16.08.2019

Linux: Configuring hosts per ssh in parallel: pssh

If you have to set up some hosts in a way, that a number of commands has to be executed on each node, than you should consider PSSH:

http://manpages.ubuntu.com/manpages/bionic/man1/parallel-ssh.1.html

The installation is straight forward:
root@zerberus:~# apt-get install pssh
Paketlisten werden gelesen... Fertig
Abhängigkeitsbaum wird aufgebaut.       
Statusinformationen werden eingelesen.... Fertig
Die folgenden Pakete wurden automatisch installiert und werden nicht mehr benötigt:
  btrfs-tools geoip-database-extra libcryptui0a libjs-openlayers seahorse-daemon
Verwenden Sie »apt autoremove«, um sie zu entfernen.
Die folgenden NEUEN Pakete werden installiert:
  pssh
0 aktualisiert, 1 neu installiert, 0 zu entfernen und 8 nicht aktualisiert.
Es müssen 29,0 kB an Archiven heruntergeladen werden.
Nach dieser Operation werden 135 kB Plattenplatz zusätzlich benutzt.
Holen:1 http://de.archive.ubuntu.com/ubuntu bionic/universe amd64 pssh all 2.3.1-1 [29,0 kB]
Es wurden 29,0 kB in 0 s geholt (71,0 kB/s).
Vormals nicht ausgewähltes Paket pssh wird gewählt.
(Lese Datenbank ... 488993 Dateien und Verzeichnisse sind derzeit installiert.)
Vorbereitung zum Entpacken von .../archives/pssh_2.3.1-1_all.deb ...
Entpacken von pssh (2.3.1-1) ...
pssh (2.3.1-1) wird eingerichtet ...
Trigger für man-db (2.8.3-2ubuntu0.1) werden verarbeitet ...
But executing on ubuntu is a little bit tricky:
If you want to do a test, you have to know, that ubuntu has renamed the binary to parallel-ssh. pssh is not known at commandline:

schroff@zerberus:~$ parallel-ssh -i -H "localhost 127.0.0.1" ls -l .bashrc
[1] 00:04:48 [SUCCESS] 127.0.0.1
-rw-r--r-- 1 schroff schroff 3815 Jul 14  2017 .bashrc
[2] 00:04:48 [SUCCESS] localhost
-rw-r--r-- 1 schroff schroff 3815 Jul 14  2017 .bashrc
Please note the syntax highlighting, which i found very helpful:

04.08.2019

Oracle VM Server: Why the server uuid is important and why changes to this uuid are critical

After working a while with Oracle VM server it turns out, that a very important parameter is the UUID of a Oracle VM server.

This UUID is used by the ovs-agent (take a look at the Oracle documentation). Here a few excerpts of these chapter:
The Oracle VM Agent is a daemon that runs within dom0 on each Oracle VM Server instance. Its primary role is to facilitate communication between Oracle VM Server and Oracle VM Manager.
[...]
Oracle VM Agent is responsible for carrying out all of the configuration changes required on an Oracle VM Server instance, in accordance with the messages that are sent to it by Oracle VM Manager.
[...]
If you wish to allow another Oracle VM Manager instance to take ownership of the server, the original Oracle VM Manager instance must release ownership first.
[...]
Oracle VM Agent also maintains its own log files on the Oracle VM Server that can be used for debugging issues on a particular server instance or for auditing purposes. 

The oracle vm server gets identified at the oracle vm manager by its UUID. There is a very nice blogposting from Bjorn Naessens:
https://bjornnaessens.wordpress.com/2012/08/10/best-practices-in-ovm-2-fakeuuid-it/
He made his way through the source code and comes up with the following important things about this uuid:


From an architectural point of view, this is a really bad way, because the UUID will change, if you change the motherboard SMBIOS oder change a network MAC.
With loosing your UUID, the OVS-agent will no longer communicate with your OVM-manager and therfore you can not start/stop any VM on that host.

You can get the UUID of a server from the OVM Manager GUI:
(--> "Servers and VMs": select the server on the tree under "server pools" --> change the dropdown to "info")

How to fix a UUID change can be found here:
https://hadafq8.wordpress.com/2016/03/22/oracleovmovm-server-uuid-challenges/

20.07.2019

Firefox on Linux: password field flickering / curser blinks...

After upgrading to firefox 68 i was not able to enter the password (and configuration password) field in online registrations.
The cursor in the password fields kept flickering/blinking and on some pages firefox completely freezes.
With other browsers this does not happen, but i wanted to stay with firefox.

The solution was starting firefox with an additional environment variable:

GTK_IM_MODULE=xim firefox