/
Host key verification failed.

Start the service using:

$ sudo systemctl start lsyncd

and monitor the status and log file to make sure it’s doing what you expect.

$ sudo cat /var/log/lsyncd/lsyncd.status 

Lsyncd status report at Tue Nov 20 15:33:21 2018
Sync1 source=/etc/nginx/
There are 0 delays
Inotify watching 7 directories
1: /etc/nginx/
2: /etc/nginx/sites-available/
3: /etc/nginx/modules-available/
4: /etc/nginx/modules-enabled/
5: /etc/nginx/sites-enabled/
6: /etc/nginx/conf.d/
7: /etc/nginx/snippets/

Restarting Nginx on the Secondary

After the files have copied, you need to tell Nginx on the secondary that the config has changed. Then it needs to reload the config so it’s running as up to date as the primary.

For this I use inotify-tools by installing them on loadbal02:

$ sudo apt-get install inotify-tools

Next I created a shell script that monitors the config and reloads the service.

I created a file called /usr/sbin/ and set it as executable.

$ sudo touch /usr/sbin/
$ sudo chmod 700 /usr/sbin/
$ sudo vi /usr/sbin/

This is the content of my script:

while true; do
inotifywait -q -e modify -e close_write -e delete -r /etc/nginx/
systemctl reload nginx

It monitors the /etc/nginx/ folder (-r recursively) and any event like modify, close_write or delete will cause the script to continue and reload nginx, then loop around to wait for any more changes.

Next I made sure my script ran every time the server rebooted using crond.

$ sudo crontab -e

Added in a line to run the script at reboot:

@reboot /bin/bash /usr/sbin/

That’s it. Following a reboot the script runs happily. To monitor it you can look at the nginx error log (/var/log/nginx/error.log). This will show a process started event like:

2018/11/21 09:16:57 [notice] 736#736: signal process started

The only downside of this would be if I spanner the config on primary the service reload on the secondary will fail. eg.

2018/11/21 09:25:20 [emerg] 1819#1819: unknown directive "banana" in /etc/nginx/nginx.conf:1

This isn’t such a concern unless the primary happens to fail whilst you’re editing it. The most important part is:

Test your config before you reload the primary server!

$ sudo nginx -t
nginx: [emerg] unknown directive "banana" in /etc/nginx/nginx.conf:1
nginx: configuration file /etc/nginx/nginx.conf test failed

Then fix any issues before doing a systemctl reload.

Laravel Routing Returns 302 Redirect — November 20, 2018

Laravel Routing Returns 302 Redirect

That was a frustrating few hours. I added a route into my api.php route and every time I visited it it triggered a redirect. I saw nothing in the browser and it was like my controller function wasn’t even being called.

I put the usual dd() and dump() into my function and it wasn’t being called. I even changed the function name so it didn’t exist and thought I’d get an error message, but nothing – still a redirect.

What is going on? I expanded out the call from “Namespace\Class@function” to put in a function () {} and that was being called and ran ok.

Clearly there was something wrong with my class somewhere. The other functions within it worked fine, just this new one didn’t even seem to be there.

Sure enough a bit of Duck-Jitsu and I found this: – answer 3 is where I got my clue.

I looked at my class constructor and I was using the auth middleware to ensure the functions were not used unless authenticated.

public function __construct() {

For my function I wasn’t using any authentication, so of course I was getting a redirect. But because it’s an api call and the expected return in JSON under an XHttpResponse I wasn’t able to properly debug it. I was getting back a HTML page instead.

As a work around all I needed to do was add in an exception for my function:

public function __construct() {
  $this->middleware(['auth:api'], ['except' => [ 'myFunction' ]]);

Now all I have to do is go back and sort out the authentication for the function so I don’t need to bypass it.

Debian Upgrading from an ISO File — November 7, 2018

Debian Upgrading from an ISO File

Kind of an unusual situation, but I have a Debian jessie box that has a terrible <2MB Internet connection, no CD/DVD and the USB stick I have I don’t want to overwrite and make bootable – it already has things on it I need. But it does have the capacity to hold the Debian DVD ISO #1.

How do you upgrade Debian from an ISO without being bootable?

Mount the USB Sick

First mount the USB Drive into your stretch environment so you can use the ISO it contains. You may want to check the output of dmesg to see what device name your stick has been given.

$ sudo mkdir /mnt/usb
$ sudo mount /dev/sdb1 /mnt/usb

Now we can see the ISO in the /mnt/usb folder

$ sudo ls -lh /mnt/usb

total 12G
-r-------- 2 root root 3.4G Nov 7 11:25 debian-9.5.0-amd64-DVD-1.iso

Mount the ISO

We can then mount the ISO into another folder under /mnt

$ sudo mkdir /mnt/iso

$ sudo mount -t iso9660 -o loop /mnt/usb/debian-9.5.0-amd64-DVD-1.iso /mnt/iso

We have a mounted ISO

$ sudo ls -lh /mnt/iso

total 1.5M
-r--r--r-- 1 root root 146 Jul 14 11:27 autorun.inf
dr-xr-xr-x 1 root root 2.0K Jul 14 11:27 boot

Edit Your Installation Sources

Next we edit the file /etc/apt/sources.list so it only contains the path to our ISO to install from. Take a copy of the original one or just comment out the existing lines.

deb file:///mnt/iso stretch main contrib

You may also want to check any source list files under sources.list.d and move them out whilst you upgrade.

Carry Out the Upgrade

Just continue as you normally would using upgrade/dist-upgrade to deliver your new OS. Making sure you do an update first so you read your news sources file.

$ sudo apt-get update

$ sudo apt-get upgrade

$ sudo apt-get dist-upgrade

Because you’re not getting the install from the internet and apt isn’t able to trust the source, you will have to accept to install the upgrades by ignoring the security warning.

When you’re done make sure you uncomment/put back the sources.list to point at the internet and replace the version with the new one eg. change jessie to stretch.

Java Decompiler — November 6, 2018

Java Decompiler

Today I’ve been working on a problem where properties being loaded into our CRM system from a GIS DTF file are doing some strange updates. It appears that the vendor in their wisdom has decided to populate user defined fields that we already use!

The Loader is written in Java, I have a .jar file and can extract the .class files, but they’re all compiled.

A bit of searching reveals an online decompiler I can use:

I started using it to decompile one .class file at a time and quickly became bored. So tried the whole .jar file. It happily decompiled the file and returned a single zip file containing the decompiled .class files as .javafiles.

Now I can scan the .java files to find out what other SQL calls they are making to fill other fields we might be using.

DBeaver – SQL GUI —

DBeaver – SQL GUI

I’ve used a few SQL GUI’s over the years, SQuirreL, DBVisualizer, HeidiSQL, MySQL Workbench, but the one that stands out recently is DBeaver.

It’s got a community and enterprise edition. The community does everything I need and connects to all the SQL servers we use, Microsoft SQL, MySQL, Postgres/PostGIS.

Being Java based it’s cross platform, so you can use it in Windows too.