Jerry Penner

Sorting Directories on FAT File Systems

2020-04-27T12:18:00-06:00

I have a car stereo in which I can plug a USB stick and play music or audio book files. It handles MP3, OGG, FLAC, and so on, so it's great that way. Newer vehicles let you play music from your phone, but I have no music on my phone, so that's not something I use. However, the software on the stereo that reads the files off the USB stick does not sort the files. If the tracks are copied onto the USB stick in order 10, 3, 8, 1, 4, 9, 7, 5, 8, 6, 2, then that is the order they will be played (unless using shuffle mode, in which case the original order does not matter).

Note that this technique applies only to FAT (FAT-32, VFAT) file systems.

To sort the files, I copy the MP3 files I want into a directory on the USB stick, and then run this script:

#!/bin/bash
#
#  Sort files alphabetically in the current directory.

FILES=()

for FILE in *; do
    FILES+=("${FILE}")
done

TEMPDIR=$(mktemp -d work_XXXXXXX)

echo ${#FILES[@]} files
for FILE in "${FILES[@]}"; do
    mv "${FILE}" "${TEMPDIR}"
done

for FILE in "${TEMPDIR}"/*; do
    mv "${FILE}" .
done


rmdir ${TEMPDIR}

I have this script, named sort-dir, in my PATH, so I type:

cd /media/usb/ARTIST/ALBUM
sort-dir

and now that directory is sorted and plays in-order on my car stereo.

Back when I wrote this script, I looked around for FAT file system directory sorters, and there a variety out there, some commercial offerings, but this tool does the job simply, quickly, and reliably.

Finding Files in a Relative Time Range

2020-04-27T11:53:00-06:00

The find command allows you to find files within a range of dates. For example, let's say you wish to find all files modified in the past month, and show the file's size, modification date, and pathname. Use this:

find . -type f -mtime -31 -printf '%10s %TY-%Tm-%Td %P\n'

Each flag is described here:

-type f: restricts results to plain files; no directories or links
-mtime 31: restricts results to files less than 31 days old
-printf '%10s %TY-%Tm-%Td %P\n': custom output format to show file size in bytes, modification date, and pathname relative to the directory given to find, which in this example is the current directory (.)

Now if you wanted to find all files modified between 6 months and a year ago, you would use two -mtime N directives like so:

find . -type f -mtime +180 -mtime -365 -printf '%10s %TY-%Tm-%Td %P\n'

The changes from the first command, -mtime +180, and -mtime -365, instruct find to filter out files older (+) than 180 days and younger (-) than 365 days.

Debian Packages: Finding Modified Files

2020-04-22T10:52:00-06:00

You have an installed package and you would like to see the if any of its installed files have been changed. If there are changes, you would like to see the differences.

Verify Package

The solution to finding modified package files is the dpkg -V *PACKAGE_NAME* command. It lists any files whose md5sums do not match those in the package metadata.

Example:

    $ dpkg -V minidlna
    ??5?????? c /etc/minidlna.conf

Show Differences in Modified Package Files

get the package locally

    apt-get download minidlna
    PKG=minidlna.*deb

look at the list of files in the package

    dpkg-deb --contents ${PKG}

Get the tarfile of the package and extract the file of interest to stdout:

    dpkg-deb --fsys-tarfile ${PKG} \
      | tar xfO - ./etc/minidlna.conf

Now put it all together. Given a debian package, DEB, and a file of interest, FILE, produce a difference listing using the following bash script:

#!/bin/bash

DEB="$1"
shift
FILES=("${@}")


error() {
    echo "$@" 1>&2
    exit 1
}


WORKDIR=$(mktemp -d)
trap "rm -rf ${WORKDIR}" 0 1 2 15

(cd ${WORKDIR}; apt-get download ${DEB})
DEB_FILE=$(eval echo ${WORKDIR}/${DEB}*.deb)

[ -f "${DEB_FILE}" ] || error "${DEB}: ${DEB_FILE} not found."

for FILE in "${FILES[@]}"; do
    MEMBER=$(dpkg-deb --contents ${DEB_FILE} |grep "${FILE}" |awk '{print $NF}')
    if [ -n "${MEMBER}" ]; then
        diff -u <(dpkg-deb --fsys-tarfile ${DEB_FILE} \
                  |tar xfO - "${MEMBER}") "${FILE}"
    fi
done

Here is a sample run:

    $ debdiff minidlna /etc/minidlna.conf
    Get:1 http://ports.ubuntu.com/ubuntu-ports bionic/universe arm64 minidlna arm64 1.2.1+dfsg-1 [128 kB]
    Fetched 128 kB in 2s (61.7 kB/s)
    --- /dev/fd/63  2020-04-22 10:51:12.718656103 -0600
    +++ /etc/minidlna.conf  2019-03-01 22:34:52.672223536 -0700
    @@ -78,11 +78,11 @@

     # Name that the DLNA server presents to clients.
     # Defaults to "hostname: username".
    -#friendly_name=
    +friendly_name=My Media Server

     # Serial number the server reports to clients.
     # Defaults to the MAC address of nework interface.
    -#serial=
    +serial=104857665536

     # Model name the server reports to clients.
     #model_name=Windows Media Connect compatible (MiniDLNA)

Swapping CapsLock and LeftCtrl

2020-04-08T22:32:00-06:00

Some folks prefer the Left Control key just to the left of the A key on their keyboards. If this is you, read on.

Linux

If you are the only user of your machine, you can edit /etc/default/keyboard and add or change the XKBOPTIONS line so it reads as:

    XKBOPTIONS="ctrl:swapcaps"

[I don't think this affects X sessions, so there is more to do.]

XFCE4

If you share your machine with others, change the keyboard mapping in your own account. Under the Xfce4 desktop environment (Xubuntu), open the Session and Startup settings in your Settings menu or System Settings application (xfce4-settings-manager).

Select the Application Autostart tab and click and the application configuration dialog opens:

Fill in the fields:

Name: Swap CapsLock/LCtrl
Description: swap CapsLock and LeftCtrl
Command: /usr/bin/setxkbmap -option "ctrl:swapcaps"

This creates a file in $HOME/.config/autostart called Swap CapsLock-Ctrl.desktop that contains:

    [Desktop Entry]
    Encoding=UTF-8
    Version=0.9.4
    Type=Application
    Name=Swap CapsLock/Ctrl
    Comment=swap CapsLock and Left-Ctrl
    Exec=/usr/bin/setxkbmap -option "ctrl:swapcaps"
    OnlyShowIn=XFCE;
    StartupNotify=false
    Terminal=false
    Hidden=false

Variations

If ctrl:swapcaps does not tweak your keyboard as you like, read the manual page for keyboard(5):

    man keyboard

In its FILES sections it suggests looking at /usr/share/X11/xkb/rules/xorg.lst for a complete list of options. Here are some of them:

`ctrl:nocaps`	Caps Lock as Ctrl
`ctrl:lctrl_meta`	Left Ctrl as Meta
`ctrl:swapcaps`	Swap Ctrl and Caps Lock
`ctrl:ac_ctrl`	At left of 'A'
`ctrl:aa_ctrl`	At bottom left
`ctrl:rctrl_ralt`	Right Ctrl as Right Alt
`ctrl:menu_rctrl`	Menu as Right Ctrl
`ctrl:swap_lalt_lctl`	Swap Left Alt with Left Ctrl
`ctrl:swap_lwin_lctl`	Swap Left Win with Left Ctrl
`ctrl:swap_rwin_rctl`	Swap Right Win with Right Ctrl
`ctrl:swap_lalt_lctl_lwin`	Left Alt as Ctrl, Left Ctrl as Win, Left Win as Left Alt

Odroid-C2 Media Server

2019-03-23T15:26:00-07:00

An Odroid-C2 single-board computer makes a decent home media server. It has gigabit ethernet, it runs Linux, and it's faster than a Raspberry Pi.

The Odroid-C2 has the ability to display 4K video and I am hoping to actually have this machine play movies out to the TV. So far, that part is not working.

What does work, however, is serving media to the Xbox 360, iPads, phones, and other computers. This it does without a hitch.

Operating System

There are at least two choices for operating systems on the C2: Ubuntu Linux or Android. Official Odroid-C2 operating system links.

On my system, I chose to go with the microSD-card storage as opposed to the faster eMMC storage. So far, I've had no trouble related to storage speed.

Post O/S Configuration

Once the operating system is installed, it's time to customize the system. We'll do the following:

Update the system software.

# sudo apt-get update && sudo apt-get dselect-upgrade -y

Install additional software.

# sudo apt-get install aptitude firefox minidlna samba -y

Set the hostname.

# sudo sed -i -e 'iYOUR_HOSTNAME' -e '1,$d' /etc/hostname

Set the time zone and locale.

Edit /etc/default/locale to (for example):

LANG="en_CA.UTF-8"
LANGUAGE="en_CA:en"

Edit /etc/locale.gen and uncomment your desired locale names. For example:

en_CA ISO-8859-1
en_CA.UTF-8 UTF-8
en_US ISO-8859-1
en_US.ISO-8859-15 ISO-8859-15
en_US.UTF-8 UTF-8

Add a new admin user.

# GRP="$(grep ':.*odroid' /etc/group
         |awk -F: '{print $1}'
         |tr '\n' ',' |sed 's/,$//')"
# useradd -r -m -G ${GRP}

Add a regular (family) user. Upon startup, the C2 will auto-login to this account.
Create a passwordless SSH configuration from your development machine to the C2.
Tighten up SSH security.
Connect USB storage containing media (music, videos).
Configure MiniDLNA.
Configure Samba.