APT: How to prefer local packages over remote?

I recently had to test some of my locally generated MariaDB debian packages. So, created a local repository of generated packages and added it to sources.list file. However, since these packages required some other packages stored on a mirror, I had to add the mirror to the sources.list file as well. Since, this mirror also contained the packages that I intended to test, now when I try to install the packages, APT would always pick/prefer the ones stored on the mirror. How to solve this? How to make APT prefer the local packages instead? Lets start by taking a peek into the sources.list file:

$cat /etc/apt/sources.list
# remote repo
deb http://mirror.jmu.edu/pub/mariadb/repo/5.5/ubuntu precise main

# local repo
deb file:///home/nirbhay/project/repo/maria/testing/debian/5.5/debs binary/

$ sudo apt-cache policy mariadb-galera-server
  Installed: (none)
  Candidate: 5.5.37+maria-1~precise
  Version table:
     5.5.37+maria-1~precise 0
        500 file:/home/nirbhay/project/repo/maria/testing/debian/5.5/debs/ binary/ Packages
        500 http://mirror.jmu.edu/pub/mariadb/repo/5.5/ubuntu/ precise/main i386 Packages

The following tips can help you fix this problem :

  1. If remote and local packages have the same version (as in my case), place one that you want to be preferred higher in sources.list file.

  2. APT prefers authenticated repository over unauthenticated. So, as against the above case, even if the local repository is placed over the remote, APT will prefer remote one if its authenticated and the local repository is not. In that case, –allow-unauthenticated can be used to make local packages take precedence.

  3. In case local and remote packages have different versions, APT would always prefer the package with higher version. However, this rule can be eased by apt-pinning, where a higher priority is assigned to a particular repository. For example, local repository can be pinned with higher priority (or precedence in APT’s context) by adding a file under /etc/apt/preferences.d with .pref extension and the following content :

    Package: *
    Pin: origin ""
    Pin-Priority: 1000

    This has been explained really well in this thread.

Lastly, do not forget to run “apt-get update” for changes to take effect.

Generating SSH key pair

SSH key pair is a set of private/public keys used in securing network communication. These keys are normally required for passwordless SSH login to a remote host running SSH daemon (sshd). Here is how you would generate a pair of RSA keys:

$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/nirbhay/.ssh/id_rsa):
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/nirbhay/.ssh/id_rsa.
Your public key has been saved in /home/nirbhay/.ssh/id_rsa.pub.
The key fingerprint is:
5f:1a:b5:50:a8:b6:d6:2b:48:1b:b6:df:4c:54:a2:28 nirbhay@nirbhay-VirtualBox
The key's randomart image is:
+--[ RSA 2048]----+
|           ..    |
|          ..     |
|         .o o    |
|       .o. = .   |
|       ...o      |
$ ls ~/.ssh/
id_rsa  id_rsa.pub

Now that we have the private/public key files, all you need to do is copy/append the public key (id_rsa.pub) contents to the remote machine’s ~/.ssh/authorized_keys (600) file. DO NOT share the “private key”.

Note: On debian-based distributions, ssh-keygen is provided by openssh-client package.

Generating SSL certificates

** The (self-signed) SSL certificate generated by the procedure mentioned in this article should be used for testing purpose only **

Generating an SSL certificate is very simple. All you need is openssl package installed on your system. A key point to note here is that SSL certificates contain public key, which is always generated in pair with a private key. Here is the step-by-step procedure to generate one:

  1. Private key
    Lets first generate a 2048-bit RSA private key.

    openssl genrsa -out privkey.pem 2048

    $ openssl genrsa -out privkey.pem 2048
    Generating RSA private key, 2048 bit long modulus
    unable to write 'random state'
    e is 65537 (0x10001)
    $ ls

    So, we have the private key in place. This will be used to generate the certificate.

    If “unable to write ‘random state'” bothers you, then check this out for a possible solution: http://stackoverflow.com/a/94458

  2. The self-signed certificate
    A certificate can now be generated using the following command.

    openssl req -new -x509 -key privkey.pem -out cacert.pem -days 1095

    $ openssl req -new -x509 -key privkey.pem -out cacert.pem -days 1095
    You are about to be asked to enter information that will be incorporated
    into your certificate request.
    What you are about to enter is what is called a Distinguished Name or a DN.
    There are quite a few fields but you can leave some blank
    For some fields there will be a default value,
    If you enter '.', the field will be left blank.
    Country Name (2 letter code) [AU]:XX
    State or Province Name (full name) [Some-State]:XX
    Locality Name (eg, city) []:XX
    Organization Name (eg, company) [Internet Widgits Pty Ltd]:XX
    Organizational Unit Name (eg, section) []:XX
    Common Name (e.g. server FQDN or YOUR name) []:XX
    Email Address []:XX
    $ ls
    cacert.pem  privkey.pem

These files can easily be tested by starting a test SSL/TLS server (s_server(1) and connecting to it using a client (s_client(1)).

$ openssl s_server -port <port> -cert /path/to/cacert.pem -key /path/to/privkey.pem

$ openssl s_client -host <server-host> -port <server-port> -key /path/to/privkey.pem

Reference : https://www.openssl.org/docs/HOWTO/
Thats all!

Go projects in MySQL/MariaDB ecosystem

Please let me know if you come across a MySQL/MariaDB Go project not listed here.