Recover grub after windows update

Run this in Windows as an administrator:

bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi

Or:

bcdedit /set "{bootmgr}" path \EFI\ubuntu\grubx64.efi

If you are using PowerShel.

Shell History with date

Include in /root/.bashrc

# History with date
HISTTIMEFORMAT="%F-%T " 

 or

HISTTIMEFORMAT="%d/%m/%y %T "

 
Optional: Clear history
history -c 

Logoff and login again.

Select specific range os lines

Select specific range os lines:

head -22 file.txt | tail -5

 

Insert character at specified position

awk '{$2="#"$2;print $0}' your_file

This will add # to the start of the second (space-separated) column regardless of which position it occurs at.


sed -r -e 's/^.{15}/&#/' file

Insert '#' in position 15

Add / Remove users from AD groups with Powershell

For a users list:

1 - create a file (ex: add-users.ps1);
2 - paste the commands and change file name and group;
3 - the first line of users list must be UserName;
4 - Run the ps1 file with admin user.

Import-module ActiveDirectory
Import-CSV "C:\list_of_users.csv" | % {
Add-ADGroupMember -Identity GROUP -Members $_.UserName
}
pause


For add only one user

Add-ADGroupMember -Identity GROUP -Members USER


To remove users, change Add-ADGroupMember to Remove-ADGroupMember

APT install only security updates

Check security updates:

sudo unattended-upgrade --dry-run -d

If previous command show packages to update:

sudo apt-get -s dist-upgrade | grep "^Inst" | grep -i securi | awk -F " " {'print $2'} | xargs apt-get install

List AD group members from linux

List group members using samba 4 samba-tool:

samba-tool group listmembers <group> -H ldap://<servername> -d0

Upgrade specific package with apt-get

apt-get install --only-upgrade <packagename>

Enable remote desktop from command line

netsh advfirewall firewall add rule name="Open Remote Desktop" protocol=TCP dir=in localport=3389 action=allow

Active / deactive windows firewall command line

Windows Firewall on computers running Windows Vista, Windows 7 and Windows Server 2008 is enabled by default. You may need turn it off for various reasons.
This is how you do it using a command prompt:

• To Turn Off:
• NetSh Advfirewall set allprofiles state off
• To Turn On:
• NetSh Advfirewall set allprofiles state on
• To check the status of Windows Firewall:
• Netsh Advfirewall show allprofiles

psexec for linux

wget http://downloads.sourceforge.net/project/winexe/winexe-1.00.tar.gz
tar xzvf winexe-1.00.tar.gz

cd winexe-1.00/source4/
./autogen.sh
./configure
make

bin/winexe -U user%password //xps8500 'cmd'

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Windows\system32>

Squid regex

\.sex\.com
\.redtube\.com

I also recommend you to block this way to cover all the possibilities:

^http://.*\.*sex\.com/*.*
^http://.*\.*redtube\.com/*.*

Let me explain what are you telling to squid to do with this regex:

^ = this is the beginning of the url

http:// = is the protocol that is always required

. = anything, for example, can be a subdomain or a www

* = the expression BEFORE (the subdomain or www) can happen or not

\ = the next char is not "anything" but a real dot

. = the real dot...

* = ...that can happen or not

sex = the domain

. = next char is a real real dot again

com = top level domain

/* = a dash that can happen or not (covering all the possible websites configurations here)

.* = anything can happen or not after the last dash (/index.php, blah blah)

colored tail

tail, with specific pattern colored
tail -F file | egrep --color 'pattern|$'
OR
tail -f file | egrep --color=always $\|PATTERN
tail -f file | egrep --color=always $\|"PATTERN1|PATTERN2"

tail with coloured output with the help of perl - need more colours? here is a colour table: http://www.tuxify.de/?p=23 Show Sample Output
tail -f FILE | perl -pe 's/KEYWORD/\e[1;31;43m$&\e[0m/g'

Colorize matching string without skipping others this is useful to highlight only some code without losing other lines (eg. software, logs, scripts)
egrep --color=auto 'usb|' /var/log/messages

Shutdown or Restart windows server via linux

Use this command to shutdown the computer remotely:
net rpc shutdown --ipaddress ip --user username%password

Add -r if you want to restart, not shutdown:
net rpc shutdown -r -f --ipaddress ip --user username%password

Get all IPs from host

Ubuntu 16.x
ifconfig | grep inet |awk '{print $2}'


Ubuntu 18.x
ifconfig | grep inet |awk '{print $3}'

nmap essential

Scan IP
nmap 192.168.1.1

Scan network
nmap 192.168.1.0/24

Fast scan
nmap -F 192.168.1.1

Scan machines up
nmap -sP 192.168.1.0/24

Read hosts for a file (one IP or name per line)
nmap -iL /tmp/test.txt

detect remote services (server / daemon) version numbers
nmap -sV 192.168.1.1

Turn on OS and version detection
nmap -v -A 192.168.1.254
nmap -A -iL /tmp/test.txt

Find out if a host/network is protected by a firewall
nmap -sA 192.168.1.254

Scan a host when protected by the firewall
nmap -PN 192.168.1.1

Scan TCP port 80
nmap -p T:80 192.168.1.1

Scan UDP port 53
nmap -p U:53 192.168.1.1

Scan two ports
nmap -p 80,443 192.168.1.1

Scan a host using TCP ACK (PA) and TCP Syn (PS) ping
nmap -PS 192.168.1.1
nmap -PS 21,80,443 192.168.1.1
nmap -PA 192.168.1.1

Scan a host using IP protocol ping
nmap -PO 192.168.1.1

Display the reason a port is in a particular state
nmap --reason 192.168.1.1

Only show open (or possibly open) ports
nmap --open 192.168.1.1

Show all packets sent and received
nmap --packet-trace 192.168.1.1
nmap --packet-trace server1.cyberciti.biz

Scan a host using UDP ping
nmap -PU 192.168.1.1

Stealthy scan
nmap -sS 192.168.1.1

TCP scan
nmap -sT 192.168.1.1

Find out the most commonly used TCP ports using TCP ACK scan
nmap -sA 192.168.1.1

Cloak a scan with decoys
nmap -n -Ddecoy-ip1,decoy-ip2,your-own-ip,decoy-ip3,decoy-ip4 remote-host-ip
nmap -n -D192.168.1.5,10.5.1.2,172.1.2.4,3.4.2.1 192.168.1.5


How do I save output to a text file?
nmap 192.168.1.1 > output.txt
nmap -oN /path/to/filename 192.168.1.1
nmap -oN output.txt 192.168.1.1

Linux Uptime history

Report the historical and statistical running time of system, keeping it between restarts. Like uptime command but with more interesting output.

apt-get install tuptime

tuptime

Colored tail command

apt install multitail
multitail -c /var/log/syslog

OR

apt install grc
grc tail -f /var/log/apache2/error.log

OR

apt install colortail
colortail -f /var/log/apache2/error.log

Locking a directory

For privacy of my data I wanted to lock down /downloads on my file server. So I ran:

chmod 0000 /downloads

The root user can still has access and ls and cd commands will not work. To go back:

chmod 0755 /downloads

Enable Google TCP BBR congestion control

Increase your Linux server Internet speed with TCP BBR congestion control

You must use the Linux kernel version 4.9 or above. On a Debian/Ubuntu Linux type the following grep command/egrep command:

$ grep 'CONFIG_TCP_CONG_BBR' /boot/config-$(uname -r)
$ grep 'CONFIG_NET_SCH_FQ' /boot/config-$(uname -r)
$ egrep 'CONFIG_TCP_CONG_BBR|CONFIG_NET_SCH_FQ' /boot/config-$(uname -r)

Edit the /etc/sysctl.conf file or create a new file in /etc/sysctl.d/ directory:
$ sudo vi /etc/sysctl.conf
OR
$ sudo vi /etc/sysctl.d/10-custom-kernel-bbr.conf

Append the following two lines:
net.core.default_qdisc=fq
net.ipv4.tcp_congestion_control=bbr

$ sudo reboot
OR
$ sudo sysctl --system

You can verify new settings with the following sysctl command. Run:
$ sysctl net.core.default_qdisc
net.core.default_qdisc = fq

$ sysctl net.ipv4.tcp_congestion_control
net.ipv4.tcp_congestion_control = bbr

more info:
https://cloud.google.com/blog/products/gcp/tcp-bbr-congestion-control-comes-to-gcp-your-internet-just-got-faster

Display Bandwidth Usage on Network Interface By Host

Linux Display Bandwidth Usage on Network Interface By Host Using iftop command

sudo apt-get install iftop

iftop
iftop -i interface
iftop [options]

However, iftop works best when you use filters. For example, if you want to find out how much bandwidth users are wasting or trying to figure out why the network is slow, run:
# iftop -f icmp

You can display or analyses packet flowing in and out of the 192.168.1.0/24 network:
# iftop -F 192.168.1.0/24

Disable output for DNS traffic by using filter code such as:
# iftop -f 'not port domain'

Linux cmatrix

sudo apt install cmatrix

cmatrix -bas

 -a: Asynchronous scroll
 -b: Bold characters on
 -B: All bold characters (overrides -b)
 -f: Force the linux $TERM type to be on
 -l: Linux mode (uses matrix console font)
 -o: Use old-style scrolling
 -h: Print usage and exit
 -n: No bold characters (overrides -b and -B, default)
 -s: "Screensaver" mode, exits on first keystroke
 -x: X window mode, use if your xterm is using mtx.pcf
 -V: Print version information and exit
 -u delay (0 - 10, default 4): Screen update delay
 -C [color]: Use this color for matrix (default green) ex: red, blue, white
 

Adminer on Ubuntu 18.04

Download the latest Adminer into our server

sudo mkdir /usr/share/adminer
sudo mkdir /usr/share/adminer/adminer
sudo mkdir /usr/share/adminer/editor

sudo wget "http://www.adminer.org/latest.php" -O /usr/share/adminer/adminer/latest.php

sudo ln -s /usr/share/adminer/adminer/latest.php /usr/share/adminer/adminer/index.php

echo "Alias /adminer /usr/share/adminer/adminer" > /etc/apache2/conf-available/adminer.conf

sudo a2enconf adminer.conf

reload the Apache config

sudo systemctl reload apache2

Access the adminer interface at
http://<Server_IP_or_Domain>/adminer/

Install adminer-editor:

Download from
https://www.adminer.org/en/editor/#download

Copy file to /usr/share/adminer/editor and rename to index.php

echo "Alias /adminer-editor /usr/share/adminer/editor" >> /etc/apache2/conf-available/adminer.conf

reload the Apache config

sudo systemctl reload apache2

Access the adminer interface at
http://<Server_IP_or_Domain>/adminer-editor

Fix MYSQL authentication issue in Ubuntu 18.04

Secure your MySQL installation and set the root password

sudo mysql_secure_installation

From here, you can just press Y and then ENTER to accept the defaults for all the subsequent questions.

Fix authentication issue caused by Ubuntu using auth_socket plugin by default for the root user.
You can set the root user to use the mysql_native_password instead to fix this issue, and we will have to set the root password again to correct this.

log in as sudo to mysql using the username and password set before.

sudo mysql -u root

in MySQL enter the following

USE mysql;

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';

Note:

For security make this password different than your server's password, and dont use the root user in any application that requires a database to store and pull data from.

FLUSH PRIVILEGES;

exit;

File /etc/mail.rc

File /etc/mail.rc

set smtp=10.1.1.1:587
set from=user@example.com
set smtp-use-starttls
set ssl-verify=ignore
set smtp-auth=login
set smtp-auth-user=user@example.com
set smtp-auth-password=Password

Copy AD group

$Source_Group = "CN=Group,OU=Unity,DC=example,DC=com" 
$Destination_Group = "CN=Group,OU=Unity,DC=example,DC=com" 
 
$Target = Get-ADGroupMember -Identity $Source_Group 
foreach ($Person in $Target) { 
    Add-ADGroupMember -Identity $Destination_Group -Members $Person.distinguishedname 
}

Send desktop notification from shell scripts

Install packages
sudo apt-get install libnotify-bin

send some notification
notify-send "rsnapshot done :)"

#another example
...
alert=18000
live=$(lynx --dump http://money.rediff.com/ | grep 'BSE LIVE' | awk '{ print $5}' | sed 's/,//g;s/\.[0-9]*//g')
[ $notify_counter -eq 0 ] && [ $live -ge $alert ] && { notify-send -t 5000 -u low -i   "BSE Sensex touched 18k";  notify_counter=1; }
...

-t 5000: Specifies the timeout in milliseconds ( 5000 milliseconds = 5 seconds)
-u low : Set the urgency level (i.e. low, normal, or critical).
-i gtk-dialog-info : Set an icon filename or stock icon to display (you can set path as -i /path/to/your-icon.png).


A Note About GUI Tools and Cronjob

You need to request local display/input service using export DISPLAY=[user’s machine]:0 command if you are using cronjob to call your scripts. For example, call /home/vivek/scripts/monitor.stock.sh as follows which uses zenity tool:

@hourly DISPLAY=:0.0 /home/vivek/scripts/monitor.stock.sh

SSH timeout interval

A user can log in to the server via ssh, and you can set an idle timeout interval to avoid unattended ssh session. Open sshd_config and make sure following values are configured:
ClientAliveInterval 300
ClientAliveCountMax 0

You are setting an idle timeout interval in seconds (300 secs == 5 minutes). After this interval has passed, the idle user will be automatically kicked out (read as logged out).

Find and fix World-Writable Files

Anyone can modify world-writable file resulting into a security issue. Use the following command to find all world writable and sticky bits set files:

find /dir -xdev -type d \( -perm -0002 -a ! -perm -1000 \) -print

You need to investigate each reported file and either set correct user and group permission or remove it.

Linux partitions security

Create separate partitions for Apache and FTP server roots.
Edit /etc/fstab file and make sure you add the following configuration options:

noexec – Do not set execution of any binaries on this partition (prevents execution of binaries but allows scripts).  
nodev – Do not allow character or special devices on this partition (prevents use of device files such as zero, sda etc).  
nosuid – Do not set SUID/SGID access on this partition (prevent the setuid bit).

Sample /etc/fstab entry to to limit user access on /dev/sda5 (ftp server root directory):

/dev/sda5  /ftpdata          ext3    defaults,nosuid,nodev,noexec 1 2