Category: Linux

SSH Too many authentication failures

When i ssh into a server, i get following error

root@lab:~# ssh [email protected] -p 3333
Received disconnect from 14.18.58.78: 2: Too many authentication failures
root@lab:~#

I checked server log (/var/log/auth.log) and found following

Nov 13 19:06:42 lab sshd[32030]: error: maximum authentication attempts exceeded for root from 188.40.131.92 port 52956 ssh2 [preauth]
Nov 13 19:06:42 lab sshd[32030]: Disconnecting: Too many authentication failures [preauth]

This error happens when you have several SSH keys. When you try to connect to remote server, ssh client try to autenticate to remote server using SSH keys present on your computer. If you have several keys, ssh client make that much login attempts if the keys are valid for remote server you are trying to login.

ssh server deamon have a settings MaxAuthTries. Default value for this settings is 6. If number of invalid login attempt exceeds the value of MaxAuthTries, you will get above error.

You can see all SSH keys on your computer with

ssh-add -l

If you have many keys, consider removing some of the keys from agent using ssh-add command.

To fix this error edit file

vi /etc/ssh/sshd_config

Check if the file have entry for MaxAuthTries, if yes, increase its value. If no entry present in the server add it.

MaxAuthTries 8

Restart sshd service.

systemctl restart sshd

You can see how many login attemts you make using ssh -v option (verbose).

root@server12:~# ssh -v [email protected] -p 3333
OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data /root/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 174.138.58.78 [174.138.58.78] port 3333.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/identity type -1
debug1: identity file /root/.ssh/identity-cert type -1
debug1: identity file /root/.ssh/id_rsa type 1
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Ubuntu-4ubuntu2.8
debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.8 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-sha1 none
debug1: kex: client->server aes128-ctr hmac-sha1 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<2048<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host '[174.138.58.78]:3333' is known and matches the RSA host key.
debug1: Found key in /root/.ssh/known_hosts:139
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering public key: /home/boby/.ssh/id_rsa
debug1: Authentications that can continue: publickey,password
debug1: Offering public key: boby@hon-pc-01
debug1: Authentications that can continue: publickey,password
debug1: Offering public key: redbridgefinance-mumbai
debug1: Authentications that can continue: publickey,password
debug1: Offering public key: aws-eb
debug1: Authentications that can continue: publickey,password
debug1: Offering public key: aws-austin-boby
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /root/.ssh/identity
debug1: Offering public key: /root/.ssh/id_rsa
Received disconnect from 174.138.58.78: 2: Too many authentication failures
root@server12:~#

See SSH

November 13, 2020

Copying file using scp

scp is secure copy. That is you can copy file between servers over ssh connection.

scp [-1246BCpqrv] [-c cipher] [-F ssh_config] [-i identity_file]
         [-l limit] [-o ssh_option] [-P port] [-S program]
         [[user@]host1:]file1 [...] [[user@]host2:]file2

Example

scp file.extn user@remote-server-ip:/path/

For server with ssh on non default port, for eg: 3333

scp -P 3333 iberiaca_vshare.sql [email protected]:/root/

See rsync, Linux Commands

November 13, 2020

install fantastico on Cpanel Server
For installing fantastico, run following command on ssh
```
cd /usr/local/cpanel/whostmgr/docroot/cgi 
wget -N http://files.betaservant.com/files/free/fantastico_whm_admin.tgz
tar -xzpf fantastico_whm_admin.tgz 
rm -rf fantastico_whm_admin.tgz
```
Now Login to WHM

WHM -> Plugins -> Fantastico De Luxe WHM Admin (scroll down the left menu).

After installing Fantastico De Luxe WHM Admin will auto-update your existing installation. All files will moved or created to /var/netenberg.

See Cpanel Server
November 13, 2020
SSH Tunnel
If you have a server with SSH access, you can use it as sock 5 proxy or for port forwarding with just ssh access.

Socks5 Proxy

SSH tunnel can be used for browsing security. It act like a socks5 proxy.
```
ssh root@SERVER_IP -D 7373
```
OR
```
ssh -f -N root@REMOTE_SERVER_IP -D 7373
```
SERVER_IP is IP of the remote server, that you will be using as sock 5 server.

You can configure your browser to use sock5 proxy with IP address 127.0.0.1 and port 7373. You can change port by changing port in above commands.

-N = Do not execute a remote command. This is useful for just forwarding ports.
-f = go into background mode.

Forwarding Remote Port to local

You have a remote server that run a service on some port, that is not accessable to public. This is useful for services like MySQL, redis that is bind to 127.0.0.1 by default for security reason.
```
ssh -L 9999:127.0.0.1:3306 root@REMOTE_SERVER_IP
```
Example
```
ssh -L 9999:127.0.0.1:3306 [email protected]
```
MYSQL running on remote server will be available on port 9999 on local computer.

You can add -f -N option in cause you need above ssh command run in background.

Forwarding local port to remote server

Lets say you have a local web site running on your computer, you need to show this to your customer. You can’t make the web site from your computer as you are behind NAT network and your router don’t support port forwarding.

To forward local port to remote server, run
```
ssh -R REMOTE_PORT:localhost:LOCAL_PORT root@REMOTE_SERVER_IP
```
Example
```
ssh -R 8080:localhost:80 [email protected]
```
Service running on port 80 on local computer will be available on remote server on port 8080. Your customer can view the web site using url REMOTE_SERVER_IP:8080

See SSH, SSH Port Forwarding
November 13, 2020
bash: man: command not found
When running man command on a debian server, i get error
```
root@lab:~# man sftp
-bash: man: command not found
root@lab:~#
```
This is because man-db package not installed on the server. To fix, install man-db package with
```
apt install man-db
```
See Errors
November 13, 2020
host

Find Reverse-DNS/PTR using dig, nslookup, host

November 9, 2020
Find Reverse-DNS/PTR using dig, nslookup, host
Reverse-DNS/PTR is used by mail servers. It is used to map an IP address to FQDN or hostname.

To find Reverse DNS record for an IP address, run
```
nslookup IP_ADDR_HERE
```
In this example IP 51.38.246.115 have a Reverse DNS record ok.serverok.in

Using dig

You can also use dig command to find PTR record for an IP address.
```
dig -x IP_ADDR_HERE
dig +short -x IP_ADDR_HERE
```
Using host
```
host IP_ADDR_HERE
```
See DNS
November 9, 2020
Percona Monitoring and Management

Percona Monitoring and Management is an Open Source monitoring software for MySQL, PostgreSQL and MongoDB.

https://www.percona.com/software/database-tools/percona-monitoring-and-management

It is based on grafana and node_exporter. You can see source code at

https://github.com/percona/pmm

Install instructions for Percona Monitoring and Management available at

https://www.percona.com/software/pmm/quickstart

See MySQL

November 9, 2020
Enable FTP for EasyEngine Website
To Enable FTP for EasyEngine web sites, we need to install pure-ftpd. On Ubuntu/Debian, run
```
apt install -y pure-ftpd
```
Enable virtial FTP users
```
ln -s /etc/pure-ftpd/conf/PureDB /etc/pure-ftpd/auth/PureDB
touch /etc/pure-ftpd/pureftpd.pdb
```
In EasyEngine, we sites files are owned by www-data user, this user have a UID of 33. By default pure-ftpd won’t allow this. To enable users with UD 33 to login, run
```
echo 1 > /etc/pure-ftpd/conf/MinUID
```
Now lets create FTP user for a web site running in EasyEngine.
```
pure-pw useradd  FTP_USER_HERE -u www-data -g www-data -d /opt/easyengine/sites/DOMAIN_NAME_HERE/app/
```
In above command replace

FTP_USER_HERE = FTP user for the web site, this can be any name, no space

DOMAIN_NAME_HERE = the domain name of the web site that is hosted in EasyEngine, that you need FTP access.

When you run above command, you will be asked to select password for the FTP user, this can be used to login to FTP server.

Before you can login to FTP server with newly created virtual FTP user, you need to run
```
pure-pw mkdb
systemctl restart pure-ftpd
```
Change FTP Password

If you want to change FTP user for a user, you can run
```
pure-pw passwd FTP_USER_HERE
pure-pw mkdb
systemctl restart pure-ftpd
```
Passive FTP Configuration

Many cloud hosting providers like AWS, Google Cloud, Oracle Cloud, AliCloud servers use NAT networking. That is your VM have private IP and your public IP is routed to your VM. In such case, you need to enable Passive FTP, for this run
```
echo "30000 50000" > /etc/pure-ftpd/conf/PassivePortRange
echo "YOUR_PUBLIC_IP" > /etc/pure-ftpd/conf/ForcePassiveIP
```
YOUR_PUBLIC_IP = replace this with your public IP address.

Restart pure-ftpd
```
systemctl restart pure-ftpd
```
Firewall configuration

For Passive FTP, you need to open following ports in your firewall
```
tcp 21
tcp 30000:50000
```
On Oracle Cloud server, i edited file
```
vi /etc/iptables/rules.v4
```
Find
```
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
```
Replace with
```
-A INPUT -p tcp -m state --state NEW -m tcp --dport 21 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 30000:50000 -j ACCEPT
```
Now restore firewall rules with
```
iptables-restore < /etc/iptables/rules.v4
```
Now FTP will work.

See EasyEngine
November 8, 2020

Uninstalling Software in Debian Server

To uninstall a software on Debian server, run

apt remove PKG_NAME

Example

uninstall software on debian server

To all installed software with specific name, run

dpkg-query -l PKG_NAME

Example

root@lab:~# dpkg-query -l 'nginx*'
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version          Architecture Description
+++-==============-================-============-=========================================================
ii  nginx          1.14.2-2+deb10u3 all          small, powerful, scalable web/proxy server
ii  nginx-common   1.14.2-2+deb10u3 all          small, powerful, scalable web/proxy server - common files
un  nginx-doc                        (no description available)
un  nginx-extras                     (no description available)
ii  nginx-full     1.14.2-2+deb10u3 amd64        nginx web/proxy server (standard version)
un  nginx-light                      (no description available)
root@lab:~#

In above list, packages start with

ii = installed
un = currently not installed on the server

When you uninstall a package, it won’t remove all config files, such packages list as uninsalled (un). To completely delete a package, its config file and data, use

apt remove --purge PKG_NAME

Example

apt remove --purge apache2

After removing a software package, you may need to run apt autoremove to remove any unused dependency.

apt autoremove

See apt

November 7, 2020

EasyEngine Create Site

To create HTML web site

ee site create example.com --html

To create PHP web site

ee site create example.com --php

To create PHP/MySQL web site

ee site create example.com --mysql

To enable LetsEncrypt SSL, add –letsencrypt

ee site create example.com --letsencrypt

Create WordPress site

ee site create example.com --wp # install wordpress without any page caching
ee site create example.com --w3tc # install wordpress with w3-total-cache plugin
ee site create example.com --wpsc # install wordpress with whisp-super-cache plugin
ee site create example.com --wpfc # install wordpress + nginx fastcgi_cache
ee site create example.com --wpredis # install wordpress + nginx redis_cache

Create WordPress site with PHP 7.3 and cache enabled

ee site create domain.com --type=wp --php=7.3 --cache --ssl=le

Secify wordpress admin user and email during site creation

ee site create stunningbeachwear.ee.serverok.in --type=wp --php=7.4 --cache --ssl=le --admin-user=admin [email protected]

Create WordPress multi site

ee site create example.com --wpsubdir # install wpmu-subdirectory without any page caching
ee site create example.com --wpsubdir --w3tc # install wpmu-subdirectory with w3-total-cache plugin
ee site create example.com --wpsubdir --wpsc # install wpmu-subdirectory with wp-super-cache plugin
ee site create example.com --wpsubdir --wpfc # install wpmu-subdirectory + nginx fastcgi_cache
ee site create example.com --wpsubdir --wpredis # install wpmu-subdirectory + nginx redis_cache

WordPress Multisite with subdomain

ee site create example.com --wpsubdom # install wpmu-subdomain without any page caching
ee site create example.com --wpsubdom --w3tc # install wpmu-subdomain with w3-total-cache plugin
ee site create example.com --wpsubdom --wpsc # install wpmu-subdomain with wp-super-cache plugin
ee site create example.com --wpsubdom --wpfc # install wpmu-subdomain + nginx fastcgi_cache
ee site create example.com --wpsubdom --wpredis # install wpmu-subdomain + nginx redis_cache

Ref: https://easyengine.io/docs/commands/site/create/

See EasyEngine

November 7, 2020

Disable SELinux on CentOS/RHEL
To disable SELinux

Method 1
```
sed -i 's/SELINUX=enforcing/SELINUX=disabled/' /etc/selinux/config
setenforce 0
```
Method 2

edit file
```
vi /etc/selinux/config
```
Find
```
SELINUX=enforcing
```
Replace with
```
SELINUX=disabled
```
Reboot the server with
```
reboot
```
You can disable selinux for current session by running command
```
setenforce 0
```
See SELinux
November 7, 2020

Category: Linux

Socks5 Proxy

Forwarding Remote Port to local

Forwarding local port to remote server

Using dig

Using host

Change FTP Password

Passive FTP Configuration

Firewall configuration

Create WordPress site

Create WordPress multi site

WordPress Multisite with subdomain

Method 1

Method 2