Admins eHow SysAdmin Tips & Tricks

August 20, 2014

Force public key authentication on SSH daemon (disable password authentication)

Filed under: Debian,linux,Security — Tags: , , , , , , — admin @ 2:18 pm

It is a very good security practice to completely disable password authentication on your Linux server and use public key authentication method.
In order to do that you need to create your own public/private key pair and put the public key in ~/.ssh/authorized_keys

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mkdir -p ~/.ssh
echo 'ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDHV80zPWjPAwKo8Be0k1ypBRMdYDC0H2eQchu3MFsEp8av2F/18GNuHsbyMWp0p1uovP5LGZ/oPZ1ISJxLxxOBiqv0fOyb8uTDYWUUITgGvq9Fppj3BNYTjnLCUAVMKdP3VJ7IPk69ygYR1nhAXiv3dSfeG74f2eo3ZYhrylsVS2G84DUh47FuEFOsfn5s2wXVjwAgqdKBhiVQZWrptf6TEK3fZTVg4rCiRJ+YiIwTZr/CfFHbdqOiwDlGR5fWo0PHHq31lrQXzkASfi3C+ahQFnHsy4+8LdCq+TjzC3J6PbuXP1wpLdm1iP35f61hU1wX2hwhyxdvE+SBXT/PpSVB' >> ~/.ssh/authorized_keys

DISCLAIMER : The above key is my public key, if you put it on your server, I will be able to login into your server 😀
Now add/change the following config to the BEGINNING of /etc/ssh/sshd_config

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ChallengeResponseAuthentication no
PasswordAuthentication no
UsePAM no
PubkeyAuthentication yes

and restart ssh service :

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service ssh restart

In order to check that only public key authentication is available run the following command on the server :

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ssh -o PreferredAuthentications=none -o NoHostAuthenticationForLocalhost=yes localhost -p 22

and you should get this error :

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Permission denied (publickey).

Note : Before closing your current SSH session, I highly recommend you to test that actually you can login into your server by new method. otherwise you may be locked out of your server.

March 20, 2010

How to Disable Password Expiration on Windows Server 2008

Filed under: General,Security,Windows — Tags: , , , , , — admin @ 2:31 pm

If you’re not using Active Directory, your “Local Security Policy” dictates things like password complexity rules, account lockouts, and password expiration. To turn off password expiration:

1) Login as Administrator or a user with Administrator rights
2) Launch “Local Security Policy”: Start > Administrative Tools > Local Security Policy
3) Expand “Account Policies”
4) Select Password Policy
5) Set Maximum Password age to “0”

Source : Ryan’s Tech Notes

August 27, 2009

How to change windows 2003 administrator password from RDP.

Filed under: General,Security,Windows — Tags: , , — admin @ 6:48 am

In order to connect to a windows VPS remotely , you need to use a software named “Remote Desktop Connection” which is bundled with all versions of windows.
under windows XP it is located under : All Programs –> Accessories –> Communications
under windows Vista it is located under : All Programs –> Accessories
after running this software you will see the following window , enter the IP or host name of your VPS into the computer filed and click on Connect.

after a few seconds a new windows will be opened and you will be asked for the username and password , enter the username and password which is provided by your windows VPS provider. usually the username is Administrator.
if you enter the login details successfully , the desktop of windows VPS will be shown to you.

After you are logged into VPS , follow the below instructions :

Press CTRL+ALT+END buttons simultaneously , the following menu will appear :

Click on Change Password :

Fill the fields and click on OK.

Done 🙂

June 7, 2009

Change Linux Password from PHP Script

Filed under: CentOS,Debian,General,PHP — Tags: , , , — admin @ 8:48 pm

There are a few scripts available on net which allow you to change a linux user password from PHP. but all of them are very complex and hard to implement , so after some hours of work , I’ve written this PHP script 🙂 it is very simple , in order for this to work you need to allow your webserver to run sed command as root through sudoers , or allow your webserver to write on your /etc/shadow file.

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$username='USERNAME';
$password='PASSWORD';  // New Password
$sed='/bin/sed'; //Path to sed command
$salt = substr($username, 0, 2);
$pass_crypt = crypt($password, $salt);
$pass_crypt=str_replace("/","\/",$pass_crypt);
system($sed." -i 's/".$username.":[a-zA-z0-9/$\.]*/".$username.":".$pass_crypt."/g' /etc/shadow",$retval);

June 2, 2009

MySQL Change root password

Filed under: General,MySQL — Tags: , , , — admin @ 8:58 am

If you have never set a root password for MySQL, the server does not require a password at all for connecting as root. To setup root password for first time, use mysqladmin command at shell prompt as follows:

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mysqladmin -u root password NEWPASSWORD

However, if you want to change (or update) a root password, then you need to use following command

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mysqladmin -u root -p'oldpassword' password newpass

For example, If old password is abc, and set new password to 123456, enter:

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mysqladmin -u root -p'abc' password '123456'

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