How to terminate or cancel an unresponsive ssh session.

While connected to a remote host through an ssh connection using Putty or other ssh clients, your client might freeze and not respond to any keyboard activity. In order to force an exit, there is a “secret” keyboard shortcut – Enter~. [ Enter followed by ~ followed by .(dot) ]

[daniel@kauai ~]$ ssh daniel@linuxfreelancer.com

Hostname..........: svm1010.xenvps-server.net
Uptime............: 21:25:34 up 14654 days, 15:00,  2 users,  load average: 0.09, 0.19, 0.17
Server IP.........: 173.230.241.181
Operating System..: Ubuntu 10.04.4 LTS
Username..........: daniel

daniel@svm1010:~$ uname
Linux

***Press*** Enter~.  {Enter key, followed by '~', followed by '.'}

daniel@svm1010:~$ Connection to linuxfreelancer.com closed.

[daniel@kauai ~]$ 

After you press the Enter~. the connection will be aborted and your session will return to the connection originating client shell.

Alternatively, you can background the ssh session with Enter~Ctrl+Z and then foreground it with fg command.

References –

https://serverfault.com/questions/283129/why-do-consoles-sometimes-hang-forever-when-ssh-connection-breaks

ipython tutorial and how to delete sensitive data from history

ipython is program which allows you to run python code in an interactive shell. Although Python itself when run from CLI opens an interactive shell as well, ipython is much more powerful and greatly improves your productivity. Some of the things you can do with ipython but not the default python shell is command or code and file name completion, view history, copy/paste a single or multiline code, nicely colored help with in the shell, run Linux commands such as ls or cat, scroll up/down to previous commands, automatically adds spaces after you press enter, etc.

Installation

pip install ipython

Quick demo
Start ipython by typing the

ipython

command in your CLI –

daniel@lindell:/tmp$ ipython
Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
Type "copyright", "credits" or "license" for more information.

IPython 5.4.1 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: print('ipython')
ipython

In [2]: 

With in the ipython interactive shell you can run any python code, let us walk through some examples –


  In [1]: x=2

In [2]: x
Out[2]: 2

In [3]: mylist=[1,2,3,4,5]

In [4]: [i**3 for i in mylist]
Out[4]: [1, 8, 27, 64, 125]

In [5]: with open('/etc/hosts') as fp:
   ...:     for line in fp:
   ...:         if 'localhost' in line:
   ...:             print line
   ...:             
127.0.0.1	localhost

::1     ip6-localhost ip6-loopback


In [6]: ls /opt/
ansible/  google/  vagrant/

In [7]: 

Go back to previously typed commands / History
With ipython, you can either press the UP arrow key or type

 history 

command to view history. ipython keeps session history as well as all input and output lines in a SQLite file which is located in

~/.ipython/profile_default/history.sqlite 

You can view and modify this file using

sqlite3

tool –

daniel@lindell:/tmp$ sqlite3 ~/.ipython/profile_default/history.sqlite
SQLite version 3.11.0 2016-02-15 17:29:24
Enter ".help" for usage hints.
sqlite> .schema
CREATE TABLE sessions (session integer
                        primary key autoincrement, start timestamp,
                        end timestamp, num_cmds integer, remark text);
CREATE TABLE history
                (session integer, line integer, source text, source_raw text,
                PRIMARY KEY (session, line));
CREATE TABLE output_history
                        (session integer, line integer, output text,
                        PRIMARY KEY (session, line));
sqlite> 

Deleting sensitive data from history
You can delete any line from history by using SQL. First use SELECT statement to find the line number and then use DELETE statement to delete it. In this example, we are deleting line number 10 from the history table –

sqlite> select * from history;
sqlite> .schema history
CREATE TABLE history
                (session integer, line integer, source text, source_raw text,
                PRIMARY KEY (session, line));
sqlite> delete from history where line=10;

References –
https://ipython.org/
http://www.sqlitetutorial.net/sqlite-delete/

How to copy to a clipboard in Linux

Problem statement – You have a file with hundreds or thousands of lines and you want to copy the contents of this file and paste it to an external application, for instance to a browser.

Solution – The first attempt is to try to cat the file and scroll down with your mouse to select each line. This is time consuming or in some cases might not work if there are too many lines as some of the lines will ‘scroll out of the terminal’. One way of getting around this is to use “xclip” – a command line interface to X selections (clipboard).

In my case I wanted to copy the contents of ‘/tmp/ipaddresses.txt’ file to a browser for blogging. The file had 10000 lines. I used the following commands, first to install xclip and then to copy the file contents to a clipboard –

apt-get -y install xclip
xclip -sel cli < /tmp/ipaddresses.txt

The xclip command basically does a selection (-sel) from the file into the clipboard(-cli), where you can copy paste to any other external application.

References
https://linux.die.net/man/1/xclip

https://stackoverflow.com/questions/5130968/how-can-i-copy-the-output-of-a-command-directly-into-my-clipboard