Category: Tech, Code & AI

  • Raspberry Pi print server with no server-side driver

    Raspberry Pi print server with no server-side driver

    There are numerous articles which step through how to configure CUPS to turn an RPi into a print server but I bumped into a problem because there are no drivers available for my Brother MFC-7340 printer for ARM (only available for i386) and I was not keen work on the source code/compile/etc.

    The quick fix is to turn it into a RAW (a.k.a. HP JetDirect) print server.

    Install CUPS

    sudo apt-get install cups

    Configure CUPS

    Edit /etc/cups/cupsd.conf.

    Scroll down until you see the Listen configuration directive. Comment it out. This will make CUPS available over the network.

    # Only listen for connections from the local machine
    # Listen localhost:631
    Port 631

    Look for the <Location /> directive, and add Allow all (or a specific list of IPs, if your local network is not secure) to allow access.

    <Location />
      # Allow remote access...
      Order allow,deny
      Allow all
    </Location>
    

    Save the file and restart CUPS.

    sudo /etc/init.d/cups restart

    Configure Printer

    Now connect your printer to the USB port on the RPi.

    Now you should be able to use a browser and go to https://<ip.address.of.rpi>:631/admin to reach the CUPS web UI.

    1. Under Printers, click Add Printer.
    2. You should see your printer appear under Local Printers. Select it and click Continue.
    3. You can accept the default names on the next screen and click Continue.
      • You do not need to enable Share This Printer.
      • Make a note of the printer Name. You will need this later.
    4. In the next screen, click on Select Another Make/Manufacturer.
      • Select Raw and click Continue.
      • Select Raw Queue (en) and click Add Printer.

    Install xinetd

    sudo apt-get install xinetd

    Configure xinetd

    Edit /etc/services and scroll to the end. Add the following line:

    jetdirect 9100/tcp

    Create a new file /etc/xinetd.d/jetdirect and add the following, replacing Brother_MFC-7340 with your printer name configured in CUPS above.

    service jetdirect
    {
    socket_type = stream
    protocol = tcp
    wait = no
    user = root
    server = /usr/bin/lp
    server_args = -d Brother_MFC-7340 -o raw
    groups = yes
    disable = no
    }

    Save the file and restart xinetd.

    sudo /etc/init.d/xinetd restart

    Connect your computer

    Now, go to your computer and connect to the printer. These are steps for Macs.

    • Go to System PreferencesPrinters and Scanners.
    • Click on [+] to add a new printer.
    • Select IP
      • Address: <ip.address.of.rpi>
      • Protocol: HP JetDirect
      • Queue: <Blank>
      • Name: Enter a name of your choice here, e.g. Office Printer.
      • Use: Click Select Software and use the correct driver for your printer here.

    You should now be able to print to the new printer on your Mac.

    P.S. Sometimes you may need to connect your printer via USB to your Mac so that it installs the correct drivers first, then you can unplug the USB and select the drivers when configuring IP printers.

  • Telnet missing in macOS 10.13 High Sierra

    Although Telnet is barely used anymore as a remote access protocol/tool, it is still a very popular debugging tool for tech professionals.

    Unfortunately the quick fix here is to use netcat (nc).

    alias telnet nc
  • Flash crashing with vSphere Client, fix for Mac

    Flash crashing with vSphere Client, fix for Mac

    Looks like a new Adobe Flash (a.k.a. Shockwave Flash) update caused widespread panic with users of the web-based flash vSphere Client 6.x leaving them with a “Shockwave Flash has Crashed” message and no vSphere Client. The immediate fix is to downgrade Adobe Flash.

    VMware has released an official KB 2151945 but it only provides instructions for Windows users.


    Here’s how to fix for Mac users

    1. Go to Adobe’s Archived Adobe Flash Player versions page.
    2. Scroll down to Flash Player Archives and download Flash Player 27.0.0.159 (released 10/10/2017) or use this direct link.
    3. Once the package is downloaded it should extract automagically. If it does not, extract it.
    4. Open the folder fp_27 and sub-folder 27_0_r0_159.
    5. Double click uninstall_flashplayer27_0r0_159_mac.dmg to mount the image, and run the Adobe Flash Player Uninstaller. This should uninstall the existing Flash Player on your computer.
    6. You will need to close your browser(s) at this point. Bookmark this page for reference later.

    For users of Firefox

    1. After uninstalling, double click flashplayer27_0r0_159_mac.dmg and then (re)Install Adobe Flash Player. Your browser(s) should still remain closed at this point.
    2. You will be prompted to select how you want Adobe to update Flash. Be sure to select Notify me to install updates.
    3. Unmount the two disk images you mounted earlier.

    For users of Chrome

    1. Delete the current flash version. Open Terminal, and run these commands:
      cd ~/Library/Application\ Support/Google/Chrome/PepperFlash/
      rm -rf 27.0.0.170
    2. Double click flashplayer27_0r0_159_macpep.dmg and then (re)Install Adobe Flash Player.
    3. You will be prompted to select how you want Adobe to update Flash. Be sure to select Notify me to install updates.
    4. Unmount the two disk images you mounted earlier.

    You should now be able to get back to work in VMware vSphere Client. Drop me a note if the instructions do not work for you, I’ll be glad to update the content.

  • Why are multiple subnets needed in vSphere ESXi?

    Why are multiple subnets needed in vSphere ESXi?

    Most know that having different subnets for management traffic, vMotion, storage, etc. is a best practice but some may not understand why.

    Routing 101: Two paths to the same place

    Let’s take for example you have a laptop and is connected to both wifi and LAN at home/office (on the same subnet). Which connection is being used when you browse the Internet or even print to a local network printer?

    The answer is the first connection you are hooked up to, or the more technically correct answer is the route that is of a higher order of preference. When two NICs are connected on the same subnet, your local routing table will have two entries to the directly connected subnet, e.g.

    192.168.1.0/24 via en1 metric 100
    192.168.1.0/24 via en0 metric 100

    When a packet is sent (e.g. to your gateway at 192.168.1.1), the operating system will look up the route table and pick the first match, and in this instance it would be en1. Of course if the two routes have different metrics, then the metric of a smaller number gets the preference.

    But if you have both NICs connected to different subnets, e.g.

    192.168.1.0/24 via en1 metric 100
    172.16.1.0/24 via en0 metric 100

    Then it becomes clear which path to take when you try to get to your printer at 172.16.1.15 or your NAS at 192.168.1.100.

    The same thing happens when you have two (or more) vmkernel NICs on the same subnet. Separating the subnets will ensure that the desired traffic takes the correct path out.

    Interface binding

    Some may wonder why can’t interface binding be used, similar to running ping -I <intf>? The answer is yes! Interface binding is used for Multi-NIC vMotion (5.1 and newer) and for the Software iSCSI initiator where iSCSI multi-pathing requires two or more different vmknics within the same subnet. But this works only with vMotion, the Software iSCSI initiator, or other specific ESXi services designed to have NIC binding.

    To allow NIC binding to work, the general requirement is that only one active physical NIC can be present in the NIC teaming configuration, e.g.

    // vSwitch setup
    vSwitch0 = eth0, eth1
    vSwitch1 = eth2, eth3
    vSwitch2 = eth4, eth5
    
    // No port binding
    vmk0 management 192.168.1.11/24 via vSwitch0 (active: eth0, eth1)
    vmk1 iscsi-hb 172.16.1.11/24 via vSwitch1 (active: eth2, eth3)
    
    // Port binding services
    vmk2 iscsi-1 172.16.1.12/24 via vSwitch1 (active: eth2, unused: eth3)
    vmk3 iscsi-2 172.16.1.13/24 via vSwitch1 (active: eth3, unused: eth2)
    vmk4 vmotion-1 172.16.2.11/24 via vSwitch2 (active: eth4, standby: eth5)
    vmk5 vmotion-2 172.16.2.12/24 via vSwitch2 (active: eth5, standby: eth4)

    vSphere 5.1 and iSCSI heartbeat

    iSCSI heartbeat which uses regular ICMP ping does not bind to a specific interface prior to vSphere 5.1. Back in the good old days, it was a best practice to create 3 vmknics and leave the vmknic with the lowest index number for iSCSI heartbeat to give it a routing priority. In vSphere 5.1 and later VMware addressed this and made iSCSI heartbeat bind to an interface but there have been reports of it not working as intended.

    vSphere 6.0 and TCP/IP Stacks

    VMware introduced independent routing tables (know as TCP/IP stacks) in vSphere 5.5 but it was cumbersome to configure via CLI. In vSphere 6.0 three different TCP/IP stacks are available by default so that Management, vMotion and Provisioning (cloning, snapshots, etc.) traffic can be configured to route differently. For the Cisco guys this is easily explained as VRF. This introduction allows vMotion and Provisioning traffic to be routed. Although not usually needed, vMotion routing will be required if you want Long Distance vMotion to get across two different (routed) subnets.

  • Why IT tender and PIC is bullsh*t

    Why IT tender and PIC is bullsh*t

    This is in response to Ben’s note on Faecbook.

    No money, no honey.

    Businesses have limited budget for technology as it is a usually a cost center (regardless if it is classified as CapEx or OpEx) unless the business is like Uber where technology drives the business profits. The quality of a technology is often intangible and difficult to measure, and so the pressure is on the price. This is a sad fact.

    If you can’t beat them, join them?

    It is a battle day-in and day-out on my job to either convince customers (very difficult) or to beat cheaper vendors by price (easy) simply because, like it or not, I am running a business and not a charity and I need to pay salaries. As an unfortunate result of price competition, I may not be able to deliver the quality of work that I desire. I cannot afford to spend all my time trying to deal with customers who do not appreciate the value of good technology and that is also the reason why I tend to be selective with my customers.

    What’s (not) cheap and free?

    What needs to be fixed is the notion that technology is cheap and consulting is free. This bullsh*t idea started with the Singapore Government and has trickled down to several MNCs and Government-linked organisations. I’ve stopped attending long meetings and helping write tender specs only for jobs to be given to the lowest bidder with an outsourced team. Not forgetting it usually takes forever to get a bid out, then when the bid is awarded, they are behind time and want it done now.

    Even if a tender comes in with a spec, it is often terribly written and participating in a bid is a hell lot of paperwork with not much money to be made, and on top of that — many unknowns and liquidated damages to bear.

    Tenders only make sense for off-the-shelf and boxed products and should go away for bespoke products and consulting work. Nobody walks into LV or Prada to pick the lowest bidder.

    The fever medicine dilemma.

    Try going to a pharmacy and say: “I want a drug that reduces my fever.” There are easily 3-4 different types of medicine with different applications, strengths, safety and side effects. Most of us only know Panadol, but is that really what we need?

    You see, even with well written specs (not usually the case), no two bids will ever be exactly the same (except maybe for boxed software licenses, like Microsoft Office.) How can price be a major selection criteria? Such a notion is simply flawed. If you have ever done a home renovation and gotten quotes from contractors you will know how incredibly difficult it is to have apples-to-apples comparison because every contractor will have their own ideas, style, materials and workmanship. There’s no telling until the actual work is being done.

    IT projects are many times more complicated, and more often than not there will be changes to specifications as the project progresses (which brings me to a different discussion about not billing by project and scope but instead by time.)

    I can say with confidence and years of experience that technical specifications do not and can not normally prescribe software quality.

    Free legal advise.

    Ask a lawyer: “I want to sue this guy; tell me how much it costs.” You will almost always get a range, and it can be a huge range.

    There’s a reason why lawyers charge by time and do not limit themselves to a scope. Software developers and technology consultants are no different: We take into consideration a situation or requirement and analyse them, then we act upon them and then also react on the results. The latter part is often missed.

    Good advisory can save your ass and a whole lot of time and money, but it is very common that businesses expect free consultancy prior to work being done. Working on a software project is not just software alone; there are many moving pieces including the choice of technology (frameworks, databases, etc.), infrastructure design and operational expertise.

    Expecting free consulting is no different than asking a building architect to work for free, and then paying only for the building construction costs. And no, we can not and should not “build in” the costs of consulting into development. They are two different things.

    The graduate stagnation syndrome.

    Let me make this clear that the ones who suffer are going to be the employees of businesses, not the business itself or the bosses. Businesses can and will always find ways to create profits, and if the profits can’t be had from sales, it will come from expenses (i.e. benefits) and salaries. We graduate some 4-5 thousand technology students from Polytechnics and Universities each year. The good firms can not hire everyone. It is not the fault of these young graduates that their skills stagnate over the years — they simply have been put in an environment that does not cultivate their growth.

    As a technologist myself, I understand how good work gives growth and satisfaction to passionate people, and this is also something difficult to measure but will significantly improve corporate culture.

    Which is cheaper: iPad software or waiter?

    With regards to the Productivity and Innovation Credit (PIC): PIC has made a lot of people (aheem, fly-by-night vendors) rich, but it has also made it difficult for people like us who are trying to do real business and deliver good services because we do not actively sell PIC. In our experience, the real customers will never ask: “how much can we claim from PIC?” PIC is a bonus to them — their priority is to get stuff done.

    I’ve seen countless people burnt by PIC and what’s worse is that it gives people an impression that technology acquisition is cheap. We can not use cheap technology (as is the case of a sushi joint with a sub-standard iPad software) to replace a trained employee (waiter). This causes job and salary issues because employees are now measured against “cheap” technology.

    The ABC food market story.

    I met this old man at the ABC food center: He was with his classmates and I got to know him from a car club. I have to make a point here that these old folks aren’t your normal uncles or aunties; their classmates were Goh Chok Tong and Tan Cheng Bok, so they are pretty well off.

    One of his classmates married a wife — I can not remember, but is either Thai or Viet — and he has migrated there to live with her family and has a farm and rice field. He says he hires the locals in the village to work in his farm and he gives away the crops because people are poor. I asked why he did not use technology to help with his farm (agriculture is a very technologically advanced business), and he said something that really struck me — why replace the jobs when there are many poor people there who need the jobs.

    With that, I leave you something to think about.

  • Carculator App for Depreciation, Loan, Scrap and Rule 78

    Carculator App for Depreciation, Loan, Scrap and Rule 78

    I just wanted to put this out there. This little app I built was finally approved by the Apple for the App Store last night. I am making it FREE until the end of this year. It will be on sale for S$1.28 starting 2016.

    https://itunes.apple…ro/id1035354237

    There are two other similar apps on the App Store going for S$1.28 but neither have as complete a feature set as this, which is a reason why I found it compelling to build the app myself. It’s difficult to be calculating depreciation especially when walking around at a dealer, so the ability to save the calculation and back-reference is very important.

    You can also enter your current vehicle into it and see your scrap and loan redemption values over time. This is very valuable if you want to know how much you still owe the bank during a trade-in.

    I will probably release a “Lite” version with advertising and less features in 2016, so do grab this Pro version while you can because I will likely drop the loan redemption and save functionalities in the Lite version.

    All suggestions/feedbacks are welcome.

    P.S. Sorry, no Android version yet.