[Short Tip] Workaround MIT-SHM error when starting QT/KDE apps with SUDO

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Starting GUI programs as root usually is not a problem. In worst case, sudo inside a terminal should do the trick.

However, recently I had to start a QT application as sudo from within GNOME. It was the yubikey configuration GUI, a third party tool thus not part of any desktop environment. Executing the app failed, it only showed a gray window and multiple errors in the command line:

$ sudo /usr/bin/yubikey-personalization-gui 
X Error: BadAccess (attempt to access private resource denied) 10
  Extension:    130 (MIT-SHM)
  Minor opcode: 1 (X_ShmAttach)
  Resource id:  0x142
X Error: BadShmSeg (invalid shared segment parameter) 128
  Extension:    130 (MIT-SHM)
  Minor opcode: 5 (X_ShmCreatePixmap)
  Resource id:  0xfa
X Error: BadDrawable (invalid Pixmap or Window parameter) 9
  Major opcode: 62 (X_CopyArea)
  Resource id:  0x2800015

Workarounds like pkexec and adding a policykit rule didn’t help, either. The error indicates that there is a problem with the MIT Shared Memory Extension of X.

A good workaround is to deactivate the usage of the extension on command line:

$ sudo QT_X11_NO_MITSHM=1 /usr/bin/yubikey-personalization-gui

It works like a charm.

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[Short Tip] Splitting and merging PDF files

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I recently had to modify quite a stack of PDF files. Many of them where scanned documents, and sometimes I only needed certain pages, or had to re-arrange parts of some files in new documents. A set of handy tools to perform such low level tasks quick and easy comes along in the package poppler-utils. The package is available via the default package managers on Fedora, RHEL/CentOS, Ubuntu, Debian and others.

The command pdfseparate can be used to extract certain pages of large PDFs – in this example all pages from the third up to the fifth are separated into single page PDFs:

$ pdfseparate -f 3 -l 5 Scanned-Document.pdf Separated%d.pdf
$ ls
Scanned-Document.pdf  Separated3.pdf  Separated4.pdf  Separated5.pdf

If you want to combine for example the fifth and the third page in that order in one single, new PDF you can use pdfunite:

$ pdfunite Separated5.pdf Separated3.pdf NewDocument.pdf

Note that there is usually no output on the shell as long as everything works out fine. You can check the results with the PDF viewer of your choice, like Okular on KDE or Evince on Gnome.

[Howto] Using D-BUS to query status information from NetworkManager (or others)

920839987_135ba34fffMost of the current Linux installations rely on the inter process communication framework D-Bus. D-Bbus can be used to gather quite some information about the system – however the usage can be a bit troublesome. This howto sheds some light on the usage of D-Bus by the example of querying the NetworkManagaer interface.

Background

D-BUS enables tools and programs to talk to each other. For example tools like NetworkManager, systemd or firewalld all provide methods and information via D-Bus to query their information and change their configuration or trigger some specific behavior. And of course all these operations can also be performed on the command line. This can be handy in case you want to include it in some bash scripts or for example in your monitoring setup. It also helps understanding the basic principles behind D-Bus in case you want to use it in more complex scripts and programs.

First steps: qdbus

For this example I use qdbus which is shipped with Qt. There are corresponding tools like gdbus and others available in case you don’t want to install qt on your machine for whatever reason.

When you first launch qdbus it shows you a list of strange names which roughly remind you of the apps currently running on your desktop/user session. The point is that you are asking your own user environment – but in case of NetworkManager or other system tools you need to query the system D-Bus:

$ qdbus --system
...
 org.freedesktop.NetworkManager
...

This outputs show a list of all available services, or better said, interfaces. You can connect to these and can get a list of the objects the have:

$ qdbus --system org.freedesktop.NetworkManager
...
/org
/org/freedesktop
/org/freedesktop/NetworkManager
/org/freedesktop/NetworkManager/AccessPoint
/org/freedesktop/NetworkManager/AccessPoint/0
...

Each object has a path which identifies, well, the path to the object. That’s how you call it and everything which is connected to it.

Querying objects

Now that we have a list of objects, we can check which members belong to an object. Members can be actions which can be triggered, or information about a current state, signals, etc. – when we have access to the members things get interesting. In this case we query the object NetworkManager itself, not one of its sub-objects:

$ qdbus --system org.freedesktop.NetworkManager /org/freedesktop/NetworkManager
...
method QDBusVariant org.freedesktop.DBus.Properties.Get(QString interface, QString propname)
method QVariantMap org.freedesktop.DBus.Properties.GetAll(QString interface)
...
property read QList<QDBusObjectPath> org.freedesktop.NetworkManager.ActiveConnections
...

The output shows a list of various members. In the above given code snippet I highlighted the methods to get information – and a property which is called org.freedesktop.NetworkManager.ActiveConnections. Guess what, that property holds the information of the current active connections (there can be more than one!) of the NetworkManager. And we can ask this information (using the --literal because otherwise the output is not possible):

$ qdbus --system --literal org.freedesktop.NetworkManager /org/freedesktop/NetworkManager org.freedesktop.DBus.Properties.Get org.freedesktop.NetworkManager ActiveConnections
[Variant: [Argument: ao {[ObjectPath: /org/freedesktop/NetworkManager/ActiveConnection/0]}]]

Please note that as arguments we gave not the entire property as a whole, but we separated at the last dot. Formally we asked for the content of the property ActiveConnections at the interface org.freedesktop.NetworkManager. The interface and the property are merged in the output, but the query always needs to have them separated by a space. I’m not sure why…
But well, now we know that our active connection is actually a NetworkManager object with the path given above. We can again query that object to get a list of all members:

$ qdbus --system --literal org.freedesktop.NetworkManager /org/freedesktop/NetworkManager/ActiveConnection/0
...
method QDBusVariant org.freedesktop.DBus.Properties.Get(QString interface, QString propname)
...
property read QDBusObjectPath org.freedesktop.NetworkManager.Connection.Active.Ip4Config
...

There is again a member to get properties – and the interesting property again is an object path:

$ qdbus --system --literal org.freedesktop.NetworkManager /org/freedesktop/NetworkManager/ActiveConnection/0 org.freedesktop.DBus.Properties.Get org.freedesktop.NetworkManager.Connection.Active Ip4Config
[Variant: [ObjectPath: /org/freedesktop/NetworkManager/IP4Config/1]]

We query again that given object path and see rather promising members:

$ qdbus --system --literal org.freedesktop.NetworkManager /org/freedesktop/NetworkManager/IP4Config/1
property read QDBusRawType::aau org.freedesktop.NetworkManager.IP4Config.Addresses
property read QStringList org.freedesktop.NetworkManager.IP4Config.Domains
property read QString org.freedesktop.NetworkManager.IP4Config.Gateway
...

And indeed: if we now query these members, we get for example the current Gateway:

$ qdbus --system --literal org.freedesktop.NetworkManager /org/freedesktop/NetworkManager/IP4Config/1 org.freedesktop.DBus.Properties.Get org.freedesktop.NetworkManager.IP4Config Gateway
[Variant(QString): "192.168.178.1"]

That’s it. Now you know the gateway I have configured right now. If you do not want to query each member individually, you can simply call all given members of an interface:

$ qdbus --system --literal org.freedesktop.NetworkManager /org/freedesktop/NetworkManager/IP4Config/1 org.freedesktop.DBus.Properties.GetAll org.freedesktop.NetworkManager.IP4Config|sed 's/, /\n/g'
[Argument: a{sv} {"Gateway" = [Variant(QString): "192.168.178.1"]
"Addresses" = [Variant: [Argument: aau {[Argument: au {565356736
24
28485824}]}]]
"Routes" = [Variant: [Argument: aau {}]]
"Nameservers" = [Variant: [Argument: au {28485824}]]
"Domains" = [Variant(QStringList): {"example.com"}]
"Searches" = [Variant(QStringList): {}]
"WinsServers" = [Variant: [Argument: au {}]]}]

As you see the ipv4 addresses are encoded in reverse decimal notation. I am sure there is reason for that. A good one. Surely. But well, that’s just a stupid encoding problem, nothing else. In the end, the queries worked: the current gateway was successfully identified via D-Bus.

Methods: calling panic mode in firewalld

As mentioned above there are also methods which influence the behavior of an application. One simple example I came across is to kill all networking by calling the firewalld panic mode. For that you need the interface org.fedoraproject.FirewallD1, the object /org/fedoraproject/FirewallD1 and the method org.fedoraproject.FirewallD1.enablePanicMode:

$ qdbus --system --literal org.fedoraproject.FirewallD1 /org/fedoraproject/FirewallD1 org.fedoraproject.FirewallD1.enablePanicMode
[]

And your internet connection is gone. It comes back by disabling the panic mode again:

$ qdbus --system --literal org.fedoraproject.FirewallD1 /org/fedoraproject/FirewallD1 org.fedoraproject.FirewallD1.disablePanicMode
[]

Rights

You should also be aware that there is a rights management embedded in D-Bus – not every user is allowed to do anything. For example, as a normal user you cannot simply query all configured chains. If you call the following method:

$ qdbus --system --literal org.fedoraproject.FirewallD1 /org/fedoraproject/FirewallD1 org.fedoraproject.FirewallD1.direct.getAllChains
[Argument: a(sss) {}]

you are greeted with a password dialog before the command is executed.

Summary

D-Bus is used for inter process communication and thus can help when various programs are supposed to work together. It can also used on the shell to query information or to call specific methods as long as they are provided via the D-Bus interface. That might come in handy – some applications have rather strange ways to provide data or procedures via their user interfaces, and D-Bus offers a very generic way to interact without the need to respect any user interfaces.

Short Tip: Fix input/output error while creating LVM backed VMs with libvirt

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Today I run into a strange error where I was not able anymore to create new VMs with virt-manager: I always got an input/output error when I tried to start the machine after installation.

A look into /var/log/syslog showed quite some errors on the dm-device – note that my VMs disks usually are on logical volumes.

Sep 12 15:27:55 example kernel: [19298.163712] device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception.
Sep 12 15:27:55 example kernel: [19298.243980] Buffer I/O error on device dm-5, logical block 1081985
Sep 12 15:27:55 example kernel: [19298.243983] lost page write due to I/O error on dm-5
Sep 12 15:27:55 example kernel: [19298.243994] Buffer I/O error on device dm-5, logical block 1081986
Sep 12 15:27:55 example kernel: [19298.243994] lost page write due to I/O error on dm-5

The fix is pretty easy: when you create the disk and thus the LV for the virtual machine, make sure you tell virt-manager that it should allocate the entire disk right from the start. It looks like sparse LV images are not supported right now.

[Howto] Installing Owncloud News, a self hosted RSS reader

two_glossy_cloudsOwncloud News, a RSS news reader for the self hosting cloud service Owncloud, is available in an Alpha version. That comes right at the time Google Reader is bound to see its end soon.

I must admit that I do not understand why Google decided to shut down the Google Reader service. Social media with their unstructured news areas are nice, but no match to a well structured news feed full of read and unread news. But, there are replacements, and one pretty wise choice would be to not depend on yet another web service, but to host it yourself.

In comes Owncloud: it can already host your addresses, calendars, files and musik and can be integrated with your desktop as well. Now a RSS reader app, Owncloud News was released as an Alpha version, and indeed already looks promising:

Owncloud-Reader-General

The installation is pretty smooth as well. The requirements are a running Owncloud 5 version, so 4.5 won’t do it. The installation itself basically consists of two steps: installing and activating the so called App Framework, which is supposed to be the foundation for other Owncloud apps in the future, and afterwards installing the news app itself:

# cd /var/www
# git clone https://github.com/owncloud/appframework.git
Cloning into 'appframework'...
[...]
# git clone https://github.com/owncloud/news.git
Cloning into 'news'...
[...]

I choose /var/www here because it is recommended in the manual and because there the appropriate user has the necessary access rights. But it could be any dir, since you only link the plugins anyway:

# ln -s /var/www/appframework /var/www/owncloud/apps
# ln -s /var/www/news /var/www/owncloud/apps

Speaking about rights, make sure the web server can write cache files:

# sudo chown -R www-data:www-data /var/www/news/cache

Afterwards, login to your owncloud, and active the plugins: first the framework, followed by the actual application. Add feeds, play around, as you will see it works pretty nice.

What is still missing right now is an Android news reader which could sync with the server. When that is available as well, Owncloud News might become *the* Google Reader descendant.

Pass – A perfect shell based password manager

920839987_135ba34fffPass is a tool to store and manage passwords and other data securely and on command line – even with built in support for Git and remote Git repositories. Thus it is a welcomed alternative for existing password managers which often require a GUI, or do not provide repository support.

What it is

Pass is a shell based password manager to store passwords and login data – or anything you want, actually. The name “the standard unix password manager” however is pretty misleading: the author wanted to stress that it only uses standard Unix tools, but failed to highlight that with a catchy name and instead just created confusion.

But the author is right with his main point: pass is in fact just gluing together already well known and tested Unix tools: the encryption of all information is ensured by GPG, passwords are queried using gpg-agent, the version control and remote repository support is done by Git, and the tool itself is written in shell code. Thus you have features you can rely on – in fact, if you want you can directly access the Git repository and the Gnupg files, you do not have to use Pass at all.

Pass stores information in simple files, which can be grouped in folders. While the main idea of Pass is to store one password in one file you can actually access each file with editors to store as many information in it as you want. Each file is encrypted with the gpg key which was defined during the initial setup of Pass. As a result the Pass database is nothing else but a folder full of other folders and gpg encrypted files:

$ ls -1 $HOME/.password-store
business
commerce
financial
$ ls -1 $HOME/.password-store/business/
linkedin.com.gpg
example.com.gpg
important.com.gpg

Pass is included in all major distributions like Fedora, Ubuntu, Debian, and so on, and thus can be installed with the usual package management tools.

How it works

If you call Pass without any further options, it just outputs the content of its password store:

$ pass
Password Store
|-- business
|   |-- linkedin.com
|   |-- example.com
|   `-- important.com
|-- commerce
|   `-- amazon
|-- financial
|   |-- badbank.com
|   `-- mybank.com

The file type ending “gpg” is not shown here to not confuse users (I guess).

Showing the content of a file is straight forward:

$ pass business/example.com
login:  example
pass:   password

Adding new entries can be done with the command pass insert $FOLDER/$FILENAME. But it might be more convenient to just use the default editor to edit a new file: pass edit $FOLDER/$FILENAME. That way multi line information can be added more easily.

However, the real strength of Pass is that after each change – like adding a new password – git-add and git-commit are called: the new file is automatically committed to a local git repository:

$ pass edit business/example.com
[master 4c09c76] Added password for business/example.com using /usr/bin/vim.
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 business/example.com.gpg

As a result all changes are automatically under version control and can be reverted. But it gets better: Pass forwards arbitrary options and commands to Git itself. Thus it is possible to access the full functionality of Git – and to push the files to an online repository:

$ pass git push
Counting objects: 6, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (4/4), done.
Writing objects: 100% (4/4), 823 bytes, done.
Total 4 (delta 1), reused 0 (delta 0)
To git@example.net:pass
   aa2aff7..2011296  master -> master

That way the password store can be shared with any remote Git repository – and thus can be re-used by other clients, given that they have the proper GPG key.

Missing pieces

As shown above Pass is almost perfect if you need a way to manage passwords (or any other data at all) on command line level, including repository and encryption support.

But while Pass replaced all my other password managers literally in a few minutes there is still one big feature I miss: the support for GUI tools! It would be nice if Pass support could be included in the major Desktop Environments and major GUI programs used in the Linux desktop world:

  • KDE’s Kwallet
  • Gnome’s Keyring
  • Android
  • Firefox
  • Chrome/Chromium

To summarize it: Pass is great, but would be even better if it could server as a backend for the usual GUI tools and desktop environments. There is already an experimental iOS client, so there is at least hope for an Android client…