Ubuntu Basics

New apt vs apt-get
https://itsfoss.com/apt-vs-apt-get-difference/

apt-get update downloads the package lists from the repositories and "updates" them to get information on the newest versions of packages and their dependencies.

apt-get upgrade will fetch new versions of packages existing on the machine if APT knows about these new versions by way of apt-get update.

25 Useful commands of "apt-get and apt-cache"

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Date
Find out time zones
#timedatectl list-timezones

Set your timezone
#sudo timedatectl set-timezone America/Toronto

Enable timesyncd
#sudo timedatectl set-ntp on

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Add user
adduser webadmin
chmod -aG sudo webadmin (change secondary group to sudo -a: append)
Show user groups
groups webadmin

deluser, delgroup (userdel, groupdel, low-level utilities)

Find users and groups
cat /etc/passwd
cat /etc/group

usermod (Modify user account)
usermod -g (change primary group)
usermod -G (change secondary group)
usermod ©d /srv/files/ftp ftp (change home directory)

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Uninstall software/package

$sudo apt-get remove phpmyadmin
$sudo apt-get purge phpmyadmin
$sudo apt-get autoremove
The "apt-get remove phpmyadmin" command will uninstall the phpmyadmin package, the purge command will remove configuration files related to Ubuntu phpMyAdmin and the autoremove command will uninstall all the dependency packages that are no longer required.

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Get to bash automatically and display correct prompt
less /etc/passwd
mindaji:x:1000:1000::/home/mindaji:/bin/bash

In .bashrc
PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '

Read more...

Check ports open
netstat -ntlp | grep LISTEN

change Time Zone
sudo dpkg-reconfigure tzdata

Change IP

find out interface: ifconfig -a

sudo vi /etc/network/interfaces

Edit file interfaces:
auto eth0
iface eth0 inet static
address 192.168.1.100
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1
dns-servernames 192.168.2.32 8.8.8.8

Find installed either network ID:
#ifconfig

shut down network: #ifdown -a
start the network: #ifup -a

Restart the demon: sudo service networking restart

Ubuntu 18.10 or later
https://linuxconfig.org/how-to-configure-static-ip-address-on-ubuntu-18-10-cosmic-cuttlefish-linux

Enter the super user shell
sudo -i

sudo su

Use 'awk' to view files
sudo awk '{ FS=":"; } { print $1; }' /etc/passwd
get the first column (saperated by ":")

Full syntax:
awk 'BEGIN { action; }
/search/ { action; }
END { action; }' input_file

check open ports
nmap external IP address

Firewall ufw (refer to the pdf for more details)
1. ufw enable
2. ufw allow 25/tcp

root@ubuntu:~# ufw status numbered
Status: active

To Action From
-- ------ ----
[ 1] 80 ALLOW IN Anywhere
[ 2] 80/tcp DENY IN 162.159.209.77
[ 3] 80/tcp DENY IN 162.159.208.77
[ 4] 80/tcp DENY IN 191.96.249.53
[ 5] 80/tcp DENY IN 191.96.249.54

Check status of services
service --status-all

nano search: contro+w, find next: alt+w

check which group a user belongs to
groups mji

'top' show information like tasks, memory, cpu and swap. Press ‘q‘ to quit window.

Check performance - others
iotop (showing I/O on the system)
netstat -t (showing connections)
Take a look at the apache logfiles and find out what the server did last
set some RLimits for the apache process. When these limits are reached the process will be killed, giving you some more information

List installed packages
apt list --installed

dig google.com - find out the A record of a domain

Search for a string in all the files in a directory
example: grep -r "mydomain.com" /etc/apache2/

Check open ports
netstat -anltp | grep "LISTEN"

grep minda -r, grep -w "minda" -r (search for exact word)

Using tar to compress a directory or file
$tar -czvf archive.tar.gz stuff (stuff is a folder in the current directory)

-c: Create an archive.
-z: Compress the archive with gzip.
-v: Display progress in the terminal while creating the archive, also known as “verbose” mode. The v is always optional in these commands, but it’s helpful.
-f: Allows you to specify the filename of the archive.
-p: preserve the permissions

extract
$tar -xzvf archive.tar.gz (same, but use 'x' instead of 'c')

Exclude a directory
tar --exclude="/var/www/html/zota/pub/media/catalog/product/cache" -czvf /home/mji/backup/zota/zota_media$(date +%y%m%d_%H%M).tar.gz  /var/www/html/zota/pub/media/catalog/product/

List content of a compressed file
sudo tar -ztvf /backup/files.backup.Nov_6_2009.tar.gz

Find errors with tar
tar --exclude="/var/www/html/zota/var/backups" -czvf /home/mindaji/backup/zota/zota_$(date +%y%m%d_%H%M).tar.gz /var/www/html/zota/ > /dev/null

Using unzip
unzip file.zip -d destination_folder

apt-get update: downloads the package lists from the repositories and "updates" them to get information on the newest versions of packages and their dependencies. It will do this for all repositories and PPAs.

apt-get upgrade: will fetch new versions of packages existing on the machine if APT knows about these new versions by way of apt-get update.

apt-get dist-upgrade: will do the same job which is done by apt-get upgrade, plus it will also intelligently handle the dependencies, so it might remove obsolete packages or add new ones.

Check status of services
service --status-all

Check User ID and groups
id mji

Check secondary groups you are in:
groups $(whoami)

Change my primary group to www-data
sudo usermod -g www-data mji

Using rsync to copy
sudo rsync -rav magento2ce/ magento2ce_setup2/

Copy directory
cp -R source destination/

Copy or back up locally or remotely
rsync options source destination
-v : verbose
-r : copies data recursively (but don’t preserve timestamps and permission while transferring data
-a : archive mode, archive mode allows copying files recursively and it also preserves symbolic links, file permissions, user & group ownerships and timestamps
-z : compress file data
-h : human-readable, output numbers in a human-readable format

Exclude:
tar --exclude="/var/www/html/zota/pub/media/catalog/product/cache" -czvf /home/mji/backup/zota/zota_system$(date +%y%m%d_%H%M).tar.gz /var/www/html/zota/

Using RCP to copy file to and from remote computers

$rcp longwise_191222_1917.* mji@www.dataclubus.com:/home/mji/

https://www.lifewire.com/uses-of-command-rcp-2201078

Example:
rsync -avzh /root/rpmpkgs /tmp/backups/
To a remote computer: rsync -avz rpmpkgs/ root@192.168.0.101:/home/
To the local Machine: rsync -avzh root@192.168.0.100:/home/tarunika/rpmpkgs /tmp/myrpms

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