I became a Debian Developer

categories: blog, debian

Thanks to akira for the confetti to celebrate the occasion!

View Comments

simple email setup

categories: config, debian

I was unable to find a good place that describes how to create a simple self-hosted email setup. The most surprising discovery was, how much already works after:

apt-get install postfix dovecot-imapd

Right after having finished the installation I was able to receive email (but only in in /var/mail in mbox format) and send email (bot not from any other host). So while I expected a pretty complex setup, it turned out to boil down to just adjusting some configuration parameters.


The two interesting files to configure postfix are /etc/postfix/main.cf and /etc/postfix/master.cf. A commented version of the former exists in /usr/share/postfix/main.cf.dist. Alternatively, there is the ~600k word strong man page postconf(5). The latter file is documented in master(5).


I changed the following in my main.cf

@@ -37,3 +37,9 @@
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
+home_mailbox = Mail/
+smtpd_recipient_restrictions = permit_mynetworks reject_unauth_destination permit_sasl_authenticated
+smtpd_sasl_type = dovecot
+smtpd_sasl_path = private/auth
+smtp_helo_name = my.reverse.dns.name.com

At this point, also make sure that the parameters smtpd_tls_cert_file and smtpd_tls_key_file point to the right certificate and private key file. So either change these values or replace the content of /etc/ssl/certs/ssl-cert-snakeoil.pem and /etc/ssl/private/ssl-cert-snakeoil.key.

The home_mailbox parameter sets the default path for incoming mail. Since there is no leading slash, this puts mail into $HOME/Mail for each user. The trailing slash is important as it specifies ``qmail-style delivery'' which means maildir.

The default of the smtpd_recipient_restrictions parameter is permit_mynetworks reject_unauth_destination so this just adds the permit_sasl_authenticated option. This is necessary to allow users to send email when they successfully verified their login through dovecot. The dovecot login verification is activated through the smtpd_sasl_type and smtpd_sasl_path parameters.

I found it necessary to set the smtp_helo_name parameter to the reverse DNS of my server. This was necessary because many other email servers would only accept email from a server with a valid reverse DNS entry. My hosting provider charges USD 7.50 per month to change the default reverse DNS name, so the easy solution is, to instead just adjust the name announced in the SMTP helo.


The file master.cf is used to enable the submission service. The following diff just removes the comment character from the appropriate section.

@@ -13,12 +13,12 @@
#smtpd pass - - - - - smtpd
#dnsblog unix - - - - 0 dnsblog
#tlsproxy unix - - - - 0 tlsproxy
-#submission inet n - - - - smtpd
-# -o syslog_name=postfix/submission
-# -o smtpd_tls_security_level=encrypt
-# -o smtpd_sasl_auth_enable=yes
-# -o smtpd_client_restrictions=permit_sasl_authenticated,reject
-# -o milter_macro_daemon_name=ORIGINATING
+submission inet n - - - - smtpd
+ -o syslog_name=postfix/submission
+ -o smtpd_tls_security_level=encrypt
+ -o smtpd_sasl_auth_enable=yes
+ -o smtpd_client_restrictions=permit_sasl_authenticated,reject
+ -o milter_macro_daemon_name=ORIGINATING
#smtps inet n - - - - smtpd
# -o syslog_name=postfix/smtps
# -o smtpd_tls_wrappermode=yes


Since above configuration changes made postfix store email in a different location and format than the default, dovecot has to be informed about these changes as well. This is done in /etc/dovecot/conf.d/10-mail.conf. The second configuration change enables postfix to authenticate users through dovecot in /etc/dovecot/conf.d/10-master.conf. For SSL one should look into /etc/dovecot/conf.d/10-ssl.conf and either adapt the parameters ssl_cert and ssl_key or store the correct certificate and private key in /etc/dovecot/dovecot.pem and /etc/dovecot/private/dovecot.pem, respectively.

The dovecot-core package (which dovecot-imapd depends on) ships tons of documentation. The file /usr/share/doc/dovecot-core/dovecot/documentation.txt.gz gives an overview of what resources are available. The path /usr/share/doc/dovecot-core/dovecot/wiki contains a snapshot of the dovecot wiki at http://wiki2.dovecot.org/. The example configurations seem to be the same files as in /etc/ which are already well commented.


The following diff changes the default email location in /var/mail to a maildir in ~/Mail as configured for postfix above.

@@ -27,7 +27,7 @@
# <doc/wiki/MailLocation.txt>
-mail_location = mbox:~/mail:INBOX=/var/mail/%u
+mail_location = maildir:~/Mail

# If you need to set multiple mailbox locations or want to change default
# namespace settings, you can do it by defining namespace sections.


And this enables the authentication socket for postfix:

@@ -93,9 +93,11 @@

# Postfix smtp-auth
- #unix_listener /var/spool/postfix/private/auth {
- # mode = 0666
- #}
+ unix_listener /var/spool/postfix/private/auth {
+ mode = 0660
+ user = postfix
+ group = postfix
+ }

# Auth process is run as this user.
#user = $default_internal_user


Now Email will automatically put into the '~/Mail' directory of the receiver. So a user has to be created for whom one wants to receive mail...

$ adduser josch

...and any aliases for it to be configured in /etc/aliases.

@@ -1,2 +1,4 @@
-# See man 5 aliases for format
-postmaster: root
+root: josch
+postmaster: josch
+hostmaster: josch
+webmaster: josch

After editing /etc/aliases, the command

$ newaliases

has to be run. More can be read in the aliases(5) man page.

Finishing up

Everything is done and now postfix and dovecot have to be informed about the changes. There are many ways to do that. Either restart the services, reboot or just do:

$ postfix reload
$ doveadm reload


$ apt-get install postfix-policyd-spf-python


policy-spf_time_limit = 3600s


policy-spf unix - n n - - spawn user=nobody argv=/usr/bin/policyd-spf

DNS TXT record with value:

v=spf1 ip4: -all


debugLevel = 1 
defaultSeedOnly = 1

HELO_reject = SPF_Not_Pass
Mail_From_reject = Fail

PermError_reject = False
TempError_Defer = False

skip_addresses =,::ffff:,::1//128

FIXME: the skip_addresses field should also list all hosts that I get email forwarded from. For example if I get my josch@debian.org email forwarded to this server, then I should list the debian.org mail relay servers. A list of these can be found by doing:

ldapsearch -x -LLL -b dc=debian,dc=org -h db.debian.org 'purpose=mail relay' ipHostNumber

Otherwise, senders with an SPF record with only their own IP and a final -all will see their mail rejected by the server. This is because the email was forwarded by the debian.org relay but that IP was not in their SPF record.


$ apt-get install opendkim opendkim-tools
$ mkdir /etc/mail
$ cd /etc/mail
$ opendkim-genkey -t -s mail -d mister-muffin.de
$ cat mail.txt


Domain mister-muffin.de KeyFile /etc/mail/mail.private Selector mail Canonicalization relaxed/relaxed




milter_default_action = accept milter_protocol = 2 smtpd_milters = inet:localhost:8891 non_smtpd_milters = inet:localhost:8891

$ service opendkim restart
$ service postfix restart
View Comments

bootstrap.debian.net temporarily not updated

categories: debian

I'll be moving places twice within the next month and as I'm hosting the machine that generates the data, I'll temporarily suspend the bootstrap.debian.net service until maybe around September. Until then, bootstrap.debian.net will not be updated and retain the status as of 2014-07-28. Sorry if that causes any inconvenience. You can write to me if you need help with manually generating the data bootstrap.debian.net provided.

View Comments

botch updates

categories: debian

My last update about ongoing development of botch, the bootstrap/build ordering tool chain, was four months ago and about several incremental updates. This post will be of similar nature. The most interesting news is probably the additional data that bootstrap.debian.net now provides. This is listed in the next section. All subsequent sections then list the changes under the hood that made the additions to bootstrap.debian.net possible.


The bootstrap.debian.net service used to have botch as a git submodule but now runs botch from its Debian package. This at least proves that the botch Debian package is mature enough to do useful stuff with it. In addition to the bootstrapping results by architecture, bootstrap.debian.net now also hosts the following additional services:

Further improvements concern how dependency cycles are now presented in the html overviews. While before, vertices in a cycle where separated by commas as if they were simple package lists, vertices are now connected by unicode arrows. Dashed arrows indicate build dependencies while solid arrows indicate builds-from relationships. For what it's worth, installation set vertices now contain their installation set in their title attribute.

Debian package

Botch has long depended on features of an unreleased version of dose3 which in turn depended on an unrelease version of libcudf. Both projects have recently made new releases so that I was now able to drop the dose3 git submodule and rely on the host system's dose3 version instead. This also made it possible to create a Debian package of botch which currently sits at Debian mentors. Writing the package also finally made me create a usable install target in the Makefile as well as adding stubs for the manpages of the 44 applications that botch currently ships. The actual content of these manpages still has to be written. The only documentation botch currently ships in the botch-doc package is an offline version of the wiki on gitorious. The new page ExamplesGraphs even includes pictures.


By default, botch analyzes the native bootstrapping phase. That is, assume that the initial set of Essential:yes and build-essential packages magically exists and find out how to bootstrap the rest from there through native compilation. But part of the bootstrapping problem is also to create the set of Essential:yes and build-essential packages from nothing via cross compilation. Botch is unable to analyze the cross phase because too many packages cannot satisfy their crossbuild dependencies due to multiarch conflicts. This problem is only about the dependency metadata and not about whether a given source package actually crosscompiles fine in practice.

Helmut Grohne has done great work with rebootstrap which is regularly run by jenkins.debian.net. He convinced me that we need an overview of what packages are blocking the analysis of the cross case and that it was useful to have a crossbuild order even if that was a fake order just to have a rough overview of the current situation in Debian Sid.

I wrote a couple of scripts which would run dose-builddebcheck on a repository, analyze which packages fail to satisfy their crossbuild dependencies and why, fix those cases by adjusting package metadata accordingly and repeat until all relevant source packages satisfy their crossbuild dependencies. The result of this can then be used to identify the packages that need to be modified as well as to generate a crossbuild order.

The fixes to the metadata are done in an automatic fashion and do not necessarily reflect the real fix that would solve the problem. Nevertheless, I ended up agreeing that it is better to have a slightly wrong overview than no overview at all.

Minimizing the dependency graph size

Installation sets in the dependency graph are calculated independent from each other. If two binary packages provide A, then dependencies on A in different installation sets might choose different binary packages as providers of A. The same holds for disjunctive dependencies. If a package depends on A | C and another package depends on C | A then there is no coordination to choose C so to minimize the overall amount of vertices in the graph. I implemented two methods to minimize the impact of cases where the dependency solver has multiple options to satisfy a dependency through Provides and dependency disjunctions.

The first method is inspired by Helmut Grohne. An algorithm goes through all disjunctive binary dependencies and removes all virtual packages, leaving only real packages. Of the remaining real packages, the first one is selected. For build dependencies, the algorithm drops all but the first package in every disjunction. This is also what sbuild does. Unfortunately this solution produces an unsatisfiable dependency situation in most cases. This is because oftentimes it is necessary to select the virtual disjunctive dependency because of a conflict relationship introduced by another package.

The second method involves aspcud, a cudf solver which can optimize a solution by a criteria. This solution is based on an idea by Pietro Abate who implemented the basis for this idea back in 2012. In contrast to a usual cudf problem, binary packages now also depend on the source packages they build from. If we now ask aspcud to find an installation set for one of the base source packages (I chose src:build-essential) then it will return an installation set that includes source packages. As an optimization criteria the number of source packages in the installation set is minimized. This solution would be flawless if there were no conflicts between binary packages. Due to conflicts not all binary packages that must be coinstallable for this strategy to work can be coinstalled. The quick and dirty solution is to remove all conflicts before passing the cudf universe to aspcud. But this also means that the solution does sometimes not work in practice.

Test cases

Botch now finally has a test target in its Makefile. The test target tests two code paths of the native.sh script and the cross.sh script. Running these two scripts covers testing most parts of botch. Given that I did lots of refactoring in the past weeks, the test cases greatly helped to assure that I didnt break anything in the process.

I also added autopkgtests to the Debian packaging which test the same things as the test target but naturally run the installed version of botch instead. The autopkgtests were a great help in weeding out some lasts bugs which made botch depend on being executed from its source directory.

Python 3

Reading the suggestions in the Debian python policy I evaluated the possibility to use Python 3 for the Python scripts in botch. While I was at it I added transparent decompression for gzip, bz2 and xz based on the file magic, replaced python-apt with python-debian because of bug#748922 and added argparse argument parsing to all scripts.

Unfortunately I had to find out that Python 3 support does not yet seem to be possible for botch for the following reasons:

  • no soap module for Python 3 in Debian (needed for bts access)
  • hash randomization is turned on by default in Python 3 and therefore the graph output of networkx is not deterministic anymore (bug#749710)

Thus I settled for changing the code such that it would be compatible with Python 2 as well as with Python 3. Because of the changed string handling and sys.stdout properties in Python 3 this proved to be tricky. On the other hand this showed me bugs in my code where I was wrongly relying on deterministic dictionary key traversal.

View Comments

botch updates

categories: debian

My last update about ongoing development of botch, the bootstrap/build ordering tool chain, was three months ago with the announcement of bootstrap.debian.net. Since then a number of things happened, so I thought an update was due.

New graphs for port metrics

By default, a dependency graph is created by arbitrarily choosing an installation set for binary package installation or source package compilation. Installation set vertices and source vertices are connected according to this arbitrary selection.

Niels Thykier approached me at Debconf13 about the possibility of using this graph to create a metric which would be able to tell for each source package, how many other source packages would become uncompilable or how many binary packages would become uninstallable, if that source package was removed from the archive. This could help deciding about the importance of packages. More about this can be found at the thread on debian-devel.

For botch, this meant that two new graph graphs can now be generated. Instead of picking an arbitrary installation set for compiling a source package or installing a binary package, botch can now create a minimum graph which is created by letting dose3 calculate strong dependencies and a maximum graph by using the dependency closure.

Build profile syntax in dpkg

With dpkg 1.17.2 we now have experimental build profile support in unstable. The syntax which ended up being added was:

Build-Depends: large (>= 1.0), small <!profile.stage1>

But until packages with that syntax can hit the archive, a few more tools need to understand the syntax. The patch we have for sbuild is very simple because sbuild relies on libdpkg for dependency parsing.

We have a patch for apt too, but we have to rebase it for the current apt version and have to adapt it so that it works exactly like the functionality dpkg implements. But before we can do that we have to decide how to handle mixed positive and negative qualifiers or whether to remove this feature altogether because it causes too much confusion. The relevant thread on debian-dpkg starts here.

Update to latest dose3 git

Botch heavily depends on libdose3 and unfortunately requires features which are only available in the current git HEAD. The latest version packaged in Debian is 3.1.3 from October 2012. Unfortunately the current dose3 git HEAD also relies on unreleased features from libcudf. On top of that, the GraphML output of the latest ocamlgraph version (1.8.3) is also broken and only fixed in the git. For now everything is set up as git submodules but this is the major blocker preventing any packaging of botch as a Debian package. Hopefully new releases will be done soon for all involved components.

Writing and reading GraphML

Botch is a collection of several utilities which are connected together in a shell script. The advantage of this is, that one does not need to understand or hack the OCaml code to use botch for different purposes. In theory it also allows to insert 3rd party tools into a pipe to further modify the data. Until recently this ability was seriously hampered by the fact that many botch tools communicated with each other through marshaled OCaml binary files which prevent everything which is not written in OCaml from modifying them. The data that was passed around like this were the dependency graphs and I initially implemented it like that because I didnt want to write a GraphML parser.

I now ended up writing an xmlm based GraphML parser so as of now, botch only reads and writes ASCII text files in XML (for the graphs) and in rfc822 packages format (for Packages and Sources files) which can both easily be modified by 3rd party tools. The ./tools directory contains many Python scripts using the networkx module to modify GraphML and the apt_pkg module to modify rfc822 files.

Splitting of tools

To further increase the ability to modify program execution without having to know OCaml, I split up some big tools into multiple smaller ones. Some of the smaller tools are now even written in Python which is probably much more hackable for the general crowd. I converted those tools to Python which did not need any dose3 functionality and which were simple enough so that writing them didnt take much time. I could convert more tools but that might introduce bugs and takes time which I currently dont have much of (who does?).

Gzip instead of bz2

Since around January 14, snapshot.debian.org doesnt offer bzip2 compressed Packages and Sources files anymore but uses xz instead. This is awesome for must purposes but unfortunately I had to discover that there exist no OCaml bindings for libxz. Thus, botch is now using gzip instead of bz2 until either myself or anybody else finds some time to write a libxz OCaml binding.

Self hosting Fedora

Paul Wise made me aware of Harald Hoyer's attempts to bootstrap Fedora. I reproduced his steps for the Debian dependency graph and it turns out that they are a little bit bigger. I'm exchanging emails with Harald Hoyer because it might not be too hard to use botch for rpm based distributions as well because dose3 supports rpm.

The article also made me aware of the tred tool which is part of graphviz and allows to calculate the transitive reduction of a graph. This can help making horrible situations much better.

Dose3 bugs

I planned to generate such simplified graphs for the neighborhood of each source package on bootstrap.debian.net but then binutils stopped building binutils-gold and instead provided binutils-gold while libc6-dev breaks binutils-gold (<< 2.20.1-11). This unfortunately triggered a dose3 bug and thus bootstrap.debian.net will not generate any new results until this is fixed in dose3.

Another dose3 bug affects packages which Conflicts/Replaces/Provides:bar while bar is fully virtual and are Multi-Arch:same. Binaries of different architecture with this property can currently not be co-installed with dose3. Unfortunately linux-libc-dev has this property and thus botch cannot be used to analyze cross builds until that bug is fixed in dose3.

I hope I get some free time soon to be able to look at these dose3 issues myself.

More documentation

Since I started to like the current set of tools and how they work together I ended up writing over 2600 words of documentation in the past few days.

You can start setting up and running botch by reading the first steps and get more detailed information by reading about the 28 tools that botch makes use of as of now.

All existing articles, thesis and talks are linked from the wiki home.

View Comments
« Older Entries -- Newer Entries »