Linux

htop

• PID: process ID number.
• USER: process owner.
• PRI: process priority by the kernel.
• NI: process priority reset by the user or root.
• VIR: virtual memory the process is consuming.
• RES: physical memory the process is consuming.
• SHR: shared memory that the process is consuming.
• S: current process state.
• CPU%: percentage of CPU that the process is consuming.
• MEM%: percentage of memory that the process is consuming.
• TIME+: time measured in clock ticks since process execution started.
• Command: name of the command that started the process

Useful Shortcut Keys

u: displays all processes owned by a particular user.

p: sort processes on high CPU consumption.

m: sort processes on high memory consumption.

t: sort process on time.

Space: tag a process

c: tag a process and child processes

Shift + u: remove all tags.

Shift + f: highlight and follow a process.

Shift + h: show/hide user and kernel processes.

a: set what CPU cores a process can access.

i: set IO priority.

h: help menu.

History Command

fc -l <start> <end> | grep "docker"
# fc -l 4630 4810 | grep "docker"

Network

Check used port

sudo netstat -pna | grep 8888
# or
netstat -anv | grep LISTEN

UDP CLI Test Tool

Establish Connection

Server Side:

nc -u -l 9999

9999 is server-side port

-u is udp protocol

Client Side:

nc -u 192.168.0.100 9999

192.168.0.100 is server IP

9999 is server port

Check Connection

netstat | grep 9999

Send Package

In client side, send:

"Hi server!"

In Server side, send:

"hi, client"

more

Check Network Latency

tool 1:

# -c: 3 requests  
# -S: Set TCP SYN  
# -p: Set port to 80  
$ hping3 -c 3 -S -p 80 google.com  
HPING google.com (eth0 142.250.64.110): S set, 40 headers + 0 data bytes  
len=46 ip=142.250.64.110 ttl=51 id=47908 sport=80 flags=SA seq=0 win=8192 rtt=9.3 ms  
len=46 ip=142.250.64.110 ttl=51 id=6788  sport=80 flags=SA seq=1 win=8192 rtt=10.9 ms  
len=46 ip=142.250.64.110 ttl=51 id=37699 sport=80 flags=SA seq=2 win=8192 rtt=11.9 ms  
--- baidu.com hping statistic ---  
3 packets transmitted, 3 packets received, 0% packet loss  
round-trip min/avg/max = 9.3/10.9/11.9 ms  

tool 2:

$ traceroute --tcp -p 80 -n google.com  
traceroute to google.com (142.250.190.110), 30 hops max, 60 byte packets  
 1  * * *  
 2  240.1.236.34  0.198 ms * *  
 3  * * 243.254.11.5  0.189 ms  
 4  * 240.1.236.17  0.216 ms 240.1.236.24  0.175 ms  
 5  241.0.12.76  0.181 ms 108.166.244.15  0.234 ms 241.0.12.76  0.219 ms  
 ...  
24  142.250.190.110  17.465 ms 108.170.244.1  18.532 ms 142.251.60.207  18.595 ms  

traceroute 会在路由的每一跳（hop）发送三个数据包，并在收到响应后输出往返延迟。如果没有响应或响应超时（默认 5s），将输出一个星号 *

reference

deb package

$ dpkg -i package.deb #安装/更新一个 deb 包
$ dpkg -r package_name #从系统删除一个 deb 包
$ dpkg -l #显示系统中所有已经安装的 deb 包
$ dpkg -l | grep httpd #显示所有名称中包含 "httpd" 字样的deb包
$ dpkg -s package_name #获得已经安装在系统中一个特殊包的信息
$ dpkg -L package_name #显示系统中已经安装的一个deb包所提供的文件列表
$ dpkg --contents package.deb #显示尚未安装的一个包所提供的文件列表
$ dpkg -S /bin/ping #确认所给的文件由哪个deb包提供
#APT 软件工具 (Debian, Ubuntu 以及类似系统)
$ apt-get install package_name #安装/更新一个 deb 包
$ apt-cdrom install package_name #从光盘安装/更新一个 deb 包
$ apt-get update #升级列表中的软件包
$ apt-get upgrade #升级所有已安装的软件
$ apt-get remove package_name #从系统删除一个deb包
$ apt-get check #确认依赖的软件仓库正确
$ apt-get clean #从下载的软件包中清理缓存
$ apt-cache search searched-package #返回包含所要搜索字符串的软件包名称

tree

-L 2: Depth 2

$ tree -L 2 -N /

Only show directories:

$ tree -L 2 -d -N /

no indentation + full path

$ tree -L 2 -d -fi -N /

reference

strace

strace is a debug tool which helps you to debug your APP.

save tracing message to .txt:

$ strace -o debug.txt yourApp

check system calls:

$ strace -c yourApp

Extracting info by specific keyword, like open:

$ strace -e open yourApp

Tracing by timestamp:

$ strace -t yourApp

ltrace

lib trace tool

$ ltrace -t yourApp

Find Biggest Files and Directories in Linux

$  du -a /your_dir | sort -n -r | head -n 5

du command: Estimate file space usage. a : Displays all files and folders. sort command : Sort lines of text files. -n : Compare according to string numerical value. -r : Reverse the result of comparisons. head : Output the first part of files. -n : Print the first ‘n' lines. (In our case, We displayed first 5 lines).

Find all files modified between time A and time B

find . -type f -newermt 2007-06-07 ! -newermt 2007-06-08

Find files accessed between time A and time B

find . -type f -newerat 2008-09-29 ! -newerat 2008-09-30

Files which had their permission changed on the same day

find . -type f -newerct 2008-09-29 ! -newerct 2008-09-30

Find all Directory modified between time A and time B

find . -type f -newermt 2007-06-07 ! -newermt 2007-06-08

setting directory depth parameter

find . -maxdepth 2 -type d -newermt 2007-06-07 ! -newermt 2007-06-08

Human Readable Format

$ du -hs * | sort -rh | head -5

Display the largest folders/files including the sub-directories

$ du -Sh | sort -rh | head -5

du command: Estimate file space usage. -h : Print sizes in human readable format (e.g., 10MB). -S : Do not include size of subdirectories. -s : Display only a total for each argument. sort command : sort lines of text files. -r : Reverse the result of comparisons. -h : Compare human readable numbers (e.g., 2K, 1G). head : Output the first part of files.

Total files' number

find . -mindepth 1 -maxdepth 1 | wc -l

ls command

find 5 most-recently modified files

$ ls -1t | head -5

last 5 modified files

$ ls -1t | tail -5

softlink and hardlink

create soft link

$ ln -s {source-filename} {symbolic-filename}

verify

$ ls -l file1 link1

overwrite symlinks/Soft link

$ ln -f -s file link

unlink

$ unlink symlink_name

or

$ rm symlink_name

file numbers in a directory

ls | wc -l

reference

find command

$ find /dir -name keyword

cat command

Print 5 lines:

$ head -n 5 my.txt

print with line number:

$ cat -n my.txt

Generate a yaml file

export AWS_CLUSTER_NAME=kubeflow-demo-msp
export AWS_REGION=us-west-2
export K8S_VERSION=1.19
export EC2_INSTANCE_TYPE=m5.large

cat << EOF > cluster.yaml
---
apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: ${AWS_CLUSTER_NAME}
  version: "${K8S_VERSION}"
  region: ${AWS_REGION}

managedNodeGroups:
- name: kubeflow-mng
  desiredCapacity: 3
  instanceType: ${EC2_INSTANCE_TYPE}
EOF

check

cat cluster.yaml

ffmpeg

cut audio from video file

ffmpeg -i input.webm -ss start_time -t duration -c:a pcm_s16le output.wav
ffmpeg -i input.webm -ss 00:00:30 -t 00:00:10 -c:a pcm_s16le output.wav

Resize Video:

$ ffmpeg -i input_video.mp4 -s 640x480 -c:a copy out.mp4

Extract frame in a video(every 10 frames):

$ ffmpeg -i out.mp4 -vf "select=not(mod(n\,10))" -vsync vfr -q:v 2 img_%05d.jpg

change file format:

$ ffmpeg -i out.mp4 -c copy sample.h264

cut video:

$ ffmpeg -ss 00:01:26 -t 00:01:52 -i dog.mp4 -acodec copy -vcodec copy -async 1 cut.mp4

An image to a video:

$ ffmpeg -loop 1 -i sample.jpg -c:v libx264 -t 5 -pix_fmt yuv420p -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2"  out.mp4

jpg images to a video

$ ffmpeg -r 1/5 -f concat -i list.txt -c:v libx264 -r 25 -pix_fmt yuv420p -t 15 out.mp4

more more

Change video file pixel format

# Using the format filter (yuv420p)
ffmpeg -i in_file -filter:v "format=yuv420p" out_file

# Using the 'pix_fmt' option
ffmpeg -i in_file -pix_fmt yuv420p out_file

re-encoding

ffmpeg -i a.mp4 -c:v libx264 -crf 18 -preset slow -c:a copy output.mp4

Stack Videos

Horizontal Stack:

ffmpeg -i input0.mp4 -i input1.mp4 -filter_complex hstack=inputs=2 horizontal-stacked-output.mp4

Vertical Stack:

ffmpeg -i input0.mp4 -i input1.mp4 -filter_complex vstack=inputs=2 vertical-stack-output.mp4

2×2 Grid of Videos:

ffmpeg \
-i input0.mp4 -i input1.mp4 -i input2.mp4 -i input3.mp4 \
-filter_complex \
"[0:v][1:v]hstack=inputs=2[top]; \
[2:v][3:v]hstack=inputs=2[bottom]; \
[top][bottom]vstack=inputs=2[v]" \
-map "[v]" \
finalOutput.mp4

3×2 Grid of Videos:

ffmpeg \
-i input0.mp4 -i input1.mp4 \
-i input2.mp4 -i input3.mp4 \
-i input4.mp4 -i input5.mp4 \
-filter_complex \
"[0:v][1:v][2:v]hstack=inputs=3[top];\
[3:v][4:v][5:v]hstack=inputs=3[bottom];\
[top][bottom]vstack=inputs=2[v]" \
-map "[v]" \
finalOutput.mp4

concat videos

concat demuxer:

$ cat mylist.txt
file '/path/to/file1'
file '/path/to/file2'
file '/path/to/file3'
    
$ ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4

reference

rotate video:

$ ffmpeg -i "in.mp4" -metadata:s:v "rotate=90" -c copy "out.mp4"

or

# rotate 90 degree
#0 = 90CounterCLockwise and Vertical Flip (default)
#1 = 90Clockwise
#2 = 90CounterClockwise
#3 = 90Clockwise and Vertical Flip
# -vf "transpose=2,transpose=2" for 180 degrees.

$ ffmpeg -i in.mov -vf "transpose=1" out.mov

Resize image:

$ ffmpeg -i input.jpg -vf scale=320:240 output_320x240.png

or

$ ffmpeg -i input.jpg -vf scale=320:-1 output_320x240.png

Add image to video:

# tl=(5,5)
$ ffmpeg -i input.mp4 -i logo.png -filter_complex "overlay=5:5" -codec:a copy output.mp4

more

Convert 10-bit H.265 to 10-bit H.264

$ ffmpeg -i input -c:v libx264 -crf 18 -c:a copy output.mkv

• -crf 18 appear visually lossless

• -crf 0 lossless mode

Convert 10-bit H.265 to 8-bit H.265

$ ffmpeg -i input -c:v libx265 -vf format=yuv420p -c:a copy output.mkv

Convert 10-bit H.265 to 8-bit H.264

$ ffmpeg -i input -c:v libx264 -crf 18 -vf format=yuv420p -c:a copy output.mkv

video to GIF

Generate color_palette.png

 $ ffmpeg -i sample.mp4 -filter_complex "[0:v] palettegen" color_palette.png

Generate GIF file:

$ ffmpeg -i sample.mp4 -i color_pallet.png -filter_complex "[0:v][1:v] paletteuse" -r 10 -s 640x360  my_gif_file.gif

more

Shell Script

Array

arr=(1 2 3)

array size: ${#arr[@]}

arr[0] element: ${arr[0]}

array's all items: ${arr[*]} or ${arr[@]}

arr[0] element size: ${#arr[0]}

User Input

Input command: read -p 'name: ' uservar

Silient input command: read -sp 'name: ' uservar

Get IP last Number

var=123.444.888.235
new_var="${var%.*}.0"

reference

if else

if [condition];then
    # do something
elif [condition];then
    # do something
else
    # do something
fi    

Replace String's Character

solution 1: Use tr

E.g. Replace 192.168.0.111 to 192_168_0_111

$ server_ip=192.168.0.111
$ echo "$server_ip" | tr . _

Result:

192_168_0_111

solution 2: Use bash expansion

$ server_ip=192.168.0.111
$ result=${server_ip//[.]/_}

Result:

192_168_0_111

More usage:

Only replace first match char:

${string/substring/replacement}

Replace all match chars:

${string//substring/replacement}

Change IP In Terminal

Sample:

$ sudo ifconfig eth0 192.168.0.1 netmask 255.255.255.0

Find Top 10 Largest File/Directories

In terminal:

$ sudo du -a /var | sort -n -r | head -n 10

Check Disk Usage

df -h /var/lib/docker

Disk Mount

driver check

sudo fdisk -l

Format a disk

# sudo mkfs -t ext4 /dev/sda

Disk mount

# sudo mkdir /dev/hdd
# sudo mount /dev/sda /dev/hdd
# sudo chmod 777 /dev/hdd

Auto mount after booting

sudo vim /etc/fstab
# 파일 밑에 아래 줄 추가
#/dev/sda /dev/hdd ext4 defaults 0 0

check mount

df -h

tr command

tr is a command line utility for translating or deleting characters.

Replace character: tr -c

There are string1=aaabbbccc, string2=ab:

$ echo -n "aaabbbccc" | tr -c ab k

result:

aaabbbkkk

Delete repeated characters: tr -s

There are string1=aaabbbccc:

$ echo -n "aaabbbccc" | tr -s '[a-z]'

result:

abc

Delete Characters: tr -d

There are string1=aaabbbccc:

$ echo -n "aaabbbccc" | tr -d bbb

result:

aaaccc

Replace lowercase to uppercase

$  echo aaabbbccc | tr '[a-z]' '[A-Z]'

result:

AAABBBCCC

Chown Command

Change File or Folder's Owner

Check Folder or File's Owner

$ ls -lt

sample result:

drwxr-xr-x   2 root root       4096 Jan 15 23:34 foo

Change Owner To Specific User

$ sudo chown user1:user1 <file>

sample:

$ sudo chown wendy:wendy foo

Or use User ID:

$ chown 1000:1000 foo.txt

Check User ID:

$ id

sample result:

uid=1000(wendy) gid=1000(wendy) groups=1000(wendy),4(adm),20(dialout),24(cdrom),27(sudo),30(dip),46(plugdev),116(lpadmin),126(sambashare)

Change To Root

$ sudo chown root foo

Change Group To Root

$ sudo chown :root foo

Chaner Folder's Owner

$ chown -R wendy:wendy foo-folder

https://miseon119.github.io/whylearn.github.io/test/images/git-workflow-diagram3.png

SSH Config Setting

SSH Config File Sample

Common Remote Control Command via SSH:

$ sudo ssh Jane@192.168.0.1 

If you want to SSH your remote PC by short command such as ‘ssh JanePC', or you control many remote PCs. Maybe you need this ‘config' file instead. It usually locates in ~/.ssh/config. If not, create one.

Sample config file:

Host JanePC 
    HostName 192.168.0.1
    User Jane

Host BillPC 
    HostName 192.168.0.2
    User Bill

After saving the config file, and then open terminal type ssh JanePC. You can access Jane@192.168.0.1.

SSH X11 Forwarding

Server PC Requirement:

Step 1:

$ sudo apt-get install xauth

Step 2: Modify /etc/ssh/sshd_config file

X11Forwarding yes

Client PC Requirement:

Step 1: vim ~/.ssh/config, add ForwardX11 yes

Sample config

 Host JanePC 
    HostName 192.168.0.1
    User Jane

Host BillPC 
    HostName 192.168.0.2
    User Bill

 Host *
  ForwardX11 yes

Step 2: Test

ssh -X Jane@192.168.0.1

$ gedit

SSH Remote Control Without Password

Step 1: Generate public key

$ ssh-keygen

This will create id_rsa.pub key under ~/.ssh/ directory.

Step 2: Copy the key around remote PC

$ ssh-copy-id -i .ssh/id_rsa.pub Jane@192.168.0.1

Step 3: Test

$ ssh Jane@192.168.0.1

More SSH Config Reference.

Enable Or Disable X11 Forwarding in SSH server

Modify sshd configuration file:

$ sudo vim /etc/ssh/sshd_config

Search X11Forwarding:

X11Forwarding no

Reload or restart SSH server service:

$ sudo systemctl restart sshd

Reference

Swap Memory

In Linux OS, whenever RAM has an insufficient amount of memory to hold a process, it borrows some amount of memory from the secondary storage to store its inactive content. Here, the borrowed space from the hard disk is called Swap Memory. Linux swap is a very useful way to extend the RAM. Because it provides the necessary additional memory when RAM space has been exhausted and a process has to be continued.

Pros:

• Swap saves from crashes
• It can easily hold those inactive blocks of RAM that are hardly used once or twice and then they are never used. The freed up RAM can then be used to hold more programs that have a higher priority

Cons:

• Swap is slower than RAM. Adding a swap space won't make your computer faster, it will only help to overcome some limitations posed by the RAM size.

The safest: RAM = SWAP

Check Swap Command

$ swapon

Cut Command

Cut text's words by specific colume

 cut -c 5- < file1.txt > file2.txt

• [5-] cut start point which is 5th character.

file1.txt

aaaaabbbbbccccc

after hitting command:

file2.txt

abbbbbccccc

zip command

zip a directory but exclude some directories:

$ zip -r zip_file_name foo -x "foo/dir1/*" "foo/dir2/*"

uname

Linux Kernel Name

$ uname -s

Linux Kernel release

$ uname -r

Get Machine Architecture

$ uname --m

Processor Type

$ uname -p

Port-Forwarding

Set port-forwarding 3030 to 3030

sudo iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 3030 -j REDIRECT --to-port 3030

Check port-forwarding

sudo iptables -t nat -L --line-numbers

Delete port-forwarding

sudo iptables -t nat -D PREROUTING 3

"3" is displayed in second command.

Terminal Setting

Install Terminator

$ sudo apt-get install terminator

Set Default Terminal

$ sudo update-alternatives --config x-terminal-emulator

Troubleshooting

apt-get update error

Detailed error message

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://apt.kitware.com/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6AF7F09730B3F0A4
W: Failed to fetch https://apt.kitware.com/ubuntu/dists/focal/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6AF7F09730B3F0A4
W: Some index files failed to download. They have been ignored, or old ones used instead.

solution

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys  6AF7F09730B3F0A4

remmina codec error Ubuntun 18.04

$ sudo apt-add-repository ppa:remmina-ppa-team/remmina-next
$ sudo apt update
$ sudo apt install remmina remmina-plugin-rdp remmina-plugin-secret
$ sudo killall remmina

restart remmina

Docker Container

Gtk-WARNING **: cannot open display: :x.0

Add -v /tmp/.X11-unix:/tmp/.X11-unix -e DISPLAY=unix$DISPLAY option

ImportError: libGL.so.1: cannot open shared object file: No such file or director

e.g. unbuntu 18.04 docker

apt-get update
apt-get -y install libgl1-mesa-glx

dpkg

Error: E: Sub-process /usr/bin/dpkg returned an error code (1) when install a package.

Solution:

$ sudo rm -r /var/lib/dpkg/info/*
$ sudo dpkg --configure -a
$ sudo apt update -y

Can not open settings

Solution:

$ sudo apt-get remove gnome-control-center
$ sudo apt autoremove
$ sudo apt-get install gnome-control-center

System Settings Can't Open in Ubuntu 18.04

$ sudo apt-get remove gnome-control-center
$ sudo apt autoremove
$ sudo apt-get install gnome-control-center

journalctl command

retrieving messages from the last boot:

 journalctl -b -1

To list the boots of the system:

journalctl --list-boots

Time Ranges

journalctl --since "1 hour ago"
journalctl --since "2 days ago"
journalctl --since "2015-06-26 23:15:00" --until "2015-06-26 23:20:00"

By Unit

To see messages logged by any systemd unit, use the -u switch. The command below will show all messages logged by the Nginx web server. You can use the –since and –until switches here to pinpoint web server errors occurring within a time window.

journalctl -u nginx.service
journalctl -u nginx.service -u mysql.service

Follow or Tail

 journalctl -u mysql.service -f
 journalctl -n 50 --since "1 hour ago"

The -r parameter shows journal entries in reverse chronological order, so the latest messages are printed first.

 journalctl -u sshd.service -r -n 1

Output Formats

 journalctl -u apache2.service -r -o json-pretty

more

Check Service log

$ journalctl -u service-name.service

for the current boot:

$ journalctl -u service-name.service -b

reference1

reference2

log reference

/var/log/ File Too Large

Check Error Log:

$ tail -f /var/log/syslog

Clearing the /var/log/syslog file:

$ sudo cat /dev/null > /var/log/syslog

Reset PATH

$ source /etc/environment 

$ echo PATH

apt-get update failed

In some cases, update error like this:

Err:11 http://ppa.launchpad.net/inameiname/stable/ubuntu bionic Release
404 Not Found [IP: 91.189.95.85 80]

It mentioned inameiname message in this error.

Solution

Step 1:

$  cd /etc/apt/sources.list.d/

Step 2: Check your .list files:

$ ls -l

In my case, it's similar like this:

user@user:/etc/apt/sources.list.d$ ls -l
total 36
-rw-r--r-- 1 root root  71 Dec 29 10:34 gazebo-stable.list
-rw-r--r-- 1 root root  71 Dec 29 10:34 gazebo-stable.list.save
-rw-r--r-- 1 root root 189 Dec 29 10:34 google-chrome.list
-rw-r--r-- 1 root root 189 Dec 29 10:34 google-chrome.list.save
-rw-r--r-- 1 root root 138 Dec 29 10:34 inameiname-ubuntu-stable-bionic.list
-rw-r--r-- 1 root root 338 Dec 29 10:34 nvidia-container-runtime.list
-rw-r--r-- 1 root root 336 Dec 29 10:34 nvidia-container-runtime.list.save
-rw-r--r-- 1 root root 193 Dec 29 10:34 vscode.list
-rw-r--r-- 1 root root 193 Dec 29 10:34 vscode.list.save

-rw-r--r-- 1 root root 138 Dec 29 10:34 inameiname-ubuntu-stable-bionic.list this file maybe caused error.

Step 3:

$ sudo rm inameiname-ubuntu-stable-bionic.list

Step 4:

$ sudo apt-get update

Serial port permission denied errors

This is because the device file of the serial port does not have permissions to allow to currently logged in user to "read" or "write" to the serial device.

Confirm device user:

$ ls -l /dev/ttyUSB*

verify if the user does belong to the dialout group

$ id -Gn Jane

add the user to the "dialout" supplementary group

$ sudo usermod -a -G dialout <username>

logout and login, try the "id" command:

$ id -Gn Jane

more

dpkg common commands

Install package

$ sudo dpkg -i your.deb

Search installed package

$  sudo dpkg -l pkg_name

or

$  sudo dpkg --list pkg_name

$ dpkg -l | grep part_of_pkgName

remove

$ sudo dpkg --remove pkg_name

and

$  sudo dpkg --purge pkg_name

email

sudo apt-get install mailutils
mkfifo /var/spool/postfix/public/pickup
service postfix restart
 echo "Message Body Here" | mail -s "Subject Here" user@example.com -A backup.zip

youtube-dl

Download FHD video

youtube-dl  -f 137  https://www.youtube.com/watch\?v\=8SVrydUA6oU

GStreamer

Preinstallation

$ sudo apt-get install v4l-utils

Check v4l devices

$ v4l2-ctl --list-devices

Check supported format

$ v4l2-ctl -d /dev/video0 --list-formats-ext

Check connected devices

$ v4l2-ctl --list-formats-ext

Commands

Hello World

$ gst-launch-1.0 videotestsrc ! 'video/x-raw, width=(int)1280, height=(int)720, format=(string)I420, framerate=(fraction)30/1' ! nveglglessink -e

vl4 device

Simple display

$  gst-launch-1.0 v4l2src ! xvimagesink

or

$ gst-launch-1.0 -ev v4l2src device=/dev/video1 ! xvimagesink

Save As .mp4

Using h264 codec:

$ gst-launch-1.0 videotestsrc ! 'video/x-raw, width=(int)1280, height=(int)720, format=(string)I420, framerate=(fraction)30/1' ! omxh264enc ! 'video/x-h264, stream-format=(string)byte-stream' ! h264parse ! qtmux ! filesink location=test.mp4 -e

Read video file

Read .mp4 and decodeing:

$ gst-launch-1.0 filesrc location=test.mp4 ! qtdemux name=demux ! h264parse ! omxh264dec ! nveglglessink -e

Read webcam and encoding stream

$ gst-launch-1.0 v4l2src device=/dev/video1 ! decodebin ! videoconvert ! omxh264enc ! h264parse ! omxh264dec ! nveglglessink -e

RTP Streaming

Send to host port 5000:

$ gst-launch-1.0 v4l2src device=/dev/video1 ! decodebin ! videoconvert ! omxh264enc ! video/x-h264, stream-format=byte-stream ! rtph264pay ! udpsink host=127.0.0.1 port=5000

Receive Streaming:

$ gst-launch-1.0 udpsrc port=5000 ! application/x-rtp, encoding-name=H264, payload=96 ! rtph264depay ! h264parse ! omxh264dec ! nveglglessink -e

Jpg image processing

gst-launch-1.0 multifilesrc location=img_%06d.jpg caps=image/jpeg,framerate=30/1 ! jpegdec ! videoconvert ! jpegenc ! multifilesink location=jpgs/img_post_%06d.jpg