Improve your bash shell working experience

This article shows some hints how to improve your bash shell working experience to reach higher productivity. Just simple shortcuts that are not so well known.

Using the History

The bash history is underestimated when it comes to usability. Here some nice stuff to do with the history.

Search the history

Every command is kept in the history. The simplest way to use the history is using the cursor-up/down keys. Most users are aware or [ctrl]-r. Usually you hit [ctrl]-r (r like reverse search) several times and miss the command, roll your eyes, hit [ctrl]-c and do it again. Why not using forward search with [ctrl]-s in such a case? Well, that suspends your terminal. It comes from the ancient times and is not needed anymore.

Turn off terminal suspension

echo "stty -ixon" >> /etc/profile

Now you can search the history back and forward by using [ctrl]-r and [ctrl]-s.

Using another command with the same last argument

When you i.e. do ls a file and decide to edit it, you don’t need to retype the whole file path or using the mouse to copy-paste it. Use the [Alt]-. (dot) combination. It inserts the last argument used. So after ls -la /tmp/file.txt you type vi [Alt].. Review and hit enter to execute.

You can also reuse other than the last arguments, but this is more complex and does not speed up things a lot, copy-paste with your mouse is usually faster in such a case.

Forgot to sudo?

When you want to cat i.e. /etc/sssd/sssd.conf you need root access. As a normal user, access is denied.

[luc@fedora ~]$ cat /etc/sssd/sssd.conf
cat: /etc/sssd/sssd.conf: Permission denied
[luc@fedora ~]$ sudo !!
sudo cat /etc/sssd/sssd.conf
[domain/example.com]

The !! also called bash bang does the trick. It just repeats the same command as used before which all arguments. Be aware that the command is executed immediately.

Bash can copy-paste as well!

Copy-paste is not only available in graphical environments but in the bash shell as well.

If you need to type some different commands all with the same arguments, cut the stuff. Position the curser to the position on the line from where you want to copy and hit [ctrl]-k. When you want to paste, hit [ctrl]-y.

You may also achieve that using othercommand !*. Using !(bash bang) can be dangerous because the command will be executed immediately, the copy-paste method is more safe.

That also works with single words etc. basically everything where you cut or delete some stuff like [alt]-d, [ctrl]-w, [ctrl]-u

Using an editor for copy-paste from websites and word processors

There are a number of reasons why you don’t want to directly copy-paste to a shell. Sometimes the source content has not properly escaped line ends or its just garbage from word processors. You may want to review and edit appropriately before fire the command. There is a super lazy and convenient trick to do so.

The security usecase

Copy-Paste from a Website is a security nightmare. Copy-Paste the following two lines into an editor and you see what I mean.

Sample command
echo “Dont copy-paste”

Second sample

The HTML code used for that is:

Sample command<span style="font-size: 0; position: absolute; left: -100px; top: -100px"><br>:echo "Dont copy-paste"</span>
Second sample

Nice! Use an editor before pasting anything in a terminal, for the sake of security.

The word processor garbage usecase

Lot of documentation is written in word processors such as Libreoffice, MS-Office and others. They replace double hyphens to a single one and nasty stuff such as single quotes to backticks. Just for a thing called usability.

When copy-paste that stuff, you probably want to review and edit it first.

Set the EDITOR environment variable

If you are too lazy to fire up vim, you can set the EDITOR environment variable to an editor of your choice (vim, emacs, nano, whatever), system wide in /etc/profile or /etc/bashrc. A better idea is to put it in ~/.profile or ~/.bashrc.

echo "export EDITOR=vim" >>: ~./bashrc

Afterwards you can just hit [ctrl]-x-e and vim starts up. When save and exit vim, the command will be executed.

What are my Keybindings?

If you wonder what kind of shortcuts are defined in a shell, a lot are. use bind -p to show them.

Have fun 🙂

Oracle ditches OpenSolaris

OpenSolaris was dropped by Oracle

As many people already suspected, Oracle will ditch OpenSolaris as announced here: OpenSolaris cancelled, to be replaced with Solaris 11 Express. The first Solaris 11 Express release is expected end of this year. If is has similar usage restrictions like the Oracle 10 Express database then it will be quite useless.

OpenSolaris was a good thing for both, Sun and its customers. Customers had a continuous preview of upcoming features in new Solaris versions. Sun was getting feedback from customers. The community was able to contribute to the product. It had a similar role for Sun as Fedora has it for Red Hat Enterprise Linux (RHEL) or OpenSUSE for Novell.

Still open source, but closed development model
While most parts of Solaris are staying open source, Oracle switched the open source development model into a closed source model. Quoting the announcement: We will no longer distribute source code for the entirety of the Solaris operating system in real-time while it is developed, on a nightly basis.

This will also affect other projects and products such as FreeBSD’s ZFS support and Nexanta.

Light at the end of the tunnel
The light at the end of the tunnel is the newly founded project Illumos. A main sponsor of the project is Nextanta, as its main building block of the product is OpenSolaris.

What is the OpenSource strategy of Oracle?
It is unclear what Oracle is planning for its other open source products such as OpenOffice, MySQL and Java. In the past, all of those products have been open source enablers for companies. The is little to no information about those products.

Not really fun….

Ready to upstart?

upstart

It is time to replace the aged SysV init system with someting better

At the time when  SysV init (pronounced “System five”) appeared, hardware configurations have been quite static, no hot plug and similar fancy stuff.

SysV init is started after the kernel is loaded. The init process reads /etc/inittab and walks trough the runcontrol script and runlevels. This sequential walk-trough takes most of the time when booting a modern Unix system.

Upstart follows another approach: Starting daemons and services in parallel and event driven.  This will speed up the boot process beyond expectations.

A very nice feature of upstart is: All processes will be started in background, no more blocking of the boot process trough hanging run control scripts!

If a service unexpectedly dies, it will be respawned  automatically up to a configurable limit in times per period.

Upstart is event-driven, a event can be e.g. plugging in new hardware which ends up starting the needed service for it. There are also plans to replace cron and atd with upstart since this are basically time-triggered events. The developers also thinking about replacing the inetd, since a network connection can be considered as a event.

Transition

Since most of the software out there do not natively support upstart yet, transition methods are needed for a smooth transition from SysV init to upstart. Traditional SysV run control scrips are fully supported, even distributions slowly switch to the event/job model of upstart. E.g. one of the first distributions switched to upstart was Ubuntu 6.10, and now with Ubuntu 9.10 – three years later – they begin to ship its distribution with the first native upstart scripts.

Splitting Unix systems apart

Years ago there only have been two init systems: SysV init and BSD init, a sysadmin was comfortable to use them on whatever system. Now there are SysV init, Upstart from Ubuntu, lauchd from Apple, SMF (System Management Facility) from Sun Microsystems and possibly others. All of this SysV init replacements are working differently,  different commands, different architecture… This makes the job of a sysadmin not easier when managing a heterogeneous system landscape.

Linux distributions stay together

The good news: On the Linux side it looks like Upstart will be the future standard for system initialization, no balkanization of the Linux Landscape so far.

Linux Distribution with upstart

The following distributions are already shipping upstart:

  • Ubuntu
  • Debian
  • Fedora
  • Others?

Since Fedora 11 and 12 will be the upstream for the upcomming RHEL6 distribution it is most likely that RHEL6 comes with upstart. At openSUSE there are some discussions (see https://features.opensuse.org/305690 for details). Maybe there is a chance for openSUSE 11.3 and later on SLES12.

Further readings:

Upstart web site: http://upstart.ubuntu.com
Wikipedia article: http://en.wikipedia.org/wiki/Upstart

Have fun!


302 Redirects behind SSL-terminating proxies

Problem

You have a web site all with SSL. There is a reverse proxy or load balancer that acts as SSL termination point. Behind that reverse proxy you have an Apache web server running plain http.

Your application uses 302 redirects to announce new URLs or whatever the reason is for doing so. Since the web server does not know that https URLs should be announced, the response header is wrong and looks like following:

Location http://www.example.com/your-fancy-url

The browser interprets that location header and send a request to this non-SSL URL instead of https:///www.example.com/your-fancy-url

If your reverse proxy does not know how to handle this, a connection will time-out. How to circumvent this if you have access to the web server but not to the reverse proxy or load balancer? What to do if your load balancer (such as Blue Coat devices) are closed down appliances that are not able to rewrite response headers?

Search engines do obviously not know the answer or I simply did not asked the right question.

Solution

Since Apache version 2.2.4 mod_headers is able to rewrite response headers. Just add the following to your httpd.conf

Header edit Location ^http://(.*)$ https://$1

This configuration statement will solve your problem. Redirects triggered by your back end web servers will be re-rewritten to comply with your SSL terminating reverse proxy/load balancer.

Further reading: mod_headers

Have fun….