Android 4.2.2 how to set default install path to external SD card

You don't need root access to do this. All you need is to enable Developer Options and then enable USB debugging. Once this is done connect adb to your phone:

root@bender:~# adb shell

shell@android:/ $ pm get-install-location
0[auto]
shell@android:/ $ pm set-install-location 2
shell@android:/ $ pm get-install-location
2[external]
shell@android:/ $ logout

root@bender:~#

as you can see from pm help page:

pm get-install-location: returns the current install location.
    0 [auto]: Let system decide the best location
    1 [internal]: Install on internal device storage
    2 [external]: Install on external media

You need to set this value to 2

Jboss / Wildfly errors when accepting socket java.io.IOException: Bad file descriptor problem

Jboss/Wildfly random crashes under heavy load:

Symptoms:

Jboss/Wildfly crashes randomly with  java.io.IOException: Bad file descriptor. Undertow HTTp server does not restart but admin console and everything else is working and nothing in log files.

How to debug it:

Put this in your configuration file (standalone.xml for Wildfly)

        <logger category="org.xnio.nio">
        <level name="DEBUG"/>
        </logger>

The error:

2018-03-03 17:19:15,273 DEBUG [org.xnio.nio.tcp.server] (default Accept) Exception accepting request, closing server channel TCP server (NIO) <69a407dd>: java.io.IOException: Bad file descriptor
    at sun.nio.ch.IOUtil.configureBlocking(Native Method)
    at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:264)
    at org.xnio.nio.QueuedNioTcpServer.handleReady(QueuedNioTcpServer.java:477)
    at org.xnio.nio.QueuedNioTcpServerHandle.handleReady(QueuedNioTcpServerHandle.java:38)
    at org.xnio.nio.WorkerThread.run(WorkerThread.java:591)

What is the reason for that:

The reason is that you are probably running a BSD and the bug is in Java implementation of KQueueSelectorImpl.java in latest OpenJDK for BSD (openjdk-1.8.162 at the moment). This was tested on NetBSD 7.1.

Solution:

There is no solution at the moment. You need to move your Jboss/Wildfly to Linux. You can try changing default selector with java command line arguments (example is solution for Solaris):

java -Dxnio.nio.selector.provider=sun.nio.ch.PollSelectorProvider .......

At the moment the only solution to this is not to run it under BSD. Under Linux with EPollSelectorProvider everything works just fine.

How to filter 99.99% of ssh brute force attacks

Recently I've decided to experiment with ssh ciphers / key exchange algorithms to raise the security of my servers. This is the /etc/ssh/sshd_config I've got:

HostKey /etc/ssh/ssh_host_ed25519_key
Ciphers chacha20-poly1305@openssh.com
KexAlgorithms curve25519-sha256@libssh.org

If you don't have HostKey for Ed25519 generate it:

# ssh-keygen -t ed25519

You need to use recent version of ssh / pyTTY to be able to login to this server.
It seems that using only this Cipher/Kex filters all brute force scanners probably because they do not support it. I see only this kind of messages:

Feb 13 14:41:39 horizon9 sshd[22849]: SSH: Server;Ltype: Version;Remote: xxx.x.xx.xxx-53810;Protocol: 2.0;Client: libssh2_1.7.0
Feb 13 14:41:39 horizon9 sshd[22849]: fatal: ssh_dispatch_run_fatal: no matching cipher found [preauth]

More information about ciphers/algorithms read here:

https://cr.yp.to/ecdh.html#curve25519-paper
https://en.wikipedia.org/wiki/Salsa20
https://en.wikipedia.org/wiki/Poly1305