Miscellaneous Cheat Sheet
=========================
`< Blog <../blog.html>`_

A quick reference to all things miscellaneous and those things that have no home yet.

Created on: 2020-02-09

Tag: `cheat_sheet <tag_cheat_sheet.html>`_

HTML: jump to top of page link
------------------------------
to create a jump to top of page link::

    <a href="#">Go to top</a>

    <a href="#top">Go to top</a>

source: https://stackoverflow.com/a/11751756
 

CSS: Comments
-------------
to add comments in CSS::

    /* This is a single-line comment */

    /* This is
    a multi-line
    comment */

source: https://www.w3schools.com/Css/css_comments.asp


Linux
-----

best place to store SSL certificate and key
```````````````````````````````````````````
store SSL certificate inside::

    /etc/ssl/certs

with `777` file permission.

store SSL key inside::

    /etc/ssl/private

with `700` file permission.

source: https://stackoverflow.com/a/4267602


Download all mvk files in a HTML page
`````````````````````````````````````
Sometime we would need to download all the file of same type from an HTML page. We would do this with::

    wget --no-directories -r -l 1 --accept='*.mkv*' $LINK

source: https://serverfault.com/a/359926

Resume download with wget
`````````````````````````
To resume download with `wget`_::

    wget -c $LINK

source: https://unix.stackexchange.com/a/165881

Download only new files with wget
`````````````````````````````````
to download only new files with `wget`_::

    wget -N $LINK

source: https://superuser.com/a/283484

Download all new files from a HTML page with resume
```````````````````````````````````````````````````
If we combine all the above cheats we can download all new files of a type from a HTML page with resume::

    wget --no-directories -r -l 1 -N -c --accept='*.ext*' $LINK

Hide a particular user from login screen
````````````````````````````````````````
To hide a particular user from the login screen, first create a file with a text editor::

    sudo vim /var/lib/AccountsService/users/$USER_NAME

put the following::

    [User]
    SystemAccount=true

If the file already exist the change the value of `SystemAccount` to `true`, then save and exit the file.

source: https://askubuntu.com/a/575390

Disable user list on login screen
`````````````````````````````````
To disable user list on login screen, first create a directory, `lightdm.conf.d` inside `/etc/lightdm/`::

    sudo mkdir -p /etc/lightdm/lightdm.conf.d

Now create a file with a text editor named `10-ubuntu.conf`::

    sudo vim /etc/lightdm/lightdm.conf.d/10-ubuntu.conf

Next put the following in that file::

    [SeatDefaults]
    user-session=ubuntu
    greeter-show-manual-login=true
    greeter-hide-users=true
    allow-guest=false

Change the `user-session` to reflect your user session, for example, in Xubuntu the value would be xubuntu. Then save and exit the file. The effect will be visible after a reboot.

source: https://askubuntu.com/a/731455

Specifically for Ubuntu the following can done as well::

    sudo -i

    xhost +SI:localuser:gdm
    su gdm -l -s /bin/bash
    gsettings set org.gnome.login-screen disable-user-list true

source: http://ubuntuhandbook.org/index.php/2018/04/hide-user-list-ubuntu-18-04-login-screen/


Bash autocomplete files location
````````````````````````````````
System-wide bash autocomplete files location::

    /etc/bash_completion.d/

source: https://askubuntu.com/a/68203

Open apt manager from URL
`````````````````````````
to open apt manager from URL::

    apt:$PACKAGE_NAME

In HTML::

    <a href="apt:package">click</a> # single package
    <a href="apt:package1,package2,package3">click</a> # multipule packages

Needs to be Ubuntu 7.10 or later with `apturl` package installed and in a compatible browser.

source: https://help.ubuntu.com/community/AptURL and https://wiki.ubuntu.com/AptUrl

Do nothing when lid is closed
`````````````````````````````
to take no action when lid is closed, edit the `/etc/systemd/logind.conf` file to add::

    HandleLidSwitch=ignore

and the edit `/etc/UPower/UPower.conf` file to add::

    IgnoreLid=true

sometime WiFi is still disconnects after doing this step then we may also need to add the following in the `/etc/systemd/logind.conf`::

    HandleLidSwitchDocked=ignore

In Ubuntu 20.04 I am noticing a new option `HandleLidSwitchExternalPower` in the `/etc/systemd/logind.conf` file. We can use it as well::

    HandleLidSwitchExternalPower=ignore

source: https://askubuntu.com/a/830562

see desktop environment in use
``````````````````````````````
to see desktop environment in use::

    echo $DESKTOP_SESSION

source: https://askubuntu.com/a/125072

remove all KDE desktop element
``````````````````````````````
to remove all KDE desktop element::

    sudo apt-get purge '^kde' '^kubuntu' '^plasma'

source: https://askubuntu.com/a/829127

ubuntu server enable root user
------------------------------
to enable root user in Ubuntu server, first set the password for root user::

    sudo passwd root

then unlock the user::

    sudo passwd -u root

we can disable root user by locking::

    sudo passwd -l root

source: https://askubuntu.com/a/44419

mount directory over ssh
------------------------
to mount directory over ssh, we can use `sshfs`_. First we will install it::

    sudo apt-get install sshfs

Then enable the fuse kernel module::

    sudo modprobe fuse

Now create a directory and mount remote directory to that directory::

    mkdir $DIR

    sshfs $USER_NAME@$SERVER_IP:/$PATH $DIR

To unmount simply do::

    umount $DIR

source: https://askubuntu.com/a/412478

apt upgrade single package
--------------------------
to upgrade single package with `apt`_::

    sudo apt install --only-upgrade $PACKAGE_NAME

source: https://askubuntu.com/a/44124

QR Code
--------

Bangladesh Railway Online Ticket
````````````````````````````````
If we scan it, we see::

    TRAIN: NELSAGORE_EXPRESS (765.)     // train name and number
    STATION: DHAKA to ABDULPUR          // source station to distination station
    DATE: 01-JAN-1001 08:00             // date and time of train diperture from source station
    CLASS: S_CHAIR                      // seat class
    COACH_NO: CHA                       // coach number
    SEAT_RANGE: 1,2                     // seat number
    E-PIN: 6NZ95                        // e-pin number
    FULL NAME: Jane Doe                 // name of passenger
    MOBILE_NO: 01704522104              // phone number of passenger
    PNR_NO: 1704522104                  // not sure what is it
    ID: 1382533015                      // ID of user
    GATEWAY: EBL_BANK                   // bank with what the payment was made


Dhaka University Masters Admit
``````````````````````````````
If we scan it, we see::

    DU-ADMT<<<1001822312<<REF<<19966095654<<Regular<<62867<<<
                   ^                ^          ^       ^
                   |                |          |       |
             registration       referance    type     roll
             number like:         number      of     number
             1001-822-312                   student
              ^
              |
        registration
           year!?


Nextcloud App Password
``````````````````````
If we scan it, we see::

    nc://login/user:$USER-NAME&password:$PASSWORD&server:$PROTOCOL://URL:$PORT-IF-ANY



VeraCrypt
---------

mount volume from command line
``````````````````````````````
to mount a VeraCrypt volume from command line::

    veracrypt -t --mount /dev/sdb1 --non-interactive --stdin

This will be stuck on a blank line. Typing the volume password would mount the volume. The `-t` flag is for **text user interface**, the `--mount` flag **mounts volume interactively** which takes a device path as argument, `--non-interactive` flag **disabals user interaction** and finally the `--stdin` flag **reads password from standard input**.

source: https://www.veracrypt.fr/en/Command%20Line%20Usage.html. Thought not all options are document there and needed to be look at the `veracrypt -t --help`. 

unmount volume from command line
````````````````````````````````
to unmount a VeraCrypt volume from command line::

    veracrypt -d

The `-d` flag **dismounts volume**.

source: https://www.veracrypt.fr/en/Command%20Line%20Usage.html

list volume from command line
`````````````````````````````
to list VeraCrypt volume(s) from command line::

    veracrypt -t -l

The `-l` flag **displays a list of mounted volumes**.

source: `veracrypt -t --help` options.

console shows gibrish error
```````````````````````````
every time a command is run with `-t` flag a gibrish error showed in the terminal. Bit of searching the web showed it happens because of X11 over ssh and can be fixed with::

    export DISPLAY=:0.0

source: https://github.com/veracrypt/VeraCrypt/issues/531#issuecomment-548879342

read only after mounting on Windows
```````````````````````````````````
VeraCrypt sometimes becomes read only after mounting on Windows because of Metadata kept in Windows cache.  ::

    sudo ntfsfix -b -d "/dev/mapper/veracrypt$N"

source: https://superuser.com/questions/1115813/cannot-mount-veracrypt-partition-on-linux-mint-metadata-kept-in-windows-cache#comment1976408_1125460
and https://www.reddit.com/r/VeraCrypt/comments/a0uzur/mounting_a_veracrypt_volume_as_writable

don't prompt for format in windows
``````````````````````````````````
need to test this: https://superuser.com/a/324590

Facebook: See most recent post
------------------------------
The new Facebook UI (as of Mar 16, 2020 it is in early adopter phrase) don't have a option to see most recent post. I noticed a URL change in the old UI which works in the new UI.:

    https://www.facebook.com/?sk=h_chr


Tomcat: Web Server Location in Linux
------------------------------------
The location of the Tomcat server in Linux::

    /var/lib/tomcat7/webapps/

source: https://stackoverflow.com/a/39671086

OpenVPN: Restrict one cert per device
-------------------------------------
To restrict one cert per device in OpenVPN comment out or DO NOT USE the `--duplicate-cn` option.

source: https://forums.openvpn.net/viewtopic.php?t=18164#p49452


KeePass: Password generator character set
-----------------------------------------
KeePass Password generator as the following character set available::

    Upper-case: ABCDEFGHIJKLMNOPQRSTUVWXYZ
    Lower-case: abcdefghijklmnopqrstuvwxyz
    Digits: 0123456789
    Minus: -
    Underline: _
    Space: 
    Special: !"#$%'*+,./:;=?@\^`|~
    Brackets: []{}()<>
    Latin-1 Supplement: ¡¢£¤¥¦§¨©ª«¬­®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüþÿ


First message of Telegram
-------------------------
channel: Channel created

group: $CREATORS_DISPLAY_NAME created the group «GROUP_NAME»

Source
------
.. _wget: https://linux.die.net/man/1/wget
.. _sshfs: https://linux.die.net/man/1/sshfs
.. _apt: https://linux.die.net/man/8/apt