Category Archives: Tips and Tricks

ssh_exchange_identification: read: Connection reset by peer

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I recently upgraded my Mac Desktop and I noticed a strange problem that I was not able to SSH into my desktop from my laptop. I ultimately found out that the SSH setup that came with MacOS was having some issue as when I did ssh user@localhost on the desktop I got the same error:

ssh_exchange_identification: read: Connection reset by peer

I ended up tailing the system log using the following command:

sudo tail -f /var/log/system.log

I observed the following entries in the log whenever a SSH was attempted. 

com.apple.xpc.launchd[1] (com.openssh.sshd.[UUID][NUM]): Service exited with abnormal code: 1

It was clear that there was setup issue with the SSH that came with default MacOS installation. So I decided to spawn a separate SSH instance and watch it’s log:

sudo /usr/sbin/sshd -d -p 2222

This command showed up a lot of issues related to file permissions.

Permissions 0644 for '/etc/ssh/ssh_host_dsa_key' are too open.
Permissions 0644 for '/etc/ssh/ssh_host_ecdsa_key' are too open.
Permissions 0644 for '/etc/ssh/ssh_host_ed25519_key' are too open.

I fixed these permission issues by changing their permission to 400:

sudo chmod 400 /etc/ssh/ssh_host_dsa_key
sudo chmod 400 /etc/ssh/ssh_host_ecdsa_key
sudo chmod 400 /etc/ssh/ssh_host_ed25519_key

After this change the following command succeeded and I was able to do successful SSH connection to port 2222.

sudo /usr/sbin/sshd -d -p 2222

So I killed this process and decided to restart SSH:

sudo launchctl unload /System/Library/LaunchDaemons/ssh.plist 
sudo lsof -i:22
echo $?
sudo launchctl load /System/Library/LaunchDaemons/ssh.plist 

Once SSHD was restarted I could successfully do logins using ssh user@localhost from Desktop as well as remote login via SSH from my laptop. 

Prettify JSON on Terminal

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I love using curl command on my Mac terminal to debug my REST endpoints. However the REST call JSON output used to come in a blob of text which required further formatting in an Editor like Visual Studio Code. To allay this problem I ended up installing “jsonpp” using homebrew.

brew install jsonpp

So now I just pipe the output of my curl command to the jsonpp program and I get a fully formatted JSON.

$ curl http://localhost:8080/test | jsonpp
{
"year": 2018,
"month": 2,
"worked": 18,
"leaves": 2
}

 

 

Curl Command New Line Post Output

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I like to use curl instead of UI tools like Postman for debugging my RESTful web services traffic whenever possible. I however didn’t like my output being messed up by the bash prompt being suffixed to the output. Something like the following:

$ curl -H "$auth_token" http://localhost:8080/xyz/abc-efg
["-","A","B","C","D","E"]$

So basically what I needed was to have a new line forced after the curl output. A quick search on internet yielded this article. So I executed the following command on my terminal.

$ echo '-w "\n"' >> ~/.curlrc

After doing this when I execute the same curl command I get the following output.

$ curl -H "$auth_token" http://localhost:8080/xyz/abc-efg
["-","A","B","C","D","E"]
$

So now the bash prompt is actually coming on a new line by default!

Validating Signature in PDF documents in Acrobat Reader

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I received a digitally signed document from a trusted source. However when I proceeded to take a print it came out with “Signature Not Verified” in place of the signature field. This was not going to work so I did some googling and found out this link. It basically allowed me to validate the signature and take a printout with “Signature Valid” in place of the digital signature.

Uninstalling and reinstalling brew

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I use brew utility for all my terminal based installation needs. However recently I had to deal with a corrupted brew install. To fix this I followed this link. The uninstallation and reinstallation worked fine and I now have a working brew instance.

The commands as mentioned in the above link are:

$ cd `brew –prefix`
$ rm -rf Cellar
$ brew prune
$ rm -rf Library .git .gitignore bin/brew README.md share/man/man1/brew
$ rm -rf ~/Library/Caches/Homebrew
$ ruby -e “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)”

 

Installing pip on MacOS

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I recently started exploring python and immediately ran into the following issue:
$ pip install requests
-bash: pip: command not found

A quick google search yielded this result. So basically on MacOS you have Python preinstalled along with easy_install command. So the following command installs pip:

$ sudo easy_install pip
Searching for pip
Reading https://pypi.python.org/simple/pip/
Best match: pip 9.0.1
....
....
Processing dependencies for pip
Finished processing dependencies for pip

A quick and handy solution indeed!