apt-get update fails to fetch files,"Temporary failure resolving …" error

overview

There are two parts to your question:

• fixing temporary resolve messages
• fixing the package management issues

Temporary resolve

It is likely that this issue is either:

• temporary due to your Internet Service Provider not correctly forwarding internet naming (DNS) to either its or external DNS servers, or
• due to a change in your network has similarly blocked this naming - for example, new router/modem, reconfiguring a switch with a new configuration.

Lets look at the possible DNS resolving issues.

First, temporarily add a known DNS server to your system.

echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf > /dev/null

Then run sudo apt-get update.

If this fixes your temporary resolving messages then either wait for 24 hours to see if your ISP fixes the issue for you (or just contact your ISP) - or you can permanently add a DNS server to your system:

echo "nameserver 8.8.8.8" | sudo tee /etc/resolvconf/resolv.conf.d/base > /dev/null

8.8.8.8 is Google's own DNS server.

source

Another example DNS server you could use is OpenDNS - for example:

echo "nameserver 208.67.222.222" | sudo tee /etc/resolvconf/resolv.conf.d/base > /dev/null

package-management issues

In addition to the temporary resolve issues - you have a few package management issues that need to be corrected - I'm assuming you have tried recently to upgrade from one Ubuntu version to the next recommended version - in your case from Natty (11.04) to Oneiric (11.10)

Open a terminal and type

sudo nano /etc/apt/sources.list

Look for lines that have your a different distribution name in the list than you were expecting - in your case - you have upgraded to oneiric but you have another release name natty

For example, look for lines that look like deb http:/archive.canonical.com/ natty backports

Add a # to the beginning of the line to comment it out - for example

#deb http:/archive.canonical.com/ natty backports

Save and re-run:

sudo apt-get update && sudo apt-get upgrade

You should not have any more release naming errors.

 At the time of writing this, possible common release names include lucid, maverick, natty,oneiric, precise and quantal

http://askubuntu.com/questions/91543/apt-get-update-fails-to-fetch-files-temporary-failure-resolving-error

Speed up Firefox by moving cache into RAM in Ubuntu

By default Firefox puts its cache in your home partition.You can speed up Firefox and reduce disk writes by moving this cache into RAM if you have 1GB RAM or more.

1.Edit /etc/fstab,open terminal from Applications->Accessories menu and type:

sudo gedit /etc/fstab

Add following into this file and close it.

tmpfs /tmp tmpfs noexec,defaults,noatime 0 0
tmpfs /var/tmp tmpfs noexec,defaults,noatime 0 0

2.Edit /etc/sysctl.conf:

sudo gedit /etc/sysctl.conf

add this line and save it:

vm.swappiness=1

3. Type about:config in firefox address bar and click I'll be careful,I promise!.Right click on blank area and create a new string value called

browser.cache.disk.parent_directory,set its value to /tmp

Now,reboot your system and experience the performance.

http://ubuntuguide.net/speed-up-firefox-by-moving-cache-into-ram-in-ubuntu

Linux memory cache

Note: Linux is NOT "eating" your RAM! Please take a look at Geirha's excellent answer below to understand why...

After the above note, if you still feel "cleaning" the cache could help, you can certainly try: it's a one-liner from the terminal:

sync && echo 3 | sudo tee /proc/sys/vm/drop_caches

There's no easy way to disable the cache, but you can achieve the same effect by cleaning it as often as every minute, if you want to:

• Make it a cron-job
• Press Alt-F2, type gksudo gedit /etc/crontab, and add this line near the bottom:
  */15 * * * * root sync && echo 3 > /proc/sys/vm/drop_caches
• This cleans every 15 minutes. You can set to 1 or 5 minutes if you really want to by changing the first parameter to * or */5 instead of */15

One liner to know REAL free RAM, excepting cache

Geirha's answer explains the details, but in short, you get the number of free megabytes with:

free -m | sed -n -e '3p' | grep -Po "\d+$"

which on my 2GB command-line server returns an extremely health 1835.


http://askubuntu.com/questions/155768/how-do-i-clean-or-disable-the-memory-cache

http://www.linuxatemyram.com/

DNS stuff

Flush DNS Cache in Ubuntu 12.04 (Precise Pangolin)

To flush your system DNS Cache Resolver in Ubuntu 12.04, press Ctrl – Alt – T on your keyboard to open Terminal. When terminal opens, run the commands below to clear it.

sudo /etc/init.d/dns-clean

http://www.liberiangeek.net/2012/05/windows-7-vs-ubuntu-12-04-how-to-flush-your-system-dns-cache/


Add custom DNS

To avoid having your settings get revoked after reboots, or after periods of inactivity, you may need to make the following changes via the command line:

$ sudo cp /etc/resolv.conf /etc/resolv.conf.auto
NOTE: The dhclient.conf location may vary depending on you linux distribution.

To locate the correct file you can use:
$ sudo find /etc -name dhclient.conf

$ gksudo gedit /etc/dhcp3/dhclient.conf
# add the following line to the document before the 'return subnet-mask' command

supersede domain-name-servers 208.67.222.222,208.67.220.220;

# save and exit
$ sudo ifdown eth0 && sudo ifup eth0

You may be required to change eth0 to your own network device's name if it uses a non-standard name.

https://store.opendns.com/setup/device/ubuntu/


Check domain with custom DNS

DNS records are likely cached by your provider's DNS servers so if you want to check if the DNS changes you made were successful you can interrogate a DNS server from your domain hosting service with dig:

dig -t a ns1.myhostingcompany.com @domain_registrar_dns_server

It you want Ubuntu to start caching dns I recommend installing pdnsd together with resolvconf. nscd is buggy and not advisable.

Example: dig -t a @8.8.8.8 example.com

http://askubuntu.com/questions/2219/how-do-i-clear-the-dns-cache


Check your PC DNS in command-line

nm-tool

http://askubuntu.com/questions/152593/command-line-to-list-dns-servers


Check DNS related stuff online

http://www.iptools.com/

Linux alternative/equivalent for AcDsee

digiKam

digiKam is an advanced digital photo management application for Linux, Windows, and Mac-OSX.  The people who inspired digiKam's design are the photographers like you who want to view, manage, edit, enhance, organize, tag, and share photographs under Linux systems.

http://www.digikam.org

darktable

darktable is an open source photography workflow application and RAW developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them.

http://www.darktable.org

Shutter - Screenshot tool

Shutter is a feature-rich screenshot program. You can take a screenshot of a specific area, window, your whole screen, or even of a website – apply different effects to it, draw on it to highlight points, and then upload to an image hosting site, all within one window. Shutter is free, open-source, and licensed under GPL v3.


http://shutter-project.org

Read & Remove EXIF Data From the Command Line

Most digital cameras will insert metadata into images. This metadata is stored using the exchangeable image file format (EXIF) and can contain camera specifications, exposure settings, thumbnails, GPS coordinates and more. This article outlines some Linux command line tools you can use for reading, editing and removing EXIF metadata from images.

• Reading and Editing EXIF Metadata with ExifTool
• Reading EXIF Metadata with Jhead
• Removing EXIF Metadata with ImageMagick

Reading and Editing EXIF Metadata with ExifTool
ExifTool is powerful a Perl program that can be used to read and edit EXIF metadata in images. To install ExifTool as /usr/bin/exiftool on Fedora, install the perl-Image-ExifTool package:
su -c 'yum install perl-Image-ExifTool'
Alternatively, you can use CPAN to install ExifTool in /usr/local/bin/exiftool.
su -c "perl -MCPAN -e'install Image::ExifTool'"
After installation, you will have the exiftool command available in /usr/bin or /usr/local/bin. To view the EXIF metadata in an image, just past the image as an argument to exiftool.
exiftool dsc_0790.jpg
Here is a snippet of the output from the above command:
ExifTool Version Number : 7.60
File Name : dsc_0790.jpg
Directory : .
File Size : 4.4 MB
File Modification Date/Time : 2008:07:16 09:45:20-07:00
File Type : JPEG
MIME Type : image/jpeg
Exif Byte Order : Big-endian (Motorola, MM)
Make : NIKON CORPORATION
Camera Model Name : NIKON D200
Orientation : Horizontal (normal)
X Resolution : 300
Y Resolution : 300
Resolution Unit : inches
Software : Bibble 4.10a
Modify Date : 2007:06:23 22:00:14
Exposure Time : 1/40
F Number : 2.0
Exposure Program : Aperture-priority AE
ISO : 100
.
.
.
ExifTool has many options for editing and removing EXIF metadata in images. To see the available options, use the --help switch or read the ExifTool documentation.
exiftool --help
Reading EXIF Metadata with Jhead
Jhead is a command line tool for displaying EXIF data embedded in JPEG images. On Fedora, use Yum to install Jhead:
su -c 'yum install jhead'
Now, use /usr/bin/jhead to read EXIF metadata:
jhead dsc_0790.jpg
Here is an example of the output produced by the jhead command:
File name : dsc_0790.jpg
File size : 4654488 bytes
File date : 2008:07:16 09:45:20
Camera make : NIKON CORPORATION
Camera model : NIKON D200
Date/Time : 2007:06:23 22:00:14
Resolution : 3880 x 2608
Flash used : No
Focal length : 50.0mm (35mm equivalent: 75mm)
Exposure time: 0.025 s (1/40)
Aperture : f/2.0
ISO equiv. : 100
Exposure bias: 1.00
Whitebalance : Auto
Exposure : aperture priority (semi-auto)
GPS Latitude : ? ?
GPS Longitude: ? ?
======= IPTC data: =======
(C)Flag : 0
DateCreated : 20070623
Time Created : 220014
Record vers. : 4
Removing EXIF Metadata with ImageMagick
If you need to strip the EXIF metadata from images, use ImageMagick's mogrify command. To install ImageMagick on Fedora, use Yum:
su -c 'yum install ImageMagick'
After ImageMagick is installed, you will have /usr/bin/mogrify available. The mogrify command can be used to strip Exif data from images.
mogrify -strip imagename.jpg
If you need to process a large number of files, use find and xargs:
find ./folder_of_images -name '*.jpg' | xargs mogrify -strip


http://hacktux.com/read/remove/exif