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Download PGP Keys with Apt-key

gmendoza — Tue, 01 Dec 2009 23:46:11 +0000

When adding third party software repositories to your APT sources list, you can easily download a referenced PGP key to your APT keyring using the advanced options of the apt-key utility.

For example, if you are adding a third party repository that references the PGP key ID of 6E80C6B7, the following will work as long as the key has been uploaded to a keyserver.

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6E80C6B7 gpg: requesting key 6E80C6B7 from hkp server keyserver.ubuntu.com gpg: key 6E80C6B7: public key "Launchpad PPA for Banshee Team" imported gpg: no ultimately trusted keys found gpg: Total number processed: 1 gpg: imported: 1 (RSA: 1)

Typically, instructions on adding repositories give readers a two or three step process that involves apt-key reading a key from a text file or piped from a wget command. The above just cuts all that nonsense out.

The apt-key man page is a bit bare, but there are a few other options you might find interesting that are only mentioned in the commands help output.

apt-key Usage: apt-key [command] [arguments]

Manage apt's list of trusted keys

apt-key add - add the key contained in ('-' for stdin) apt-key del - remove the key apt-key export - output the key apt-key exportall - output all trusted keys apt-key update - update keys using the keyring package apt-key net-update - update keys using the network apt-key list - list keys apt-key finger - list fingerprints apt-key adv - pass advanced options to gpg (download key)

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Symmetric Key Encryption with GnuPG

gmendoza — Thu, 05 Nov 2009 03:59:06 +0000

If you ever want to quickly protect a file by encrypting it with a simple password, you can use GnuPG and symmetric key encryption for the job. Using this method, you can use industry strength encryption like AES256 and not have to worry about public and private keys. Just remember your password and use PGP compatible software to decrypt the files when needed.

For example, this is how you can encrypt a zip file called backup.zip and output the result to a new file called backup.zip.gpg.

gpg --symmetric --cipher-algo aes256 -o backup.zip.gpg backup.zip Enter passphrase: ******* Repeat passphrase: *******

To decrypt the file, the following will work.

gpg -d -o backup.zip backup.zip.gpg gpg: AES256 encrypted data Enter passphrase: ******* gpg: encrypted with 1 passphrase

For fun, here’s how to create a Gzip Tar archive (tar.gz) and encrypt it on the fly.

tar czvpf - SomeFiles/ | gpg --symmetric --cipher-algo aes256 -o backup.tar.gz.gpg Enter passphrase: ******* Repeat passphrase: *******

To decrypt and extract in a single command, the following also works.

gpg -d backup.tar.gz.gpg | tar xzvf - gpg: AES256 encrypted data Enter passphrase: ******* gpg: encrypted with 1 passphrase

If you’re curious to know what other ciphers are available to you, simple use the gpg --version command.

gpg --version | grep Cipher Cipher: 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH

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Quickly Identify Video File Attributes

gmendoza — Tue, 03 Nov 2009 22:59:12 +0000

If you want to gain quick insight into the basic properties of a video file from the Linux command line, there’s a few really easy methods. The information you might be interested in are audio and video codecs, resolution, frame rates, bitrates, etc.

Using mplayer, you can see some basic information about a video file. For example, the following video is using the WMV3 video codec at the resolution of 1280×720 (720p), the bitrate of 3000 kbps, etc.

mplayer video.wmv -vo null -ao null -frames 0 2>&1 /dev/null | egrep "(VIDEO|AUDIO)" VIDEO: [WMV3] 1280x720 24bpp 1000.000 fps 3000.0 kbps (366.2 kbyte/s) AUDIO: 44100 Hz, 2 ch, s16le, 96.0 kbit/6.80% (ratio: 12003->176400)

The audio rate is shown to be 44100 Hz using 2-Channel stereo, but the codec is not listed. You can get additional information with the -identify option.

mplayer video.wmv -identify -vo null -ao null -frames 0 2>&1 /dev/null | egrep "(^ID|VIDEO|AUDIO)" ID_AUDIO_ID=1 ID_VIDEO_ID=2 VIDEO: [WMV3] 1280x720 24bpp 1000.000 fps 3000.0 kbps (366.2 kbyte/s) ID_CLIP_INFO_NAME0=name ID_CLIP_INFO_VALUE0= ID_CLIP_INFO_NAME1=author ID_CLIP_INFO_VALUE1= ID_CLIP_INFO_NAME2=copyright ID_CLIP_INFO_VALUE2= ID_CLIP_INFO_NAME3=comments ID_CLIP_INFO_VALUE3= ID_CLIP_INFO_N=4 ID_FILENAME=video.wmv ID_DEMUXER=asf ID_VIDEO_FORMAT=WMV3 ID_VIDEO_BITRATE=3000000 ID_VIDEO_WIDTH=1280 ID_VIDEO_HEIGHT=720 ID_VIDEO_FPS=1000.000 ID_VIDEO_ASPECT=1.7778 ID_AUDIO_FORMAT=353 ID_AUDIO_BITRATE=0 ID_AUDIO_RATE=0 ID_AUDIO_NCH=0 ID_LENGTH=2116.00 ID_VIDEO_ASPECT=1.7778 ID_VIDEO_CODEC=wmv9dmo AUDIO: 44100 Hz, 2 ch, s16le, 96.0 kbit/6.80% (ratio: 12003->176400) ID_AUDIO_BITRATE=96024 ID_AUDIO_RATE=44100 ID_AUDIO_NCH=2 ID_AUDIO_CODEC=ffwmav2

Another great tool for identifying video attributes is idvid. idvid comes with the tovid package, so be sure to install it from your repository. It is a bit slow, but the output is very clean and easy to interpret.

idvid video.wmv -------------------------------- idvid Video identification script Part of the tovid suite, version 0.31
http://www.tovid.org
-------------------------------- Analyzing file: 'video.wmv'. This may take several minutes... ========================================================= File: video.wmv Width: 1280 pixels Height: 720 pixels Aspect ratio: 1.77:1 Frames: 63352 Duration: 00:35:13 hours/mins/secs Framerate: 1000.000 frames per second Video format: WMV3 Video bitrate: 3000000 bits per second --------------------------- Audio track 1 (Stream 0.0, AID 0): --------------------------- Codec: wmav2 Bitrate: 0000 bits per second Sampling rate: 44100 Hz ========================================================= Audio is compliant with the following formats: Not compliant with (S)VCD or DVD Video is compliant with the following formats: Not compliant with (S)VCD or DVD This video does not seem to be compliant with (S)VCD or DVD standards. If you burn it to a video disc, it may not work. =========================================================

Finally, another tool that works very well is exiftool. It’s available in the libimage-exiftool-perl package. The output is also very straight forward, and easy to interpret. It’s also a lot faster than idvid because the tool only displays metadata, which in some cases can be misleading. Mplayer and tovid actually probe the video, providing very accurate information at the cost of speed.

exiftool video.wmv ExifTool Version Number : 7.30 File Name : video.wmv Directory : . File Modification Date/Time : 2009:04:20 09:21:58 File Type : WMV MIME Type : video/x-ms-wmv File ID : 12341234-1234-1234-1234-123412341234 File Size : 823200182 Creation Date : 2009:03:31 02:52:55Z Data Packets : 102833 Play Duration : 35:16 Send Duration : 35:13 Preroll : 3000 Flags : 2 Min Packet Size : 8000 Max Packet Size : 8000 Max Bitrate : 3122812 Is VBR : False Audio Codec Name : Windows Media Audio 9.2 Audio Codec Description : 96 kbps, 44 kHz, stereo 1-pass CBR Video Codec Name : Windows Media Video 9 Video Codec Description : Professional Audio Codec ID : Windows Media Audio V2 V7 V8 V9 / DivX audio (WMA) / Alex AC3 Audio Audio Channels : 2 Audio Sample Rate : 44100 Stream Type : Video Error Correction Type : No Error Correction Time Offset : 0 s Stream Number : 2 Image Width : 1280 Image Height : 720 Title : Author : Copyright : Description : Rating : Image Size : 1280x720

As always, comments and additional tips are welcome!

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RAR and UNRAR from Linux CLI

gmendoza — Wed, 23 Sep 2009 18:09:48 +0000

Two great packages available to the Linux community are RAR and UNRAR. If you are already familiar with the RAR compression format, these allow you to create, modify and extract RAR archives. For those of you that appreciate the graphical compression application for Gnome called File Roller, these packages enable it to read RAR files. For more information about the RAR format, check out rarsoft.com.

To install from Ubuntu or Debian, its as simple as:

sudo apt-get install rar unrar

To list the files in a RAR archive, use the l or v option:

rar l video.rar

To decompress a RAR archive called video.rar, simply issue the command:

unrar e video.rar

The unrar package is only intended for decompression tasks. Otherwise, just use the rar command with the e option to extract the files to the current directory.

rar e video.rar

To compress a single file called video.avi, adding it to a RAR file called video.rar:

rar a video.rar video.avi

To compress a single file called video.avi, splitting it into approximately 50 Mb files:

rar a -v50000 video.rar video.avi

This by default creates archive files starting with video.part01.rar, video.part02.rar and following the sequence to completion. To use the older and better known extension sequence format of .rar, .r00, .r01, etc, use the -vn option like so:

rar a -v50000 -vn video.rar video.avi

To compress an entire directory recursively, use the -r option:

rar a -r Documents.rar Documents/

To extract the files from an archive, such that the original directory structure is also recreated, use the x command:

rar x Documents.rar

There are so many other features available to the RAR format, so be sure to check out the man pages or the packaged documentation.

man rar less /usr/share/doc/rar/rar.txt.gz

(if your version of less supports reading of compressed files)

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Fixing Dates in Image EXIF Tag Data from Linux

gmendoza — Mon, 22 Jun 2009 06:11:51 +0000

I recently needed to organize a large number of old digital photos that had the wrong date embedded in their EXIF tag data. The camera I used many years ago would often lose track of time and would sometimes be set to the wrong year. Applications I now use to organize photos read this data and made my albums difficult to navigate. I came across a Linux command line utility called jhead that allows you to modify this information to whatever you wish, and its easy to use in scripts as well. Installing was easy, because it’s currently in most repositories, including Ubuntu’s.

To read existing EXIF tag data, simply run jhead against an image without any options. As you can see from the example below, my date is set to the year 2022.

jhead image.jpg File name : image.jpg File size : 159390 bytes File date : 2004:01:12 07:35:23 Camera make : Samsung Camera model : Digimax 200 Date/Time : 2022:02:12 04:04:17 Resolution : 800 x 600 Flash used : Yes Exposure time: 0.045 s (1/22) Aperture : f/2.8

To clear all EXIF data from the file, use the -de option. Then recreate the EXIF fields with the -mkexif option, and check the data again. Notice the new Date/Time is set to the timestamp on the file.

jhead -de image.jpg Modified: image.jpg

jhead -mkexif image.jpg Modified: image.jpg

jhead image.jpg File name : image.jpg File size : 147751 bytes File date : 2004:01:12 07:35:23 Date/Time : 2004:01:12 07:35:23 Resolution : 800 x 600

To change the entire timestamp manually, use the -ts option. Notice, there is no space between the -ts and the option. I could not trust the month and day, so I simply chaged the date to midnight on January 1, 2003.

jhead -ts2003:01:01-00:00:00 image.jpg Modified: image.jpg

jhead image.jpg File name : image.jpg File size : 147751 bytes File date : 2004:01:12 07:35:23 Date/Time : 2003:01:01 00:00:00 Resolution : 800 x 600

For many more options, check out the man page or visit the jhead site for more info.

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Line wrapping text made easy with fold

gmendoza — Tue, 07 Apr 2009 04:37:08 +0000

Line wrapping text from the command line is easy with the fold utility, which of course is provided by the Free Software Foundation. By default, the fold command will wrap text at 80 characters, but you can of course specify the width manually. I prefer using the -s option, which will break only on spaces, making sure not to break in the middle of a word.

For example, the following command will concatenate a text file to standard output, adding line breaks only at spaces or at 72 characters, whichever comes first.

fold -s -w 72 textfile.txt

This can also be useful if you want to clearsign a message with Gnupg, but wish to line wrap it beforehand.

fold -s -w 72 textfile.txt | gpg --clearsign -u user@email.com

Add redirection if you wish to output the results to a file.

fold -s -w 72 textfile.txt > newfile.txt

As mentioned here, the fmt command also provides the same primary features of fold, but is much better. Not only does it wrap long lines, but it also fills out short lines as well. There are additional options that are worth looking into. Be sure to check out the man page!

man fmt

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Rename Files in Bulk from the Command Line

gmendoza — Mon, 07 Jul 2008 01:22:27 +0000

Renaming a large number of files can seem like a daunting task, but no worries, your trusty Linux CLI is at your service. For this example, we will rename a number of MP3’s located in multiple subdirectories with a couple very easy commands; “find” and “rename”.

By listing the following directory, you’ll see that the MP3’s have been named with “(LP Version)”, and of course I don’t like this naming convention.

cd ~/Music/Metallica/Metallica/ ls -1 01 - Enter Sandman (LP Version).mp3 02 - Sad But True (LP Version).mp3 03 - Holier Than Thou (LP Version).mp3 04 - The Unforgiven (LP Version).mp3 05 - Wherever I May Roam (LP Version).mp3 06 - Don't Tread On Me (LP Version).mp3 07 - Through The Never (LP Version).mp3 08 - Nothing Else Matters (LP Version).mp3 09 - Of Wolf And Man (LP Version).mp3 10 - The God That Failed (LP Version).mp3 11 - My Friend Of Misery (LP Version).mp3 12 - The Struggle Within (LP Version).mp3

We’ll use the “rename” command to search for and delete the string ” (LP Version)” in any of the mp3 file names.

Syntax:

rename (search command) (files) rename 's/search_for_string/replace_string_with_this/' files

To delete the matching string, simply leave the replace area empty like so:

rename 's/search_for_string//' files

Our Example:

rename 's/ $LP Version$//' *.mp3

Notice, the left and right parentheses need to be preceded with a backslash “\” character, although the spaces do not. The backslash is a metacharacter used to give you control over what your are matching against. For more info, here’s a link to a decent tutorial on the matter.

You can see the results of the command below.

ls -1 01 - Enter Sandman.mp3 02 - Sad But True.mp3 03 - Holier Than Thou.mp3 04 - The Unforgiven.mp3 05 - Wherever I May Roam.mp3 06 - Don't Tread On Me.mp3 07 - Through The Never.mp3 08 - Nothing Else Matters.mp3 09 - Of Wolf And Man.mp3 10 - The God That Failed.mp3 11 - My Friend Of Misery.mp3 12 - The Struggle Within.mp3

Now, to rename a large number of files spanning multiple directories, simply combine “rename” with the power of the “find” command.

Syntax:

find . -type f -name *.mp3 -exec rename 's/ $LP Version$//' '{}' \;

In this example, we searched starting from the current directory for only files with .mp3 in their file names. We use the find command’s -exec option to execute the rename command against the result set. See the find(1) manpage for more info.

Other useful examples:

Replace all spaces with underscores. rename 's/ /\_/g' *.mp3

Replace all uppercase with lowercase characters rename 'y/[A-Z]/[a-z]/' *.mp3

Easy stuff, and you don’t even need any fancy GUI applications to do the job!

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Vim in Color

gmendoza — Sun, 30 Sep 2007 13:48:05 +0000

Turing on colored syntax highlighting in Vim can make it easier when looking through complicated text files, scripts, and source code. To quickly turn on or off the feature, use the “syntax” command within Vim:

:syntax on :syntax off

The results are great. Here’s a screenshot of Vim in color.

To make the feature permanent, edit the file /etc/vim/vimrc, or as your Vim package maintainer may suggest, /etc/vim/vimrc.local. One can also make the change simply for their user only by editing ~/.vimrc. In all cases, simply add the following line at the end of the file:

:syntax on

Users of Ubuntu by default have vim-tiny, which as it’s name suggests, is a smaller version of the Vim editor. This version does not support syntax highlighting and a number of other features. Of course, remedying this is very easy by installing the full featured vim:

# sudo apt-get install vim

Happy editing.

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Grep in Color

gmendoza — Sun, 02 Sep 2007 16:24:43 +0000

If you would like to make it easier to visually spot what you are looking for when using “grep”, try out the “–color” flag. This option highlights any matches in the output of your search, giving you an upper hand when trying to visually scan through complicated or cumbersome sequences.

For example, if you were looking for any IP address in your /etc/hosts.deny file that has the number “209″ in it, issue the following command:

grep --color 209 /etc/hosts.deny

Here is the comparison of the same output, with and without the color option.

As you can see, one might find it very easy to miss the fact that there are some IP addresses that have multiple octets with the value of 209. The color flag really comes in handy.

UPDATE (12/13/2009): In the most recent versions of Ubuntu, a local alias has been defined in the default .bashrc for each user. This alias gives turns on color highlighting with the following line.

alias grep='grep --color=auto'

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Split and Reassemble Files

gmendoza — Mon, 04 Jun 2007 06:11:20 +0000

If you ever need to work with a large file and wish you could split it into smaller pieces, you’ll be pleased to know that it’s extremely easy to do in Linux. You can use the “split” utility that comes standard with most *nix variations. Lets take a look at a couple easy examples.

To create a test file to work with, the following will create one that’s exactly 100 megabytes. Note, I am using ‘dd’ with /dev/urandom to demonstrate that the results of the split and reassembly are completely accurate. This will be accomplished via md5 hash comparisons at the end of this process.

$ dd if=/dev/urandom of=testfile bs=1k count=102400 102400+0 records in 102400+0 records out 104857600 bytes (105 MB) copied, 23.2982 seconds, 4.5 MB/s

$ ls -lh testfile -rw-r--r-- 1 gmendoza gmendoza 100M 2007-06-03 22:45 testfile

To split the file into five 20MB files, use the split command as shown below. Note, I am producing five files with a new naming convention of “splitfiles”.

$ split -b 20971520 -d testfile splitfiles

Verify by listing all files that begin with “splitfiles”. Below, you see the new files with the appropriate sequence numbers as a result of the split command.

$ ls -l splitfiles* -rw-r--r-- 1 gmendoza gmendoza 20971520 2007-06-03 22:47 splitfiles00 -rw-r--r-- 1 gmendoza gmendoza 20971520 2007-06-03 22:47 splitfiles01 -rw-r--r-- 1 gmendoza gmendoza 20971520 2007-06-03 22:47 splitfiles02 -rw-r--r-- 1 gmendoza gmendoza 20971520 2007-06-03 22:47 splitfiles03 -rw-r--r-- 1 gmendoza gmendoza 20971520 2007-06-03 22:47 splitfiles04

To reassemble the smaller files back to their original state, concatenate them together using a simple redirect.

$ cat splitfile* > newtestfile

… and list again to show your handy work…

$ ls -lh newtestfile -rw-r--r-- 1 gmendoza gmendoza 100M 2007-06-03 22:52 newtestfile

As proof that both the original and newly reassembled files are exactly the same, check the results of a cryptographic md5 hash:

$ md5sum testfile newtestfile 54a07d5011ca893eddfab29960a7f232 testfile 54a07d5011ca893eddfab29960a7f232 newtestfile

Cool stuff.

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Useful APT Aliases

gmendoza — Fri, 01 Jun 2007 06:54:29 +0000

If you’re an avid user of Ubuntu or other Debian based Linux distributions, then you’re probably very familiar with using APT and it’s related command line utilities. You might however find it useful to create some command line aliases that shorten the time it takes to type out these repetitive tasks.

For example,

"sudo apt-get update" can be shortened to "agu". "sudo apt-get install" can be shortened to "agi". "sudo apt-get dist-upgrade" can be shorted to "agd".

A very simple way to create a set of command line aliases would be to add them to your ~/.bashrc file located in your users home directory. Here’s an example of some of my favorite APT aliases.

# Favorite Aliases
alias agu='sudo apt-get update'
alias agi='sudo apt-get install'
alias agd='sudo apt-get dist-upgrade'
alias agr='sudo apt-get remove'
alias ags='sudo aptitude search'
alias agsh='sudo apt-cache show'
alias afs='sudo apt-file search'
alias afsh='sudo apt-file show'
alias afu='sudo apt-file update'

To apply the changes immediately to your bash profile without having to log out, simply run the following command:

. .bashrc

Now, if you want to install the “vim-full” package, simply issue the following command:

agi vim-full

Remember, because “sudo” has been added to your alias, you don’t have to type it every time. It will prompt you to use the password the first time, and won’t ask again for the duration of the defined timeout period. Cool?

“apt-file” is a very useful package you should install. The alias is defined above, but is not installed by default. It allows you to search for file names in all packages from all your defined repositories. For example, lets say you’ve tried to run an application and it claims that your’re missing the library “libstdc++.so.5.0.7″. The following example tells you which packages contains a file with that name, which you can then install.

afs libstdc++.so.5.0.7 libstdc++5: usr/lib/libstdc++.so.5.0.7 libstdc++5-3.3-dbg: usr/lib/debug/libstdc++.so.5.0.7 agi libstdc++5

Although these examples have been geared towards Debian and Ubuntu, you can obviously use aliases on any Unix-like operating system. The technique of applying them just varies depending on the shell environment you are using. Have fun!

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