Ubuntuland

Ubuntu Server Guide Part 2

Many other configuration directives for sshd are available for changing the server application's behavior to fit your needs. Be advised, however, if your only method of access to a server is ssh, and you make a mistake in configuring sshd via the /etc/ssh/sshd_config file, you may find you are locked out of the server upon restarting it, or that the sshd server refuses to start due to an incorrect configuration directive, so be extra careful when editing this file on a remote server.

References

OpenSSH Website [http://www.openssh.org/]
Advanced OpenSSH Wiki Page [https://wiki.ubuntu.com/AdvancedOpenSSH]

5. FTP Server

File Transfer Protocol (FTP) is a TCP protocol for uploading and downloading files
between computers. FTP works on a client/server model. The server component is called an FTP daemon. It continuously listens for FTP requests from remote clients. When a request is received, it manages the the login and sets up the connection. For the duration of the session it executes any of commands sent by the FTP client.
Access to an FTP server can be managed in two ways:
• Anonymous
• Authenticated
In the Anonymous mode, remote clients can access the FTP server by using the default user account called 'anonymous" or "ftp" and sending an email address as the password.

In the Authenticated mode a user must have an account and a password. User access to the FTP server directories and files is dependent on the permissions defined for the account used at login. As a general rule, the FTP daemon will hide the root directory of the FTP server and change it to the FTP Home directory. This hides the rest of the file system from
remote sessions.

5.1. vsftpd - FTP Server Installation

vsftpd is an FTP daemon available in Ubuntu. It is easy to install, set up, and maintain. To install vsftpd you can run the following command:
sudo apt-get install vsftpd

 

 

5.2. vsftpd - FTP Server Configuration

You can edit the vsftpd configuration file, /etc/vsftpd.conf, to change the default
settings. By default only anonymous FTP is allowed. If you wish to disable this option, you should change the following line:
anonymous_enable=YES
to
anonymous_enable=NO
By default, local system users are not allowed to login to FTP server. To change this
setting, you should uncomment the following line:
#local_enable=YES
By default, users are allowed to download files from FTP server. They are not allowed to upload files to FTP server. To change this setting, you should uncomment the following line:
#write_enable=YES

Similarly, by default, the anonymous users are not allowed to upload files to FTP server.
To change this setting, you should uncomment the following line:
#anon_upload_enable=YES
The configuration file consists of many configuration parameters. The information about each parameter is available in the configuration file. Alternatively, you can refer to the man page, man 5 vsftpd.conf for details of each parameter.
Once you configure vsftpd you can start the daemon. You can run following command to run the vsftpd daemon:

Please note that the defaults in the configuration file are set as they are for
security reasons. Each of the above changes makes the system a little less secure,
so make them only if you need them.

6. Network File System (NFS)

NFS allows a system to share directories and files with others over a network. By using NFS, users and programs can access files on remote systems almost as if they were local files.
Some of the most notable benefits that NFS can provide are:
• Local workstations use less disk space because commonly used data can be stored on a single machine and still remain accessible to others over the network.
• There is no need for users to have separate home directories on every network machine.
Home directories could be set up on the NFS server and made available throughout the network.
• Storage devices such as floppy disks, CDROM drives, and USB Thumb drives can be
used by other machines on the network. This may reduce the number of removable
media drives throughout the network.

6.1. Installation

At a terminal prompt enter the following command to install the NFS Server:
sudo apt-get install nfs-kernel-server

6.2. Configuration

You can configure the directories to be exported by adding them to the /etc/exports file.
For example:

You can replace * with one of the hostname formats. Make the hostname declaration as specific as possible so unwanted systems cannot access the NFS mount.
To start the NFS server, you can run the following command at a terminal prompt:
sudo /etc/init.d/nfs-kernel-server start

6.3. NFS Client Configuration

Use the mount command to mount a shared NFS directory from another machine, by
typing a command line similar to the following at a terminal prompt:
sudo mount example.hostname.com:/ubuntu /local/ubuntu

The mount point directory /local/ubuntu must exist. There should be no files or
subdirectories in the /local/ubuntu directory.
An alternate way to mount an NFS share from another machine is to add a line to the /etc/fstab file. The line must state the hostname of the NFS server, the directory on the server being exported, and the directory on the local machine where the NFS share is to be mounted.
The general syntax for the line in /etc/fstab file is as follows:
example.hostname.com:/ubuntu /local/ubuntu nfs rsize=8192,wsize=8192,timeo=14,intr

 

6.4. References

Linux NFS faq [http://nfs.sourceforge.net/]

7. Dynamic Host Configuration Protocol (DHCP)

The Dynamic Host Configuration Protocol (DHCP) is a network service that enables host computers to be automatically assigned settings from a server as opposed to manually configuring each network host. Computers configured to be DHCP clients have no control over the settings they receive from the DHCP server, and the configuration is transparent to the computer's user.
The most common settings provided by a DHCP server to DHCP clients include:
• IP-Address and Netmask
• DNS
• WINS
However, a DHCP server can also supply configuration properties such as:
• Host Name
• Domain Name
• Default Gateway
• Time Server
• Print Server
The advantage of using DHCP is that changes to the network, for example a change in the address of the DNS server, need only be changed at the DHCP server, and all network hosts will be reconfigured the next time their DHCP clients poll the DHCP server. As an added advantage, it is also easier to integrate new computers into the network, as there is no need to check for the availability of an IP address. Conflicts in IP address allocation are also reduced.
A DHCP server can provide configuration settings using two methods:

MAC Address
This method entails using DHCP to identify the unique hardware address of each
network card connected to the network and then continually supplying a constant
configuration each time the DHCP client makes a request to the DHCP server using
that network device.

Address Pool
This method entails defining a pool (sometimes also called a range or scope) of
IP addresses from which DHCP clients are supplied their configuration properties
dynamically and on a fist come first serve basis. When a DHCP client is no longer on
the network for a specified period, the configuration is expired and released back to the address pool for use by other DHCP Clients.
Ubuntu is shipped with both DHCP server and client. The server is dhcpd (dynamic host configuration protocol daemon). The client provided with Ubuntu is dhclient and should be installed on all computers required to be automatically configured. Both programs are easy to install and configure and will be automatically started at system boot.

7.1. Installation

At a terminal prompt, enter the following command to install dhcpd:
sudo apt-get install dhcpd
You will see the following output, which explains what to do next:
Please note that if you are installing the DHCP server for the first
time you need to configure. Please stop (/etc/init.d/dhcp
stop) the DHCP server daemon, edit /etc/dhcpd.conf to suit your needs
and particular configuration, and restart the DHCP server daemon
(/etc/init.d/dhcp start).
You also need to edit /etc/default/dhcp to specify the interfaces dhcpd
should listen to. By default it listens to eth0.
NOTE: dhcpd's messages are being sent to syslog. Look there for
diagnostics messages.
Starting DHCP server: dhcpd failed to start - check syslog for diagnostics.
7.2. Configuration
The error message the installation ends with might be a little confusing, but the following
steps will help you configure the service:
Most commonly, what you want to do is assign an IP address randomly. This can be done
with settings as follows:
# Sample /etc/dhcpd.conf
# (add your comments here)
default-lease-time 600;
max-lease-time 7200;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option routers 192.168.1.254;
option domain-name-servers 192.168.1.1, 192.168.1.2;
option domain-name "mydomain.org";
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.10 192.168.1.100;
range 192.168.1.150 192.168.1.200;
}
This will result in the DHCP server giving a client an IP address from the range
192.168.1.10-192.168.1.100 or 192.168.1.150-192.168.1.200. It will lease an IP address for 600 seconds if the client doesn't ask for a specific time frame. Otherwise the maximum Networking (allowed) lease will be 7200 seconds. The server will also "advise" the client that it should use 255.255.255.0 as its subnet mask, 192.168.1.255 as its broadcast address, 192.168.1.254 as the router/gateway and 192.168.1.1 and 192.168.1.2 as its DNS servers.
If you need to specify a WINS server for your Windows clients, you will need to include the netbios-name-servers option, e.g.
option netbios-name-servers 192.168.1.1;
Dhcpd configuration settings are taken from the DHCP mini-HOWTO, which can be found here [http://www.tldp.org/HOWTO/DHCP/index.html].

References

DHCP FAQ [http://www.dhcp-handbook.com/dhcp_faq.html]

8. Domain Name Service (DNS)

Domain Name Service (DNS) is an Internet service that maps IP addresses and fully
qualified domain names (FQDN) to one another. In this way, DNS alleviates the need to remember IP addresses. Computers that run DNS are called name servers. Ubuntu ships with BIND (Berkley Internet Naming Daemon), the most common program used for maintaining a name server on GNU/Linux.

8.1. Installation

At a terminal prompt, enter the following command to install dns:
sudo apt-get install bind

8.2. Configuration

The DNS configuration files are stored in the /etc/bind directory. The primary
configuration file is /etc/bind/named.conf. The content of the default configuration file is shown below:
// This is the primary configuration file for the BIND DNS server named.
//
// Please read /usr/share/doc/bind/README.Debian for information on the
// structure of BIND configuration files in Debian for BIND versions 8.2.1
// and later, *BEFORE* you customize this configuration file.
//
include "/etc/bind/named.conf.options";
// reduce log verbosity on issues outside our control
logging {
category lame-servers { null; };
category cname { null; };
};
// prime the server with knowledge of the root servers
zone "." {
type hint;
file "/etc/bind/db.root";
};
// be authoritative for the localhost forward and reverse zones, and for
// broadcast zones as per RFC 1912
zone "localhost" {
type master;
file "/etc/bind/db.local";
};
41

Networking
zone "127.in-addr.arpa" {
type master;
file "/etc/bind/db.127";
};
zone "0.in-addr.arpa" {
type master;
file "/etc/bind/db.0";
};
zone "255.in-addr.arpa" {
type master;
file "/etc/bind/db.255";
};
// add local zone definitions here
include "/etc/bind/named.conf.local";
The include line specifies the filename which contains the DNS options. The directory line
in the options file tells DNS where to look for files. All files BIND uses will be relative to
this directory.
The file named /etc/bind/db.root describes the root name servers in the world. The
servers change over time and must be maintained now and then.
The zone section defines a master server, and it is stored in a file mentioned against file
tag. Every zone file contains 3 resource records (RRs): an SOA RR, an NS RR and a PTR
RR. SOA is short of Start of Authority. The "@" is a special notation meaning the origin.
NS is the Name Server RR. PTR is Domain Name Pointer. To start the DNS server, run the
following command from a terminal prompt:

You can refer to the documentation mentioned in the references section for details.

8.3. References

DNS HOWTO [http://www.tldp.org/HOWTO/DNS-HOWTO.html]

9. CUPS - Print Server

The primary mechanism for Ubuntu printing and print services is the Common UNIX
Printing System (CUPS). This printing system is a freely available, portable printing layer which has become the new standard for printing in most GNU/Linux distributions.
CUPS manages print jobs and queues and provides network printing using the standard Internet Printing Protocol (IPP), while offering support for a very large range of printers, from dot-matrix to laser and many in between. CUPS also supports PostScript Printer Description (PPD) and auto-detection of network printers, and features a simple web-based configuration and administration tool.

9.1. Installation

To install CUPS on your Ubuntu computer, simply use sudo with the the apt-get command and give the packages to install as the first parameter. A complete CUPS install has many package dependencies, but they may all be specified on the same command line.

Enter the following at a terminal prompt to install CUPS:
sudo apt-get install cupsys cupsys-client
Upon authenticating with your user password, the packages should be downloaded and installed without error. Upon the conclusion of installation, the CUPS server will be started automatically. For troubleshooting purposes, you can access CUPS server errors via the error log file at: /var/log/cups/error_log. If the error log does not show enough information to troubleshoot any problems you encounter, the verbosity of the CUPS log can be increased by changing the LogLevel directive in the configuration file (discussed below) to "debug" or even "debug2", which logs everything, from the default of "info". If you make this change, remember to change it back once you've solved your problem, to prevent the log file from becoming overly large.

9.2. Configuration

The Common UNIX Printing System server's behavior is configured through the directives contained in the file /etc/cups/cupsd.conf. The CUPS configuration file follows the same syntax as the primary configuration file for the Apache HTTP server, so users familiar with editing Apache's configuration file should feel at ease when editing the CUPS configuration file. Some examples of settings you may wish to change initially will be presented here.
Prior to editing the configuration file, you should make a copy of the original file
and protect it from writing, so you will have the original settings as a reference,
and to reuse as necessary.

Copy the /etc/cups/cupsd.conf file and protect it from writing with the
following commands, issued at a terminal prompt:

• ServerAdmin: To configure the email address of the designated administrator
of the CUPS server, simply edit the /etc/cups/cupsd.conf configuration file
with your preferred text editor, and modify the ServerAdmin line accordingly. For
example, if you are the Administrator for the CUPS server, and your e-mail address is
'bjoy@somebigco.com', then you would modify the ServerAdmin line to appear as such:
ServerAdmin bjoy@somebigco.com
For more examples of configuration directives in the CUPS server configuration file,
view the associated system manual page by entering the following command at a terminal
prompt:

Whenever you make changes to the /etc/cups/cupsd.conf configuration file,
you'll need to restart the CUPS server by typing the following command at a
terminal prompt:

Some other configuration for the CUPS server is done in the file

• Listen: By default on Ubuntu, the CUPS server installation listens only on the
loopback interface at IP address 127.0.0.1. In order to instruct the CUPS server to
listen on an actual network adapter's IP address, you must specify either a hostname,
the IP address, or optionally, an IP address/port pairing via the addition of a Listen
directive. For example, if your CUPS server resides on a local network at the IP
address 192.168.10.250 and you'd like to make it accessible to the other systems on
this subnetwork, you would edit the /etc/cups/cups.d/ports.conf and add a Listen
directive, as such:
Listen 127.0.0.1:631 # existing loopback Listen
Listen /var/run/cups/cups.sock # existing socket Listen
Listen 192.168.10.250:631 # Listen on the LAN interface, Port 631 (IPP)
In the example above, you may comment out or remove the reference to the Loopback
address (127.0.0.1) if you do not wish cupsd to listen on that interface, but would
rather have it only listen on the Ethernet interfaces of the Local Area Network (LAN).
To enable listening for all network interfaces for which a certain hostname is bound,
including the Loopback, you could create a Listen entry for the hostname socrates as
such:
Listen socrates:631 # Listen on all interfaces for the hostname 'socrates'
or by omitting the Listen directive and using Port instead, as in:
Port 631 # Listen on port 631 on all interfaces
9.3. References
CUPS Website [http://www.cups.org/]

10. HTTPD - Apache2 Web Server

Apache is the most commonly used Web Server on GNU/Linux systems. Web Servers are used to serve Web Pages requested by client computers. Clients typically request and view Web Pages using Web Browser applications such as Firefox, Opera, or Mozilla.
Users enter a Uniform Resource Locator (URL) to point to a Web server by means
of its Fully Qualified Domain Name (FQDN) and a path to the required resource. For
example, to view the home page of the Ubuntu Web site [http://www.ubuntu.com] a
user will enter only the FQDN. To request specific information about paid support
[http://www.ubuntu.com/support/supportoptions/paidsupport], a user will enter the FQDN followed by a path.
The most common protocol used to transfer Web pages is the Hyper Text Transfer Protocol (HTTP). Protocols such as Hyper Text Transfer Protocol over Secure Sockets Layer (HTTPS), and File Transfer Protocol (FTP), a protocol for uploading and downloading files, are also supported.
Apache Web Servers are often used in combination with the MySQL database engine, the HyperText Preprocessor (PHP) scripting language, and other popular scripting languages such as Python and Perl. This configuration is termed LAMP (Linux, Apache, MySQL and Perl/Python/PHP) and forms a powerful and robust platform for the development and deployment of Web-based applications.

10.1. Installation

The Apache2 web server is available in Ubuntu Linux. To install Apache2:
• At a terminal prompt enter the following command:
sudo apt-get install apache2

10.2. Configuration

Apache is configured by placing directives in plain text configuration files. The main
configuration file is called apache2.conf. In addition, other configuration files may be
added using the Include directive, and wildcards can be used to include many configuration files. Any directive may be placed in any of these configuration files. Changes to the main configuration files are only recognized by Apache2 when it is started or restarted.
The server also reads a file containing mime document types; the filename is set by the TypesConfig directive, and is mime.types by default.
The default Apache2 configuration file is /etc/apache2/apache2.conf . You can edit this file to configure the Apache2 server. You can configure the port number, document root, modules, log files, virtual hosts, etc.

10.2.1. Basic Settings

This section explains Apache2 server essential configuration parameters. Refer to the
Apache2 Documentation [http://httpd.apache.org/docs/2.0/] for more details.
• Apache2 ships with a virtual-host-friendly default configuration. That is, it is configured with a single default virtual host (using the VirtualHost directive) which can modified or used as-is if you have a single site, or used as a template for additional virtual hosts if you have multiple sites. If left alone, the default virtual host will serve as your default site, or the site users will see if the URL they enter does not match the ServerName directive of any of your custom sites. To modify the default virtual host, edit the file /etc/apache2/sites-available/default. If you wish to configure a new virtual host or site, copy that file into the same directory with a name you choose.

For example, sudo cp /etc/apache2/sites-available/default /etc/apache2/sites-available/mynewsite Edit
the new file to configure the new site using some of the directives described below.
• The ServerAdmin directive specifies the email address to be advertised for the server's administrator. The default value is webmaster@localhost. This should be changed to an email address that is delivered to you (if you are the server's administrator). If your website has a problem, Apache2 will display an error message containing this email address to report the problem to. Find this directive in your site's configuration file in /etc/apache2/sites-available.
• The Listen directive specifies the port, and optionally the IP address, Apache2 should listen on. If the IP address is not specified, Apache2 will listen on all IP addresses assigned to the machine it runs on. The default value for the Listen directive is 80.
Change this to 127.0.0.1:80 to cause Apache2 to listen only on your loopback interface so that it will not be available to the Internet, to (for example) 81 to change the port that it listens on, or leave it as is for normal operation. This directive can be found and changed in its own file, /etc/apache2/ports.conf
• The ServerName directive is optional and specifies what FQDN your site should answer to. The default virtual host has no ServerName directive specified, so it will respond to all requests that do not match a ServerName directive in another virtual host. If you have just acquired the domain name ubunturocks.com and wish to host it on your Ubuntu server, the value of the ServerName directive in your virtual host configuration file should be ubunturocks.com. Add this directive to the new virtual host file you created earlier (/etc/apache2/sites-available/mynewsite).
You may also want your site to respond to www.ubunturocks.com, since
many users will assume the www prefix is appropriate. Use the ServerAlias
directive for this. You may also use wildcards in the ServerAlias directive. For
example, ServerAlias *.ubunturocks.com will cause your site to respond to
any domain request ending in .ubunturocks.com.
• The DocumentRoot directive specifies where Apache should look for the files that
make up the site. The default value is /var/www. No site is configured there, but if you
uncomment the RedirectMatch directive in /etc/apache2/apache2.conf requests
will be redirected to /var/www/apache2-default where the default Apache2 site awaits.
Change this value in your site's virtual host file, and remember to create that directory if
necessary!
The /etc/apache2/sites-available directory is not parsed by Apache2.
Symbolic links in /etc/apache2/sites-enabled point to "available" sites. Use
the a2ensite (Apache2 Enable Site) utility to create those symbolic links,
like so: sudo a2ensite mynewsite where your site's configuration file is
/etc/apache2/sites-available/mynewsite. Similarly, the a2dissite utility
should be used to disable sites.

10.2.2. Default Settings

This section explains configuration of the Apache2 server default settings. For example, if you add a virtual host, the settings you configure for the virtual host take precedence for that virtual host. For a directive not defined within the virtual host settings, the default value is used.
• The DirectoryIndex is the default page served by the server when a user requests an index of a directory by specifying a forward slash (/) at the end of the directory name.

he or she will get either the DirectoryIndex page if it exists, a server-generated directory list if it does not and the Indexes option is specified, or a Permission Denied page if neither is true. The server will try to find one of the files listed in the DirectoryIndex directive and will return the first one it finds. If it does not find any of these files and if Options Indexes is set for that directory, the server will generate and return a list, in HTML format, of the subdirectories and files in the directory. The default value, found in /etc/apache2/apache2.conf is " index.html index.cgi index.pl index.php index.xhtml". Thus, if Apache2 finds a file in a requested directory matching any of these names, the first will be displayed.
• The ErrorDocument directive allows you to specify a file for Apache to use for
specific error events. For example, if a user requests a resource that does not
exist, a 404 error will occur, and per Apache2's default configuration, the file
/usr/share/apache2/error/HTTP_NOT_FOUND.html.var will be displayed.
That file is not in the server's DocumentRoot, but there is an Alias directive in
/etc/apache2/apache2.conf that redirects requests to the /error directory to
/usr/share/apache2/error/. To see a list of the default ErrorDocument directives, use this command: grep ErrorDocument /etc/apache2/apache2.conf
• By default, the server writes the transfer log to the file /var/log/apache2/access.log.
You can change this on a per-site basis in your virtual host configuration files
with the CustomLog directive, or omit it to accept the default, specified in
/etc/apache2/apache2.conf. You may also specify the file to which errors are logged, via the ErrorLog directive, whose default is /var/log/apache2/error.log. These
are kept separate from the transfer logs to aid in troubleshooting problems with your
Apache2 server. You may also specify the LogLevel (the default value is "warn") and the LogFormat (see /etc/apache2/apache2.conf for the default value).
• Some options are specified on a per-directory basis rather than per-server. Option is one of these directives. A Directory stanza is enclosed in XML-like tags, like so:

The Options directive within a Directory stanza accepts one or more of the following
values (among others), separated by spaces:
• ExecCGI - Allow execution of CGI scripts. CGI scripts are not executed if this option is not chosen.
Most files should not be executed as CGI scripts. This would be very
dangerous. CGI scripts should kept in a directory separate from and outside
your DocumentRoot, and only this directory should have the ExecCGI
option set. This is the default, and the default location for CGI scripts is
/usr/lib/cgi-bin.
• Includes - Allow server-side includes. Server-side includes allow an HTML file
to include other files. This is not a common option. See the Apache2 SSI Howto
[http://httpd.apache.org/docs/2.0/howto/ssi.html] for mor information.
• IncludesNOEXEC - Allow server-side includes, but disable the #exec and #include
commands in CGI scripts.
• Indexes - Display a formatted list of the directory's contents, if no DirectoryIndex
(such as index.html) exists in the requested directory.
For security reasons, this should usually not be set, and certainly should not
be set on your DocumentRoot directory. Enable this option carefully on a
per-directory basis only if you are certain you want users to see the entire
contents of the directory.
• Multiview - Support content-negotiated multiviews; this option is disabled
by default for security reasons. See the Apache2 documentation on this option
[http://httpd.apache.org/docs/2.0/mod/mod_negotiation.html#multiviews].
• SymLinksIfOwnerMatch - Only follow symbolic links if the target file or directory
has the same owner as the link.
10.2.3. Virtual Hosts Settings
Virtual hosts allow you to run different servers for different IP addresses, different host names, or different ports on the same machine. For example, you can run the website for http://www.example.com and http://www.anotherexample.com on the same Web server using virtual hosts. This option corresponds to the directive for the default virtual host and IP-based virtual hosts. It corresponds to the directive
for a name-based virtual host.
The directives set for a virtual host only apply to that particular virtual host. If a directive is set server-wide and not defined within the virtual host settings, the default setting is used.
For example, you can define a Webmaster email address and not define individual email addresses for each virtual host.
Set the DocumentRoot directive to the directory that contains the root document (such as index.html) for the virtual host. The default DocumentRoot is /var/www.
The ServerAdmin directive within the VirtualHost stanza is email the address used in the footer of error pages if you choose to show a footer with an email address on the error pages.

10.2.4. Server Settings

This section explains how to configure basic server settings.
LockFile - The LockFile directive sets the path to the lockfile used when the
server is compiled with either USE_FCNTL_SERIALIZED_ACCEPT or
USE_FLOCK_SERIALIZED_ACCEPT. It must be stored on the local disk. It should be
left to the default value unless the logs directory is located on an NFS share. If this is the case, the default value should be changed to a location on the local disk and to a directory that is readable only by root.
PidFile - The PidFile directive sets the file in which the server records its process ID (pid).
This file should only be readable by root. In most cases, it should be left to the default value.
User - The User directive sets the userid used by the server to answer requests. This setting determines the server's access. Any files inaccessible to this user will also be inaccessible to your website's visitors. The default value for User is www-data.
Unless you know exactly what you are doing, do not set the User directive to
root. Using root as the User will create large security holes for your Web server.
The Group directive is similar to the User directive. Group sets the group under which the server will answer requests. The default group is also www-data.

10.2.5. Apache Modules

Apache is a modular server. This implies that only the most basic functionality is included in the core server. Extended features are available through modules which can be loaded into Apache. By default, a base set of modules is included in the server at compile-time. If
the server is compiled to use dynamically loaded modules, then modules can be compiled separately, and added at any time using the LoadModule directive. Otherwise, Apache must be recompiled to add or remove modules. Ubuntu compiles Apache2 to allow the dynamic loading of modules. Configuration directives may be conditionally included on the presence of a particular module by enclosing them in an block. You can install additional Apache2 modules and use them with your Web server. You can install Apache2 modules using the apt-get command. For example, to install the Apache2 module for MYSQL authentication, you can run the following command from a terminal prompt:

Once you install the module, the module will be available in the
/etc/apache2/mods-available directory. You can use the a2enmod command to enable a module. You can use the a2dismod command to disable a module. Once you enable the module, the module will be available in the the /etc/apache2/mods-enabled directory.

10.3. HTTPS Configuration

The mod_ssl module adds an important feature to the Apache2 server - the ability
to encrypt communications. Thus, when your browser is communicating using SSL
encryption, the https:// prefix is used at the beginning of the Uniform Resource Locator (URL) in the browser navigation bar.
The mod_ssl module is available in apache2-common package. If you have installed
this package, you can run the following command from a terminal prompt to enable the mod_ssl module:

10.3.1. Certificates and Security

To set up your secure server, use public key cryptography to create a public and private key pair. In most cases, you send your certificate request (including your public key), proof of your company's identity, and payment to a Certificate Authority (CA). The CA verifies the certificate request and your identity, and then sends back a certificate for your secure server.
Alternatively, you can create your own self-signed certificate. Note, however, that
self-signed certificates should not be used in most production environments. Self-signed certificates are not automatically accepted by a user's browser. Users are prompted by the browser to accept the certificate and create the secure connection.
Once you have a self-signed certificate or a signed certificate from the CA of your choice, you need to install it on your secure server.

10.3.2. Types of Certificates

You need a key and a certificate to operate your secure server, which means that you can either generate a self-signed certificate or purchase a CA-signed certificate. A CA-signed certificate provides two important capabilities for your server:
• Browsers (usually) automatically recognize the certificate and allow a secure connection to be made without prompting the user.
• When a CA issues a signed certificate, it is guaranteeing the identity of the organization that is providing the web pages to the browser.
Most Web browsers that support SSL have a list of CAs whose certificates they
automatically accept. If a browser encounters a certificate whose authorizing CA is not in the list, the browser asks the user to either accept or decline the connection.
You can generate a self-signed certificate for your secure server, but be aware that a self-signed certificate does not provide the same functionality as a CA-signed certificate.
A self-signed certificate is not automatically recognized by most Web browsers, and
a self-signed certificate does not provide any guarantee concerning the identity of the organization that is providing the website. A CA-signed certificate provides both of these important capabilities for a secure server. The process of getting a certificate from a CA is fairly easy. A quick overview is as follows:
1. Create a private and public encryption key pair.
2. Create a certificate request based on the public key. The certificate request contains information about your server and the company hosting it.
3. Send the certificate request, along with documents proving your identity, to a CA. We cannot tell you which certificate authority to choose. Your decision may be based on your past experiences, or on the experiences of your friends or colleagues, or purely on monetary factors.
Once you have decided upon a CA, you need to follow the instructions they provide on how to obtain a certificate from them.
4. When the CA is satisfied that you are indeed who you claim to be, they send you a digital certificate.

5. Install this certificate on your secure server, and begin handling secure transactions.
Whether you are getting a certificate from a CA or generating your own self-signed
certificate, the first step is to generate a key.

10.3.3. Generating a Certificate Signing Request (CSR)
To generate the Certificate Signing Request (CSR), you should create your own key. You can run the following command from a terminal prompt to create the key:

openssl genrsa -des3 -out server.key 1024
Generating RSA private key, 1024 bit long modulus
.....................++++++
.................++++++
unable to write 'random state'
e is 65537 (0x10001)
Enter pass phrase for server.key:
You can now enter your passphrase. For best security, it should at least contain eight characters. The minimum length when specifying -des3 is four characters. It should include numbers and/or punctuation and not be a word in a dictionary. Also remember that your passphrase is case-sensitive.
Re-type the passphrase to verify. Once you have re-typed it correctly, the server key is generated and stored in server.key file.
You can also run your secure web server without a passphrase. This is convenient
because you will not need to enter the passphrase every time you start your
secure web server. But it is highly insecure and a compromise of the key means a
compromise of the server as well.
In any case, you can choose to run your secure web server without a passphrase by leaving out the -des3 switch in the generation phase or by issuing the following command at a terminal prompt:
openssl rsa -in server.key -out server.key.insecure
Once you run the above command, the insecure key will be stored in the
server.key.insecure file. You can use this file to generate the CSR without passphrase.
To create the CSR, run the following command at a terminal prompt:
openssl req -new -key server.key -out server.csr
It will prompt you enter the passphrase. If you enter the correct passphrase, it will prompt you to enter Company Name, Site Name, Email Id, etc. Once you enter all these details,your CSR will be created and it will be stored in the server.csr file. You can submit this CSR file to a CA for processing. The CAN will use this CSR file and issue the certificate.
On the other hand, you can create self-signed certificate using this CSR.
10.3.4. Creating a Self-Signed Certificate
To create the self-signed certificate, run the following command at a terminal prompt:
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt

The above command will prompt you to enter the passphrase. Once you enter the correct passphrase, your certificate will be created and it will be stored in the server.crt file.
If your secure server is to be used in a production environment, you probably
need a CA-signed certificate. It is not recommended to use self-signed certificate.
10.3.5. Installing the Certificate
You can install the key file server.key and certificate file server.crt or the certificate
file issued by your CA by running following commands at a terminal prompt:

You should add the following four lines to the /etc/apache2/sites-available/default
file or the configuration file for your secure virtual host. You should place them in the
VirtualHost section. They should be placed under the DocumentRoot line:
SSLEngine on SSLOptions +FakeBasicAuth +ExportCertData +CompatEnvVars +StrictRequire SSLCertificateFile /etc/ssl/certs/server.crt
SSLCertificateKeyFile /etc/ssl/private/server.key
HTTPS should listen on port number 443. You should add the following line to the
/etc/apache2/ports.conf file:
Listen 443

10.3.6. Accessing the Server

Once you install your certificate, you should restart your web server. You can run the following command at a terminal prompt to restart your web server:

You should remember and enter the passphrase every time you start your secure
web server.
You will be prompted to enter the passphrase. Once you enter the correct passphrase, the secure web server will be started. You can access the secure server pages by typing https://your_hostname/url/ in your browser address bar.

References
Apache2 Documentation [http://httpd.apache.org/docs/2.0/]

Mod SSL Documentation [http://www.modssl.org/docs/]

11. Squid - Proxy Server

Squid is a full-featured web proxy cache server application which provides proxy and
cache services for Hyper Text Transport Protocol (HTTP), File Transfer Protocol (FTP),and other popular network protocols. Squid can implement caching and proxying of Secure Sockets Layer (SSL) requests and caching of Domain Name Server (DNS) lookups, and perform transparent caching. Squid also supports a wide variety of caching protocols, such as Internet Cache Protocol, (ICP) the Hyper Text Caching Protocol, (HTCP) the Cache Array Routing Protocol (CARP), and the Web Cache Coordination Protocol. (WCCP)
The Squid proxy cache server is an excellent solution to a variety of proxy and caching server needs, and scales from the branch office to enterprise level networks while providing extensive, granular access control mechanisms and monitoring of critical parameters via the Simple Network Management Protocol (SNMP). When selecting a computer system for use as a dedicated Squid proxy, or caching servers, ensure your system is configured with a large amount of physical memory, as Squid maintains an in-memory cache for increased performance.

11.1. Installation

At a terminal prompt, enter the following command to install the Squid server:
sudo apt-get install squid squid-common

11.2. Configuration
Squid is configured by editing the directives contained within the /etc/squid/squid.conf configuration file. The following examples illustrate some of the directives which may be modified to affect the behavior of the Squid server. For more in-depth configuration of Squid, see the References section.
Prior to editing the configuration file, you should make a copy of the original file
and protect it from writing so you will have the original settings as a reference,
and to re-use as necessary.
Copy the /etc/squid/squid.conf file and protect it from writing with the
following commands entered at a terminal prompt:
sudo cp /etc/squid/squid.conf /etc/squid/squid.conf.original
sudo chmod a-w /etc/squid/squid.conf.original
• To set your Squid server to listen on TCP port 8888 instead of the default TCP port
3128, change the http_port directive as such:
http_port 8888

• Change the visible_hostname directive in order to give the Squid server a specific
hostname. This hostname does not necessarily need to be the computer's hostname. In this example it is set to weezie visible_hostname weezie
• Again, Using Squid's access control, you may configure use of Internet services proxied by Squid to be available only users with certain Internet Protocol (IP) addresses. For example, we willll illustrate access by users of the 192.168.42.0/24 subnetwork only:
Add the following to the bottom of the ACL section of your /etc/squid/squid.conf
file:
acl fortytwo_network src 192.168.42.0/24
Then, add the following to the top of the http_access section of your
/etc/squid/squid.conf file:
http_access allow fortytwo_network
• Using the excellent access control features of Squid, you may configure use of Internet services proxied by Squid to be available only during normal business hours. For example, we'll illustrate access by employees of a business which is operating between 9:00AM and 5:00PM, Monday through Friday, and which uses the 10.1.42.0/42 subnetwork:
Add the following to the bottom of the ACL section of your /etc/squid/squid.conf
file:
acl biz_network src 10.1.42.0/24 acl biz_hours time M T W T F 9:00-17:00
Then, add the following to the top of the http_access section of your
/etc/squid/squid.conf file:
http_access allow biz_network biz_hours
After making changes to the /etc/squid/squid.conf file, save the file and
restart the squid server application to effect the changes using the following
command entered at a terminal prompt:

Squid Website [http://www.squid-cache.org/]

12. Version Control System

Version control is the art of managing changes to information. It has long been a critical tool for programmers, who typically spend their time making small changes to software and then undoing those changes the next day. But the usefulness of version control software extends far beyond the bounds of the software development world. Anywhere you can find people using computers to manage information that changes often, there is room for version control.

12.1. Subversion

Subversion is an open source version control system. Using Subversion, you can record the history of source files and documents. It manages files and directories over time. A tree of files is placed into a central repository. The repository is much like an ordinary file server, except that it remembers every change ever made to files and directories.

12.1.1. Installation

To access Subversion repository using the HTTP protocol, you must install and configure
a web server. Apache2 is proven to work with Subversion. Please refer to the HTTP
subsection in the Apache2 section to install and configure Apache2. To access the
Subversion repository using the HTTPS protocol, you must install and configure a digital certificate in your Apache 2 web server. Please refer to the HTTPS subsection in the
Apache2 section to install and configure the digital certificate.
To install Subversion, run the following command from a terminal prompt:
sudo apt-get install subversion libapache2-svn

12.1.2. Server Configuration

This step assumes you have installed above mentioned packages on your system. This section explains how to create a Subversion repository and access the project.

12.1.2.1. Create Subversion Repository

The Subversion repository can be created using the following command from a terminal
prompt:
svnadmin create /path/to/repos/project
12.1.3. Access Methods
Subversion repositories can be accessed (checked out) through many different methods
--on local disk, or through various network protocols. A repository location, however, isalways a URL. The table describes how different URL schemas map to the available access methods.
Table 4.1. Access Methods
Schema
Access Method
file://direct repository access (on local disk)
http://Access via WebDAV protocol to
Subversion-aware Apache2 web server
https://Same as http://, but with SSL encryption
svn://Access via custom protocol to an svnserve
server
svn+ssh://Same as svn://, but through an SSH tunnel
In this section, we will see how to configure Subversion for all these access methods.
Here, we cover the basics. For more advanced usage details, refer to the svn book
[http://svnbook.red-bean.com/].

12.1.3.1. Direct repository access (file://)

This is the simplest of all access methods. It does not require any Subversion server
process to be running. This access method is used to access Subversion from the same machine. The syntax of the command, entered at a terminal prompt, is as follows:
svn co file:///path/to/repos/project
or svn co file://localhost/path/to/repos/project
If you do not specify the hostname, there are three forward slashes (///) -- two for
the protocol (file, in this case) plus the leading slash in the path. If you specify the
hostname, you must use two forward slashes (//).
The repository permissions depend on filesystem permissions. If the user has read/write permission, he can checkout from and commit to the repository.

12.1.3.2. Access via WebDAV protocol (http://)

To access the Subversion repository via WebDAV protocol, you must configure
your Apache 2 web server. You must add the following snippet in your
/etc/apache2/apache2.conf file:

DAV svn
SVNPath /path/to/repos
AuthType Basic
AuthName "Your repository name"
AuthUserFile /etc/subversion/passwd

Require valid-user

Next, you must create the /etc/subversion/passwd file. This file contains user
authentication details. To add an entry, i.e. to add a user, you can run the following
command from a terminal prompt:
htpasswd2 /etc/subversion/passwd user_name
This command will prompt you to enter the password. Once you enter the password, the user is added. Now, to access the repository you can run the following command:
svn co http://servername/svn
The password is transmitted as plain text. If you are worried about password
snooping, you are advised to use SSL encryption. For details, please refer next
section.

12.1.3.3. Access via WebDAV protocol with SSL encryption (https://)

Accessing Subversion repository via WebDAV protocol with SSL encryption (https://) is similar to http:// except that you must install and configure the digital certificate in your Apache2 web server.
You can install a digital certificate issued by a signing authority like Verisign.
Alternatively, you can install your own self-signed certificate.
This step assumes you have installed and configured a digital certificate in your Apache 2 web server. Now, to access the Subversion repository, please refer to the above section!
The access methods are exactly the same, except the protocol. You must use https:// to access the Subversion repository.

12.1.3.4. Access via custom protocol (svn://)

Once the Subversion repository is created, you can configure the access control. You can edit the /path/to/repos/project/conf/svnserve.conf file to configure the access control. For example, to set up authentication, you can uncomment the following lines in the configuration file:
# [general]
# password-db = passwd
After uncommenting the above lines, you can maintain the user list in the passwd file. So, edit the file passwd in the same directory and add the new user. The syntax is as follows:
username = password
For more details, please refer to the file.
Now, to access Subversion via the svn:// custom protocol, either from the same machine or a different machine, you can run svnserver using svnserve command. The syntax is as follows:
$ svnserve -d --foreground -r /path/to/repos
# -d -- daemon mode
# --foreground -- run in foreground (useful for debugging)
# -r -- root of directory to serve
For more usage details, please refer to:
$ svnserve --help
Once you run this command, Subversion starts listening on default port (3690). To access the project repository, you must run the following command from a terminal prompt:
svn co svn://hostname/project project --username user_name
Based on server configuration, it prompts for password. Once you are authenticated, it checks out the code from Subversion repository. To synchronize the project repository with the local copy, you can run the update sub-command. The syntax of the command, entered at a terminal prompt, is as follows:
cd project_dir ; svn update
For more details about using each Subversion sub-command, you can refer to the manual.
For example, to learn more about the co (checkout) command, please run the following command from a terminal prompt:
svn co help

12.1.3.5. Access via custom protocol with SSL encryption (svn+ssh://)

The configuration and server process is same as in the svn:// method. For details, please refer to the above section. This step assumes you have followed the above step and started the#Subversion server using svnserve command.
It is also assumed that the ssh server is running on that machine and that it is allowing incoming connections. To confirm, please try to login to that machine using ssh. If you can login, everything is perfect. If you cannot login, please address it before continuing further.

The svn+ssh:// protocol is used to access the Subversion repository using SSL encryption.
The data transfer is encrypted using this method. To access the project repository (for example with a checkout), you must use the following command syntax:
svn co svn+ssh://hostname/var/svn/repos/project
You must use the full path (/path/to/repos/project) to access the Subversion
repository using this access method.

Based on server configuration, it prompts for password. You must enter the password you
use to login via ssh. Once you are authenticated, it checks out the code from the Subversion repository.

12.2. CVS Server

CVS is a version control system. You can use it to record the history of source files.

12.2.1. Installation

At a terminal prompt, enter the following command to install cvs:
sudo apt-get install cvs After you install cvs, you should install xinetd to start/stop the cvs server. At the prompt, enter the following command to install xinetd:
sudo apt-get install xinetd

12.2.2. Configuration

Once you install cvs, the repository will be automatically initialized. By default, the
repository resides under the /var/lib/cvs directory. You can change this path by running following command:

Once the initial repository is set up, you can configure xinetd to start the CVS server. You can copy the following lines to the /etc/xinetd/cvspserver file.
service cvspserver
{
port = 2401
socket_type = stream
protocol = tcp
user = root
wait = no

type = UNLISTED
server = /usr/bin/cvs
server_args = -f --allow-root /var/lib/cvs pserver
disable = no
}
Be sure to edit the repository if you have changed the default repository
(/var/lib/cvs) directory.
Once you have configured xinetd you can start the cvs server by running following
command:

You can confirm that the CVS server is running by issuing the following command:
sudo netstat -tap | grep cvs
When you run this command, you should see the following line or something similar:
tcp 0 0 *:cvspserver *:* LISTEN
From here you can continue to add users, add new projects, and manage the CVS server.
CVS allows the user to add users independently of the underlying OS installation.
Probably the easiest way is to use the Linux Users for CVS, although it has
potential security issues. Please refer to the CVS manual for details.
12.2.3. Add Projects
This section explains how to add new project to the CVS repository. Create the directory and add necessary document and source files to the directory. Now, run the following command to add this project to CVS repository:
cd your/project
cvs import -d :pserver:username@hostname.com:/var/lib/cvs -m "Importing my project to CVS repository" . new_project start

 

Read More: "Ubuntu Server Guide: Part 3" 

 

 

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