e-help

OS version or Distributions Details

cat /etc/os-release
lsb_release 

To Know more about lsb_release click here

manual for unix command

man <command>
man touch
man mkdir
man watch

RAM

To Get memory info
```
free -m
```
CPU
To get cpu info
```
cat /proc/cpuinfo
```

system/kernel version

uname -a
uname -v
uname -r

System Current IP address

ifconfig
ip addr show
ip addr show eth0

free disk space

df -ah

check size of the directory

du -sh /dir/path

check open port in unix

netstat
netstat -tunlp
sudo netstat -tulp

# 0.0.0.0:PORT : It means Open port for all
# 127.0.1.1:PORT : local ip, not available outside machine 

cpu usage for given process

ps aux | grep nginx

mount a drive or check mount status

ls /mnt
mount /dev/sd2 /mnt
mount
less /etc/fstab

Application Environment Setup Using /etc/profile.d/*

When a user logs in, environment variables are set from various places.  That includes /etc/profile (for all users).

Then all the files in the /etc/profile.d directory.

Then ~/.bash_profile, then ~/.bashrc.

/etc/profile.d/ is a good place to put your application specific setups.  For example, I always use SSH for CVS (cf. RSH).  So I use:

groups - will show all the attached groups
groups <<userName>> - will show all the attached groups

# user id in hexa
id -u
#  Group in haxa
id -g

sudo user

visudo - and just follow root user 
/etc/sudoers.d/<<user>>
and the <<user>> file inside /etc/sudoers.d/<<user>> path has to be update like below

Defaults env_keep += "ftp_proxy http_proxy https_proxy"
Defaults:<<user>> !requiretty
<<user>> ALL=(ALL) NOPASSWD: ALL

chown (change owner)

chown -R username:groupname file/folder

chmod

example - drwxr-xr-x
from the other example
d is for- folder/l is for symboliclink
and it has - owner-rwx, group- rx, other -rx

*chmod table

Action	Number	Other
Read	4	-
Write	2	-
Execute	1	-

pid

all the process being create in unix can be found on /run directory
the process file extensation is .pid

network

ifconfig - give all ip details
netstat -tulpn - will show all the running port
ps -ef - show all the process id

search

grep –help # will search the search string in the (.) dir or current directory
grep -r ‘search string’ .

nc (netcat)

This tools allow you to intercept http request for debug purpose , To know more https://www.computerhope.com/unix/nc.htm
nc -zvv localhost 27017 - ping from command line
nc -l 8080 - will listen on port 8080
size of the disk and folder
du -shx * - will show all folder size in destination in GB/MB
df -h - will show the disk space
du -h -s -will show the disk space used by files and directory
du -h sort -h - will show the size of all the folder is sorting (more size folder will be on below)
du -sh * - will show the size in mb for all the folder inside root dir
du -sh foldeName - will show the size of the folder folderName
du -sh . - will show the size of the root dir
du -ks /var/lib/docker/* sort -nr head - will show the details of the size of traget folder

copy(ssh,local)

scp -i keypairFile local_path_to_copy user@hostname:/path_to_copy_in_remote
scp -r source/path ssh user@url:path/to/copy

start and stop script example

start script
-------------
export  JAVA_HOME=/home/ubuntu/software/jdk1.8.0_101;
export  JENKINS_HOME=/home/ubuntu/workspace/jenkins_home;
nohup  $JAVA_HOME/bin/java -jar /home/ubuntu/software/jenkins.war --httpPort=8081 & echo $! > jenkins_pid.txt

stop script
-------------
kill -9 $(cat jenkins_pid.txt);
rm -rf nohup.out;
rm -rf jenkins_pid.txt;

unix folder and file management

chown robert file.txt - change the user for file file.txt
groups username - create a user group
chgrp webdev file.txt - change the group name of the file.tx

chown -R user:group folderName/ - this will change the owner of the target folder

tar and untar

tar -xzvf <<file_folder_name>>.tgz  - untar the target folder
tar -zcvf <<target_folder>>.tgz <<source_folder>>

options
-z : Compress archive using gzip program
-c: Create archive
-v: Verbose i.e display progress while creating archive
-f: Archive File name

tar xf location/filename.tgz -C path/where/to/extract --strip-components=1

for more help - https://www.cyberciti.biz/faq/how-do-i-compress-a-whole-linux-or-unix-directory/

exit code

example:  exit 1 or exit 0
Exit code 0        Success
Exit code 1        General errors, Miscellaneous errors, such as "divide by zero" and other impermissible operations
Exit code 2        Misuse of shell builtins (according to Bash documentation)        Example: empty_function() {}

swap memory setup for tmp foler or other

mount -o remount,size=2G,noatime /tmp

check a http host and port is working or not

nc -zvv localhost 8081

check linux machine details

uname -a
and
cat /etc/os-release

networking

nslookup <<hostname>>
netstat -tunlp
lsof -i

ssh key pair

To generate a ssh key pair on your ~/.ssh folder
```
ssh-keygen
```

To Generate a ssh key pair in other folder

cd /folder/to/generate/ssh-key-pair
ssh-keygen -f id_rsa

Generate a new public key from a private key
```
ssh-keygen -y -f id_rsa > api2.pub
```

Validate the finger prints

ssh-keygen -l -f id_rsa
ssh-keygen -l -f id_rsa -f api2.pub

other way

ssh-keygen -t rsa -b 4096 -m PEM -f jwtRS256.key
# Don't add passphrase
openssl rsa -in jwtRS256.key -pubout -outform PEM -out jwtRS256.key.pub
cat jwtRS256.key
cat jwtRS256.key.pub

SSH tunneling

ssh -i .ssh/id_rsa -L LOCAL_EXPOSED_PORT:TARGET_MACHINE_IP:TARGET_APPLICATION_PORT username@jumphost.host.-name

crontab

To see all the cron job use

crontab -l

List all the Listen port

sudo lsof -i -P -n | grep LISTEN
#if you want to kill a port
sudo kill -9 <port>

watch

watch -n 5 <command> - run the in each 5 sec.

netstat

This command will list all the tcp and udp port with pid and other stuff. after that you can use kill commaond kill -9 <pid>

netstat -vanp tcp | grep 8080 # for mac
netstat -tunlp # for unix/linux