Posted by gmendoza on September 23, 2009 under Tech Tips | 
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)
Posted by gmendoza on June 21, 2009 under Tech Tips |
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.
Posted by gmendoza on April 9, 2009 under Tech Tips |
Previously, I posted on using rsync over SSH for file synchronization. While this works very well when pushing data in one direction, it’s not well suited for synchronizing modifications that are made on both sides. An excellent bidirectional utility for that type of job is Unison, which sports many of the same benefits as rsync, but has some distinct advantages for more complex synchronization scenarios.
A basic example would be to synchronize a local directory called “MyDocs” with a remote SSH server. From the following output, you can see that this directory contains four text files.
ls -ld ~/MyDocs
drwxr-xr-x 2 gmendoza gmendoza 4096 2009-04-09 16:05 /home/gmendoza/MyDocs
ls -l ~/MyDocs
total 12
-rw-r--r-- 1 gmendoza gmendoza 31 2009-04-09 16:09 file1.txt
-rw-r--r-- 1 gmendoza gmendoza 31 2009-04-09 16:09 file2.txt
-rw-r--r-- 1 gmendoza gmendoza 31 2009-04-09 16:09 file3.txt
-rw-r--r-- 1 gmendoza gmendoza 31 2009-04-09 16:09 file4.txt
The first time you run Unison for this particular directory structure, both sides will create a local index and hash table. You’ll get a warning and will be prompted with a message, asking you to hit the space bar if you accept. If the root directory on the remote side does not exist yet, you’ll also be prompted to accept the changes.
unison MyDocs ssh://host2/MyDocs
Contacting server...
Connected [//host1//home/gmendoza/MyDocs -> //host2//home/gmendoza/MyDocs]
Looking for changes
Warning: No archive files were found for these roots, whose canonical names are:
/home/gmendoza/MyDocs
//host2//home/gmendoza/MyDocs
(snipped for brevity...)
Press return to continue.[] Waiting for changes from server
Reconciling changes
local host2
dir ----> / [f]
Proceed with propagating updates? [] y
Propagating updates
UNISON 2.27.57 started propagating changes at 16:14:30 on 09 Apr 2009
[BGN] Copying from /home/gmendoza/MyDocs to //host2//home/gmendoza/MyDocs
[END] Copying
UNISON 2.27.57 finished propagating changes at 16:14:30 on 09 Apr 2009
Saving synchronizer state
Synchronization complete (1 item transferred, 0 skipped, 0 failures)
Subsequent synchronizations are shown as the following.
unison MyDocs ssh://host2/MyDocs
Contacting server...
Connected [//host1//home/gmendoza/MyDocs -> //host2//home/gmendoza/MyDocs]
Looking for changes
Waiting for changes from server
Reconciling changes
Nothing to do: replicas have not changed since last sync.
For the following example, I have modified file1.txt on host1, and file2.txt on host2. Both file3.txt and file4.txt have been modified on each side. The great thing about unison is that when there is a conflict, you have the opportunity to view the differences and select which direction you wish to synchronize. Pressing the “x” key displays some basic information about the files that differ. In this case, I have chosen the files with the most recent timestamp. You choose the file direction by pressing the greater and less-than symbols, “>” and “<".
unison MyDocs ssh://host2/MyDocs
(snipped)
local host2
changed <-?-> changed file3.txt [] x
local : changed file modified on 2009-04-09 at 16:16:29 size 50
host2 : changed file modified on 2009-04-09 at 16:16:43 size 55
changed <==== changed file3.txt [] <
changed <-?-> changed file4.txt [] x
local : changed file modified on 2009-04-09 at 16:17:20 size 56
host2 : changed file modified on 2009-04-09 at 16:16:59 size 41
changed ====> changed file4.txt [] >
changed ----> file1.txt [f]
<---- changed file2.txt [f]
Proceed with propagating updates? [] y
Propagating updates
UNISON 2.27.57 started propagating changes at 16:18:27 on 09 Apr 2009
[BGN] Updating file file3.txt from //host2//home/gmendoza/MyDocs to /home/gmendoza/MyDocs
[BGN] Updating file file4.txt from /home/gmendoza/MyDocs to //host2//home/gmendoza/MyDocs
[BGN] Updating file file1.txt from /home/gmendoza/MyDocs to //host2//home/gmendoza/MyDocs
[BGN] Updating file file2.txt from //host2//home/gmendoza/MyDocs to /home/gmendoza/MyDocs
[END] Updating file file3.txt
[END] Updating file file2.txt
[END] Updating file file4.txt
[END] Updating file file1.txt
UNISON 2.27.57 finished propagating changes at 16:18:27 on 09 Apr 2009
Saving synchronizer state
Synchronization complete (4 items transferred, 0 skipped, 0 failures)
Unison also has a GTK front end for the graphically inclined. Be sure to check out all the documentation for a full understanding of syntax.