Tag Archives: vps

How to configure secure SSH on CentOS

Hello everyone! In this tutorial I will show you how to increase server security by tuning up configuration of SSH.

Before you begin

There are basically two requirements for this tutorial:

You need to have working SSH keys. You need to be able to login to your server by using them. After completing this tutorial, SSH keys will be the only way to access server. If you won't be able to login by using them, well, you will lose access to your server. In order to add user and configure keys you can follow this tutorial.
Make sure that at least one of the users is in wheel group (has access to sudo). Root should not have access to login via SSH. So if you will block this option and you won't have any sudo user, you won't be able to do much on the server. Follow this tutorial in order to configure sudo.

Disable password authentication for SSH on CentOS

sudo vi /etc/ssh/sshd_config

Now we need to find the line for password authentication and change it to:

PasswordAuthentication no

Unfortunately, disabling this option can still lead to password authentication by using PAM-based authentication. In order to fully disable authentication with password, make sure that PAM is also disabled:

ChallengeResponseAuthentication no

Also we need to make sure that this line is uncommented. It will enable SSH login by using public key:

PubkeyAuthentication yes

Save the file and exit from the editor. In order to apply changes, you need to restart SSH daemon:

service sshd restart

After that, try to open new SSH session in new window. Do not logout from your current session! If you won't be able to login with new session, you can undo the changes with existing session. If you will be able to successfully login, you can proceed.

How to secure SSH on CentOS even more?

There are still some things that will help you improve SSH security. Edit the same configuration file as before. Below You will find the configuration options that I usually use for SSH.

Disable root login

PermitRootLogin no

This option will disable root login via ssh. So it means that from now on you won't be able to login to your server as root via ssh.

Allow only specific users to be able to login via SSH

AllowUsers developer

By default you are able to login as any user that is created inside the system. It can be easily limited to particular users. Just give space separated list after AllowUsers. It might not be present in your config, so you need to add this line (for instance at the end of the file).

AllowUsers developer vagrant

Enable protocol 2 for ssh

Protocol 2

This option is set by default in most CentOS installation, but just make sure that there's no version 1 instead. It's less secure protocol.

Ignore rhost

IgnoreRhosts yes

It will disable insecure access via RSH.

Disable login for users with empty passwords

PermitEmptyPasswords no

This line will disable login for users that have empty passwords. Make sure that your account has password set, before changing that!

Enable strict mode for ssh

StrictModes yes

SSH will check users's permission in their home directory before accepting login. It should be set to yes because users may leave their directory or files world-writable. Again, this might be tricky. It's the best to change that, restart SSHD daemon and try to login from new session. If you have any problems, you can undo this change with existing session. If you have any issues with that, try to set valid permissions for your .ssh directory and files inside. Also set valid username and group for your files:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/*
chown -R YOUR_USERNAME:YOUR_USERNAME ~/.ssh

Disable other authentication methods

GSSAPIAuthentication no
KerberosAuthentication no

If you don't plan to login with GSS API, or Kerberos you can disable them as well.

Disable X11 Forwarding

X11Forwarding no

If you don't use X11 you can safely disable it as well.

Show last login

PrintLastLog yes

Nice feature is to show last successful login after you will login via SSH.

Restart SSH daemon

Remember that after any changes inside the file You need to restart sshd daemon:

sudo service sshd restart

SSH crypto

In addition to changes above that should be applied, you can increase SSH security even more by configuring ciphers and available algorithms (thanks to @Amar for the suggestion:)

This is usually safe to execute, but you must remember that not all algorithms are supported by various tool. Here you can find great chart showing, which tools support given algorithms. But let's be honest, most of you is probably using OpenSSH which supports all the changes I will present here. However if you are using different tool and you won't be able to login to your server, check with the page and enable additional algorithms.

These config options will probably not be listed in your config file. You need to just add them somewhere, like at the end of the file.

Configure server authentication

HostKey /etc/ssh/ssh_host_ed25519_key
HostKey /etc/ssh/ssh_host_rsa_key

Server must confirm the identity to the client. There are bunch of algorithms available, but this is the list of most secure.

This might be present in your configuration file, also there might be more not commented lines with HostKeys. Leave only these two enabled and comment out the rest.

Configure key exchange

KexAlgorithms curve25519-sha256@libssh.org

There are many more key exchange algorithms, but this is probably the most secure.

Configure ciphers

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com

Ciphers are used to encrypt the data. As with key exchange, there are multiple algorithms. These are the safest.

MACs - Message Authentication Codes

MACs hmac-ripemd160,hmac-ripemd160-etm@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,umac-128@openssh.com,umac-128-etm@openssh.com

MACs are used for data integrity. Again, line above contains the safest algorithms only.

After these changes, don't forget to restart sshd daemon.

Easier way?

You can use our Ansible LAMP on Steroids project to make configuration of your server easier!

If you don't know what Ansible is, check our tutorial first.

Clone our repository and setup your server faster with LAMP on steroids.

Create sudo users and groups in CentOS

2 Replies

I will show you how to organise groups and users in CentOS.

As an example we will create account for user named developer. The purpose of this account is:

logging via SSH instead of using root account
access to sudo command for management tasks
write access to website files
read access to logs

Create list with available groups

If you are on fresh system it's handy to create a list with all available groups. It's also handy to check which users belongs to that groups. It might be helpful after some time when you need to decide if given group was at the beginning or can it be safely removed. getent command can help you with that.

getent group > /etc/initial-group-list
cat /etc/initial-group-list

Remove group from the system

If you need to remove group from CentOS simply use following command:

sudo groupdel NAME_OF_THE_GROUP_TO_DELETE

Create new group

In order to create group you need to use groupadd command:

sudo groupadd NAME_OF_THE_NEW_GROUP

I usually add group named www (or www-data, whatever works for you). To this group I add php daemons, nginx workers etc. It makes life easier with writing to files. In order to create such group execute following command:

sudo groupadd www

Create list with available users

Same like with group, I like to have list of initial users. In order to create such list you can use getent too:

getent passwd > /etc/initial-users-list
cat /etc/initial-users-list

Delete user from CentOS

In case you would like to remove any user from the system, use following command:

sudo userdel -r USERNAME_TO_REMOVE

-r flag will remove also his home directory. If you wish to delete the user, but to keep his files, omit this flag.

Create new user in CentOS

Let's create new user developer that we mentioned at the beginning:

sudo adduser developer

and create the password for his account:

sudo passwd developer

If you want to add developer user to www group created before use usermod command:

sudo usermod -g www developer

If you want to add this user sudo powers (and you should if you want to use this user instead of root), add it to wheel group. wheel group is special group in CentOS configured in sudoers file. Whoever belongs to this group can have sudo powers.

sudo usermod -g wheel developer

Optional parameters to useradd command

There are lot of additional parameters for useradd command but there are two especially useful.

First one is helpful when you don't want to create user home directory. It means that user will not have it's own place under /home directory to store it's files. This option is helpful when you are creating user for system service like Apache httpd for instance. So in order to create user with no home directory use --no-create-home:

sudo useradd httpd --no-create-home

Another useful feature is to specify shell of given user. It's nice if you want to cut of possibility to login to the system via SSH for instance. Add --shell /sbin/nologin to disable login for given user, like so:

sudo useradd httpd --shell /sbin/nologin --no-create-home

You can use --shell and --no-create-home parameters separately:)

How to setup SSH keys for new created user?

Each user should have RSA key-pair. It makes life easier and you should use it if you want to login to different servers, use GIT etc. In order to create such user key-pair you first need to login to user you created. Most probably you are using root account to execute all commands, but you should never ever login via SSH as a root.

It's much better to create separate user for system management and use only this account. Login via SSH to your server to account your created. In my case it's developer user so my command looks like this:

ssh developer@IP_OF_THE_SERVER_HERE

Once you'll be logged in (after providing the password), you can create RSA key pair. Execute following command:

ssh-keygen -t rsa -b 4096

-t rsa means that it will be RSA key, but this is standard for creating SSH keys. Fun part is with strength of the key -b 4096. By default it's 1024 bits, but to make it harder to break I usually provides 4096. It's not necessary, but you should do that. Some services requires key length to be minimum 2048, but it's better to create even longer one.

Generator will ask you some questions, but you should generally confirm them with enter and leave the defaults. When it comes to SSH on the server, I usually don't set the password. It makes life easier in automated scripts etc.

After that private and public key should be generated as expected. You can find them in ~/.ssh directory.

Add authorized key to user

In order to login with SSH keys to the server, instead of using password you need to add authorized key to developer user. In my opinion it's must have feature as using password login is super risky. Again, been there, done that, I was hacked, even when my password was strong. With SSH logging even strongest bruteforce attack will fail:)

You need to add your key to ~/.ssh/authorized_keys on the server. If You have ssh-copy-id command available just execute:

ssh-copy-id developer@IP_OF_YOUR_SERVER

Make sure that you are executing this command from your computer, not from the server. If you don't have SSH key created locally, you can generate it in the same way as on the server, by using ssh-keygen command.

If uou don't have ssh-copy-id available (for instance from Windows), you can do it manually.

ssh developer@IP_OF_YOUR_SERVER
cd ~/.ssh
vi authorized_keys
//Press "i" to enter in input mode, paste there your code (usually it's right click of the mouse) and :wq (colon, w, q) it will save and quit from vi 
chmod 600 authorized_keys

So here how it goes:

ssh to the server as usual with password.
Change location to .ssh directory.
Create authorized_keys file with vi
Paste there your local public key, save the file and quit
Set permissions on authorized_keys.

Test ssh login with keys

Now You can try to log in with Your key.

ssh developer@IP_OF_YOUR_SERVER -i path/to/your/PRIVATE/key/file

You shouldn't be prompted for your account password!

Easier way?

If you don't want to spend your precious time executing each of these commands by hand, you can use Ansible and our LAMP on steroids project to speed things up!

If you don't know what Ansible is - you can read our tutorial about it here.

LAMP on steroids project is available on GitHub here.

How to secure server with iptables?

1 Reply

Hi there! In this tutorial I would like to show you how to increase server security by using iptables as a firewall. To be honest, not many people are actually using iptables or any firewall. I think that this is bad practice, because you they allow all traffic to go in and out. You should always limit the possible entry points to your server.

Firewalld vs iptables

Since CentOS 7, we have new tool called firewalld. This is not actually an alternative to iptables. firewalld is a wrapper for iptables. Many people say, that it's easier to use than iptables, but to be honest I believe that it's not flexible enough. Maybe I'm wrong, but I'd love to see some advanced example, how to transform iptables rules below to firewalld 🙂 If you want to use firewalld instead of iptables, unfortunately you need to read different tutorial. Here is great article about firewalld from DigitalOcean.

How to install iptables on CentOS7?

Before we will install iptables, we need to get rid of firewalld first :

sudo yum remove firewalld -y

Next, we can install iptables:

sudo yum install iptables iptables-services -y

iptables-services is simple script that will help us save and restore firewall rules.

Secure iptables rules for CentOS

First, let's check if there are any rules by executing following command:

sudo iptables -S

If you will get following output:

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT

It means that you allow all traffic, both incoming and outgoing to your server. However if you have anything more than output above, copy it to separate file as a backup.

The easiest way of adding rules is by editing iptables rules file. Open the file, or create one if it doesn't exists:

sudo vi /etc/sysconfig/iptables

I will describe whole file line by line, but at the bottom of this post you can find whole content that I'm using for iptables.

Opening and closing tags

*filter

File must contains two indicators:

start of the ruleset *filter
end of the ruleset COMMIT

You need to have both in order to get iptables configured properly. Between these two lines, you can add iptables rules.

Clear all existing rules

-X
-F
-Z

At the very beginning I'd like to clear whole rules. In other words - enable all traffic. The reason is that I want to be able to execute that file over and over again, and I will always set the rules that I have in file. No other rules will be applied (for instance rules added by command line).

Allowing loopback

-A INPUT -i lo -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
-A INPUT -d 127.0.0.0/8 -j REJECT
-A OUTPUT -d 127.0.0.0/8 -j REJECT

Next thing is to allow all loopbacks. Those are local connection and blocking them might cause errors in some connections. In addition we will block those which doesn't use lo0.

Keep established connections

-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

All connections that are active now, should remain untouched. It will prevent from interruption of services.

PING command

-A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
-A INPUT -p icmp --icmp-type echo-reply -j ACCEPT
-A INPUT -p icmp --icmp-type echo-request -j ACCEPT
-A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT

In most cases you will need to be able to ping server. These rules will allow two things. First - you'll be able to ping your own server. Second - you will be able to execute ping from your server. Both are usually needed and quite useful.

Protection from PING of Death attack

-N PING_OF_DEATH
-A PING_OF_DEATH -p icmp --icmp-type echo-request -m hashlimit --hashlimit 1/s --hashlimit-burst 10 --hashlimit-htable-expire 300000 --hashlimit-mode srcip --hashlimit-name t_PING_OF_DEATH -j RETURN
-A PING_OF_DEATH -j DROP
-A INPUT -p icmp --icmp-type echo-request -j PING_OF_DEATH

Ping is cool, however you might get attacked with Ping of Death attack. Here is simple protection.

Prevent some nasty attacks

-N PORTSCAN
-A PORTSCAN -p tcp --tcp-flags ACK,FIN FIN -j DROP
-A PORTSCAN -p tcp --tcp-flags ACK,PSH PSH -j DROP
-A PORTSCAN -p tcp --tcp-flags ACK,URG URG -j DROP
-A PORTSCAN -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
-A PORTSCAN -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP
-A PORTSCAN -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL ALL -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL NONE -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL SYN,FIN,PSH,URG -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP
-A INPUT -f -j DROP
-A INPUT -p tcp ! --syn -m state --state NEW -j DROP

This is really nice piece of rules that will prevent port scanning, SYN flood attacks, invalid packages, malformed XMAS packets, NULL packets, etc.

UDP traffic

-A INPUT -p udp --sport 53 -j ACCEPT
-A OUTPUT -p udp --dport 53 -j ACCEPT
-A INPUT -p udp --sport 123 -j ACCEPT
-A OUTPUT -p udp --dport 123 -j ACCEPT

I enable usually only ports for outgoing traffic (from our server to outside world). There are two ports that I'd like to open:

53 - DNS port. It's a must if you want to use curl or yum. If you will have it closed, you will not resolve any domain name.
123 - NTP port. If you are using chrony or ntpd, you need to enable that port to allow NTP deamon synchronisation.

TCP traffic

# Open TCP ports for incoming traffic
-A INPUT -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT
-A INPUT -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT
-A INPUT -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

# Open TCP ports for outgoing traffic
-A INPUT -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT

With TCP it's more complicated, but it's not that hard. First, you need to think what traffic you need to access from your server (outgoing traffic). I usually allow only SSH, HTTP and HTTPS traffic. Yum requires HTTP and HTTPS ports for pulling new packages. You will need it also for wget or curl. SSH is not mandatory, but if you want to pull packages from git via ssh protocol, you will need it as well.

I usually enable the same for incoming traffic. If you have httpd or nginx installed, you need to enable port 80. If you are using SSL for HTTPS, you need to enable 443 also. In addition to these two ports you must enable port 22 for SSH. If you will block this, you won't be able to get access to your server!

Block everything else

-A INPUT -j DROP
-A FORWARD -j DROP
-A OUTPUT -j DROP

At the very end, before closing COMMIT tag I add these three rules. So everything that was not specified above will be dropped. Both incoming and outgoing traffic.

How to apply rules?

There are two ways how you can apply the rules. First, save the changes in iptables file. First method is not permanent method. It's good way of testing your firewall before saving them permanently. If anything will go wrong, you can just restart the server and you will have all traffic open. Make sure that you check SSH access with these rules. Log out and try to login after applying rules.

So non permanent way of applying rules is:

sudo iptables-restore < /etc/sysconfig/iptables

Try to check rules with iptables -S to see the difference:) Check if everything is working fine. If so, you can set them permanently. After each server restart, rules will be applied automatically.

sudo systemctl start iptables.service
sudo systemctl enable iptables.service

If you want to reload rules, simply edit the file, add what you need and restart iptables service:

sudo systemctl restart iptables.service

You can use our Ansible LAMP on Steroids project to make configuration of your server easier!

It is based on Ansible. If you don't know what Ansible is, check our tutorial first.

Clone our repository and setup your server faster with LAMP on steroids.

Whole content of iptables rules

*filter

# Clear all iptables rules (everything is open)
-X
-F
-Z

# Allow loopback interface (lo0) and drop all traffic to 127/8 that doesn't use lo0
-A INPUT -i lo -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
-A INPUT -d 127.0.0.0/8 -j REJECT
-A OUTPUT -d 127.0.0.0/8 -j REJECT

# Keep all established connections
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

# Allow ping
-A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
-A INPUT -p icmp --icmp-type echo-reply -j ACCEPT
-A INPUT -p icmp --icmp-type echo-request -j ACCEPT
-A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT

# Protect from ping of death
-N PING_OF_DEATH
-A PING_OF_DEATH -p icmp --icmp-type echo-request -m hashlimit --hashlimit 1/s --hashlimit-burst 10 --hashlimit-htable-expire 300000 --hashlimit-mode srcip --hashlimit-name t_PING_OF_DEATH -j RETURN
-A PING_OF_DEATH -j DROP
-A INPUT -p icmp --icmp-type echo-request -j PING_OF_DEATH

# Prevent port scanning
-N PORTSCAN
-A PORTSCAN -p tcp --tcp-flags ACK,FIN FIN -j DROP
-A PORTSCAN -p tcp --tcp-flags ACK,PSH PSH -j DROP
-A PORTSCAN -p tcp --tcp-flags ACK,URG URG -j DROP
-A PORTSCAN -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
-A PORTSCAN -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP
-A PORTSCAN -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL ALL -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL NONE -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL SYN,FIN,PSH,URG -j DROP
-A PORTSCAN -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP

# Drop fragmented packages
-A INPUT -f -j DROP

# SYN packets check
-A INPUT -p tcp ! --syn -m state --state NEW -j DROP

# Open ports for outgoing UDP traffic
-A INPUT -p udp --sport 53 -j ACCEPT
-A OUTPUT -p udp --dport 53 -j ACCEPT
-A INPUT -p udp --sport 123 -j ACCEPT
-A OUTPUT -p udp --dport 123 -j ACCEPT


# Open TCP ports for incoming traffic
-A INPUT -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT
-A INPUT -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT
-A INPUT -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

# Open TCP ports for outgoing traffic
-A INPUT -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT


# Drop all other traffic
-A INPUT -j DROP
-A FORWARD -j DROP
-A OUTPUT -j DROP

COMMIT

What's next?

We secured our system with basic firewall. That will increase the security of our server. In one of the next episodes we will change the configuration of our SSH and therefore make it more secure.

As always You can use our Ansible playbook for faster provisioning of our server. You can find it on GitHub.

How to install and configure latest version of MySQL on CentOS?

1 Reply

Hi there! Today I want to show you how to install latest version of MySQL Community server (5.7.16) on CentOS 7. I will show you how to install it, set root password, configure server and optimize it for performance. Also I will show you how to create databases and assign users to them.

How to install MySQL on CentOS in latest version

When you try to install MySQL on bare CentOS, you will actually install MariaDB (fork of MySQL) instead. It comes with version 5.5.* It's up to you what you want to use, but I prefer MySQL. Especially 5.7 version. There is great performance boost and lot of new features added, comparing to 5.5 or 5.6.

If you have any data on MySQL, it's best to create a backupof data, before you will change anything. Here is a tutorial how to perform backup of MySQL databases.

Before you will actually install MySQL, make sure that MariaDB is not installed. You can just remove it. TIP: removing MariaDB will not remove any databases. It will remain on your hard drive.

sudo yum remove mariadb -y

So let's get to installation. First you need to enable MySQL repository. It's easy by adding following file to yum repositories:

sudo vi /etc/yum.repos.d/mysql-community.repo

and place there following content:

[mysql57-community]
name=MySQL 5.7 Community Server
baseurl=http://repo.mysql.com/yum/mysql-5.7-community/el/7/$basearch/
enabled=1
gpgcheck=1
gpgkey=http://dev.mysql.com/doc/refman/5.7/en/checking-gpg-signature.html

Save the changes. It will enable MySQL repository where from you can install latest version.

Installation is pretty easy:

sudo yum install mysql-community-server -y

That's it! You have MySQL installed in latest version!

Setting root password in MySQL

Setting root password for MySQL is important. You should not leave your database server unprotected, even if you only plan to use localhost connection.

Before you will start anything, make sure that MySQL is up and running:

sudo systemctl start mysqld

If this is fresh installation of MySQL (MariaDB or older version of MySQL was never installed) , MySQL will generate temporary password.

You can find it by using following command:

grep 'temporary password' /var/log/mysqld.log

You will get random password, for instance something like wG]_xj8tus. This is current password to root account. Keep in mind that this is only temporary password. It will expire, so you need to change it as soon as possible.

In order to change root password I like to use mysqladmin tool. So execute following command:

mysqladmin -u root -pwG]_xj8tus password NEW_STRONG_ROOT_PASSWORD

You need to replace wG]_xj8tus with the password from grepping log file. Note that there is no space after -p argument. Also replace NEW_STRONG_ROOT_PASSWORD with your new root password. Keep in mind, that it needs to be strong password, containing lower and upper case characters, numbers and special characters. MySQL 5.7 comes with plugin that validates password strength. It won't allow you changing password to something that is easy to guess or brute force.

If you just upgrading MySQL/MariaDB, your root password will be the same. You can of course change it with mysqladmin if you wish.

However if you are upgrading from MySQL/MariaDB version prior to 5.7 it's nice to execute following command:

mysql_upgrade -u root -p

Type your root password. It will check all the data and alter tables for 5.7 rules.

You might ask - how about mysql_secure_installation? You can also use this command for setting root password after installation. However when you install fresh version of MySQL 5.7 there is no test database, anonymous users etc. Everything is clean and secured.

Configuration of MySQL 5.7

I like to tune up default MySQL configuration. With 5.7 version, lot of defaults are set in order to provide high security and performance. However there are few things I like to change. Most of the stuff is stored under /etc/my.cnf file. MySQL is reading configuration from there during startup. You can also change it dynamically, but here I will focus only on this file.

Edit the file first:

sudo vi /etc/my.cnf

There will be some defaults, you can leave them as they are. Most probably, all options here will be missing, so you need to add them under [mysqld] section.

Temporary in-memory tables

tmp-table-size=32M
tmp-heap-table-size=32M

I increase the size of temporary in-memory tables created by MySQL. If you are doing lot of advanced GROUP BY queries, you will probably have to increase it. Make sure that you are setting both to the same value. If one will be lower, second one will be limited to lower value as well.

Query caching

Query caching is disabled by default. It caches result sets from most frequent queries to database. It usually give nice performance boost to MySQL server:

query-cache-type=1
query-cache-size=32M

InnoDB buffer

Also another performance boost is creating buffer for InnoDB pools. It will keep the data in RAM, so reads will be much faster. Make sure to not to set these values higher than your RAM limits. It should be large enough to store as much data as possible.

innodb-buffer-pool-instances=1
innodb-buffer-pool-size=128M

Logging slow queries

Slow queries can kill your server. It's nice to know earlier that something is going on. I usually turn this on and check it frequently for such queries. If there are some complicated / not optimal queries, you should fix them as soon as possible.

slow-query-log=1
slow-query-log-file=/var/lib/mysql/localhost-slow-query.log<

TIMESTAMP fields behavior

If you would check MySQL log during startup, you can note that there is a warning regarding TIMESTAMP fields. You can read more about these changes here. If you want to suppress that warning, use following option

explicit-defaults-for-timestamp=1

In order to apply changes, you need to restart MySQL daemon:

sudo systemctl restart mysqld

Few notes about playing with configuration. You must know that it's not easy and it's highly depends on number of tables, queries, inserts and lot of other factors. I usually use two tools. First is MySQLTuner that can get you some insights about what to change in order to gain performance. Usually it's just tuning query cache, and InnoDB buffer size. However practice shows that it doesn't always show correct values. Sometimes you can get slower performance instead.

So I use other tool - Datadog. You can also use New Relic, or any other monitoring tool that generates charts. So I usually change one thing at the time. I'm restarting MySQL server and waiting around 48h to see if it's actually performing better or not. This might seem to be slow approach but it's definitely safe:)

But before you start to playing with your configuration, make sure that you don't have slow queries or large tables that you scan without indexes. Sometimes just adding index will reduce query time. No need to change MySQL configuration files:)

MySQL group

MySQL during installation create it's own group - mysql. Most of the data files, and logs have mysql:mysql ownership. It makes it hard to read the logs when you are non-root user. You need to use sudo to get access to logs. You can make it simpler by adding user to mysql group. When user will be in such group, he can easily read logs. In my case, user is named developer.

sudo usermod -a -G mysql developer

Create databases and users

Probably the most important part from MySQL user is how to create database and users? First login to MySQL with your root account:

mysql -u root -p

And then start with creating databases. You need to enter following query:

CREATE DATABASE database_name_here;

Replace database_name_here with your database name. I like to create name for database from domain. So for instance for blacksaildivision.com, database name would be blacksaildivision. Remember that you can't use the . in database name.

Once you have your database, you should create dedicated user that only has access to this database. Having separate user per database is good approach from security perspective.

In order to create user in database execute following query:

CREATE USER 'blacksaildivision'@'localhost' IDENTIFIED BY 'NotEasyToGuessPassword123^#';

It will create blacksaildivision user that can connect to MySQL server only via localhost. It means that he won't have access from outside. After IDENTIFIED BY you need to type password for user you want to create. Same rules as for root password, it can't be easy to guess.

After user is created it's time to give him access to database you created before. Query goes like this:

GRANT ALL PRIVILEGES ON blacksaildivision.* TO 'blacksaildivision'@'localhost';

So you give user full access to blacksaildivision database. .* means that he should have access to all tables in blacksaildivision database. After TO you need to specify user that you created in step before.

To apply privileges, you need to reload them. Fire following query:

FLUSH PRIVILEGES;

And that's it! Create as many databases and users as you wish:) You can test connection to database with new credentials from command line. First exit from current MySQL session and than use following command:

mysql -u blacksaildivision -p blacksaildivision

-u stands for user, -p means that user will connect by using password. Last thing is database name you want to connect to.

Start MySQL on system boot

Last thing is to add MySQL to boot list. So after CentOS will start, MySQL will start as well:

sudo systemctl enable mysqld

Remember that you can use our lamponsteroids project based on Ansible that will automate whole server setup:)

PHP – how to install from source on CentOS

10 Replies

In this tutorial I would like to show you how to install latest version of PHP on CentOS 7. If you are using PHP you most probably will want to have latest version of PHP7. PHP 5 support officially ends this year. Version 7 is now commonly used. It gives lot of performance boost and new features.

Unfortunately default version that comes from repo in CentOS 7 is PHP 5.4, so you can't use yum command without any custom repo like remi. Including custom repository is one way of installing desired PHP version. Another option is to compile it from source code. This tutorial will show you how to do that. It's not as hard as it might sounds:)

Install required tools for compilation

In order to compile PHP from source you need to install few tools and libraries. First you need EPEL repository to be enabled. This repository contains more recent version of packages. Most probably you have it installed already, but just to be sure, execute following command:

sudo yum install epel-release -y

Once you have it installed execute following command to install required packages:

sudo yum install autoconf libtool re2c bison libxml2-devel bzip2-devel libcurl-devel libpng-devel libicu-devel gcc-c++ libmcrypt-devel libwebp-devel libjpeg-devel openssl-devel -y

Download and unpack PHP Source code

Next step is downloading PHP source code. Easiest option is to download it from GitHub PHP releases. Choose the version you would like to install. In my case it's 7.2.3. Copy link to tar.gz archive and execute following commands:

curl -O -L https://github.com/php/php-src/archive/php-7.2.3.tar.gz
tar -zxvf php-7.2.3.tar.gz
cd php-src-php-7.2.3

It will download the archive from GitHub, unpack the sources and change working directory to unpacked sources.

Compile PHP

Now it's time to compile PHP. First we need to build configure command. In order to do that execute following command:

./buildconf --force

Once configure command is created we can use it to configure PHP installation. This process will enable certain PHP extensions such as PDO, FPM, OPCache, GD library etc. If you need any libraries that are not provided here, you can execute ./configure --help option and check if there is something you need. Following command will install PHP with most common extensions:

./configure --prefix=/usr/local/php --enable-fpm --disable-short-tags --with-openssl --with-pcre-regex --with-pcre-jit --with-zlib --enable-bcmath --with-bz2 --enable-calendar --with-curl --enable-exif --with-gd --enable-intl --enable-mbstring --with-mysqli --enable-pcntl --with-pdo-mysql --enable-soap --enable-sockets --with-xmlrpc --enable-zip --with-webp-dir --with-jpeg-dir --with-png-dir

Apart from enabling extensions command above will also set where PHP will be installed. In my case it's /usr/local/php location. If you will want to remove compiled PHP you will simply have to remove entire directory given under --prefix option.

Next it's time to compile PHP. Please be aware that it takes few minutes:

make clean
make

Install compiled PHP

Once PHP is compiled it is time to install it. Simply execute following command:

sudo make install

PHP Configuration

PHP-FPM setup

Before we will be able to run PHP from Apache we need to setup PHP-FPM worker. After installation there should be PHP-FPM default configuration file in installation directory. We will alter the file and then change it a bit.

cd /usr/local/php/etc
mkdir fpm.d
cp php-fpm.conf.default php-fpm.conf
vi php-fpm.conf

We need to uncomment/change these lines:

include=etc/fpm.d/*.conf
pid = /var/run/php-fpm.pid
error_log = log/php-fpm.log

COPY EVERYTHING UNDER Pool Definitions TO CLIPBOARD AND REMOVE IT FROM php-fpm.conf FILE
;;;;;;;;;;;;;;;;;;;;
; Pool Definitions ;
;;;;;;;;;;;;;;;;;;;;

include=/etc/fpm.d/*.conf - by default there is one pool defined inside php-fpm.conf file. The best way to solve it is the same way as we solved Apache vhosts. We will include each pool in separate directory. In php-fpm.conf file one pool is already defined. We need to delete it from this file and put it inside fpm.d directory. We will have better control over the pools. The easiest way is just to Cut it from this file and paste it into new one.

Now let's create the file inside fpm.d for our example.com domain:

cd fpm.d
vi example.com.conf

PASTE TEXT FROM CLIPBOARD HERE AND CHANGE THESE LINES:

[www] -> [example_com] //Must be unique per file
user = apache
group = www
listen = 127.0.0.1:9000 //Port must be unique per file
catch_workers_output = yes
slowlog = /var/www/example.com/logs/php-fpm.slow.log
request_slowlog_timeout = 30s
php_flag[display_errors] = off
php_admin_value[error_log] = /var/www/example.com/logs/php-fpm.error.log
php_admin_flag[log_errors] = on
php_admin_value[memory_limit] = 64M
php_admin_value[open_basedir] = /var/www/example.com/htdocs

Each pool must have different name. So we need to change it from [www] to something else, for instance to domain name. It'll be easier to find the issues inside log files.

We set user and group to the same user as apache to have access to files.

Port will be different per pool. Standard way is to start from port 9000. Next will be 9001 etc.

We will catch errors and log them to file. In addition we set logging for slow requests.

Nice part is that we can overwrite the settings from php.ini here. So we can overwrite error_log or memory_limit for instance. We should also set open_basedir so PHP will have access only to files inside our htdocs directory. Our server will be more secure with this setting.

php.ini and OPCache configuration

Second thing is php.ini file. After installation php.ini file should located in /usr/local/php/lib. This is only the location. After compiling from source You won't anything there so we need to copy it from uncompressed sources.

cd /usr/local/php/lib
cp ~/sources/php-5.6.6/php.ini-development ./php.ini
vi php.ini

This is pretty large file with lot of configuration settings. Fortunately we only need to change some of the options:

short_open_tag = On
open_basedir = /var/www
disable_functions = exec,passthru,shell_exec,system,proc_open,popen
expose_php = Off
max_execution_time = 30
memory_limit = 64M
date.timezone = Europe/Warsaw
error_reporting = E_ALL & ~E_DEPRECATED & ~E_STRICT
display_errors = Off
display_startup_errors = Off
log_errors = On
post_max_size = 5M
upload_max_filesize = 4M

opcache.enable=1
opcache.memory_consumption=64
opcache.interned_strings_buffer=16
opcache.max_accelerated_files=7000
opcache.validate_timestamps=0 ;set this to 1 on production server
opcache.fast_shutdown=1

So we set few things here, enable <? tag, limit access to files from PHP level, disabled dangerous functions, adjusts timezone, security, max execution times, errors etc. In addition we have enable OPCache for PHP.

Each one of these options are well commented inside php.ini file. If You don't like the settings here or You need something else, feel free to change it for Your purposes.

Useful shell scripts for PHP

/etc/init.d/php-fpm

As You probably remember during Apache setup we create script so we can use service command to start / stop Apache process. Now we will do the same for PHP-FPM

With PHP source code there comes ready script for that purpose.

cd /etc/init.d
cp ~/sources/php-5.6.6/sapi/fpm/init.d.php-fpm php-fpm
vi php-fpm

Now we need to setup configuration for the file:

prefix=/usr/local/php
exec_prefix=${prefix}

php_fpm_BIN=${exec_prefix}/sbin/php-fpm
php_fpm_CONF=${prefix}/etc/php-fpm.conf
php_fpm_PID=/var/run/php-fpm.pid

Save the file and add executable permission.

chmod +x php-fpm
servcie php-fpm status
service php-fpm start
servcie php-fpm status

After that we should have php-fpm process up and running!

Add PHP to $PATH

We can do one more thing to make our life easier:) Add PHP executable to PATH, so we'll be able to call php command from every directory.

echo 'pathmunge /usr/local/php/bin' > /etc/profile.d/php.sh

Execute such command, log out, log in and You'll be able to execute:

php -v

Setup Apache for PHP-FPM

Now is the time to finally setup Apache for .php files. Let's edit one of the Virtual Hosts now.

vi /usr/local/apache2/conf/vhosts/example.com.conf

<VirtualHost *80>
    ServerName example.com

    <LocationMatch "^/(.*\.php(/.*)?)$">
        ProxyPass fcgi://127.0.0.1:9000/var/www/example.com/htdocs/$1
    </LocationMatch>

////Rest of the file below

So basically we need to proxy all files with .php extension to our PHP-FPM process. Also we need to restart Apache and make sure PHP-FPM is running httpd server:

service php-fpm start
service httpd restart

How to test if PHP is working?

We need to test if our PHP installation works. The easiest way to debug and check what's going on would be to create test.php file inside our /var/www directory.

vi /var/www/example.com/htdocs/test.php

and paste phpinfo() function there:

<?php

phpinfo();

Save the file and open the file in Your browser, assuming that your vagrant setup is correct. For instance http://example.com/test.php or 192.168.99.99/test.php

If everything is OK you should get information about PHP installation. Well done!

What's next

We are one step closer to our LAMP server. The only thing we are missing now is MySQL which we will install in upcoming episodes.

If You are running Ansible for provisioning You can find everything from this series inside my GitHub.

Apache hardening with mod_security

2 Replies

In this part of setup complete webserver we will harden Apache with popular mod_security. Mod_security is a small module that works like application firewall. It protect the app before most common attacks and vulnerabilities. It's good to have such thing on the webserver.

I assume that You have Apache already installed, if not check out previous part - How to install Apache on CentOS?

[sc:lamp_series]

How to install mod_security on Apache httpd server

First thing is installation of required tools. We need them to compile mod_security.

yum install automake libtool libxml2-devel

Next thing that we need is to download and decompress mod_security. Download links can be found on official mod_security page.

cd ~/sources
wget https://www.modsecurity.org/tarball/2.9.0/modsecurity-2.9.0.tar.gz
tar -zxvf modsecurity-2.9.0.tar.gz

Now it's time to compile mod_security. While ./confgure we need to pass paths to axps and apr binaries. All binaries should be inside bin directory in apache installation path.

cd modsecurity-2.9.0
./autogen.sh
./configure --with-apxs=/usr/local/apache2/bin/apxs --with-apr=/usr/local/apache2/bin/apr-1-config --with-apu=/usr/local/apache2/bin/apu-1-config
make
make install
cp /usr/local/modsecurity/lib/mod_security2.so /usr/local/apache2/modules

If there was no error mod_security is ready to use. It can be found in /usr/local/modsecurity We need to copy generated .so file to apache extension directory.

ModSecurity and OWASP rules

mod_security is nothing without the rules that tells what attacks should be blocked. Fortunately there is a great package with lot of rules provided by OWASP. We will use such rules package to harden Apache HTTPD. So let's download, unzip and copy the rules to apache configuration directory.

cd ~/sources
wget -O owasp.tar.gz https://github.com/SpiderLabs/owasp-modsecurity-crs/tarball/master
mkdir /usr/local/apache2/conf/crs
tar -zxvf owasp.tar.gz -C /usr/local/apache2/conf/crs --strip 1
cd /usr/local/apache2/conf/crs
cp modsecurity_crs_10_setup.conf.example modsecurity_crs_10_setup.conf

Now we are ready to use ModSecurity!

ModSecurity configuration

In previous article we added httpd-security.conf file with some basic rules that improves Apache security. We will modify this file to load mod_security with OWASP rules and add some basic configuration. You need to know that mod_security is pretty large module with tons of configuration option. You can find them in ModSecurity reference manual.

vi /usr/local/apache2/conf/extra/httpd-security.conf

Once You open the file add these lines somewhere in the file:

LoadModule security2_module modules/mod_security2.so

<IfModule security2_module>
      Include conf/crs/modsecurity_crs_10_setup.conf
      Include conf/crs/base_rules/*.conf
      # Include conf/crs/experimental_rules/*.conf
      # Include conf/crs/optional_rules/*.conf

      SecRuleEngine On
      SecRequestBodyAccess On
      SecResponseBodyAccess On 
      SecResponseBodyMimeType text/plain text/html text/xml application/octet-stream
      SecDataDir /tmp

      # Debug log
      SecDebugLog /usr/local/apache2/logs/modsec_debug.log
      SecDebugLogLevel 3

      SecAuditEngine RelevantOnly
      SecAuditLogRelevantStatus ^2-5
      SecAuditLogParts ABCIFHZ
      SecAuditLogType Serial
      SecAuditLog /usr/local/apache2/logs/modsec_audit.log
</IfModule>

So from the top:

First we need to load mod_security module.
Next are rules from OWASP that we will include to ModSecurity. We need to include the setup and base rules. OWASP core rule set comes with lot more features that are marked as optional or experimental. We can enable those rules, but we also need to remember that it might not play well with our website. It's rather testing by trial and error then one rule will work well on every website. But in general including base_rules is OK.
SecRuleEngine enables detection and blocking of malicious attacks.
SecRequestBodyAccess enable inspection of data transported request bodies
SeResponseBodyAccess buffer response bodies matched by SecResponseBodyMimeType
SecDataDir working directory for ModSecurity temporary purposes
Next thing is Debug log. By default all error logs goes to apache error log, but we can set different path to debug log. Best practice would be to change it per domain inside particular VirtualHost file. In previous article we setup directory structure and we have logs directory there. It would be wise to used it for debug log as well.
Audit Log is complementary log for Debug log. It has detail information about every error. It's disabled by default so we need to enable it and turn on logging relevant (warnings and errors) issues. Next options are for configuration the audit log. In general there are lot more of discussing at this topic.

If You want to learn more about how to setup and read mod_security logs, here is really great article about mod_security logging by Infosec Institue.

Now we just need to save the file restart apache and our httpd server has better security.

service httpd restart

What's next?

If You are following our series, You should have now part of LAMP stack (Linux Apache MySQL PHP). Apache is secured with mod_security.

Small note to those who would like to install mod_evasive as well to increase the security. To be honest, it's really not worth to install it on Apache. Why? Because when You run multiple instances via MPM mod_evasive doesn't share the info between the MPM instances. It means that one instance of apache can block the attacker but others wont. So if You have many MPM workers mod_evasive is just useless.

As always, if You are using Ansible for server provisioning You can use ready playbook, that will cover everything in this series. You can find it on GitHub.

In next episode we will add P to our LAMP server.

How to install EPEL repository on CentOS

3 Replies

We need to install EPEL repository for our CentOS. This will be first step to setup our working Web Server. EPEL is additional repository for yum, with tons of useful packages which we won't find in default base repository. We will use it in the future so let's start using it now;)

In this post we will also setup local vagrant box. We will be using it for future operations like installing Apache or Varnish.

[sc:lamp_series]

Vagrant setup

The best idea without messing everything out is to use Vagrant.

If You don't have Vagrant installed please download and install it first. After installation You should be ready to use Vagrant. Create directory in place where You want to keep Your vagrant file.

mkdir vms
cd vms

Next thing what we need to do is to download CentOS box. We need the box to replace default one that comes with Vagrant. We will use chef/centos-6.6 from Vagrant boxes directory. You can search more boxes here if You want, for instance You can use 6.5 instead of 6.6. Decision is Yours:)

vagrant box add chef/centos-6.6

Vagrant will download the image of OS You selected. It might take a while, depending on Your network performance.

Next we need to init Vagrant instance.

vagrant init chef/centos-6.6

It will create Vagrantfile in Your directory. You can check out this file in any editor. This file has basic Vagrant configuration, you can adjust the options like forwarded ports, synced folders etc. For now, let's leave this configuration file and let's bring our machine to life!

vagrant up

It will init the machine. After that You can login via SSH and start playing around:)

vagrant ssh

tl;dr

mkdir vms
cd vms
vagrant init chef/centos-6.6
vagrant up
vagrant ssh

How to install EPEL

Installing EPEL on CentOS is really easy. First of all You need to get the URL for EPEL repo. If You are just following the instructions in this tutorial You can execute the command. But for instance if You have 32bit version instead of 64bit You need to replace x86_64 to i386

yum install http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

Depending on Your vagrant / server setup You might need to execute this command as root or at least as sudo user. If You are just following the steps in this tutorial You are probably Vagrant user. If You execute this command You will see permission denied error. Start this command with sudo (sudo yum install http://....) and everything should be OK:)

Next thing that we need to do is to import GPG key for this repo:

rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-6

And basically that's it! You are now able to use EPEL packages with yum!

To validate the installation You can execute yum repolist command and You should see epel Extra Packages for Enterprise Linux 6 - x86_64

yum repolist

It means that everything is OK. Now, if You want to install any packages with the EPEL repository You need to use

yum --enablerepo=epel install PACKAGE_NAME

tl;dr

yum install http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rp -y
rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-6

Using Ansible to install EPEL

If You are using Ansible for server provisioning as I do, You can find ansible-webserver project on GitHub

https://github.com/astaz3l/ansible-webserver

It has EPEL role, that will help You install EPEL via Ansible