Category: Linux

gpg: failed to start the dirmngr
When i add a key with apt-key command, i get error

root@ip-172-31-47-128:~# apt-key adv –recv-keys –keyserver keys.gnupg.net E1F958385BFE2B6E
Executing: /tmp/apt-key-gpghome.0BP6Ro2t54/gpg.1.sh –recv-keys –keyserver keys.gnupg.net E1F958385BFE2B6E
gpg: failed to start the dirmngr ‘/usr/bin/dirmngr’: No such file or directory
gpg: connecting dirmngr at ‘/tmp/apt-key-gpghome.0BP6Ro2t54/S.dirmngr’ failed: No such file or directory
gpg: keyserver receive failed: No dirmngr
root@ip-172-31-47-128:~#

To fix this, run
```
apt -y install dirmngr
```
Once installed, apt-key command worked properly.

root@ip-172-31-47-128:~# apt-key adv –recv-keys –keyserver keys.gnupg.net E1F958385BFE2B6E
Executing: /tmp/apt-key-gpghome.BLNQkuFGIQ/gpg.1.sh –recv-keys –keyserver keys.gnupg.net E1F958385BFE2B6E
gpg: key E1F958385BFE2B6E: public key “X2go Debian/Ubuntu Packaging ” imported
gpg: Total number processed: 1
gpg: imported: 1
root@ip-172-31-47-128:~#

See Install x2go server in Debian 9
May 31, 2018
Install Remote Desktop in Debian/Ubuntu
To install and use Linux remote server as desktop, first install lite weight desktop environment like XFCE on your server.
```
apt update
apt install xfce4 -y
```
Install XRDP
```
apt install xrdp
```
You need to create a user to be used for desktop.
```
useradd -m -s /bin/bash desktop
```
Set password for the user
```
passwd desktop
```
Now login as this user and create .xsession file.
```
su - desktop
echo xfce4-session >~/.xsession
```
Exit out of this user
```
exit
```
Restart XRDP
```
service xrdp restart
```
Now you will be able to connect to this server with any RDP client like you connect to Windows Server (Windows Remote Desktop).
May 30, 2018
Desktop
May 30, 2018
Security
ZAP Attack Proxy – open source software to detect vulnerability.
Disable PHP insecure functions with disable_functions
Find IP with Most Access from Apache Log
Monitor file changes in your Website
inotifywait
Stop xmlrpc.php attack on Cpanel Server
Stop SSH bruteforce with endlessh
https://suricata.io

Check for hacker files
```
find ./ -name '*.php' -exec grep 'Spy Shell' {} \; -print
find ./ -name '*.php' -exec grep 'system(' {} \; -print
find ./ -name '*.php' -exec grep 'exec(' {} \; -print
find ./ -name '*.php' -exec grep 'passthru(' {} \; -print
```
Disable PHP Files on Upload folder
```
deny from all
```
May 29, 2018
Disable PHP insecure functions with disable_functions
When hacking vulnerable web sites, hackers use PHP functions that allow program execution or disk access to get access to server.

Some most commonly used functions are exec, shell_exec and system. These commands allow hackers to execute program as web server user. Most applications may not need these functions, so these functions can be safely disabled with out affecting functionality of your web site.

To disable insecure functions, create a file php.ini with following content
```
disable_functions = "exec,passthru,shell_exec,system,proc_open,popen,parse_ini_file,show_source"
allow_url_fopen = Off
allow_url_include = Off
```
If you have dedicated server or VPS, you can disable these functions server wide by editing php.ini of your server.

Once change is made, make sure it is working properly by checking phpinfo page.
May 29, 2018

Install MongoDB 4 on CentOS 7

Create file

vi /etc/yum.repos.d/mongodb-org-4.0.repo

Add

[mongodb-org-4.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/testing/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-4.0.asc

Install MongoDB with

yum install -y mongodb-org

Set MongoDB to start on boot.

chkconfig mongod on

Start MongoDB

service mongod start

May 27, 2018

Enable Gzip in Amazon Linux

To verify Apache module is loaded, run

[root@ip-172-31-29-220 ~]# apachectl -M | grep deflate
 deflate_module (shared)
[root@ip-172-31-29-220 ~]#

Create file

vi /etc/httpd/conf.d/gzip.conf

Add following content


  # Restrict compression to these MIME types
  AddOutputFilterByType DEFLATE text/plain
  AddOutputFilterByType DEFLATE text/html
  AddOutputFilterByType DEFLATE application/xhtml+xml
  AddOutputFilterByType DEFLATE text/xml
  AddOutputFilterByType DEFLATE application/xml
  AddOutputFilterByType DEFLATE application/xml+rss
  AddOutputFilterByType DEFLATE application/x-javascript
  AddOutputFilterByType DEFLATE text/javascript
  AddOutputFilterByType DEFLATE text/css
  AddOutputFilterByType DEFLATE image/png
  AddOutputFilterByType DEFLATE image/gif
  AddOutputFilterByType DEFLATE image/jpeg

  # Level of compression (Highest 9 - Lowest 1)
  DeflateCompressionLevel 9

  # Netscape 4.x has some problems.
  BrowserMatch ^Mozilla/4 gzip-only-text/html

  # Netscape 4.06-4.08 have some more problems
  BrowserMatch ^Mozilla/4\.0[678] no-gzip

  # MSIE masquerades as Netscape, but it is fine
  BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html

  
    # Make sure proxies don't deliver the wrong content
    Header append Vary User-Agent env=!dont-vary

Restart Apache with

service httpd restart

To verify gzip is working, run

curl -I -H 'Accept-Encoding: gzip,deflate' http://YOUR-SITE-URL/ 2>/dev/null | grep gzip

You will see something like

NOTE: gzip compression only works if you have a reasonably large file. If your file is very small, then gzip won’t do anything.

See gzip

May 26, 2018

Install Google Chrome in Ubuntu

To install Google Chrome Browser in Ubuntu, run

wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
dpkg -i google-chrome-stable_current_amd64.deb
apt install -f

Google Chrome

May 26, 2018

Download a site using SFTP
To download all content of a web site using SFTP, use
```
lftp sftp://USERNAME@IP_ADDR:22 -e 'mirror --verbose --use-pget-n=8 -c /remote/path/ /local/path/'
```
You may encounter lftp Fatal error: Host key verification failed error if you have connected to this SFTP server before. In such case, just login to sevrer using SSH, this will add the key to your known_hosts file.

In this example, i am downloading all files from SFTP server. I used . for remote path as i need everything on FTP home folder downloaded.

See lftp
May 21, 2018
Disable Signup Notification in vShare Youtube Clone
vShare youtube clone script allow you to start your own video sharing web site. You can get the script from

https://www.vshare.in

To disable Signup notification for admin, run following SQL.
```
update sconfig set svalue="0" where soption="notify_signup";
```
See vShare Youtube Clone Script
May 19, 2018

wget

Mirroring a site with wget
wget print content to screen
wget force IPv4/6 download

Download Multiple Files

To download multiple files from FTP server, run

wget ftp://backup2.serverok.in/backup1/*.tar.gz --ftp-user=USER --ftp-password=PASSWORD

Download all files in a folder

wget -r -l1 --no-parent http://cloud.serverok.in/public/

Download Entire Website

wget \
 --recursive \
 --no-clobber \
 --page-requisites \
 --html-extension \
 --convert-links \
 --restrict-file-names=windows \
 --domains example.com \
 --no-parent \
     www.example.com

wget --mirror --convert-links --adjust-extension --page-requisites --no-parent https://domain.com/

Download with Limit Rate

wget -c --limit-rate=60k http://dn.serverok.in/1.mkv

This limits the download rate to 60.0KB/s

Back to Linux Commands

May 16, 2018

Mirroring a site with wget
To mirror a web site for local viewing, you can use
```
wget --mirror --convert-links --html-extension --wait=2 -o log http://www.domain.com
```
–convert-links = After downloading, convert the links suitable for local viewing.
May 16, 2018