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Amateur Radio

FCC Investigating Whether Cuban Government Is Jamming HAM Radio

https://www.vice.com/en/article/y3dxzg/fcc-investigating-whether-cuban-government-is-jamming-ham-radio

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Projects

Waiting for warmer weather

Waiting for warmer weather to continue working on the Mitsubishi MT372 tractor.

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Projects

Mitsubishi MT372 Diesel Mini Tractor

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Computers Home Improvement Information Technology

2012 WAP Install

My 2012 wireless access point installation. Used the existing doorbell wiring to pull CAT5e to the switch in the basement. Doorbell works and everything looks tidy.

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Beekeeping Gardening

BEES!!!

My mountain mint brings all the bees to the yard.

Honey bee on mountain mint

Honey bee on mountain mint

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Amateur Radio Home Improvement

Pulleys for G5RV antenna

I bought two of these pulleys for my G5RV antenna. Nylon cord comes from the antenna’s insulators and is tied to a brick on each side. This allows the antenna to move with the wind or a tree limb.

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Information Technology

SSH/SFTP Rsync backups done with chroot

Rsync

Rsync, for those who aren’t familiar, is a file copy tool, which, after the first copy, will only send changes during subsequent updates. This makes it a very efficient tool, especially when used over an internet connection.

Anyway, to enable rsync from server A to server B, it is common to perform the login via key. This means that on Server A you’d generate a SSH keypair for your backup user, then copy the public key that was generated into the ~/.ssh/authorized_keys file for your backup user on Server B.

Because rsync is going to be executed automatically via cron script, it is necessary to create the key file without a password.

Jail

  • Configure your SSH server
    • Open up /etc/ssh/sshd_config
    • At the end of the file, tell SSH to create a chroot jail for your backup user:
      ChrootDirectory %h
      AllowTcpForwarding no
      PermitTunnel no
      X11Forwarding no

      Note, because of the way chroot works, you’ll need to make sure the chroot directory is owned by ROOT, even if it’s actually the home directory of your backup user.

  • Save, and restart your SSH server.

This gets you part of the way, you should now be able to SSH/SFTP into Server B using your backup user, and when connected, you will be restricted to the location set in ChrootDirectory.

Unfortunately, rsync needs more than this, and in order to copy files it’ll need access to the shell (I’m assuming bash), as well as the rsync application itself, together with whatever libraries are required.

Therefore, it becomes necessary to create a partial chroot image in the backup user’s chroot directory. You could do this the traditional way (e.g. by using something like debootstrap), which will create a mirror of your base operating system files in the chroot jail. However, this generally takes a few hundred megabytes at least, and if all you want is to copy some files, you don’t want to give access to more than you need.

Instead, I opt to create a skeleton chroot jail by hand.

The goal here is to mirror the filesystem of your server inside the chroot jail, so that if a file exists in /foo/bar, then you need to copy it to /home/backup-user/foo/bar, and make sure it’s owned by root.

  • Copy bash from /bin/bash to the directory /home/backup-user/bin/
  • Copy rsync (on my system this was in /usr/bin)
  • Next, you need to copy the symbolic link libraries to which these files are linked against. You can use the tool ldd to interrogate the executable and get a list of files to copy, e.g:
    root@server-b:/home/backup-user# ldd /bin/bash
        linux-vdso.so.1 =>  (0x00007fff52bff000)
        libtinfo.so.5 => /lib/x86_64-linux-gnu/libtinfo.so.5 (0x00007f412810a000)
        libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f4127f06000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f4127b79000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f4128340000)

    Copy the files which have directories into the appropriate locations, e.g./lib/x86_64-linux-gnu/libtinfo.so.5 should go into/home/backup-user/lib/x86_64-linux-gnu/

  • Do the same for /usr/bin/rsync
Categories
Computers Gallery: Tech Junk

Android Apps – August 2015

Here are the Android Apps I regularly use as of August 2015.

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Home Improvement

Electric Earwig

A few weeks ago our downstairs heat pump failed. Cause? An earwig fell (or crawled?) into the space between the contacts on the 24 volt relay that send 240 volts AC to the heat pump. When it was zapped, it became stuck to the relay contact until cleaned.

Earwig on 24v relay

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Information Technology

xrdp (Remote Desktop) on Lubuntu 14.04

Updated February 6, 2016!

To use Microsoft’s Remote Desktop to connect to a Lubuntu 14.04 machine, use xrdp. xrdp uses vnc4server to spin up LXDE sessions on your Lubuntu machine.

To begin, install xrdp:

sudo apt-get install xrdp

If you try connecting to your machine, you’re going to get a grey desktop. xrdp is trying to use the command “startx” to start a window manager. On Lubuntu, this will not work. You need xrdp to use the command “lxsession”.

To make this change, you need to edit /home/[your_username]/.xsession:

nano /home/[your_username]/.xsession

…and make it look like this:

#!/bin/sh

/usr/bin/lxsession -s Lubuntu -e LXDE

Save .xsession, reboot your computer, and try connecting from your Remote Desktop client. Voilà!