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Command Line History in Ubuntu Terminal

by Chris Jean

March 9th, 2009

I’ve had a lot of fun recently posting about how to do stuff on the command line in Linux. My focus is specifically for Ubuntu users, but the information and techniques can be used for any Linux distro.

Since I’m probably going to end up with a lot of content under this topic, I’ve decided to create a dedicated tag: Mastering the Command Line. I’ve gone through my older posts on this topic and tagged them as well. So, make sure to check out Mastering the Command Line if you want to know how to become a command line power user.

Back to today’s topic. You’re starting to learn how to use the command line, but it’s annoying to always have to type in similar commands over and over. If only there were a way to pull up commands that you’ve already run to run again as is or to quickly modify. Today, I’m going to teach you how to do exactly this.

Categories Linux, Tips 'n Tricks
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Convert DOS-Formatted Files to Unix-Format in Ubuntu and CentOS

by Chris Jean

March 8th, 2009

Have you ever seen a bunch of ^M characters in a text file? This odd character at the end of a line can also be represented as a Ctrl+M or <CTRL>M. You don’t know what it is, and you want it to go away.

Today, I’ll help you understand what that odd ^M character is, why it is in some of your documents, and how to get rid of them.

Categories Development, Linux, Tips 'n Tricks
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Food For Thought

by Chris Jean

March 7th, 2009

I’m more or less taking the night off. I’ll leave you some good reading material that should cover just about any reader that comes here.

Make Linux: Harder – Better – Faster
This page is a great compilation of links on how to improve security, speed, functionality, or appearance of your Linux system.
Firefox Minefield
Very interesting version of Firefox that is in development. Apparently, it is capable of massive speed and gives Chrome a run for its money.
Conky
A highly-customizable graphical system monitor for your Linux desktop.
Armed and Dangerous
A blog I just happened upon today that has many great reads. The topics are varied, but there should be a little something for everyone. I was hooked with the My comment to the FCC on DRM post, as I share many of the feelings that the author does on the subject.
Swift Weasel
This project builds Firefox from source to provide optimized builds for the Linux platform. It’s still in the early stages but has potential.

I hope that my big post yesterday makes up for my weak one today. 🙂

Categories Linux, Random Ramblings, Tips 'n Tricks
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Multitasking from the Linux Command Line + Process Prioritization

by Chris Jean

March 6th, 2009

Did you know that you aren’t limited to working on one thing at a time while on a Linux command line? You can actually “minimize” a program that you are in, get back to the command line, and then return to the program whenever you’d like.

When you run a program or script on the Linux command line (from now on referred to as the shell), you are creating a new job. For those that are used to GUI environments, each of these jobs is somewhat like a window on the desktop. Just as you can have multiple windows and switch between them, the shell is capable of managing multiple jobs and allows you to switch between them.

There is a lot to cover, so let’s start simple by describing what states a shell job can be in.

Categories Development, Linux, Tips 'n Tricks
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Cleaning Out Old Linux Kernels in Ubuntu

by Chris Jean

March 5th, 2009

Without the Linux kernel, Ubuntu (and all the other Linux distros) would not exist. Despite this, most Linux users don’t know what a kernel is nor understand that the reason that Ubuntu is a Linux distro is because the kernel is Linux. All most users of any Linux distro is likely to know is that they will eventually have a large number of kernels installed on their system cluttering up their boot menu.

Describing what a kernel is and what it does is beyond the scope of this post. I do highly recommend that you first read the Wikipedia article on computer kernels followed by the article on the Linux kernel itself. I’d really like to do a post explaining what a kernel is in simple terms so that readers can gain a better appreciation for it and what it does for your distro. Please leave a comment letting me know if you are interested in this writeup.

Anyways, back to the topic at hand. What do we do with all these kernels that litter our boot menu? How do we remove them not just from our boot menu but from our file system as well?

Categories Linux, Tips 'n Tricks
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4 Great Tools to Find Files Quickly in Ubuntu

by Chris Jean

March 4th, 2009

Many of you fellow Ubuntu users will be familiar with the “Search for Files” tool that allows you to look for files. As is true with most things in Linux, there are great desktop tools, but more power can be found in Terminal than any streamlined desktop tool can match.

Today, I’d like to introduce you to a few tools that can turn a chore of finding files into an easy process.

locate

The first tool that you should become comfortable with is also one of the simplest. The locate program works in a similar fashion to most graphical search tools.

Using

Let’s say that you’ve read up on how to modify X to provide enhanced video performance. The document that you are reading says to modify the xorg.conf file, but the document doesn’t say where that is and you don’t know how to find it. You can use locate to find it for you quickly:

[chris@home ~]$ locate xorg.conf
/etc/X11/xorg.conf
/usr/share/man/man5/xorg.conf.5.gz
/var/lib/x11/xorg.conf.md5sum
/var/lib/x11/xorg.conf.roster

It’s clear that /etc/X11/xorg.conf is the file we’re looking for, but what if dozens or even hundreds of results were returned? How could you manage all of that? If you know a little bit about regular expressions (every Linux user really should learn the basics), you can easily use regular expressions to search for directories or files. For example, we can search for an exact match for xorg.conf with the following command:

[chris@home ~]$ locate -r '/xorg.conf$'
/etc/X11/xorg.conf

If you want to look for files without case sensitivity, you can use the -i option. For example:

[chris@home ~]$ locate -i 'monthly report'
/home/chris/Documents/August Monthly Report.doc
/home/chris/Documents/July Monthly Report.doc
/home/chris/Downloads/latest monthly report.doc

Something that may confuse you when you first start using locate is that it not only returns matches, but if the match is a directory, it also lists all of the directories and files under that directory. For example:

[chris@home ~]$ locate Desktop
/home/chris/Desktop
/home/chris/Desktop/Head Shot.jpg
/home/chris/Desktop/Skype.lnk
/home/chris/Desktop/Steam.lnk
...

That command returns more than a thousand entries on my system. To reduce the results down to a list of entries that match the search term without all the contained files and directories, use the -b option:

[chris@home ~]$ locate -b Desktop
/home/chris/Desktop
/home/chris/bin/recordSoundAndDesktop.sh
/opt/HipChat4/lib/QtQuick/Controls/Styles/Desktop
/usr/include/qt4/QtGui/QDesktopServices
/usr/include/qt4/QtGui/QDesktopWidget
/usr/lib/libreoffice/program/wizards/common/Desktop.py
/usr/lib/libreoffice/share/gallery/computers/Computer-Desktop.png
/usr/lib/python2.7/dist-packages/xdg/DesktopEntry.py
/usr/lib/python2.7/dist-packages/xdg/DesktopEntry.pyc
/usr/lib/python3/dist-packages/xdg/DesktopEntry.py
/usr/lib/python3/dist-packages/xdg/__pycache__/DesktopEntry.cpython-35.pyc
/usr/lib/x86_64-linux-gnu/qt5/qml/QtQuick/Controls/Styles/Desktop
/usr/share/kde4/apps/kio_desktop/DesktopLinks
/usr/share/man/man3/File::DesktopEntry.3pm.gz
/usr/share/perl5/File/DesktopEntry.pm
/usr/share/sounds/KDE-Window-All-Desktops-Not.ogg
/usr/share/sounds/KDE-Window-All-Desktops.ogg

There are still quite a few matches, but we no longer have a sort through all the extra results to find what we’re looking for.

Important Note

The locate command relies on a slocate database to function. This database caches the file system directory and file names and allows the locate command to operate in moments rather than taking long periods of time to search the entire file system.

This ability doesn’t come without cost though. By default, your system will run a command to update this database once a day at 6:25am. This command will update the database with any changes made to the file system since the last update.

If you’ve made changes recently, such as added or removed large amounts of files and directories, and you want to use the locate command to search through these new directories and files, you can manually update the slocate database at any time with the following command:

[chris@home ~]$ sudo updatedb

Depending on the volume of changes made since the slocate database was last updated, this could take a few seconds to a few minutes to update. Once it’s done, you’re ready to search again with locate.

which

locate is great for searching the entire file system. However, sometimes you just want to find where a command lives. That’s where which comes into play.

which only does one thing, but it does it well. Given the name of a command, which will tell you where the file for that command resides in the file system.

Let’s imagine that we want to find out where the firefox command resides. We can simply run the following to find out:

[chris@home ~]$ which firefox
/usr/bin/firefox

Why would you ever want to search specifically for a command? Imagine that you have some code that needs to replace an old command. You really need to remove the the old one (I usually rename it to the same name followed by “.bak” to keep it around in case I need it) first before putting the new one in its place. which will help you find the file quickly and easily so you don’t have to search everywhere to find it.

whereis

The whereis command is similar to which but goes one step further. Not only does it tell you where the executable file is located at, but it will also locate the source, man page, and other associated directories as well.

Keeping with the which example, let’s ask whereis about the firefox command:

[chris@home ~]$ whereis firefox
firefox: /usr/bin/firefox /usr/lib/firefox /etc/firefox /usr/share/man/man1/firefox.1.gz

This helped me find /usr/lib/firefox/plugins earlier when working on the solution for Flash as that location is where the global add-ons for Firefox are stored.

find

find is the ultimate search tool, the Swiss Army knife of Linux search if you will. find can do everything from search for files based on last modified times, owners and groups, permissions, type (file, directory, symbolic link, etc), whether the file is readable/writable/executable by the current user, file size, whether the file or directory is empty, and much more. You can also search for matches by regular expression.

When you use this tool in combination with the xargs command (which I’ll have to cover some other time), you can do truly amazing things on the command line. Imagine being able to recursively search through the current directory for files ending with “.bak” that were last modified more than 100 days ago and then deleting them with one command:

[chris@home ~]$ find . -name '*.bak' -type f -mtime +100 -print0 | xargs -0 /bin/rm -f

It will look very complex at first, but when you master the art of using find, it will become second nature. Soon, you’ll wonder how you ever searched for things without it.

To be frank, there is much more to find than I am willing to cover and there are many, many great introductions to the tool that do a better job than I would. So, I’ll simply point you to three great references that can be used to get going with find.

Example uses of the Linux Command find
(I apologize for the horrible colors in advance) Unix/Linux “find” Command Tutorial
Using the find command

Happy searching.

Categories Linux, Tips 'n Tricks
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Change Timezone in CentOS

by Chris Jean

March 3rd, 2009

You just got your new CentOS dedicated server, and you notice that times in your logs aren’t quite right. You check the time from the command line (run date), and find that the timezone is set to US Eastern or some other timezone. How do you get this changed?

Unfortunately, this is not an easy thing to figure out. Fortunately though, it’s not hard to do with the right directions.

Categories Linux, Tips 'n Tricks
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Using Vi/Vim as a Command Line Editor

by Chris Jean

February 27th, 2009

In many of my Tips ‘n Tricks or tutorial posts, I have commands that involve editing/creating files in Vi. For those that have never used Vi, it can be a daunting experience trying Vi for the first time.

There are many holy wars fought over the best editor to use from the *nix command line. I won’t claim that Vi is the best; rather, Vi is simply what I’m used to, it’s powerful, and it is always available on servers that I work on.

In order to best help those that don’t know how to use Vi but are interested in learning, this will serve as a very brief tutorial on how to get started.

Categories Development, Linux, Tips 'n Tricks
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Unzip Multiple Files from Linux Command Line

by Chris Jean

February 26th, 2009

Here’s a quick tip that will help you work with multiple zip files on the command line.

If you are in a folder and have three zip files in it (a.zip, b.zip, c.zip) that you want to unzip, “no problem,” you think. “I can take care of that with one command.” And you quickly run the following:

[gaarai@tenshi ~]$ unzip *.zip

However, rather than having the unzip program nicely unzip each file one after another, you receive the following:

[gaarai@tenshi ~]$ unzip *.zip
Archive:  a.zip
caution: filename not matched:  b.zip
caution: filename not matched:  c.zip
[gaarai@tenshi ~]$

I’m sure that this is not what you were expecting. I know I certainly wasn’t expecting this when I first tried it. However, this problem can help us understand more of how the command line works.

The Problem

Whenever you use a wildcard (*), the shell itself will expand that and pass the results to the program rather than the program handling the expansion itself. That means that our previous command was actually expanded to the following before being executed:

[gaarai@tenshi ~]$ unzip a.zip b.zip c.zip

Again, this may not look odd since other programs (such as mkdir, chmod, etc) can take one or more arguments and repeat the process for each. However, unzip is different and actually has use for the additional arguments. If you specify additional arguments after the zip file name, unzip will try to only extract those specific files from the archive rather than all the files.

The previous command told unzip that it should extract b.zip and c.zip from inside the a.zip archive. Since those files don’t exist inside a.zip, we get the unexpected error output seen earlier.

You might think that you will have to manually unzip each archive one at a time, but you’d be wrong.

The Solution

Just because the shell expands out wildcard characters automatically doesn’t mean that programs can’t as well. The simple solution to this problem is to quote the argument to prevent the shell from interpreting it:

[gaarai@tenshi ~]$ unzip '*.zip'
Archive:  c.zip
   creating: c/
  inflating: c/test.txt

Archive:  a.zip
   creating: a/
  inflating: a/test.txt

Archive:  b.zip
   creating: b/
  inflating: b/test.txt

3 archives were successfully processed.
[gaarai@tenshi ~]$

That’s all there is to it. I’ve seen solutions from coding loops in bash script to running find combined with xargs, but none of that is necessary. Simply let the unzip command itself take care of things for you.

Categories Linux, Tips 'n Tricks
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Multiple Firefox Profiles in Ubuntu

by Chris Jean

February 23rd, 2009

When Windows was my main OS, I was a big fan of Portable Firefox. With Portable Firefox, I could do multiple installations of Firefox on my system that could be customized to run concurrently with other installs of Firefox. This allowed me to have tailored installations with different sets of plugins and features.

Why would I want to run more than one Firefox at a time? For me, the reason is that it eases development. Here are a few ways that I use multiple installs:

One install that was just the default install with no additional tweaks or add-ons and would have all cached data, authenticated sessions, and cookies cleared when closed. This was a great browser to use when I would test new code to make sure that it ran well on a stock Firefox. It also gave me a clean cookie and authentication slate so I could test sessions from scrath without clearing my main browser’s history, sessions, etc. If I wiped the slate clean on this browser, nothing was lost.
Since having a large variety of add-ons in Firefox has a tendency to slow things down, I had another browser that included all the major development tool add-ons. I would load this browser up when I needed to explore the DOM in detail, debug layout issues, debug Javascript, etc. This allowed me to streamline my main browser down to just the add-ons that I use frequently.
Since Portable Firefox isn’t installed and just resides in its own folder, I could load multiple versions of Firefox. This made it easy to test for compatibility problems between different versions.
I even played around with the idea of having a browser specifically for media. I would use it for music sources like Pandora and for video sources like Hulu or Red vs. Blue.

Last week, I looked around for a solution like Portable Firefox for Ubuntu. I quickly found a solution that wasn’t nearly as difficult as doing multiple installs: multiple profiles.

Categories Linux, Tips 'n Tricks
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