At work I routinely have to ssh from host A to host B and then to host C. It is not possible to establish a direct link from A to C, so I’ve been manually establishing a connection from one to the other, which is annoying. Today I finally got around to setting up a better solution, which depends on having a unix-like system on all nodes. Host A is running Windows with cygwin, and hosts B and C are running Mac OS and Linux. Another assumption is that you have the same user name on all nodes, although there are ways to get around it if you don’t.
1) Add these lines to ~/.ssh/config (which you may have to create).
Host hostC.domain.edu hostC
ProxyCommand ssh hostB -W %h:%p
Now, when I type “ssh hostC” on my PC, it hops through hostB and logs into hostC automatically with no further typing.
What is happening is that when you ssh to hostC, ssh substitutes another command for /bin/sh on hostB (which is normally executed by default), and forwards stdin and stdout to this new command (that’s what the –W is for), which is an ssh to rsndds. The effect is to hop through hostB. Because I’ve set up keys without pass phrases on all machines, no password is required. If you don’t have keys set up, it will still work, but will ask for passwords.
If you want to use pass phrases, you can use ssh-agent on hostA and hostB, which will ask only once and then store the keys in memory until the next reset of ssh-agent (probably a reboot).
If you have a different user name on hostB, simply specify it like this:
Host hostC.domain.edu hostC
ProxyCommand ssh user@hostB -W %h:%p
You can create as many of these special entries in your config file as you wish, each specifying special rules for creating connections to your unique networks. Isn’t ssh cool?
When I started figuring out how to do this, I thought of it as “tunneling,” but technically that’s probably not correct; that name is given to using ssh for encrypted port forwarding. Nevertheless, you can think of it as a tunnel, allowing you to ssh from one machine to another using an intermediate machine, all without your intervention.No comments
I love the arid, desolate area north of the San Francisco Peaks. It’s a high desert environment pocked with volcanic cinder cones of all shapes, sizes, and ages. Many kinds of animals and plants can be fond here, but one thing I don’t usually find is other people. This is a place where you can spend hours or days on your own, surrounded by spectacular views on all sides.
Here is Tycho after we summited the crater just to the northeast of SP crater, which is in the background on the right. The long winds blew up from the painted desert, keeping the winter storm away for the most part. These craters on on the west side of 89, across from Wupatki. You can tell that Tycho has been mole or prairie-dog hunting.
These photos are from a few hikes taken last weekend with my Flagstaff Freethinker buddies. This is strawberry crater, which has some Anasazi ruins on top. It’s not a particularly difficult or long hike, although the forest road that leads to its base can be rough, specially in inclement weather. Strawberry crater is on the east side of 89, just south of Wupatki.
The endless scrubby terrain inhabited by people since before antiquity.
In the distance, the sun punches through to brilliantly illuminate the Vermilion Cliffs.
The lesser peak of Strawberry crater.
This Thanksgiving I certainly do have a lot to be thankful for. A beautiful family of recent emergence, and great old friends who are my rock. I got to visit them both in a 1700-mile circuit from Flagstaff to the Denver area and back. There are too many pictures to feature them all, but here’s a few good ones, followed by the lot.
On the tail end of a work trip to Hawaii, I tacked on a few days for myself. The goal: scuba diving. There’s a lot of things to do on Oahu, and it’s hard to make a choice, but I focused almost entirely on diving. Still, I have pictures from around the island – it’s so beautiful, I just can’t help myself.
One of the things I love about flying to Hawaii is how no matter what time it is, you can go to the beach, and that’s always what I do. Nothing washes away the combined filth and exhaustion of air travel like the ocean. Here’s some scenes from Waikiki:
On another day I wandered around Kakaako beach park, which has a lot of stray cats (and stray people):
Here’s some random images of the shoreline on the east side:
Here’s one from the north shore, where a 40-knot wind fueled perfect, mach-1 windsurfing:
…and finally, of course, the diving! I was having camera problems, so my color balance and image quality were all messed up.
Here’s the outflow pipes at electric beach, which I dived with new friends Zack, Heather and Daniel.
Clouds of fish in the warm outflow.
From another dive, some crappy pictures of sharks… I was playing with a new camera and didn’t do very well.
Some other reef scenes:
…and a lot of other images you can look through if you are so inclined.
Recently I attended a meetup Kayak/Hike trip to lower Antelope canyon arranged by local Flagstaffian Kyle. He did a great job and there were a lot of cool people on the trip. Here is a brief description of what we did:Start at Antelope Marina and kayak to the beginning of the canyon via the Colorado River. Kayak through the upper canyon until you are beached at the trailhead of Antelope Canyon. From here we will hike until the canyon ends. Afterwards we will kayak back to the marina.
As we got further and further along, the canyon became more twisted and beautiful. A narrow twisting slot emptied us out into a fork; we went left. This eventually led us to a series of wet troughs filled with opaque water; there was no telling if they were 2 inches or 6 feet deep until we waded into them. Several of them were neck-deep or worse, and at one point we encountered a slippery wall requiring a rope. We turned around after encountering a second such wall and deciding that although we could climb it, we didn’t have enough time. The red rock, shadowy canyon depths, spectacular sandstone formations, and the total silence of the slot canyon’s depths create a breathtaking experience.
To do this properly, we’d need to stay in Page and start early. Next time…
Here’s a post from another visit to Hart Prairie. A group of friends watched the sunset and enjoyed one another’s company. It’s things like this that really make me love where I live: beautiful surroundings and great people. The most salient feature of this visit were all of the hummingbird moths who were making the most of the late fall flowers. They are enormous plump moths with cute faces.
A little while ago, I picnicked with some friends at Hart Prairie. The weather was perfect and it was classic Northern Arizona: incredible beauty accessible in only a few minutes. Grown-ups, kids, and dogs were all satisfied.
It is time to introduce Lindsey to the family… a trip east was made, and EVERYBODY was visited. I do mean everybody. I didn’t get pictures of everybody though, for which I am sorry. I became overwhelmed with events! We visited my Dad and his family, my Aunt and her family, my friends from college, the dinner party involving my Mom’s husband and friends, the ship I have volunteered with for over two decades, my friends in Maryland, and even my workplace. Somehow we managed to find time to spend a day and a half just being tourists.
I have an Asus RT-N16 router and after years of perfect service encountered intermittent operation; the unit would operate for hours at a time and then turn off randomly. It would turn itself back on after some time, perhaps 20 minutes. This behavior continued to deteriorate until it would only stay on for perhaps 10 seconds. It felt like an overheating problem, but I was incorrect. As with all problem-solving nowdays, I first consulted the ‘net and found this link.
The capacitor pictured in the link looked perfect, and when I used my ‘scope to examine the quality of the DC power rail it looked fine, but having lots of spare capacitors and nothing to lose I replaced it anyway, and it was fixed!
Moral of the story: capacitors don’t have to be visibly damaged to be faulty. They don’t even have to stop working to need replacement! Also, the quality of the DC power rail is a tricky thing to use, because if the power supply is adequate for most purposes but fails under a particular kind of stress, you will have to a) figure that out and b) observe it while that even is occurring; this can be an elusive thing. It’s possible that had I measured its capacitance, it would have been fine; it could just be that its ESR had risen to unacceptable levels and failed under the high-current demand imposed when the unit’s transmitter quickly used a lot of power. This is a typical failure mode for capacitors; as they get older they still function, but have poor ripple rejection despite having their original value in Farads.
I didn’t have a capacitor of the same physical size, so I removed the defective one, soldered jumper wires and installed a physically large 2500 uF unit where there was room in the chassis a few inches away. It’s been working perfectly for weeks now.2 comments
While on a work trip to coastal Oregon, an urgent need arose for me to be in the middle of Vancouver island. I got there about 24 hours later by driving to Portland, Flying to Seattle, and taking a ship to Victoria, then driving to the work site in the hinterlands. Strangely enough, for such a whirlwind trip, I had an oddly relaxed schedule that allowed me to make a few stops and enjoy things along the way. First, the Oregon coast:
I even had time to stop at cape lookout state park for a couple of miles of hiking:
A little cliff climbing at the end of the cape!
I made it down to the bottom, where I was rewarded with this:
While in Seattle waiting for the ship to Canada, I spent some time at the Pike Place market. It was a beautiful fall day, and there were lots of people out on the promenade.
To my utter delight and surprise, a carrier group was doing a drive-by,complete with aircraft of various kinds, and escort ships of varying nationalities!
Then, it was time to get aboard the Victoria clipper for a hop across the Strait to Victoria, BC, Canada. Seattle looked great in the background.
Mount Rainier looks great on the horizon.
The clipper really rocks- it throws up a spray that creates a little rainbow!
The clipper arrives in Victoria.
A couple of hours into the countryside…
Some boring telecommunications work done, I returned to catch a flight out of Victoria. I had just enough time to stop at the famed Butchart gardens. Everything was in bloom.