The calibre Content server

The calibre Content server allows you to access your calibre libraries and read books directly in a browser on your favorite mobile phone or tablet device. As a result, you do not need to install any dedicated book reading/management apps on your phone. Just use the browser. The server downloads and stores the book you are reading in an off-line cache so that you can read it even when there is no internet connection.

To start the server, click the Connect/share button and choose Start Content server. You might get a message from your computer’s firewall or anti-virus program asking if it is OK to allow access to calibre.exe. Click the Allow or OK button. Then open a browser (preferably Chrome or Firefox) in your computer and type in the following address:

http://127.0.0.1:8080

This will open a page in the browser showing you your calibre libraries, click on any one and browse the books in it. Click on a book, and it will show you all the metadata about the book, along with buttons to Read and Download the book. Click the Read button to start reading the book.

Note

The address used above http://127.0.0.1:8080 will only work on the computer that is running calibre. To access the server from other computers/phones/tablets/etc. you will need to do a little more work, as described in the next section.

Accessing the Content server from other devices

There are two types of remote device access that you will typically need. The first, simpler kind is from within your home network. If you are running calibre on a computer on your home network and you have also connected your other devices to the same home network, then you should be easily able to access the server on those devices.

Accessing the server from devices on your home network

After starting the server in calibre as described above, click the Connect/share button again. Instead of the Start Content server action, you should see a Stop Content server action instead. To the right of this action will be listed an IP address and port number. These look like a bunch of numbers separated by periods. For example:

Stop Content server [192.168.1.5, port 8080]

These numbers tell you what address to use to connect to the server in your devices. Following the example above, the address becomes:

http://192.168.1.5:8080

The first part of the address is always http:// the next part is the IP address, which is the numbers before the comma and finally we have the port number which must be added to the IP address with a colon (:). If you are lucky, that should be all you need and you will be looking at the calibre libraries on your device. If not, read on.

Trouble-shooting the home network connection

If you are unable to access the server from your device, try the following steps:

1. Check that the server is running by opening the address http://127.0.0.1:8080 in a browser running on the same computer as the server.

2. Check that your firewall/anti-virus is allowing connections to your computer on the port 8080 and to the calibre program. The easiest way to eliminate the firewall/anti-virus as the source of problems is to temporarily turn them both off and then try connecting. You should first disconnect from the internet, before turning off the firewall, to keep your computer safe.

3. Check that your device and computer are on the same network. This means they should both be connected to the same wireless router. In particular neither should be using a cellular or ISP provided direct-WiFi connection.

4. If you have non-standard networking setup, it might be that the IP address shown on the Connect/share menu is incorrect. In such a case you will have to figure out what the correct IP address to use is, yourself. Unfortunately, given the infinite diversity of network configurations possible, it is not possible to give you a roadmap for doing so.

5. If you have setup a username and password, first try it without that to see if it is causing issues. Some e-ink devices have browsers that do not handle authentication. You can sometimes workaround this by including the username and password in the URL, for example: http://username:password@192.168.1.2:8080.

6. If you are stuck, you can always ask for help in the calibre user forums.

Accessing the server from anywhere on the internet

Warning

Before doing this you should turn on username/password protection in the server, otherwise anyone in the world will be able to access your books. Go to Preferences → Sharing → Sharing over the net and enable the option to Require username and password to access the content server.

While the particular details on setting up internet access vary depending on the network configuration and type of computer you are using, the basic schema is as follows.

1. Find out the external IP address of the computer you are going to run the server on. You can do that by visiting the site What is my IP address in a browser running on the computer.

2. If the computer is behind a router, enable port forwarding on the router to forward the port 8080 (or whatever port you choose to run the calibre Content server on) to the computer.

3. Make sure the calibre server is allowed through any firewalls/anti-virus programs on your computer.

4. Now you should be able to access the server on any internet-connected device using the IP address you found in the first step. For example, if the IP address you found was 123.123.123.123 and the port you are using for the calibre server is 8080, the address to use on your device becomes: http://123.123.123.123:8080.

5. Optionally, use a service like no-ip to setup an easy to remember address to use instead of the IP address you found in the first step.

Note

For maximum security, you should also enable HTTPS on the Content server. You can either do so directly in the server by providing the path to the HTTPS certificate to use in the advanced configuration options for the server, or you can setup a reverse proxy as described below, to use an existing HTTPS setup.

The server interface

The server interface is a simplified version of the main calibre interface, optimised for use with touch screens. The home screen shows you books you are currently reading as well as allowing to choose a calibre library you want to browse. The server in calibre gives you access to all your libraries, not just a single one, as before.

The book list

The server book list is a simple grid of covers. Tap on a cover to see the detailed metadata for a book, or to read the book. If you prefer a more detailed list, you can change the default view by clicking the three vertical dots in the top right corner.

Sorting and searching of the book list should be familiar to calibre users. They can be accessed by clicking their icons in the top right area. They both work exactly the same as in the main calibre program. The search page even allows you to construct search queries by clicking on authors/tags/etc., just as you can using the Tag browser in the main program.

A much loved feature of the main program, Virtual libraries is present in the server interface as well. Click the three vertical dots in the top right corner to choose a Virtual library.

The book viewer

You can read any book in your calibre library by simply tapping on it and then tapping the Read button. The book viewer is very simple to operate. You can both tap and swipe to turn pages. Swiping up/down skips between chapters. Tapping the top quarter of the screen gets you the detailed controls and viewer preferences.

If you leave the Content server running, you can even open the same book on multiple devices and it will remember your last read position. If it does not you can force a sync by tapping in the top quarter and choosing Sync.

Browser support

The new calibre server makes lots of use of advanced HTML 5 and CSS 3 features. As such it requires an up-to-date browser to use. It has been tested on Android Chrome and iOS Safari as well as Chrome and Firefox on the desktop.

The server is careful to use functionality that has either been already standardised or is on the standards track. As such if it does not currently work with your favorite browser, it probably will once that browser has caught up.

If you are using a particularly old or limited browser or you don’t like to run JavaScript, you can use the mobile view, by simply adding /mobile to the server address.

Note

On iOS, Apple allows only a single browser engine, so Firefox, Chrome and Safari are all actually the same browser under the hood. The new server interface requires iOS 10.3.2 or newer. On Android, the server has been tested with Chrome version 58 and newer.

Enabling offline support

Browser makers have been trying to force people to use SSL by disabling advanced features in their browsers for plain HTTP connections. One such casualty is ApplicationCache, which was what was used in calibre for offline support. As a result now-a-days sadly, offline mode works only as long as you keep the browser tab open. In addition, in Firefox on Android, you will need to type about:config and create a preference called browser.tabs.useCache and set it to true.

Managing user accounts from the command-line only

The calibre program has a nice section in Preferences to allow you to manage user accounts for the server. However, if you want to run the standalone server and cannot run the main calibre program on the same computer/user account, you can also manage users using just the command-line.

You can manage user accounts using the --manage-users option to the standalone calibre-server program. Suppose you want to store the user database in the folder /srv/calibre, then you create it by running:

calibre-server --userdb /srv/calibre/users.sqlite --manage-users

Just follow the prompts to create user accounts, set their permission, etc. Once you are done, you can run the server as:

calibre-server --userdb /srv/calibre/users.sqlite --enable-auth

It will use the user accounts you created in the previous step.

Integrating the calibre Content server into other servers

Here, we will show you how to integrate the calibre Content server into another server. The most common reason for this is to make use of SSL or to serve the calibre library as part of a larger site. The basic technique is to run the calibre server and setup a reverse proxy to it from the main server.

A reverse proxy is when your normal server accepts incoming requests and passes them onto the calibre server. It then reads the response from the calibre server and forwards it to the client. This means that you can simply run the calibre server as normal without trying to integrate it closely with your main server.

Using a full virtual host

The simplest configuration is to dedicate a full virtual host to the calibre server. In this case, run the calibre server as:

calibre-server

Now setup the virtual host in your main server, for example, for nginx:

http {
    client_max_body_size 64M;  # needed to upload large books
}

server {
    listen [::]:80;
    server_name myserver.example.com;

    location / {
        proxy_pass http://127.0.0.1:8080;
    }
}

Or, for Apache:

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so

<VirtualHost *:80>
    ServerName myserver.example.com
    AllowEncodedSlashes On
    ProxyPreserveHost On
    ProxyPass "/"  "http://localhost:8080/"
</VirtualHost>

Using a URL prefix

If you do not want to dedicate a full virtual host to calibre, you can have it use a URL prefix. Start the calibre server as:

calibre-server --url-prefix /calibre --port 8080

The key parameter here is --url-prefix /calibre. This causes the Content server to serve all URLs prefixed by /calibre. To see this in action, visit http://localhost:8080/calibre in your browser. You should see the normal Content server website, but now it will run under /calibre.

With nginx, the required configuration is:

http {
    client_max_body_size 64M;  # needed to upload large books
}

proxy_set_header X-Forwarded-For $remote_addr;
location /calibre/ {
    proxy_buffering off;
    proxy_pass http://127.0.0.1:8080$request_uri;
}
location /calibre {
    # we need a trailing slash for the Application Cache to work
    rewrite /calibre /calibre/ permanent;
}

For Apache, first enable the proxy modules in Apache, by adding the following to httpd.conf:

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so

The exact technique for enabling the proxy modules will vary depending on your Apache installation. Once you have the proxy modules enabled, add the following rules to httpd.conf (or if you are using virtual hosts to the conf file for the virtual host in question):

AllowEncodedSlashes On
RewriteEngine on
RewriteRule ^/calibre/(.*) http://127.0.0.1:8080/calibre/$1 [proxy]
RedirectMatch permanent ^/calibre$ /calibre/

That’s all, you will now be able to access the calibre Content server under the /calibre URL in your main server. The above rules pass all requests under /calibre to the calibre server running on port 8080 and thanks to the --url-prefix option above, the calibre server handles them transparently.

Note

When using a reverse proxy, you should tell the calibre Content server to only listen on localhost, by using --listen-on 127.0.0.1. That way, the server will only listen for connections coming from the same computer, i.e. from the reverse proxy.

Note

If you have setup SSL for your main server, you should tell the calibre server to use basic authentication instead of digest authentication, as it is faster. To do so, pass the --auth-mode=basic option to calibre-server.

Creating a service for the calibre server on a modern Linux system

You can easily create a service to run calibre at boot on a modern (systemd) based Linux system. Just create the file /etc/systemd/system/calibre-server.service with the contents shown below:

[Unit]
Description=calibre Content server
After=network.target

[Service]
Type=simple
User=mylinuxuser
Group=mylinuxgroup
ExecStart=/opt/calibre/calibre-server "/path/to/calibre library folder"

[Install]
WantedBy=multi-user.target

Change mylinuxuser and mylinuxgroup to whatever user and group you want the server to run as. This should be the same user and group that own the files in the calibre library folder. Note that it is generally not a good idea to run the server as root. Also change the path to the calibre library folder to suit your system. You can add multiple libraries if needed. See the help for the calibre-server command.

Now run:

sudo systemctl start calibre-server

to start the server. Check its status with:

sudo systemctl status calibre-server

To make it start at boot, run:

sudo systemctl enable calibre-server

Note

The calibre server does not need a running X server, but it does need the X libraries installed as some components it uses link against them.

Note

The calibre server also supports systemd socket activation, so you can use that, if needed, as well.

© Copyright Kovid Goyal. Last updated on Oct 18, 2024.