De retour chez OVH

Je suis de retour chez OVH. C’est plus cher, je n’ai plus de backup automatique et plus les garanties offertes par un serveur virtuel mais au moins ça fonctionne. Si vous envisagez de passer chez 1And1, préparez vous à rejoindre le cercle des utilisateurs mécontents (et généralement engagés sur 12 ou 24 mois).

J’ai eu la mauvaise surprise de m’appercevoir que MySQL en Debian/stable était plus vieux que le MySQL de CentOS 5. Mais je m’en suis apperçu après coup, il me semblait évident que ça ne serait pas le cas. Si vous vous êtes un jour demandé ce que ça faisait de lancer un serveur MySQL avec des fichiers provenants d’une version plus récentes… Et bien ça ne donne rien de bon, les requêtes aboutissent rarement et de façon aléatoire (la même requête peut fonctionner ou ne pas fonctionner). On reçoit un bon paquet d’erreurs “Lost connection to the server”.

Pour un projet sur lequel je travail pendant mon temps libre avec d’autres personnes, j’utilise maintenant NetBeans + Dropbox.
NetBeans c’est pour moi le meilleur IDE PHP du moment mais le soucis c’est qu’en mode FTP il ne fait qu’envoyer les fichiers modifiés. Lors de la création du projet NetBeans il télécharge tous les fichiers et après il ne fait que les envoyer. Cela a pour conséquence notable d’empêcher le travail à plusieurs.
Pour remedier à ça en plus de l’accès FTP j’ai mis un répertoire DropBox partagé sur le serveur et ça marche niquel. Les développeurs et le serveur sont synchronisés. Bien sur je fais 2x plus de backups parce que ça fait assez peur.

Sinon j’ai tenté d’installer Nexenta 3b1 sur une machine VMWare et ça n’a malheureusement pas du tout marché. L’installeur était très très très long et il a crashé peu après avoir atteint 100%. Je ne m’attendais pas à grand chose la part d’un système qui met 3h à s’installer de toute façon.

Posted in French. Tags: , , , . No Comments »

Linux prioritization : do more with less

I find the concept of prioritization very interesting. It just enables you to do more with less. Doesn’t that sound great ?

Let’s say you want to be able to respond to user requests as fast as possible but update your data in a low priority manner :
You can set the process CPU priority from -20 (high priority) to 19 (low priority) by using the command :

1
nice -n <priority> <command>

You can set the process IO priority in 4 classes (0: none, 1: realtime, 2: best-effort, 3: idle) with some priorities within these classes (0-7, lower being higher prio). But you have to enable the CFQ (Complete Fair Queueing) scheduler first by typing something like that :

1
echo cfq >/sys/block/hda/queue/scheduler

So the ultimate low priority command will be

1
ionice -c 3 nice -n 20 <command>

But sometimes changing the CPU and IO priority won’t change much because the problem you might have might occur within the SQL server for say. So what you do ? Well, you could slow down your low priority program. If you have a low priority php script, you could do it like that :

1
2
3
4
5
6
7
<?php
while( true ) {
    list( $load ) = explode(' ', file_get_contents('/proc/loadavg') );
    echo 'sleeping '.$load."s\n";
    usleep( $load * 1000000);
}
?>

This program will make a loop that will slow down with the increasing load. It means that this program will always keep space of the system, even if it’s run hundreads of time.

So yeah, you can now manage efficiently CPU and disk. Are you done ? Not really, there’s still the memory issue. Memory (RAM) is always fast unless there’s no memory left, then it’s paged and everything becomes thousand times slower. You can only disable the virtual memory (swap on Linux), set some memory allocation limits (with ulimit), but that’s pretty much it.
I would personnally recommend to disable swap and always take more RAM than needed. On servers swap prevent them from having to kill process, but they are so much slowed by it that the whole system is slowed down. And then even ssh server is so slow you have an ssh timeout before reaching the shell.

So, Linux has a great scheduling capacity. But what about NOT scheduling AT ALL ? Well, Linux is also very able to do that. You can put some process in real-time mode, these processes won’t be interupted by anything unless they are sleeping or waiting for an I/O event.
You can use the Real-Time (RT) mode using the rtprio command :

1
rtprio 99 <command>

Stupid C++ vs C# performance comparison

I found out that there is a much better test than the one i did here. In fact the main interest of the post is this spreadsheet :

I recently did a simple and stupid comparison test between C++ (g++) and C# .Net (mono).

My point here is that C# can actually be considered as a very fast language. It allows automatic hardware-specific optimization.
Lot of people think it’s like a java, it has a virtual machine. But in fact it just compiles everything into native language when it accesses methods. This is the whole purpose of the JIT (Just Int Time compiler).

If you feel the JIT compiler is a possible reason of slowness (it slows down the program startup), you can pre-compile your assemblys (mono –aot on linux). If you feel the mono files are a drawback, you can bundle everything in one file using mkbundle. You can read more about this here.

The only real drawback you have in the .Net framework is the garbage collector. It prevents the C# .Net it from being a realtime language/framework. But in real life usage it doesn’t slow much.

The purpose of the following test is to show that C++ isn’t faster than C# “as is”. I KNOW C# can not be faster than C++ because C# can do few hardware specific optimizations when you can do all of them in C++.

But if you’re searching for arguments to choose C# .Net over native C++, you should also consider these :

SO ! Here is the test…

I wrote these two sample programs :

One in C++ :

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
#include <iostream>
using namespace std;
 
long stupidThing( long nb ) {
	long out = 1;
	while( nb > 0 )
		out *= nb--;
 
 
	return out;
}
 
int main() {
 
	long total = 0;
 
	for( int i = 0; i < 1000000; ++i )
		for( long l = 0; l < 100; ++l )
			total += stupidThing( l );
 
	cout << "Total : " << total << endl;
 
	return 0;
}

One in C# :

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
using System;
 
namespace test {
        class Program {
                static long stupidThing( long nb ) {
                        long ret = 1;
                        while ( nb > 0 )
                                ret *= nb--;
                        return ret;
                }
 
                static void Main( string[] args ) {
 
                        long total = 0;
 
                        for ( int i = 0; i < 1000000; ++i )
                                for ( long l = 0; l < 100; ++l )
                                        total += stupidThing( l );
                        Console.WriteLine( "Total : {0}", total );
                }
        }
}

First of all, I open a shell in real-time priority, because I don’t want my other processses to mess with my tests :

1
# rtprio 99 bash

Then I compile the two programs :

1
2
# gmcs test.cs
# g++ -O4 test.cpp -o test

And then I launch my test :

On a 64 bits host :

1
Kernel : 2.6.9-023stab051.3-smp #1 SMP Wed Nov 4 18:36:34 MSK 2009 x86_64 x86_64 x86_64 GNU/Linux
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
# time ./test ; time ./test ; time ./test ; time mono test.exe ; time mono test.exe ; time mono test.exe
Total : -6192109806162068864
 
real    0m12.433s
user    0m12.394s
sys     0m0.049s
Total : -6192109806162068864
 
real    0m12.415s
user    0m12.411s
sys     0m0.014s
Total : -6192109806162068864
 
real    0m12.430s
user    0m12.411s
sys     0m0.026s
Total : -6192109806162068864
 
real    0m10.311s
user    0m10.287s
sys     0m0.029s
Total : -6192109806162068864
 
real    0m10.254s
user    0m10.247s
sys     0m0.011s
Total : -6192109806162068864
 
real    0m10.250s
user    0m10.255s
sys     0m0.012s

C# clearly beats C++ here. Well

On a 32 bits host :

1
Kernel : 2.6.30-2-686 #1 SMP Fri Dec 4 00:53:20 UTC 2009 i686 GNU/Linux
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
# time ./test ; time ./test ; time ./test ; time mono test.exe ; time mono test.exe ; time mono test.exe
Total : 100461056
 
real    1m10.927s
user    1m7.376s
sys     0m0.056s
Total : 100461056
 
real    1m12.590s
user    1m8.976s
sys     0m0.020s
Total : 100461056
 
real    1m13.279s
user    1m9.532s
sys     0m0.056s
Total : -6192109806162068864
 
real    2m22.492s
user    2m15.260s
sys     0m0.136s
Total : -6192109806162068864
 
real    2m23.002s
user    2m15.760s
sys     0m0.104s
Total : -6192109806162068864
 
real    2m25.102s
user    2m17.709s
sys     0m0.144s

C++ beats C# here, but in 32 bits C++ use other types whereas C# use the same. In C# long is always 64 bits, in C++ it can be 64 bits or 32 bits (depending on the current architecture).

I haven’t tested this on strings but I’m pretty sure it would be slower in .Net as sizeof(Char) == 2 in C# .Net. It means that each string is two times bigger in C# .Net than in C++.

Redirect port on Linux

Sometimes, you just need to redirect a port on Linux. The solution I could find is to add an entry into xinetd. Here is a sample /etc/xinetd.d file I have, it just redirects the 587 (tcp) port to the 993 port of gmail’s servers. I have to do this because Virgin Mobile France blocks the 993 tcp port.
If you’re in the same situation, you can use my server to access you gmail IMAP access. You just have to set the server name to “webingenia.com” and the port to “587″.

1
2
3
4
5
6
7
8
9
10
11
12
13
service submission
{
        disable = no
        flags = REUSE
        port = 587
        socket_type = stream
        protocol = tcp
        user = root
        redirect = 74.125.45.109 993
        #server = /usr/bin/nc
        #serer_args = 74.125.45.109 993
        wait = no
}

Mono Tools for Visual Studio

I talked about this earlier.

The mono tools for Visual Studio is a commercial product that easily enables you to test and port your Windows applications to mono.

As I told before this is really a great idea. Because I think Visual Studio is the best IDE and Linux is the best server OS (in my opinion, it’s more efficient and more robust than Windows Server). So, I think it’s the perfect gateway between this two very different (but very close since Mono appeared) environments to achieve greatness.

And if you don’t want to buy it, well, you don’t have to. Mono is free and you can very easily test your Windows programs on it. You just have to install mono, copy your exe (plus its required DLLs) to the Linux host and type something like “mono SampleProgram.exe”.

JObexFTP from Ricardo Schmidt

Ricardo Schmidt made a great multi-platform TC65 control and file management tool called JOBextFTP. This can be used for anyone whose Module Exchange Suite (MES) doesn’t work or doesn’t work correctly.

The biggest effort is put on managing the OBEX file transmission protocol, but it also does offer some simple methods that can be integrated in your development process, like “turnOn”, “turnOff”, “getTime”, “runApp”.

I’m really sorry but I didn’t take the time to test it as I’m currently not making some TC65 development. But it looks very operational to me.

Maybe I should start a list of useful TC65 applications. I can already see this one to help you deploy programs and files locally and my SMSOTAP to help you deploy programs remotely.

Here is the email Ricardo Schmidt sent me :
I modified and formated some parts of the original mail.

Hello Florent,

With Ondrej ObexTool sources, that I met through your blog, I made up a new tool (think OO). So I made a library to help developers make multiplatform easy communication with TC65 and simmilar modules.
I’m already using it in a desktop configuration program for my M2M application and it just works great.
It have some TODOs and maybe some bugs, but it have a nice object oriented programming. Also I abused of the exceptions, becouse this project is not just an application, but also a library. You can use it to develop your configurator programs, its very easy to do with it.
The code is fully in english, but in future I pretend make it multilanguage. For now it just garantees that TC65 is going to work with it, but I belive TC65i and XT75 should work as TC65, since it under the same AT “platform”.

Some nice features in the library :

  • Auto turns on/off the module
  • If for some previous crash it stayed in DATAMODE, it sends the +++
    until it get the COMMANDMODE again.
  • You can choose for seeing verbose messages and for seeing the AT
    communication.
  • You can send a String as a file to the module.
  • You recieve a file as a String from module (since writing a file is easy).
  • Working in windows platf (under test)

Some nice features in the application :

  • Argument configurable on/off module, verbose and show atcomand.
  • Download, upload and list files just in one connection (no limit) ex.: jobexftp /dev/ttyACM0 -u arq1.ext arq2.ext arq3.ext arq4.ext -l -d filetodown.ext -V -A
  • Option to just stdout the file. (sometimes we just need to see the
    contents)

TODOs:

  • Documentation (kinda important)
  • Auto run jars (in library is ready, just for app)
  • Choose folder to send the file (easy task)
  • MacOSX adaption (maybe its already working, I dont have any macs to test)
  • Multilanguage

The listing comes in the XML from library, I think that this should be treated just in the applications, since the xml is very good for programming analyse.

Hope you like it.

You can get the latest sources from project kenai : http://www.kenai.com/projects/jobexftp

Kenai is NetBeans integrated, and it uses subversion. This project is opensource under GPL (application) and under LGPL (library).

Thank you for the attention,
Ricardo Schmidt

Yum Transaction Check Error on x64 CentOS

If you encounter a “Transaction Check Error” on yum on a x64 system during an install, an update or an upgrade, you will find out that most of the time, you can’t remove the problematic packages. But it’s very likely that the problem comes from a i386 version of a package. The easiest way to proceed is just to remove the i386 version of each software or library as it appears on the Transaction Check Error.

I had a problem with postgresql-libs (i386) which was required by subversion (i386). I removed the postgresql-libs (and I had to remove subversion), but both of them were also in a x86_64 version, so it didn’t change anything. They were just garbage packages.

Posted in English. Tags: , , . No Comments »

PHP 5.2 on CentOS

PHP 5.2 brings lots of little useful features and CentOS 5.3 comes with PHP 5.1. So most of my PHP apps failed. The easiest way to solve this is to :

  • Edit /etc/yum.repos.d/CentOS-Testing.repo and put this :
    1
    2
    3
    4
    5
    6
    
    [c5-testing]
    name=CentOS-5 Testing
    baseurl=http://dev.centos.org/centos/5/testing/$basearch/
    enabled=1
    gpgcheck=1
    gpgkey=http://dev.centos.org/centos/RPM-GPG-KEY-CentOS-testing
  • Launch :
    1
    
    yum update php

Source :
http://www.freshblurbs.com/install-php-5-2-centos-5-2-using-yum

Posted in English. Tags: , , . No Comments »

get start-stop-daemon on any Linux distribution

I switched from Debian to CentOS because I had the choice between an old 32 bits Debian 4.0 or a brand new 64 bits CentOS 5.3. And I have some scripts that use the great “start-stop-daemon” tool, which isn’t available on CentOS.

The easiest way to solve this problem is to get dpkg from Debian and then try to compile it. It’s likely that it will fail because libselinux (and it’s subsidiary library libsepol) won’t be registered in the pkgconfig dir. But we don’t really care as we only need start-stop-daemon, not dpkg.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
# wget http://ftp.de.debian.org/debian/pool/main/d/dpkg/dpkg_1.14.25.tar.gz
# tar -xf dpkg_1.14.25.tar.gz
# cd dpkg-1.14.25/
# ./configure >/dev/null
configure: WARNING: x86_64 not found in cputable
configure: WARNING: linux-gnu not found in ostable
Package libselinux was not found in the pkg-config search path.
Perhaps you should add the directory containing `libselinux.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libselinux' found
configure: WARNING: no curses library found
# make >/dev/null
processarc.o: In function `process_archive':
/root/dpkg-1.14.25/src/processarc.c:166: warning: the use of `tmpnam' is dangerous, better use `mkstemp'
archives.o: In function `tarobject':
/root/dpkg-1.14.25/src/archives.c:634: undefined reference to `matchpathcon'
/root/dpkg-1.14.25/src/archives.c:640: undefined reference to `setfscreatecon'
/root/dpkg-1.14.25/src/archives.c:802: undefined reference to `setfscreatecon'
/root/dpkg-1.14.25/src/archives.c:804: undefined reference to `freecon'
/root/dpkg-1.14.25/src/archives.c:826: undefined reference to `setfscreatecon'
/root/dpkg-1.14.25/src/archives.c:618: undefined reference to `is_selinux_enabled'
collect2: ld returned 1 exit status
make[2]: *** [dpkg] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
# cd utils
# make install
gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I.. -DLOCALEDIR=\"/usr/local/share/locale\" -idirafter ../libcompat -I../lib    -g -O2 -MT start-stop-daemon.o -MD -MP -MF .deps/start-stop-daemon.Tpo -c -o start-stop-daemon.o start-stop-daemon.c
mv -f .deps/start-stop-daemon.Tpo .deps/start-stop-daemon.Po
gcc -std=gnu99  -g -O2  -Wl,-O1 -o start-stop-daemon start-stop-daemon.o ../libcompat/libcompat.a
make[1]: Entering directory `/root/dpkg-1.14.25/utils'
test -z "/usr/local/sbin" || /bin/mkdir -p "/usr/local/sbin"
  /usr/bin/install -c 'start-stop-daemon' '/usr/local/sbin/start-stop-daemon'
make[1]: Nothing to be done for `install-data-am'.
make[1]: Leaving directory `/root/dpkg-1.14.25/utils'

And you should have it !

Server moved

I’ve switched from my two three years old dedicated servers to one brand new virtual server. Reasons are : These servers costed me too much and they were becoming old (risk of failure increases). It wasn’t worth it.

I spent last night doing that because I didn’t want to interrupt anybody using these servers.

My two servers were running some Debian and I’m now switching to a CentOS virtual server. I was a little bit worried at first that CentOS would have a crappy package management system, but its yum is in fact working the same way as Debian’s apt-get and OpenSuse’s zypper. The oool thing is that these three package management systems roughly work the same way : install , you don’t have to learn a new “ultimate” way to upgrade your software (like on FreeBSD). By the way, the faster package management system is yum, and the slowest one is zypper.

The biggest problem I had so far was to move all the databases. Previously, I was always using some Debian hosts, I was using exactly the same version of MySQL, so I just had to copy the MySQL datadir and logs files. Here, I had to export/import everything.

CentOS has an antique 1.2.4 version of Mono (when the current version is 2.4). I couldn’t manage to compile from the tarball but compiling from the SVN worked fine.

1
2
3
4
5
6
7
8
9
]# /usr/local/bin/mono --version
Mono JIT compiler version 2.5 (/trunk/mono r140917 Sat Aug 29 05:29:19 CEST 2009)
Copyright (C) 2002-2008 Novell, Inc and Contributors. www.mono-project.com
        TLS:           __thread
        GC:            Included Boehm (with typed GC and Parallel Mark)
        SIGSEGV:       altstack
        Notifications: epoll
        Architecture:  amd64
        Disabled:      none