Thursday, 18 April 2019

Uploading ISO's to storage domains in oVirt

oVirt currently doesn't allow you to upload ISO's over its web interface - you'll need to use the cli to do this.

If you wish to upload an ISO to an ISO storage domain you should issue you should issue:

engine-iso-uploader --iso-domain <storage-domain-name> upload <path-to-iso>

Wednesday, 10 April 2019

Tuesday, 9 April 2019

Preventing kernel modules from being loaded at the bootloader / grub in CentOS 7 / RHEL

Although this will typically done with the mod probe there are situations where the need to disable specific kernel modules before loading the kernel are necessary. One such situation is while I was installing a fresh instance of CentOS on an older server.

At the CentOS bootloader select the relevant entry and hit tab. You should now be able to edit the Linux kernel (vmlinuz) boot parameters.

Simply append:


and hit enter.

This should theoretically work on all modern kernels / distros - so is not just limited to CentOS / RHEL.


Saturday, 16 March 2019

Using yum to download a package and all it's associated dependencies

This tutorial will demonstrate how to do a download-only of a package and all of it's dependancies.

To elaborate - I recently installed Fedora 29 on a Macbook, but unfortunately there was no native support for the WLAN driver.

However it was available from RPMFusion - packaged under 'akmod-wl' - however downloading this and all of it's dependancies would have taken a long time - so instead we can use plugin for yum called 'yum-downloadonly':

yum install yum-downloadonly

We can then issue something like follows to download the required packages on a working computer which is running Fedora 29 (though ensure it is running exactly the same minor version as well!):

sudo yum install --downloadonly --downloaddir=/tmp akmod-wl

However this is not ideal largely due to the fact that it will download all required packages that the system needs. If some of these packages are already installed on the system they will be omitted.

So instead I came up with the idea of quickly building a jail with the basic packages to get yum up and running (this would mimic the newly installed OS):

mkdir -p /chroot/fedora29/var/lib/rpm

rpm --root /chroot/fedora29 --initdb

yumdownloader --destdir=/var/tmp fedora-release
cd /var/tmp
rpm --root /chroot/fedora29 -ivh --nodeps fedora-release*rpm

sudo yum install --installroot=/chroot/fedora29 --downloadonly --downloaddir=/tmp akmod-wl

Then copy everything from the temp folder onto the new workstation and issue:

rpm -i *

Friday, 15 March 2019

Generating a new UUID for XFS/EXT2/3/4 filesystems

Although very rare there will be circumstances were you encounter duplicate filesystem UUIDs.

Upon mounting one e.g.:

mount -t auto /dev/sdb1

mount: wrong fs type, bad option, bad superblock on /dev/sdb1

Tailing dmesg provides the clue as to what has gone wrong:

[ 1103.580854] XFS (xvdp1): Filesystem has duplicate UUID xxxxxx-yyyyyy-zzzzz-aaaa-bbbbbbbbbbb - can't mount

So we'll need to change the UUID of one of disks - to do this with an XFS filesystem we can use:

xfs_admin -U generate /dev/sdb1

and with the EXT family we can use:


<generated UUID>

tune2fs /dev/xvdp1 -U <generated UUID>

Finally attempt to remount:

mount -t auto /dev/sdb1

Tuesday, 12 March 2019

Checking switch port bandwidth utilisation with SNMP / Nagios

In order to monitor port bandwidth utilization on Cisco switches via SNMP we'll firstly need to install a plugin from the Nagios Exchange called 'iftraffic2':

Download and install the plugin:

cd /usr/local/nagios/libexec
curl -O check_iftraffic
chmod +x check_iftraffic

The usage for the plugin is as follows:

./check_iftraffic -H <hostname> -C <community-string> -r -i <interface-name> -b <interface-capacity> -u <interface-unit> -w <warning-limit-percentage> -c <critical-limit-percentage>

We'll need to obtain the interface name of the interface we wish to poll - we can use snmpwalk to do this for us:

yum -y install net-snmp-utils
snmpwalk -v 2c -c <community-string> <hostname>

> IF-MIB::ifDescr.67 = STRING: Port-channel1
> IF-MIB::ifDescr.68 = STRING: Port-channel2
> IF-MIB::ifDescr.69 = STRING: Port-channel3
> IF-MIB::ifDescr.70 = STRING: Port-channel4

Note: '' is the OID for interface descriptions - more information can be found here.

We'll also need the interface capacity:

snmpwalk -v 2c -c <community-string> <hostname>

> IF-MIB::ifSpeed.67 = Gauge32: 2000000000
> IF-MIB::ifSpeed.68 = Gauge32: 2000000000
> IF-MIB::ifSpeed.69 = Gauge32: 2000000000
> IF-MIB::ifSpeed.70 = Gauge32: 2000000000

Now note that the OID '' returns the interface capacity in bits per second - so we'll need to convert this to gigabits per second (as the plugin doesn't support bits per second) - so we do:

2000000000 / 1000000000 = 2 (Gigabits)

For this example we'll use 'Port-channel1' - so the plugin would be executed as follows:

./check_iftraffic -H <hostname> -C <community-string> -r -i Port-channel1 -b 2 -u g -w 70 -c 85

The -b switch specifies our 2 Gbps and the -u switch instructs the plugin that we are giving the measurements in Gigabits.

If successfull you should have something like the following:

> Total RX Bytes: 1000.00 MB, Total TX Bytes: 2000.00 MB<br>Average Traffic: 5.75 MB/s (2.2%) in, 1.48 MB/s (0.6%) out| inUsage=2.2,50,70 outUsage=0.6,50,70 inAbsolut=10000000 outAbsolut=20000000

Now we simply need to setup the respective command and service definitions in nagios e.g.:

### commands.conf

# check switch port bandwidth
define command{
    command_name check_bandwidth
    command_line /usr/local/nagios/libexec/check_iftraffic -H $HOSTADDRESS$ -C $ARG1$ -r -i $ARG2$ -b $ARG3$ -u g -w 50 -c 70

### switches.conf

define service{
    use generic-service
    host_name SWITCH-STACK
    service_description HHSVRSTK Uplink: Bandwidth Utilization
    check_command check_bandwidth!<community-string>!Port-channel1!2
    normal_check_interval 1
    retry_check_interval 1

Monday, 11 March 2019

Setup Nagios Core for SNMP traps with snmptrapd and snmptt

We'll firstly need to download and execute the installer script from

sudo yum -y install bzip2

cd /tmp
sh ./

This will install and setup snmptrapd and snmptt while ensuring the firewall is configured properly (udp/162 - however you may wish to lock this down further)

We'll then need to add our MIB's - for this example I'll be using a combination of SG200/300 switches and so will download the MIB's from:

In the commerical version of Nagios you can add these with ease through the GUI - however if you (like me) are using Core you'll need to use the addmib tool:

cd /tmp
cd MIBs_Sx200_v1.4.1.03
mkdir /usr/share/snmp/mibs/Cisco-SG200-300
mv *.mib /usr/share/snmp/mibs/Cisco-SG200-300

and add them with:

find /usr/share/snmp/mibs/Cisco-SG200-300 -maxdepth 1 -type f -exec addmib {} \;

We can now send a test trap with:

snmptrap -v 2c -c public localhost '' linkUp ifDescr s eth0 ifAdminStatus i 1 ifOperStatus i 1

You should now see this logged to /var/log/snmptt/snmpttunknown.log

However this wasn't the case for me - everything I was sending was being dropped / didn't show up in the snmptt log. After inspecting the service log for snmptrapd I quickly noticed the following warning:

Mar 11 14:51:33 host.internal snmptrapd[2752]: NET-SNMP version 5.7.2
Mar 11 14:51:33 host.internal systemd[1]: Started Simple Network Management Protocol (SNMP) Trap Daemon..
Mar 11 15:31:28 host.internal snmptrapd[2752]: No access configuration - dropping trap.
Mar 11 15:31:41 host.internal snmptrapd[2752]: No access configuration - dropping trap.

This behaviour is expected by default - as the snmptrapd team decided (wisely) to utilize authentication for incoming SNMP traps - however oddly this shouldn't have been an issue since the installer script from nagios added 'disableAuthorization yes' to '/etc/snmp/snmptrapd.conf' - however after reloading the service all was well - so I can only imagine the config had been added and the service did not reload / restart as intended.

tailing /var/log/snmptt/snmptt.log shows:

Mon Mar 11 16:03:56 2019 . Normal "Status Events" localhost - A linkUp trap signifies that the SNMP entity, acting in an eth0 up up

NOTE: Unknown MIB's will be sent to /var/log/snmptt/snmpttunknown.log

You'll also notice that in the nagios logs the following warning:

'Warning:  Passive check result was received for service 'SNMP Traps' on host 'localhost', but the service could not be found!'

So it looks like snmptt is successfully sending the information to nagios - however nagios does not know what to do with it!

We'll proceed by defining the service it's trying to submit data for:

define service {
  name SNMP Traps
  service_description SNMP Traps
  active_checks_enabled 1 ; Active service checks are enabled
  passive_checks_enabled 1 ; Passive service checks are enabled/accepted
  parallelize_check 1 ; Active service checks should be parallelized
  process_perf_data 0
  obsess_over_service 0 ; We should obsess over this service (if necessary)
  check_freshness 0 ; Default is to NOT check service 'freshness'
  notifications_enabled 1 ; Service notifications are enabled
  event_handler_enabled 1 ; Service event handler is enabled
  flap_detection_enabled 1 ; Flap detection is enabled
  process_perf_data 1 ; Process performance data
  retain_status_information 1 ;
  retain_nonstatus_information 1 ;
  check_command check-host-alive ;
  is_volatile 1
  check_period 24x7
  max_check_attempts 1
  normal_check_interval 1
  retry_check_interval 1
  notification_interval 120
  notification_period 24x7
  notification_options w,u,c,r
  contacts contact1,contact2
  register 0

define service {
  use SNMP Traps
  host_name localhost
  service_description TRAP
  check_interval 120

We can then test the serviced is working correctly with:

/usr/local/nagios/libexec/eventhandlers/submit_check_result localhost TRAP 2 "TESTING"

The changes should now be reflected on the nagios check status.

The next step is to load the relevant MIB files so we can translates the O.I.D's. In this tutorial we will be checking link status of a port so we'll need 'IF-MIB..txt' (which should come as part of the default installation - if not see here:

We'll proceed by generating the snmptt.conf with:

rm -rf /etc/snmp/snmptt.conf
snmpttconvertmib --in=/usr/share/snmp/mibs/IF-MIB.txt --out=/etc/snmp/snmptt.conf --exec='/usr/local/nagios/libexec/eventhandlers/submit_check_result $r TRAP 2'

Open up the snmptt.conf file and ensure that the EXEC line for EVENT 'linkUp' returns 0 opposed to '2' and leave EVENT 'linkDown' as it is.

and reload the service with:

sudo service snmptt reload

We can then test it with: snmptrap -v 2c -c public localhost '' linkDown ifDescr s fa0/1 ifAdminStatus i 0 ifOperStatus i 0

and then check it reverts with:

snmptrap -v 2c -c public localhost '' linkUp ifDescr s fa0/1 ifAdminStatus i 0 ifOperStatus i 0

Thursday, 7 March 2019

Setting up NPS / RADIUS for use with a Cisco 2960X

Below is a sample configuration to get up and running with Radius:

2960X Configuration

conf t
radius server <server-name>
address ipv4 <server-ip>
key <shared-secret>

aaa new-model # create new aaa model
aaa authentication login default group radius local-case # allow radius and local user authentication by default
aaa authorization exec default group radius local-case if-authenticated #  allow radius and local user authorisation by default

aaa accounting system default start-stop group radius # only account for radius

umasks: Ensuring httpd / apache is assigning the appropriate permissions on files / directories

I came across an issue the other day where the user httpd was running as was part of group that had been assigned permissions to the www root. Typically the user httpd runs under will be the owner of these files and directories and as a result will almost always have adequate permissions to read, write and execute. However in this case because it was part of a group instead the default umask setting of 022 was preventing the httpd user from writing to the files.

The umask can be worked out as follows - for example a umask of 002:

Directories: 777 - 002 = 775

Files: 666 - 002 = 664

i.e. the owner and group are able to read, write and execute directories and everyone else can only read and execute them. While the owner and group can write, write files and everyone else can only read them.

In order to apply these to httpd we can simply add the following line under the service stanza in /lib/systemd/system/httpd.service:

vim /lib/systemd/system/httpd.service

UMask = 0002

and finally ensure httpd is restarted with:

sudo systemctl daemon-reload
sudo systemctl httpd restart

Tuesday, 19 February 2019

Debugging with the puppet agent command

To enable debugging on a puppet agent you can issue:

puppet agent --test --noop --debug --trace

The above command does not actually carry out any changes - it only simulates what could have happened. Removing the '--noop' switch allows us to actually carry out those changes e.g.:

puppet agent --test --debug --trace

Tuesday, 5 February 2019

Creating your first Puppet module

This tutorial will be a quick demonstration of how to create, build and test a basic puppet module.

Firstly generate the puppet module with:

mkdir ~/workbench && cd ~/workbench

puppet module generate username-webmin --skip-interview

This will generate the following directory structure:

└── webmin (module directory)
    ├── examples
    │   └── init.pp (example of how to initailize the class)
    ├── Gemfile (used to describe dependancies needed for the module / Ruby)
    ├── manifests (holds the module manifests i.e. contains a set of instructions that need to be run)
    │   └── init.pp (the default manifest - it defines our main class: webmin)
    ├── metadata.json (contains module metadata like author, module description, dependancies etc.)
    ├── Rakefile (essentially a makefile for Ruby)
    ├── (contains module documentation)
    └── spec (used for automated testing - is optional)
        ├── classes
        │   └── init_spec.rb
        └── spec_helper.rb

If we do a cat on the init.pp within the examples directory:

cat examples/init.pp

include ::webmin

This include statement can be used in other manifests in Puppet and simply imports the webmin class.

In older modules you might have seen a params manifest (params.pp) - this design pattern has recently been replaced with the release of Hiera v5 with in-module data (

This means that we need to construct our Hiera hierarchy in the form of 'hiera.yaml' in our module. This will typically look like this:

cat webmin/hiera.yaml

version: 5

  datadir: 'data'
  data_hash: 'yaml_data'

  - name: 'Full Version'
    path: '%{}-%{facts.os.release.full}.yaml'

  - name: 'Major Version'
    path: '%{}-%{facts.os.release.major}.yaml'

  - name: 'Distribution Name'
    path: '%{}.yaml'

  - name: 'Operating System Family'
    path: '%{}-family.yaml'

  - name: 'common'
    path: 'common.yaml'

Note: It's important to keep in mind that the hierarchy is reusable e.g. avoid adding in specific networks or environments.

We'll also need to create our data directory to hold our yaml data in:

mkdir webmin/data
touch webmin/data/Debian-family.yaml
touch webmin/data/RedHat-family.yaml
touch webmin/data/common.yaml

For the sake of time and simplicity I have confined the yaml data to a few OS families.

As seen in the hierarchy anything defined within the 'Operating System Family' take presidense over anything in 'common'. However if this module were to be applied to say OpenSUSE only settings in common.yaml would be applied - so it's important to ensure that there are suitable defaults in common data.

We'll proceed by defining our variables within the init.pp (manifests directory):

class webmin (
  Boolean $install,
  Optional[Array[String]] $users,
  Optional[Integer[0, 65535]] $portnum,
  Optional[Stdlib::Absolutepath] $certificate,
  notify { 'Applying class webmin...': }

In the above class we are defining several variables that will allow the user to customise how the module configures webmin. As you'll notice three of them are optional - so if they are undefined we'll provide the defaults our self in the manifest.

At this point we might want to verify the syntax in our init.pp manifest is valid - we can do this with:

puppet parser validate webmin/manifests/init.pp

We will also create two more classes - one for setup / installation of webmin and the other for configuration of it:

touch /webmin/manifests/install.pp && touch /webmin/manifests/configure.pp

We'll declare these in our init.pp like follows:

class webmin (
  Boolean $install,
  String $webmin_package_name,
  Optional[Array[String]] $users,
  Optional[Integer[0, 65535]] $portnum,
  Optional[Stdlib::Absolutepath] $certificate,
  notify { 'Applying webmin class...': }

  contain webmin::install
  contain webmin::configure

  -> Class['::webmin::configure']


And then declare the classes:

cat /webmin/manifests/install.pp

# @summary
#   This class handles the webmin package.
# @api private
class webmin::install {

  if $webmin::install {

    package { $webmin::webmin_package_name:
      ensure => present,

    service { $webmin::webmin_package_name:
    ensure    => running,
    enable    => true,
    subscribe => Package[$webmin::webmin_package_name],




cat /webmin/manifests/configure.pp

# @summary
#   This class handles webmin configuration.
# @api private
class webmin::configure {



You'll notice that although we have defined variables in the parent class we have not actually defined what these will be yet. This is where Hiera will come in - so to data/common.yaml we add:

webmin::webmin_package_name: webmin
webmin::install: true
webmin::users: ~
webmin::portnum: 10000
webmin::certificate: ~

We'll also need to add repositories for webmin - as by default (to my knowledge at least) it's not included in any of the base repositories included with Redhat or Debian.

In order to configure repositories for particular operating systems we will need to use the yum and apt modules. Module dependencies are defined in the 'metadata.json' file - for example:

"dependencies": [
  { "name": "puppet/yum", "version_requirement": ">= 3.1.0" },
  { "name": "puppetlabs/apt", "version_requirement": ">= 6.1.0" },
  { "name": "puppetlabs/stdlib", "version_requirement": ">= 1.0.0" }

So your metadata.json would look something like:

  "name": "username-webmin",
  "version": "0.1.0",
  "author": "Joe Bloggs",
  "summary": "A module used to perform installation and configuration of webmin.",
  "license": "Apache-2.0",
  "source": "",
  "project_page": "",
  "issues_url": "",
  "dependencies": [
  { "name": "puppet/yum", "version_requirement": ">= 3.1.0" },
  { "name": "puppetlabs/apt", "version_requirement": ">= 6.1.0" },
  { "name": "puppetlabs/stdlib", "version_requirement": ">= 1.0.0" }
  "data_provider": null

Because we haven't packaged up the module yet we'll need to install the dependencies manually i.e.:

puppet module install puppetlabs/apt
puppet module install puppet/yum

We'll then need to copy them to our working directory (~/workbench) e.g.:

cp -R /etc/puppetlabs/code/environments/production/modules/{yum,apt,stdlib} ~/workbench

We'll use Hiera to configure the OS specific settings for the repositories:

cat webmin/data/RedHat-family.yaml

version: 5

    - 'webmin_repo'

        ensure: 'present'
        enabled: true
        descr: 'Webmin Software Repository'
        baseurl: ''
        mirrorlist: ''
        gpgcheck: true
        gpgkey: ''
        target: '/etc/yum.repos.d/webmin.repo'

cat webmin/data/Debian-family.yaml

version: 5

        location: ''
        release: 'stretch'
        repos: 'contrib'
        key: '1B24BE83'
        key_source: ''
        include_src: 'false'

Let's check everything looks good:

puppet parser validate manifests/*.pp

We'll now try and apply our manifests and see if they apply correctly:

puppet apply --modulepath=~/workbench webmin/tests/init.pp

With any luck you will now have webmin installed and should also see our notify messages we included earlier.

Finally we can publish the module with:

sudo puppet module build webmin-reloaded

We can now distribute this internally or alternatively upload it for public consumption at the Puppet Forge.

To test the built module you can run:

sudo puppet module install ~/Workbench/username-webmin-0.1.0.tar.gz

Wednesday, 30 January 2019

php-fpm Log Location (RHEL / PHP7)

More of a note to myself but php-fpm no longer appears to write logs a long with the web server's (at least not on 7.0.27 on RHEL.

The various logs are written to:


Friday, 25 January 2019

Linux: Server Not Syncing with NTP (Stuck in INIT state)

The service was confirmed running and set to start on boot:

sudo service ntpd status

Redirecting to /bin/systemctl status ntpd.service
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2019-01-25 12:11:16 GMT; 13min ago
  Process: 32649 ExecStart=/usr/sbin/ntpd -u ntp:ntp $OPTIONS (code=exited, status=0/SUCCESS)
 Main PID: 32650 (ntpd)
   CGroup: /system.slice/ntpd.service
           └─32650 /usr/sbin/ntpd -u ntp:ntp -g

We can quickly check if NTP is not properly synchronised with the 'ntpstat' command:

> ntpstat
  time server re-starting
   polling server every 8 s

We can also check the connection status of the ntp server with:

ntpq -p

     remote           refid      st t when poll reach   delay   offset  jitter
================================================   .INIT.          16 -    -  512    0    0.000    0.000   0.000
 ec2-52-53-178-2 .INIT.          16 -    -  512    0    0.000    0.000   0.000 .INIT.          16 -    -  512    0    0.000    0.000   0.000

From the above (specifically the INIT state) my immediate thought was that it was a firewall issue somewhere. 

It's worth checking the EC2 instance SG to ensure that the server can reach udp/123 outbound. However remember to also check the Network ACL (it's stateless) and ensure that udp/123 can get out as well.

ntpd was attempting to initiate a connection with the ntp servers however never got past this phase. After confirming the firewall rules, sg's, ACL's etc.  (i.e. 123/udp outbound and ensuring that session states were maintained) I decided to directly query one of the NTP servers with:

ntpdate -d

This was successful so it seemed something else was causing this.  

In the end I realised it was failing because ntpd was binding with localhost and was attempting to access the external NTP servers (obviously failing because they are unroutable from a loopback device!)


listen interface


listen interface

in /etc/ntp.conf  and restarting ntpd resolves the issue:

     remote           refid      st t when poll reach   delay   offset  jitter
===============================================   2 u   27   64    1   11.206   52.795   0.000      2 u   26   64    1   12.707   53.373   0.000
 ntp3.wirehive.n     2 u   25   64    1   14.334   53.125   0.000
 h37-220-20-12.h      2 u   24   64    1   19.211   53.350   0.000