Setup a Postfix Alias Email Account

Recently, my business had the need to create an email account for general inquiries. Since I’m currently the only employee, the email will be sent to me, but I’d like to publish a contact email address in some instances rather than my personal email address.

The email address I decided to publish rather than my own was contact@lakonacomputers.com. In order to avoid setting up an user account on the mail server for a user named contact (and creating a mail store for the user), I decided to create an alias for contact and set myself as the contact user. This way, when email is received by Postfix for contact, the email will be sent to my mail store in my user directory.

The Configuration

First check the main.cf file (located at /etc/postfix on my Ubuntu server) to find the alias file configured for Postfix. Look for the following lines.

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

This tell us where the aliases file is located, so we open the file and you will see something like this:

# /etc/aliases
mailer-daemon: postmaster
postmaster: jason
nobody: root
hostmaster: root
usenet: root
news: root
webmaster: jason
www: root
ftp: root
abuse: root
noc: root
security: root

I simply added contact: jason to the file and then run the newaliases command to inform postfix of the update of aliases file. Voila, now when messages are sent to contact@lakonacomputers.com, the message will be sent to my user.

Basic iptables Firewall

The iptables software is a user space application for configuring packet filtering in the Linux kernel. iptables is used to set rules for packets that travel through a host’s network stack and at certain points, called hooks, the iptables rules are evaluated and actions, such as dropping a packet, can be executed. In this post I will draft a script to setup the iptables’ rules for a firewall and then set that script to be executed at boot time. Continue reading

Adding a Samba Share

This post will use Samba Version 4.1.6-Ubuntu (the version in use on Ubuntu 14.04 LTS Server at the time of this writing) to setup Samba (smb) shares from a drive attached to a server on a local network. Three shares will be created: dropbox, hub, and restricted which will correspond to directories on the attached drive with the same names (although the names of shares and directories can differ).

The dropbox share will allow any user to connect and read, add, and remove objects from it. The hub, will allow any user to connect and read files, but only listed users will have the ability to add and remove them. Finally the restricted share will only allow access and privileges to certain users.

Mount the Drive in the File System

First, find and mount the drive that will host the shares in the file system. Use lsblk to print the device list, then mount the device — in our example the device that represents our drive is /dev/sdb1.

> lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0   149G  0 disk 
├─sda1   8:1    0 145.1G  0 part /
├─sda2   8:2    0     1K  0 part 
└─sda5   8:5    0   3.9G  0 part [SWAP]
sdb      8:16   0   1.8T  0 disk 
└─sdb1   8:17   0   1.8T  0 part 

> sudo mount /dev/sdb1 /media/share

To automatically mount this device, grab the UUID of the disk with blkid and add it to the /etc/fstab file (I’m using vim, but use whatever text editor you like). Once the fstab file has been edited correctly, the drive will be mounted automatically during system start up.

> sudo blkid
/dev/sda1: UUID="ed9feafe-6654-4173-9967-7b6fe43581b5" UUID_SUB="532b088c-66f9-4ca2-8664-d80ff7612891" TYPE="btrfs" 
/dev/sda5: UUID="678e7a38-6367-4305-929f-b96ae36d7329" TYPE="swap" 
/dev/sdb1: LABEL="Black" UUID="46E6328FE6327EED" TYPE="ntfs" 

> sudo vim /etc/fstab

Add the following line to fstab, save and close the file.

UUID=46E6328FE6327EED /media/share ntfs defaults 0 2

Creating the Share and Controlling Access

Before we begin editing the Samba configuration file, it’s a good idea to make a backup of the original. Also, access to the share is controlled by Samba, so we also need to create users within the Samba program.

> sudo cp /etc/samba/smb.conf /etc/samba/smb.conf.orig

> sudo smbpasswd -a [user]
New SMB password:
Retype new SMB password:
Added user [user].

The following are the definitions of the shares we’ve set out to create:

dropbox

Before defining our dropbox, we change the ownership of the /media/share/dropbox directory to facilitate the requirement that anyone can access/read/write/delete files and directories. In this case, I’ve chosen to set the nobody user and nogroup group as having ownership of the dropbox.

> sudo chown nobody:nogroup /media/share/dropbox

Now, we can create the definition of the share.

[dropbox]
 path = /media/share/dropbox
 browseable = yes
 read only = no
 guest ok = yes
 force user = nobody
 force group = nogroup
 force create mode = 664
 force directory mode = 775

The path directive tells where in the file system the share is located, and browseable determines whether or not the share will be advertised on the network (in the network neighborhood on Windows systems). By setting read only to ‘no’, we’ve declared that users who can access the share can write to it, and by setting guest ok to ‘yes’ we’re not restricting access.

Forcing the user and group to nobody and nogroup respectively we’re ensuring files and directories created in the dropbox will be owned by the unprivileged Posix user and group of the same corresponding names. Forcing create mode makes sure files are created with read and write privileges to users accessing the share, and force directory mode makes sure directories are created with read, write, and execute permissions.

hub

[hub]
 path = /media/share/hub
 browseable = yes
 read only = yes
 guest ok = yes
 write list = [user]
 force user = nobody
 force group = nogroup
 force create mode = 664
 force directory mode = 775

This share is a lot like the last one, but notice this share has been declared read only. This means that, although anybody can find and connect to the share, only those users listed in the write list can write new files and delete files within the share.

restricted

The restricted share will not be advertised on the network and only certain users will be allowed to access it. When these users do gain access they will have read and write permissions permissions on all files and full permissions on directories. Unix users that will have access to this share must be the user or in the group that the share forces users to use.

[restricted]
  path = /media/share/restricted
  browseable = no
  read only = no
  guest ok = no
  valid users = [user]
  force user = [user]
  force group = restricted
  force create mode = 664
  force directory mode = 775

 

Adding a PHP Program to WordPress

I recently switched my blog from my own programming to using WordPress. I have long recognized  WordPress as good a software project and it has stood the test of time. Not only has the software been around since 2003, it has continued to improve. The improvements to WordPress have allow the software to run more and more projects (although it’s still used, in my opinion, too often where it doesn’t fit right).

For my needs I thought it would work well. I’m running a business while attending university and keeping up with certifications, so I didn’t want to spend the time to make it easier to post to my blog — which had been on my to do list — so I just installed WordPress. The installation took a matter of minuets and after a bit of time looking though themes I quickly had my site up and running with the CMS and looking decent with a freely available theme.

The Problem

I wanted to add a table to my site that shows the books I’ve read. I wanted the book’s title to be displayed along with the author(s) and a picture of the book. I did not want to write out the HTML each time and the WordPress interface doesn’t make working with tables easy.

The Approach

I’m a member of paperbackswap.com, and on their site they maintain a list of books that I’ve read. I can export this list as a CSV file. I thought it would be nice to place this CSV file in my site’s directory structure and have a PHP script parse the file and generate the desired table. This lead me to ask the following questions:

  1. How do I add a custom page to WordPress?
  2. How do I control that page with PHP?

Thanks to the user Adam Hopkinson on Stackoverflow, I had these questions answered and was ready to begin adding my custom PHP page to my WordPress site.

The Execution

First, I created a directory for my custom pages in the WordPress directory structure named my-pages. Then, I uploaded the CSV file from paperbackswap into this directory. I named the file readBooks.csv. The fields of the CSV file were: title, ISBN10, and ISBN13. I really don’t need the ISBNs for my purposes but it didn’t hurt to leave them there (I may use them in the future, and I can always leave those fields blank when adding to the list), but I was going to need a field for the book’s cover image. I decided that would become the first field of the CSVs.

Next, I created the new page by following Adam’s instructions. To make things easier, I linked to this page (which is in the WordPress themes directory) into the my-pages directory and named the page books.php; my directory looked like so:

$> ls -hal
lrwxrwxrwx 1 jason www-data   35 Oct 11 20:20 books.php -> ../wp-content/themes/vito/books.php
-rwxrwxr-x 1 jason www-data 4.1K Oct 13 02:03 readBooks.csv

The books.php page is a copy of my theme’s template, and contains its PHP code. I thought it would be too messy to insert my code directly into this template so I created a “controller” for it which contains the page specific PHP. Then I included the controller in the page so that I can call the function needed to print the books table. Here’s the head of books.php:

$> head books.php
<?php
/*
 * Template Name: books
 */

require_once(ABSPATH.'my-pages/booksController.php');
?>

At this point, I started drafting the code that would parse the CSV file and print my table. I found that it was advantageous to create a Book class that would serve as a constructor. I would give the new Book object’s constructor an associative array containing the fields parsed from the CSV file. The Book objects would also provide a __toString method which would return an HTML table row containing the given book’s data. The function that instantiates the Books would take care of generating the rest of the HTML table.

By now the my-pages directory structure looked like this:

ls -F
classes/  img/  booksController.php*  books.php@  readBooks.csv*

I added the classes directory to hold the definition of the Book class (and future classes, should I decide to create new pages) and the img directory to contain the book covers. With all this in place, when I want to add a book to the Books page, I simply upload the cover image to the img directory and enter the book’s details in the readBooks.csv file and voilà, the book would be added to the books table.