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====== Technical Information: General Linux Topics ======
  * [[http://www.livenix.org|LiveNIX]]
  * [[:tech:linux:alpine:start|Alpine]]
  * [[:tech:linux:slackware:start|Slackware]]
  * [[:tech:linux:ubuntu:start|Ubuntu]]
  * [[:tech:linux:centos:start|CentOS/RHEL]]

[[:tech:linux:desktop:start|So, You're Ready for the Linux Desktop ...]] \\

===== Links/Resources =====
  * Firefox 64-bit [[http://download-origin.cdn.mozilla.net/pub/firefox/releases/|downloads]]
  * [[http://www.brendangregg.com/perf.html|Interesting site on Linux performance topics]] ([[https://lwn.net/Articles/370423/|and some more here]])
  * [[https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-gitlab-on-ubuntu-16-04|Setting up GitLab Community Edition]]

===== KVM/Qemu Basics =====
<code>qemu-img create -f qcow2 sda 18G</code>
<code>lvcreate -L 100G -n vmnamehome vgvms</code>

===== Misc Tech Trivia =====

==== X11 Display Auth ====
  * From display owner **(where X is display number)**: ''xauth extract cookiefilename :**X**''
  * For remote user, get cookie file and:  ''xauth merge cookiefilename''

==== Storage Management ====
  * Good article: [[https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-with-mdadm-on-ubuntu-18-04]]
  * Set up RAID5 with ''mdadm'':<code>mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sdX /dev/sdY /dev/sdZ</code>
  * Check status: ''cat /proc/mdstat''
  * Configure for availability after boot: \\ //(**NOTE**: this must be done after recovery status is complete)//<code>
mdadm --detail --scan >> /etc/mdadm/mdadm.conf
update-initramfs -u
</code>
  * Scrub to prevent bit-rot: ''echo check > /sys/block/md**X**/md/sync_action'' \\ (use ''cat /proc/mdstat'' to monitor)
  * Tune re-build speed ([[https://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html]]): \\ To show limits: ''sysctl dev.raid.speed_limit_min ; sysctl dev.raid.speed_limit_max'' \\ To increase speed, enter: ''sysctl -w dev.raid.speed_limit_min=value'' \\ In ''/etc/sysctl.conf''<code>dev.raid.speed_limit_min = 50000
## good for 4-5 disks based array ##
dev.raid.speed_limit_max = 2000000
## good for large 6-12 disks based array ###
dev.raid.speed_limit_max = 5000000</code>
  * Sample LVM with ''mdadm'' RAID:<code>
pvcreate -M2 /dev/md0
vgcreate -s 64 newvg /dev/md0
lvcreate -L 128G -n newlv newvg
mkfs -t ext4 /dev/newvg/newlv
</code>

==== OverlayFS ====
  * Ensure ''overlay'' module is loaded //(modprobe overlay)//
  * Mount syntax looks like:<code>mount -t overlay -o lowerdir=ldir,upperdir=udir,workdir=wdir overlayfs overlaydir</code>
==== Encrypted filesytem-in-a-file ====
This uses ''dm-crypt'' LUKS support, which is all part of the kernel (I believe) // (in ''Ubuntu'', make sure the ''lvm2'' package is installed) // :
<code>
dd if=/dev/urandom of=.diskimg bs=1M count=1024
losetup --find --show /home/rk4n3/.diskimg
cryptsetup -c aes-xts-plain64:sha256 -s 512 -v -y luksFormat /dev/loopX
cryptsetup luksOpen /dev/loopX diskname
mkfs -t ext4 /dev/mapper/diskname
mount /dev/mapper/diskname /home/rk4n3/sec
</code>

Here is similar, but for burning an encrypted DVD:
<code>
dd if=/dev/zero of=dvd.img bs=1M count=4400
losetup --find --show dvd.img
cryptsetup -c aes-xts-plain64:sha256 -s 512 -v -y luksFormat /dev/loopX
cryptsetup luksOpen /dev/loopX dvdimg
mkisofs -l -r -allow-leading-dots -allow-lowercase -allow-multidot -J -joliet-long -o /dev/mapper/dvdimg dir2burn
</code>
Cleaning up after ...
<code>
cryptsetup luksClose /dev/mapper/dvdimg
losetup -d /dev/loopX
</code>
Mounting ...
<code>
cryptsetup luksOpen /dev/sr0 yourdvdname
mount -o ro /dev/mapper/yourdvdname /mount/point/dir
</code>

==== Disable TouchPad ====
Run: ''xinput list'' \\
There will be a list that looks similar to:
<code>
⎡ Virtual core pointer                    	id=2	[master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer              	id=4	[slave  pointer  (2)]
⎜   ↳ ETPS/2 Elantech Touchpad                	id=12	[slave  pointer  (2)]
⎜   ↳ Logitech USB Receiver                   	id=15	[slave  pointer  (2)]
⎣ Virtual core keyboard                   	id=3	[master keyboard (2)]
    ↳ Virtual core XTEST keyboard             	id=5	[slave  keyboard (3)]
    ↳ Power Button                            	id=6	[slave  keyboard (3)]
    ↳ Video Bus                               	id=7	[slave  keyboard (3)]
    ↳ Video Bus                               	id=8	[slave  keyboard (3)]
    ↳ Power Button                            	id=9	[slave  keyboard (3)]
    ↳ Sleep Button                            	id=10	[slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard            	id=11	[slave  keyboard (3)]
    ↳ MSI WMI hotkeys                         	id=13	[slave  keyboard (3)]
    ↳ Logitech USB Receiver                   	id=14	[slave  keyboard (3)]
</code>
Run this command for the ID that matches trackpad device: \\
''xinput set-prop 12 "Device Enabled" 0'' \\


=== Create a tmpfs filesystem ===
At the command-line:
<code>mount -t tmpfs -o size=512m tmpfs /home/someone</code>
In the ''/etc/fstab'':
<code>tmpfs            /home/someone         tmpfs      nodev,uid=1801,gid=100,size=512M  0  0</code>

=== Ubunutu's color PS1 spec ===
<code>
export PS1='\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\ $'
</code>


=== Simple NIC speed test ===
On one machine:<code>nc -vvlnp 12345 > /dev/null</code>
On the other:<code>dd if=/dev/zero bs=1M count=1K | nc -vvn x.x.x.x 12345</code>


==== POS Receipt Printing ====
Epson ESC/POS command reference: [[https://reference.epson-biz.com/modules/ref_escpos/index.php?content_id=72]] \\
Nice article here:  [[https://mike42.me/blog/2015-03-getting-a-usb-receipt-printer-working-on-linux]] ... \\
Use ''dmesg'' to verify that ''usblp'' has seen the printer (''lp//X//'' device should be in ''/dev/usb''):
<code>
dmesg
[12724.994550] usb 8-4: new full-speed USB device number 5 using ohci-pci
[12725.168956] usb 8-4: New USB device found, idVendor=04b8, idProduct=0e03
[12725.168963] usb 8-4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[12725.168968] usb 8-4: Product: TM-T20
[12725.168971] usb 8-4: Manufacturer: EPSON
[12725.168975] usb 8-4: SerialNumber: ....
[12725.175114] usblp 8-4:1.0: usblp1: USB Bidirectional printer dev 5 if 0 alt 0 proto 2 vid 0x04B8 pid 0x0E03
</code>

Here's PHP code for a simple output:
<code PHP>
/* ASCII constants */
const ESC = "\x1b";
const GS="\x1d";
const NUL="\x00";

/* Output an example receipt */
echo ESC."@"; // Reset to defaults
echo ESC."E".chr(1); // Bold
echo "FOO CORP Ltd.\n"; // Company
echo ESC."E".chr(0); // Not Bold
echo ESC."d".chr(1); // Blank line
echo "Receipt for whatever\n"; // Print text
echo ESC."d".chr(4); // 4 Blank lines

/* Bar-code at the end */
echo ESC."a".chr(1); // Centered printing
echo GS."k".chr(4)."987654321".NUL; // Print barcode
echo ESC."d".chr(1); // Blank line
echo "987654321\n"; // Print number
echo GS."V\x41".chr(3); // Cut
exit(0);
</code>

===== Some Fun Stuff =====
==== Some cool bash prompts ====
<code>export PS1=$'\e[32m\u262F ${USER}@\e[33m${SYS} \u2622\u25AC\u25B6\e[0m '</code>
<code>export PS1=$'\e[32m\u250F\u2501\e[33m ${USER}@${SYS} \e[31m\u2622\e[36m ${PWD}\n\e[32m\u2517\u2501\u276F\u276F\u276F\e[0m '</code>
<code>export PS1=$'\e[32m\u250F\u2501\e[33m ${USER}@$(uname -n) \e[31m\u2622\e[36m \w\n\e[32m\u2517\u2501\u276F\u276F\u276F\e[0m '</code>

=== Some resource links ===
  * Draw-to-recognize unicode characters: [[http://shapecatcher.com|Shapecatcher]]
  * Lookup: [[https://unicode-table.com/en/#geometric-shapes|unicode character table]]

[[tech:linux:fun:poweredbylinux|Interesting things powered by linux]]

 \\
// Links: [[:tech:start|Tech Info]] ... [[:mantis:start|Mantis Area]] //
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