28. June 2018

How to install .NET Core 2.1 on Linux Mint 18.3 Sylvia

Default instructions for installation of .NET Core 2.1 do not contain instructions how to install the technology on Linux Mint.

You may have a temptation to go with Ubuntu instructions, but you’ll end up in troubles with installing libicu60 or libicu57.

The instructions compatible with Linux Mint 18.3 Sylvia are instructions for Linux Debian 8 (not 9).

Commands for repository configuration:

wget -qO- https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor > microsoft.asc.gpg
sudo mv microsoft.asc.gpg /etc/apt/trusted.gpg.d/
wget -q https://packages.microsoft.com/config/debian/8/prod.list
sudo mv prod.list /etc/apt/sources.list.d/microsoft-prod.list
sudo chown root:root /etc/apt/trusted.gpg.d/microsoft.asc.gpg
sudo chown root:root /etc/apt/sources.list.d/microsoft-prod.list

Commands for installation:

sudo apt-get update
sudo apt-get install dotnet-sdk-2.1

Just for the record, the content of /etc/apt/sources.list.d/microsoft-prod.list is:

deb [arch=amd64] https://packages.microsoft.com/debian/8/prod jessie main

24. July 2014

couriertls: /etc/courier/esmtpd.pem: error:0906D06C:PEM routines:PEM_read_bio:no start line

After upgrade of Linux distribution Courier stopped to accept emails delivered over TLS or SSL.

There was just nice error message in the log file:

couriertls: /etc/courier/esmtpd.pem: error:0906D06C:PEM routines:PEM_read_bio:no start line

Long story short. The problem was in pem file.

Previous versions of Courier-SSL were able to read files with Windows EOL. The new version is failing with this nice error.

Solution is simple: get rid of Windos EOL.

You can use e.g. dos2unix

dos2unix esmptd.pem

Restart services and everything will work :)

22. March 2014

Kivy – buildozer android debug failed with libstdc++.so.6: cannot open shared object file

Kivy is awesome library for developing GUI applications in Python.

It’s possible to build same application for desktop, Android or iOS. It’s something like Cordova/PhoneGap for JavaScript.

I was following Kivy crash course 2: Building an android apk tutorial recorded by Alexander Taylor.

I was trying to build application on Linux Debian for Android:

buildozer android debug

Build failed with quite strange message:

[mergemanifest] Manifest merger disabled. Using project manifest only.
     [echo] Handling aidl files...
     [aidl] Found 1 AIDL files.
     [aidl] Compiling 1 AIDL files.
     [aidl] /home/georgik/.buildozer/android/platform/android-sdk-21/platform-tools/aidl: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory

BUILD FAILED

assets/private.mp3: /home/georgik/idea/kivytest/.buildozer/android/app/sitecustomize.pyo
Traceback (most recent call last):
  File "build.py", line 431, in 
    make_package(args)
  File "build.py", line 346, in make_package
    subprocess.check_call([ANT, arg])
  File "/usr/lib/python2.7/subprocess.py", line 540, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['ant', 'debug']' returned non-zero exit status 1

The reason of this problem is not so obvious.

My operating system is 64bit, but Android build system requires 32 bit version of stdc++ library.

Fix is very easy. Just install lib32stdc++6 package :-)

apt-get install lib32stdc++6

If build is still failing, because of other missing libraries, then you can use online Debian package search to find missing dependencies: https://www.debian.org/distrib/packages

Other missing 32bit libraries are often libz, libncurses5:

apt-get install lib32z1 lib32ncurses5

17. December 2013

Debian – upgrade from Apache 2.2 to 2.4 – Starting web server: apache2 failed!

Debian maintainers changed default Apache from version 2.2 to 2.4. Not a big deal?

I was just upgrading one package and it had dependency on whole new Apache. I said yes to upgrade, because I had no bigger issues with Apache upgrade in past.

Wohoo. This upgrade was very funny, because Apache 2.4 was not able to start due to conflicting configurations. The coolest part was that Subversion stopped working, but that’s different story.

The problematic part was that Apache failed to start with nice message:

[FAIL] Starting web server: apache2 failed!
[warn] The apache2 instance did not start within 20 seconds. Please read the log files to discover problems ... (warning)

I checked the log file /var/log/apache2/error.log, but there was no hint what went wrong.

Apache was working even though startup script reported error. :-)

After a while I found that there were some important changes in /etc/apache2/apache2.conf. I compared this file with /etc/apache2/apache2.conf.dpkg.dist.

It was necessary to update following lines in apache2.conf:

Mutex file:${APACHE_LOCK_DIR} default
PidFile ${APACHE_PID_FILE}
#LockFile /var/lock/apache2/accept.lock - disable this, old value

Then it was possible to start Apache without problem:

[ ok ] Restarting web server: apache2.

10. March 2012

Tomcat 7 listen on port 80 – Linux Debian

The default installation of Tomcat 7 for Linux Debian is listening on port 8080.

When you want to change the port to 80 then you have several options.

You can use iptables and redirect communication from port 8080 to port 80.

iptables -t nat -P PREROUTING -p tcp -m tcp --dport 80 -j REDIRECT --to-port 8080

The more straight forward approach is to bind Tomcat directly to port 80. First of all change port 8080 to 80 in file /etc/tomcat7/server.xml.

You’ll see error messages in /var/log/tomcat7/catalina.out when you try to restart Tomcat:

SEVERE: Failed to initialize connector [Connector[HTTP/1.1-80]]
org.apache.catalina.LifecycleException: Failed to initialize component [Connector[HTTP/1.1-80]]
Caused by: java.net.BindException: Permission denied

The problem is that default installation of Tomcat 7 for Linux Debian allows to bind only ports higher than 1023. You need to allow binding to privileged ports.

Open file /etc/defaults/tomcat7 and change option from:

#AUTHBIND=no

to:

AUTHBIND=yes

Restart Tomcat and it will listen on port 80.