Starting Ensim Pro For Linux SSL Tunnel [FAILED]

At work, I was unable to access my Ensim control panel (on RHEL4); the browser kept timing out. So I thought I’d restart it to see if that would fix it. I did the usual:

/etc/init.d/epld restart

And got this error

Stopping Ensim Pro For Linux Control Panel [ OK ]
Stopping Ensim Pro For Linux SSL Tunnel [FAILED]
Starting Ensim Pro For Linux Control Panel [ OK ]
Starting Ensim Pro For Linux SSL Tunnel [FAILED]

I checked the log file and see this:

cat /usr/lib/ensim/frontend/httpd/logs/error_log

…No space left on device: mod_rewrite: could not create rewrite_log_lock

Problem Found

A quick google search told me it was a semaphore problem. So I ran the ipcs command to check my config:

ipcs -l

—— Semaphore Limits ——–
max number of arrays = 128
max semaphores per array = 250
max semaphores system wide = 32000
max ops per semop call = 32
semaphore max value = 32767

Then ran the ipcs command to see how many were semaphores were left:

service httpd stop
ipcs -s | grep apache | wc -l

It showed 110. Not 128, but maybe enough to cause problems. PLUS, it “should” be zero with apache stopped.


With apache and epld stopped, I ran this command

ipcs -s | grep apache | gawk ‘{ print $2 }’ | xargs -n 1 ipcrm sem

Then started apache/epld again. All is fine.

service httpd start
/etc/init.d/epld start

Exif Tool Revisited

Lately, I’ve been seriously considering switching platforms from Canon to Nikon. Specifically, to the Nikon D300. And, I have the lens choice narrowed down to either the Nikkor 17-55 f2.8 or the Nikkor 24-70 f2.8.

So, I decided to run the numbers again to see which would be a better choice based on which focal length I shoot most.

Phil Harvey’s Exif Tool is the way to check that.

Turns out that over 76% of my shots are between 17 and 55mm. Whereas only 66% are between 24 and 70mm. Of course, I adjusted for the 1.6 to 1.5 crop difference.

For longer shots, I’m considering the Sigma 100-300 f4.

So, if you’re unsure what your next lens purchase should be… check the stats from what you’ve been shooting.

Your Linux Boot Disk Full?

While trying to run a YUM update on a CentOS server today, I got an error message about my /boot partition being full. I ran a df -h and sure enough, there was only 100k left. (My standard install uses 100MB for the boot partition.)

Here’s what I did to fix it.

rpm -q kernel

That returns a list of installed kernel updates. In my case I had more than 25…


To remove some of the older ones, run:

yum remove

or to get several at one time:

yum remove kernel-2.6.9-42.*

I recommend leaving a few of the older ones in case you need to revert one day.

Upgraded to PocketWizards

The Cactus units aren’t incredibly reliable. Often they don’t fire… and I can’t figure out why.

I had a “real” assignment to shoot, so I upgraded to the PocketWizard Plus II. Like all the reviews say, they are rock-solid. Not one single misfire in over 1500 shots last month.

Highly recommended.

Cactus Wireless Flash Trigger V2s

I just received the Cactus Wireless Flash Trigger V2s from Gadget Infinity. The cost was $32.95 plus $5.00 for “Regular Airmail.” It took about a week to arrive from Hong Kong.

My goal was simple… eliminate the PC sync cable from my camera to the strobes in my very small studio (as cheaply as possible).

The new setup: The receiver is plugged into a Novatron M500 using an old PC Sync cable. The transmitter is on my Canon 40D.

Overall it works ok. There are a few quirks that may be specific to my setup.

1) I must use 1/200th shutter speed. Anything else results in a partially dark frame.

2) Occasionally, it doesn’t trigger the strobe. Maybe 1 out of 20 times. However, I think this is a cable contact issue. After twisting the connection to ensure it is well seated, I’ve gotten better results.

The range is more than acceptable for what I need: 150′ (45 meters) indoors with no obstructions. Your mileage may vary.

Packaging is pretty simple.


The pc cable fits snug, but I found twisting it after inserted ensures fewer failed shots.

It includes this flash stand (that I doubt I’ll ever use). It’s hidden under the packaging. If you aren’t looking for it, you’ll accidentally throw it in the trash.

Transmitter on the Canon 40D.

Update: Camera Dojo also has a good review of the Cactus Flash trigger on their site.

Speed Up seems to get slower and slower. Plus it crashes at least once a week. As I started looking around the web to find a solution I ran across this post from Tim Gaden at his blog:

He describes this solution:

Open Terminal, then run these three commands:

ls -lah ~/Library/Mail/Envelope\ Index
sqlite3 ~/Library/Mail/Envelope\ Index vacuum
ls -lah ~/Library/Mail/Envelope\ Index

I’ve just ran it myself and it only dropped the size of my index from 73MB to 60MB, but it DID speed up Mail considerably. I’ll have to wait and see if it helps the crashing.

Using Linux Tail to Trim Your Files

This tip is for my friend Scarb. For years I’ve used the Linux command “tail -f” for watching logs… but only recently did I discover its versatility for extracting parts of files.

Need to grab only the last 25 lines of a file?

tail -n 25 somefile.txt

How about the last 200000 bytes redirected to another file?

tail -c 200000 somefile.txt > newfile.txt

Using ExifTool to find your most used focal length

I would like to get a better quality zoom lens, so I’ve started looking around the web for recommendations on replacements. The options seem endless. I’m even considering a couple of primes instead of one zoom.

Background: I only have two lens; the EF-S 17-85mm kit lens that came with my Canon 40D and a Canon EF 80mm 1.8.

Naturally, one of my first questions is… what focal length should I get? The 17-85 is a good range, but do I really use the different lengths? Could I just get a nicer, wide prime and physically move in or out to compose?

That got me thinking… I wonder what focal length I use most of the time?

The answer:
I use my 50mm 25% of the time
I use my 17-85mm 75% of the time

17mm: 17% of the time (Yes, I double checked the math.)
50mm: 25% of the time
85mm: 14% of the time
Most of the remainder is wider than 50mm (47%)

Picture 1.png

How do I know?
Phil Harvey has created a really cool command line tool called ExifTool that can scan all your photos and export a list! From there, you can open in Excel and evaluate your data. It works on Windows or Mac.

I think I will look for a better lens in the 17-55 range. And also something longer than 85mm.

Phil’s Website:


How it works: I use Lightroom on a Mac to manage my photos, so I navigated to my Pictures directory in terminal:

cd /Users/(myusername)/Pictures

then ran this script

exiftool -r -T -filename -focallength -ext CR2 2008 > 2008.txt

That scans all files ending in “CR2” in the 2008 directory (AND all subfolders) and exports them to a file containing the image name and the focal length. The file is named 2008.txt. I opened the txt file in Excel and created a pivot table to find the sum of each focal length (or you could use another method).

Feel free to comment if you want to try it, but need help.