How convert mkv to mp4

•  convert an input video file into a MKV file using VP8 encoding with VORBIS audio encoding

           ffmpeg -i input_video.avi -f matroska -vcodec vp8 -acodec libvorbis output_video.mkv

• convert a video into a video using VP9 for video encoding and OPUS as audio encoding

           ffmpeg -i input_video.avi -f matroska -vcodec vp8 -acodec aac output_video.mkv

How enable ssh on ubuntu

To enable SSH:

sudo apt-get install openssh-server
After instalation the SSH service should be started automatically. You can start, stop or restart the service manually:

sudo service ssh start              (stop|restart)
To edit settings:

To change the port, root login permission, you have to edit the /etc/ssh/sshd_config file via:

sudo nano /etc/ssh/sshd_config

Remove # from the line 13.
9 # OpenSSH is to specify options with their default value where
10 # possible, but leave them commented.  Uncommented options override the
11 # default value.
12 
13 Port 22
14 #AddressFamily any
15 #ListenAddress 0.0.0.0
16 #ListenAddress ::

Install MySQL Server on Ubuntu

1. Install MySQL: 
• sudo apt-get update 
• sudo apt-get install mysql-server
2. Start the ubuntu terminal
• sudo mysql -u root -p
3. Create a database
• create database food
4. Start the ubuntu terminal
• sudo mysql -u root food -p 

Create a bootable USB stick on ubuntu

1. Use the search field in Ubuntu "Startup Disk Creator"
2. Select Startup Disk Creator
3. Choose Source disc "some.iso" and Disk to Use "USB stick"

Securely erasing a storage device

Shred command-line utility overwrites data in a file and in a whole device

Set all bits to zero after the last iteration by adding the option -z

•  sudo shred -v -n1 -z /dev/sdX

• After this is necessary to create partition 

                     sudo apt-get install gparted

                     sudo gparted

How to create bootable USB Media from ISO in Ubuntu Linux

1. Startup Disk Creator is a built-in application in Ubuntu Linux

2.  Convert iso file into bootable usb media  using ddrescue

• install ddrescue

                sudo apt update
                sudo apt install gddrescue

• check block device name

                sudo fdisk -l
                eg.  /dev/sdf

• enter the command as follows:

               sudo ddrescue Downloads/openSUSE-Leap-15.0-DVD-x86_64.iso /dev/sdf --force -D


                

Create partition and filesystem

1.  List all of the drive.
                           
                     sudo fdisk -l
   
2.              sudo fdisk  /dev/sdc1

admin@ubuntu:~$ sudo fdisk /dev/sdc1

Welcome to fdisk (util-linux 2.27.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0x83851831.

Command (m for help):

3.             press "p"  show info

Command (m for help): p
Disk /dev/sdc: 512 MiB, 536870912 bytes, 1048576 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x83851831

4.   press "n"   add new partition with defaults

Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1):
First sector (2048-1048575, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-1048575, default 1048575):

Created a new partition 1 of type 'Linux' and of size 511 MiB.

5. press "m"   it shows options

Command (m for help): m

Help:

  DOS (MBR)

   a   toggle a bootable flag

   b   edit nested BSD disklabel

   c   toggle the dos compatibility flag

  Generic

   d   delete a partition

   F   list free unpartitioned space

   l   list known partition types

   n   add a new partition

   p   print the partition table

   t   change a partition type

   v   verify the partition table

   i   print information about a partition

   .........

6. press "t"  change partition type

Command (m for help): t

Selected partition 1

Partition type (type L to list all types): L

 0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris

 1  FAT12           27  Hidden NTFS Win 82  Linux swap / So c1  DRDOS/sec (FAT-

 2  XENIX root      39  Plan 9          83  Linux           c4  DRDOS/sec (FAT-

 3  XENIX usr       3c  PartitionMagic  84  OS/2 hidden or  c6  DRDOS/sec (FAT-

 4  FAT16 <32m 40="" 80286="" c7="" div="" extended="" linux="" nbsp="" syrinx="" venix="">

 5  Extended        41  PPC PReP Boot   86  NTFS volume set da  Non-FS data

 6  FAT16           42  SFS             87  NTFS volume set db  CP/M / CTOS / .

 7  HPFS/NTFS/exFAT 4d  QNX4.x          88  Linux plaintext de  Dell Utility

 8  AIX             4e  QNX4.x 2nd part 8e  Linux LVM       df  BootIt

 9  AIX bootable    4f  QNX4.x 3rd part 93  Amoeba          e1  DOS access

 a  OS/2 Boot Manag 50  OnTrack DM      94  Amoeba BBT      e3  DOS R/O

 b  W95 FAT32       51  OnTrack DM6 Aux 9f  BSD/OS          e4  SpeedStor

 c  W95 FAT32 (LBA) 52  CP/M            a0  IBM Thinkpad hi ea  Rufus alignment

 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a5  FreeBSD         eb  BeOS fs

 f  W95 Ext'd (LBA) 54  OnTrackDM6      a6  OpenBSD         ee  GPT

10  OPUS            55  EZ-Drive        a7  NeXTSTEP        ef  EFI (FAT-12/16/

11  Hidden FAT12    56  Golden Bow      a8  Darwin UFS      f0  Linux/PA-RISC b

12  Compaq diagnost 5c  Priam Edisk     a9  NetBSD          f1  SpeedStor

14  Hidden FAT16 <3 61="" ab="" boot="" darwin="" div="" f4="" nbsp="" speedstor="">

16  Hidden FAT16    63  GNU HURD or Sys af  HFS / HFS+      f2  DOS secondary

17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fb  VMware VMFS

18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fc  VMware VMKCORE

1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid fd  Linux raid auto

1c  Hidden W95 FAT3 75  PC/IX           bc  Acronis FAT32 L fe  LANstep

1e  Hidden W95 FAT1 80  Old Minix       be  Solaris boot    ff  BBT

Partition type (type L to list all types): 83

Changed type of partition 'Linux' to 'Linux'.

7.     press "p"

Command (m for help): p

Disk /dev/sdc: 512 MiB, 536870912 bytes, 1048576 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: dos

Disk identifier: 0x83851831

Device     Boot Start     End Sectors  Size Id Type

/dev/sdc1        2048 1048575 1046528  511M 83 Linux

8.    press "w"

Command (m for help): w

The partition table has been altered.

Calling ioctl() to re-read partition table.

Syncing disks.

9. reboot

10.   Create filesystem.

sudo mkfs -t ext2 /dev/sdc
mke2fs 1.42.13 (17-May-2015)
Found a dos partition table in /dev/sdc
Proceed anyway? (y,n) y
Creating filesystem with 131072 4k blocks and 32768 inodes
Filesystem UUID: d4b77d55-6837-4cfb-9235-ccc8f7716e8b
Superblock backups stored on blocks:
        32768, 98304

Allocating group tables: done
Writing inode tables: done
Writing superblocks and filesystem accounting information: done