Git Cheatsheet

Roll a Repo Back to a Given Commit

git reset --hard <commit_id>
git push -f

Find files that have changed in the last 2 days

git log --pretty=format: --name-only --since="2 days ago" | sort | uniq

View the history of a file

gitk filename

Push a new local branch to a remote Git repo

git push -u origin branch_name

Move uncommitted changes to a new branch

git checkout -v <branch-name>

make your changes

git add --all .
git commit -m "<message>"

now you can switch back and forth and see the changes

commit only modified or deleted files, not new files

git commit -am "<message">

References

Saltstack Cheatsheet

Get System Info

salt '*' pillar.items
salt '*' grains.items

Downgrade a System

git clone git://github.com/saltstack/salt
cd salt
git checkout v<version number>
sudo python setup.py install --force

References

Stack Overflow

Responsive at Last!

It might be a little late to the party, but I finally got around to putting together some responsive stylesheets. This site should now be rocking out on the iPhone like it’s 2007! The old stylesheet scaled well enough, but the updates should hopefully make things a bit more elegant on small screens while at the same time make better use of the additional real estate on larger screens.

Use Netcat to Test Bandwidth

So I needed a handy, low overhead way to test bandwidth between myself and a remote server. SCP was handy and was able to give me a relative thumbs up or down, but the overhead distorted the figures. dd and netcat to the rescue.

Open socket on machine “A”

while [ True ]; do nc -v -l 2222 > ddTest; done

Push a file from machine “B” to machine “A”

dd if=/dev/zero bs=50M count=1 | nc <ip of machine A> 2222

OpsWorks Notes

Finally got a chance to get down and dirty creating Chef recipes for use in OpsWorks. These are primarily just some notes for myself.

Debugging

Resources

sed RE Substitution

For next time I forget…

sed -i .bk -E 's/text to replace (text to keep)/replaced text \1/' file

Each instance of (something) will be treated as a variable which can be called with \#

Software RAID example

For next time I forget…

/sbin/mdadm --create /dev/md1 --chunk=256 --level=raid1 --raid-devices=2 /dev/xvdm /dev/xvdn

Default font size in Notes.app

Maybe I just wasn’t looking in the right place, but I couldn’t find how to set the default font size in Notes.app.

vi /Applications/Notes.app/Contents/Resources/en.lproj/DefaultFonts.plist

Spam Mitigation Technologies

I guess I’ve been out of the email management scene for awhile now; I’m totally behind on DKIM and DMARC. I was introduced to these two technolgies by way of an article posted to ISC Diary by Johannes Ullrich titled "How to send mass e-mail the right way".

Sender Policy Framework

SPF makes use of DNS records which define which servers are authorized to send email for a given domain. This DNS record should enumerate each server which is allowed to send email on behalf of that domain. After the list of servers, the final part of the record should include a ~all or, preferably, a -all. The former is a called a “softfail” i.e. the receiving server should treat emails from non-listed servers with suspicion. The latter is a hard fail which indicates that emails should not be accepted if they do not come from a listed server.

The -all is important. This is what helps to prevent your inbox from being flooded with spam, or even worse, phishing emails that allege to come from your bank, etc. If your email server rejects spoofed emails, you have no opportunity to click on them and their malicious badness.

DomainKeys Identified Mail

DKIM is a method for servers (not users) to digitally sign emails so that they can be validated by recipient servers.

Header Details

Manual DNS Query

dig <selector>._domainkey.<domain>.<tld> txt

Domain-based Message Authentication, Reporting and Conformance

DMARC is the mechanism that, among other things, determines how email should be treated based on the SPF and DKIM evaluations. This again relies on DNS records; the sending domain publishes a record with instructions on how email purported to be sent from that domain should be treated. The receiving email server queries these instructions upon receiving an email and acts accordingly, potentially even sending a report back to the origin domain.

Coincidentally, I recently upgraded my mail server and it now includes DKIM support. After reading the ISC Diary article, I decided to take a closer look at DKIM and get my server configured to use it. In a general sense, it’s similar to SPF in that it’s a mechanism utilized at the server level to determine if a given email came from a legitimate source. Like SPF, DKIM is (partially) implemented by way of DNS records. However, unlike SPF, DKIM inserts a header in the email when it’s being sent to include the domain’s public key. The recipient server will then compare the received public key to the sender’s DNS records and pass or fail the email accordingly, inserting those results into the header as it’s delivered. If you take a look at some emails in your inbox, you may find this information in the full hearders. For instance, an email sent from a Yahoo account has this in the headers:

DKIM-Signature:
v=1;
a=rsa-sha256;
c=relaxed/relaxed;
d=yahoo.com;
s=s1024;
t=1390992156;
bh=BWCYkcoQVlLa9vCcxk+HHaO7+yl8AQX4MBV1syoqzRE=;
h=X-YMail-OSG:Received:X-Rocket-MIMEInfo:X-Mailer:References:Message-ID:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type;
b=ZXgvPU6uXRANhke79swu/qAzvfcbwKVl993ao8TEzOrj/1TX78UQ6vbmKq1aVC48lBJGHcQ2UNrcFmXs3GFXyv6kMZ/Tp3TKi86HeE2RWVEIkEgJ1ihIssBfU0KxTWocHCfaJn9W0uIrfE+gX8rH4vr9ZFeGlH77+xVH5wiUeyY=

Which resulted in my server adding the following header after verifying the public key:

Authentication-Results: dkim=pass (1024-bit key) header.d=yahoo.com; domainkeys=pass (1024-bit key)

Because of email’s distributed nature, adoption by ISPs and vendors is key. According to dmarcian.com, DMARC —and therefore likely DKIM as well— is supported for over 3 billion email users with big names like Facebook, Gmail, and Outlook on board.

Unfortunately, while my email server supports DKIM, it does not yet have DMARC support. Until that’s added, I’ve created filters that tag emails that fail DKIM verification, marks them as read, and files them into my "junk" folder.

DNS Record Anatomy

_dmarc.<domain>.<tld>

See dmarc.org for more tags.

Example
v=DMARC1 p=reject pct=100 rua=mailto:dmarcreport@example.com asfp=s

TracFone Follow-up

I just wanted to post a follow-up to my previous post regarding my switch to TracFone. Our experience so far has been very positive. We’ve accomplished the two things we sought: 1. maintain quality and 2. lower costs.

We discovered that the phones we purchased from TracFone are using the same provider we previously had, at least in our home calling area. This was a good thing because we were pleased with the quality and reliability of our previous provider.

It’s taken some time to get over the whole "oh no, am I going to run out of minutes" concern. At first, I felt as though I was constantly checking my remaining minutes and worried to stay on a call too long. This fear has started to subside. We signed up for TracFone’s "value plan"; minutes and days are automatically renewed every month. I signed up for the lowest tier plan (fewest minutes and therefore cheapest overall) and my wife singed up for the highest tier plan as she uses her phone more. We both get more minutes than we’ve been using in a month. Seeing our rollover minutes build up month after month has helped dissipate our worries. The other nice thing about the Value Plans is that, if we build up a huge pile of minutes, we can downgrade to a lower tier Value Plan and save even more money for a few months.

As it stands, we’ve cut our wireless bill almost in half. Over time, by making adjustments to our plans, we should be able to cut it even further.

This is a personal website. Unless otherwise stated, the content and opinions expressed here are my own and not those of my employer.