Read this article
http://linux-mm.org/Drop_Caches
Basically, run commands
sync
sudo echo 3 > /proc/sys/vm/drop_caches
If you want to control "swappiness" (to what extent apps are swapped), read following posts:
http://kerneltrap.org/node/3000
http://lwn.net/Articles/92892/
Basic command: sudo echo 0-100 > /proc/sys/vm/swappiness
Very interesting talk. Helpful to those who want to build scalable distributed systems.
Video: http://vimeo.com/10506751
Transcript is here: http://carsonified.com/blog/dev/steve-huffman-on-lessons-learned-at-reddit/
One interesting lesson is lesson 3: open schema.
They combined relational data model and key-value store. Relational data model is powerful (in some sense) and can naturally represent real-world data models. However, as data set size grows, it seems that relational databases cannot scale up easily. As a result, many large companies develop their own storage systems - Amazon's Dynamo, Google's BigTable, Cassandra, etc. Some use key-value model which seems to be able to scale better than relational model. To change schema does NOT incur much overhead. Different rows/entities can have different number of columns/attributes.
Another post on caching in web app: http://www.mysqlperformanceblog.com/2010/05/19/beyond-great-cache-hit-ratio/
Let's say you want to create a file whose size is 1K. You can achieve that by using either of following two commands:
dd if=/dev/zero of=file bs=1024 count=1
dd of=file bs=1024 count=0 seek=1
In my test, the generated files are different. The second command generates a file with holes. You can try command stat file. The output in my machine is:
File: `bigfile' Size: 1024 Blocks: 0 IO Block: 4096 regular file
The number of allocated blocks is 0 although size of the file is 1024.
Note: if sparse file is not supported, it may write 1024K zeros to the file.
As a user, you don't need to worry about whether the file is sparse or not. It will grow as needed.
I tried to use some Karmic sources for my Intrepid. Of course, this is bad. The reason I had to do it was the package of new version I needed only exist in Karmic repository.
After installing a package, suddenly I got the following error when I tried to use gvim
"gvim: error while loading shared library: libgailutil.so.18: cannot open shared object file: No such file or directory"
Obviously, the old libgail18 was removed which is needed by Intrepid. Because I used unmatched sources, the apt-get did not detect any problem.
I tried to install libgail18 using command
sudo apt-get install libgail18
It did not work and the error message is
Package libgail18 is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source However the following packages replace it: libgtk2.0-0 E: Package libgail18 has no installation candidate
Finally, I figured out the cause is package libgtk2.0-0, libgtk2.0-0-common, etc. These packages are too new for Intrepid. They are for Karmic. So I tried to remove these packages using command
sudo apt-get remove libgtk2.0-0 libgtk2.0-0-common etc
However, apt-get always gave error messages which told me those packages were needed by lots of other packages. It is obviously true. Also I tried command
sudo apt-get install --reinstall libgtk2.0-0
It also did not work. The error message is the package cannot be found. Again the cause I think was the those installed packages were too new and did not match version of ubuntu.
It turned out that I need to use dpkg command
dpkg --remove –-depends libgtk2.0-0 libgtk2.0-0-common etc
Then use following command to fix the broken dependencies:
sudo apt-get install –f
libgtk2.0-0, libgtk2.0-0-common of correct versions are downloaded and installed.
Probably following commands are needed to clean up:
sudo dpkg --configure –a
dpkg-reconfigure
One big difficult I encountered was it was hard to collect detailed log about which files are created/updated/removed by which package during installation. It makes much easier to locate those packages which remove needed files.
User A connects to server S using ssh. X11 forward is enabled using –Y option. Then X11 should work smoothly.
User A connects to server S using ssh. X11 forward is enabled. Then user A switches to another User B (using command su B or ssh localhost –l B). After that, X11 forward won't work. The error should look like
"SSH gateway: X11 authentication failed. Error: Can't open display:" or
"Error: Can't open display:".
Readers may ask why user A does not directly connect to server S as user B given user A knows password of user B. The reason is that sometimes user B is a restricted user account so that he cannot log in remotely.
your_host_name/unix:11 MIT-MAGIC-COOKIE-1 d1e63de6fd7bc3800d868c3b64ca4531 your_host_name/unix:0 MIT-MAGIC-COOKIE-1 e044d47b672dcade1362cd632236f919 your_host_name/unix:10 MIT-MAGIC-COOKIE-1 2aa3bc47d1c209fd06577f4b45f83383Pick the entry with the same display number as the output in step 1)
your_host_name/unix:11 MIT-MAGIC-COOKIE-1 d1e63de6fd7bc3800d868c3b64ca4531
Or you can combine step 1), 2), 3) and 4) into one long command:
(tmpfile=/tmp/xauth_tmp_entry; \
xauth extract ${tmpfile} :$(echo $DISPLAY|cut -d : -f 2 ); \
chmod a+r ${tmpfile}; \
su user_name -c "xauth merge ${tmpfile}"; \
rm ${tmpfile} )
Note: replace user_name with the real target user name.
Each time the user reconnects the remote machine using ssh, the whole process described above must be redone :-( The reason is that sshd may choose another display number and cookie value.
From ssh manual:
"ssh will also automatically set up Xauthority data on the server machine. For this purpose, it
will generate a random authorization cookie, store it in Xauthority on the server, and verify
that any forwarded connections carry this cookie and replace it by the real cookie when the
connection is opened. The real authentication cookie is never sent to the server machine (and
no cookies are sent in the plain)."
http://blogs.gnome.org/markmc/2005/02/25/ssh-x-forwarding-and-xauth/
Every time a user connects to a remote server using ssh, a proxy X server is created. And that X server is used by the sshd process (a new process is forked each time a new connection comes in). The process is like:
user ---> server ---> fork a new process,
create a proxy X server
create pseudo terminal, etc. |
|
V
a program that needs X is used
|
|
V
local display <--- verify <--- the X output is forwarded by sshd to client
It seems that after a user connects to a remote server using ssh, another proxy X server is not created when the user ssh to localhost or 127.0.0.1.
http://groups.google.com/group/android-ndk/browse_thread/thread/d6c5e8f25f1ee543
#include <android/log.h> __android_log_print(ANDROID_LOG_INFO, "your_tag", "fmt string", parameter1, parameter2);
Then you will see it in logcat output.
Read file build/platforms/android-1.5/common/include/android/log.h in ndk for more info.
http://alexgorbatchev.com/wiki/SyntaxHighlighter
I found that usage pattern was changed in recent releases.
Original sample usage:
<pre class="java:nocontrols" name="code">
your code
</pre>
New sample usage:
<pre class="brush:java">
your code
</pre>
Change your posts to use new version of Syntax Highlighter:
Invoke following command in vim:
%s/<pre \(.*\)class="\(\w\+\)*\(:\w\+\)*" \(.*\)>/<pre class="brush:\2" \1 \4>/g
Google blogger/blogspot provides an option to let users decide whether hard-returns in the post are converted to <br/>
Set it by clicking: Your blog admin page –> Settings -> Formatting -> Convert line breaks
Originally, I set it to "yes". Latter I decided to manually insert <br/> instead of using automatical hard-return conversion. So I set the option to "no". As a result, my previous posts were messed up because different lines were concatenated into a single line.
I used vim to convert those posts to new format.
Append <br/> to each line %s/$/<br\/>/g
Sometimes, you don't want to append new lines to block-level elements such as div, ol.
Use following vim commands:
%s/\(<\/div>\s*\)\@<!$/<br\/>/g
%s/\(<\/ul>\s*\)\@<!$/<br\/>/g
%s/\(<\/ol>\s*\)\@<!$/<br\/>/g
%s/\(<\/dl>\s*\)\@<!$/<br\/>/g
......
Vim regular expression: http://vimdoc.sourceforge.net/htmldoc/pattern.html#pattern-overview
Another option is to write a script to download posts, adjust returns/newlines, and publish them.
See this post for details:
http://www.osnews.com/story/22691/Activate_Windows_7_s_Hidden_God_Mode_
Just try:
GodMode.{ED7BA470-8E54-465E-825C-99712043E01C}
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