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  • mysqld refusing connections from localhost

    - by Dennis Rardin
    My mail server (Ubuntu 10.04) uses mysql for virtual domains, virtual users. For some reason, mysqld has started refusing connections from localhost. I see these in the mail server log: Oct 6 00:31:14 apollo postfix/trivial-rewrite[16888]: fatal: proxy:mysql:/etc/postfix/mysql-virtual_domains.cf(0,lock|fold_fix): table lookup problem and: Oct 7 13:39:15 apollo postfix/proxymap[25839]: warning: connect to mysql server 127.0.0.1: Lost connection to MySQL server at 'reading initial communication packet', system error: 0 I also get the following in auth.log: Oct 6 22:33:31 apollo mysqld[31775]: refused connect from 127.0.0.1 Telnet to the local port: root@apollo:/var/log/mysql# telnet localhost 3306 Trying ::1... Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. Connection closed by foreign host. root@apollo:/var/log/mysql# I am not sure why this started happening, but there was a disk failure in a RAID 1 pair a bit earlier that day. So it's possible I have a damaged config file or something. But mail was working for at least an hour after the drive event, so who knows for sure? phpmyadmin works fine, and the databases themselves look like they're intact. I think/believe that selinux and iptables are disabled and not running. So ... why is mysqld refusing connections from localhost? What should I check? What processes might cause this if a .conf file or possibly a binary was damaged? Which other log files might contain clues? I've enabled "general logging" in /etc/mysql/my.cnf, but I get no interesting or informative entries there. Thanks, m00tpoint

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  • Why Wireshark does not recognize this HTTP response?

    - by Alois Mahdal
    I have a trivial CGI script that outputs simple text content. It's written in Perl and using CGI module and it specifies only the most basic headers: print $q->header( -type => 'text/plain', -Content_length => $length, ); print $stuff; There's no apparent issue with functionality, but I'm confused about the fact that Wireshark does not recognize the HTTP response as HTTP--it's marked as TCP. Here is request and response: GET /cgi-bin/memfile/memfile.pl?mbytes=1 HTTP/1.1 Host: 10.6.130.38 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20100101 Firefox/11.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: cs,en-us;q=0.7,en;q=0.3 Accept-Encoding: gzip, deflate Connection: keep-alive HTTP/1.1 200 OK Date: Thu, 05 Apr 2012 18:52:23 GMT Server: Apache/2.2.15 (Win32) mod_ssl/2.2.15 OpenSSL/0.9.8m Content-length: 1048616 Keep-Alive: timeout=5, max=100 Connection: Keep-Alive Content-Type: text/plain; charset=ISO-8859-1 XXXXXXXX... And here is the packet overview (Full packet is here on pastebin) No. Time Source srcp Destination dstp Protocol Info tcp.stream abstime 5 0.112749 10.6.130.38 80 10.6.130.53 48072 TCP [TCP segment of a reassembled PDU] 0 20:52:23.228063 Frame 5: 1514 bytes on wire (12112 bits), 1514 bytes captured (12112 bits) Ethernet II, Src: Dell_97:29:ac (00:1e:4f:97:29:ac), Dst: Dell_3b:fe:70 (00:24:e8:3b:fe:70) Internet Protocol Version 4, Src: 10.6.130.38 (10.6.130.38), Dst: 10.6.130.53 (10.6.130.53) Transmission Control Protocol, Src Port: http (80), Dst Port: 48072 (48072), Seq: 1, Ack: 330, Len: 1460 Now when I see this in Wireshark: there's usual TCP handshake then the GET request shown as HTTP with preview then the next packet contains the response, but is not marked as an HTTP response--just a generic "[TCP segment of a reassembled PDU]", and is not caught by "http.response" filter. Can somebody explain why Wireshark does not recognize it? Is there something wrong with the response?

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  • Quickly set up a Windows Server and automatically install and configure software

    - by Chris
    Yesterday I spent far too much time downloading and installing software on Windows Server 2008. I only had to install a simple server for SQL Server 2008 Express using Microsoft's Web Platform Installer, then configure it to enable remote connections. Everything had to be attended, wasting my time. On a Linux system, this would be trivial to automate, but this is Windows. I do this very rarely, but in the future I would like to make this take as little time as possible. I could do a disc image with everything I installed and configured, but is there a better way? I know nothing of advanced deployment techniques on Windows. Ideally I would like to be able to remotely re-install the OS, or have an unattended install (which I know is possible). Any tips to make the software I need easier to and install and configure with minimal interaction necessary would be helpful. I don't expect everything I asked for to be possible and easy to do. Basically, If any part of it can be done quicker or at least without user input, that's what I'm looking for.

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  • KeePass lost password and/or corruption due to Dropbox/KeePassX

    - by GummiV
    I started using Keepass about a month ago to hold my passwords and online accounts info. Everything was stored in a single .kdb file, only protected with a password. I'm using Windows 7. Now Keepass can't open my .kdb file with the error "Invalid/wrong key". I'm fairly confident I have the right password. Altough I might have mixed up a few letters I've tried about two dozen different combinations to minimize that possibility - but can't rule it out though. My guess is however that the .kdb file got corrupted, either due to Dropbox syncing (only using it on one computer though) or because I edited the file using KeePassX on Ubuntu (dual boot on the same computer, accessing a mounted Win7 NTFS partition), or possibly a combination of both. I have tried restoring older versions(even the original one) from Dropbox and trying out all possible passwords without any luck. (which does seem to rule out KeePassX as the culprit, since oldest copies are before I edited the file from Ubuntu) I have tried opening the file with the "Repair KeePass Database file" which always gives the "0xA Invalid/corrupt file structure" (the same error for when a wrong password is typed). I was wondering if there was any way for me to salvage my hard-gathered data. I know generally that brute force cracking is not feasible, but since I can remember probably more than half of the usernames/passwords, any maybe the fact that one of them does come up fairly often (my go-to pass for trivial stuff), that might simplify the brute force process to a doable time frame. Maybe the brute-force thing might incorporate the fact that I know the password length and what characters it's made from. (If we assume corruption, not a password-blackout on my part) I could do some programming if there are any libraries or routines that I could use. Other people seem to have had a similar probem http://forums.dropbox.com/topic.php?id=6199 http://forums.dropbox.com/topic.php?id=9139 http://www.keepassx.org/forum/viewtopic.php?t=1967&f=1 So hopefully this question will become a suitible resource for people when searching the web. Feel free to tell me if you think this should rather be a community wiki.

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  • Howto enable SMPTS (465) postfix CentOS

    - by user197284
    I need help is enabling SMTPS. I use postfix , dovecot with MySQL(virtual domains). I do not know how to enable SMTPS(465). I already added tls related settings and key and certificate in the "/etc/postfix/main.cf" OS: Centos 6.4 64 bit Please my /etc/postfix/master.cf file here # ========================================================================== # service type private unpriv chroot wakeup maxproc command + args # (yes) (yes) (yes) (never) (100) # ========================================================================== smtp inet n - n - - smtpd -o content_filter=smtp-amavis:127.0.0.1:10024 -o receive_override_options=no_address_mappings pickup fifo n - n 60 1 pickup -o content_filter= -o receive_override_options=no_header_body_checks cleanup unix n - n - 0 cleanup qmgr fifo n - n 300 1 qmgr #qmgr fifo n - n 300 1 oqmgr tlsmgr unix - - n 1000? 1 tlsmgr rewrite unix - - n - - trivial-rewrite bounce unix - - n - 0 bounce defer unix - - n - 0 bounce trace unix - - n - 0 bounce verify unix - - n - 1 verify flush unix n - n 1000? 0 flush proxymap unix - - n - - proxymap smtp unix - - n - - smtp # When relaying mail as backup MX, disable fallback_relay to avoid MX loops relay unix - - n - - smtp -o fallback_relay= # -o smtp_helo_timeout=5 -o smtp_connect_timeout=5 showq unix n - n - - showq error unix - - n - - error discard unix - - n - - discard local unix - n n - - local virtual unix - n n - - virtual lmtp unix - - n - - lmtp anvil unix - - n - 1 anvil scache unix - - n - 1 scache # # ==================================================================== # Interfaces to non-Postfix software. Be sure to examine the manual # pages of the non-Postfix software to find out what options it wants. # ==================================================================== maildrop unix - n n - - pipe flags=DRhu user=vmail argv=/usr/local/bin/maildrop -d ${recipient} uucp unix - n n - - pipe flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient) ifmail unix - n n - - pipe flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient) bsmtp unix - n n - - pipe flags=Fq. user=foo argv=/usr/local/sbin/bsmtp -f $sender $nexthop $recipient # # spam/virus section # smtp-amavis unix - - y - 2 smtp -o smtp_data_done_timeout=1200 -o disable_dns_lookups=yes -o smtp_send_xforward_command=yes 127.0.0.1:10025 inet n - y - - smtpd -o content_filter= -o smtpd_helo_restrictions= -o smtpd_sender_restrictions= -o smtpd_recipient_restrictions=permit_mynetworks,reject -o mynetworks=127.0.0.0/8 -o smtpd_error_sleep_time=0 -o smtpd_soft_error_limit=1001 -o smtpd_hard_error_limit=1000 -o receive_override_options=no_header_body_checks -o smtpd_bind_address=127.0.0.1 -o smtpd_helo_required=no -o smtpd_client_restrictions= -o smtpd_restriction_classes= -o disable_vrfy_command=no -o strict_rfc821_envelopes=yes # # Dovecot LDA dovecot unix - n n - - pipe flags=DRhu user=vmail:mail argv=/usr/libexec/dovecot/deliver -d ${recipient} # # Vacation mail vacation unix - n n - - pipe flags=Rq user=vacation argv=/var/spool/vacation/vacation.pl -f ${sender} -- ${recipient} retry unix - - n - - error proxywrite unix - - n - 1 proxymap Please help to enable SMTPS. I have amavis enabled

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  • Wifi antenna extension with F-connector/RG-6(RG-59) cable?

    - by rjz2000
    In an older house, the wire mesh in walls surrounding the furnace behave like a Faraday cage and block wifi signals. It is also difficult to lay new cable, however there is television cable to multiple locations due to there once having been a roof-installed, television antenna. It would be relatively trivial to install the wifi router at the center distribution point, then have the antenna broadcasting/receiving the signal plugged in at each of the old television outlets. I assume that it would not be too difficult to find an adapter for SMA <- F-type connectors. The cable is actually RG-59 rather than RG-6, but I assume that it still has relatively good RF isolation along its length, which is no more than a couple hundred feet in any direction. Does anyone know a problem with the idea? Will a router get confused if there is /too little/ interference between the two antenna? Is that length of cable (~100ft) too long for the signal a router broadcasts? I have seen that it is also possible to use old ~$30/each FiOS cable modems available on eBay to extend a network over television cable. However, that seems like a less elegant solution, and might interfere with upnp and dlna services I'd like to have work on a single network. Thanks if anyone has answers or suggestions before I try this project!

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  • Wifi antenna extension with F-connector/RG-6(RG-59) cable?

    - by rjz2000
    In an older house, the wire mesh in walls surrounding the furnace behave like a Faraday cage and block wifi signals. It is also difficult to lay new cable, however there is television cable to multiple locations due to there once having been a roof-installed, television antenna. It would be relatively trivial to install the wifi router at the center distribution point, then have the antenna broadcasting/receiving the signal plugged in at each of the old television outlets. I assume that it would not be too difficult to find an adapter for SMA <- F-type connectors. The cable is actually RG-59 rather than RG-6, but I assume that it still has relatively good RF isolation along its length, which is no more than a couple hundred feet in any direction. Does anyone know a problem with the idea? Will a router get confused if there is /too little/ interference between the two antenna? Is that length of cable (~100ft) too long for the signal a router broadcasts? I have seen that it is also possible to use old ~$30/each FiOS cable modems available on eBay to extend a network over television cable. However, that seems like a less elegant solution, and might interfere with upnp and dlna services I'd like to have work on a single network. Thanks if anyone has answers or suggestions before I try this project!

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  • Is it possible for the Subversion Apache module to serve html files with an html content-type without using the svn:mime-type property?

    - by Martin Pain
    I am aware that if you set the svn:mime-type Subversion property on a .html file to text/html then when viewing the file in a browser through the Subversion module in Apache httpd it will be served with a Content-Type: text/html header, enabling the browser to render it as HTML rather than plain text. However, I am looking for a way to do this without using the svn:mime-type property. I'm aware that you can configure your svn client to automatically add the property - this is not what I want, as I do not want to ensure all users have these settings. I'm also aware that I could create a pre-commit hook that rejects the commit if the properties are not set, in order to force users to set the property - I might fall back to that, but I'm looking for something less intrusive. I'm also aware that I could use a post-commit hook to add the properties automatically on the server-side. I'd rather not do that (as users then have to update immediately after their commit, and it's not trivial to write) - I'm looking for a better alternative. Perhaps something with rewrite rules in the Apache server?

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  • Can My Personal GMail Query A Remote LDAP Server?

    - by Maarx
    I have a personal GMail account, from which I frequently send e-mail to a great many various users of a specific business. The corporation has been kind enough to provide me with the credentials to access their LDAP server, with which I would like my GMail web client to be able to auto-complete partial addresses or names for which that LDAP server has an entry. Is there any way I can get a personal GMail account (or it's corresponding entire Google account) account to incorporate an LDAP server into it's Contacts? If I cannot get it to query dynamically and on-demand, is there an idiot-proof way (assuming the client permits, which they may not) to query the LDAP server for it's entire database, save it, and bulk import it to GMail? Perhaps, even, something I could set to repeat periodically (weekly, perhaps), without human interaction? If I did the latter, I assume it would be trivial to import all of these contacts under a single category that could be easily manipulated from within the GMail web-based client. I have been a staunch user and supporter of the GMail web-based client since it's instantiation, but this one is kind of a deal-breaker for me. If it's impossible, what do you suggest I do?

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  • Users getting 'flooded' with not read notifications (NRNs) for old emails and meeting requests

    - by Exile
    I'm being placed under quite a lot of pressure from senior management over a relatively trivial issue. Basically the vast majority of users are complaining that they receive not read notifications (NRNs) for old emails and meeting requests in large numbers multiple times a day. I know something strange is happening because some are delivered at silly times in the morning (i.e 3AM or 4AM). The problem I have is that these some of these NRNs are from meeting requests and messages that are 120 days old, so some users have deleted the original message so I don’t actually know if the NRN is from an email or meeting request. This is typical of what users receive as a NRN: From: Sender Sent: 23 March 2012 04:16 To: Recepient Subject: Not read: Accepted: Status update Your message To: Sender Subject: Accepted: Status update Sent: Wednesday, November 23, 2011 8:59:00 AM (UTC) Dublin, Edinburgh, Lisbon, London was deleted without being read on Friday, March 23, 2012 4:15:32 AM (UTC) Dublin, Edinburgh, Lisbon, London. ... From: Sender Sent: 18 March 2012 01:13 To: Recepient Subject: Not read: Gold delivery - Sourcing module Your message To: Sender Subject: Gold delivery - Sourcing module Sent: Friday, November 18, 2011 9:37:58 AM (UTC) Dublin, Edinburgh, Lisbon, London was deleted without being read on Sunday, March 18, 2012 1:12:37 AM (UTC) Dublin, Edinburgh, Lisbon, London. I have done a search and found the following: http://support.microsoft.com/kb/2544246 http://support.microsoft.com/kb/2471964 But we already installed 'Update Rollup 6 for Exchange Server 2010 Service Pack 1' back in December, so I am not sure what we can do to fix this?

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  • Attempting to emulate Apache MultiViews with Nginx try_files

    - by Samuel Bierwagen
    I want a request to http://example.com/foobar to return http://example.com/foobar.jpg. (Or .gif, .html, .whatever) This is trivial to do with Apache MultiViews, and it seems like it would be equally easy in Nginx. This question seems to imply that it'd be easy as try_files $uri $uri/ index.php; in the location block, but that doesn't work. try_files $uri $uri/ =404; doesn't work, nor does try_files $uri =404; or try_files $uri.* =404; Moving it between my location / { block and the regexp which matches images has no effect. Crucially, try_files $uri.jpg =404; does work, but only for .jpg files, and it throws a configuration error if I use more than one try_files rule in a location block! The current server { block: server { listen 80; server_name example.org www.example.org; access_log /var/log/nginx/vhosts.access.log; root /srv/www/vhosts/example; location / { root /srv/www/vhosts/example; } location ~* \.(?:ico|css|js|gif|jpe?g|es|png)$ { expires max; add_header Cache-Control public; try_files $uri =404; } } Nginx version is 1.1.14.

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  • ldap-authentication without sambaSamAccount on linux smb/cifs server (e.g. samba)

    - by umlaeute
    i'm currently running samba-3.5.6 on a debian/wheezy host to act as the fileserver for our department's w32-clients. authentication is done via OpenLDAP, where each user-dn has an objectclass:sambaSamAccount that holds the smb-credentials and an objectclass:shadowAccount/posixAccount for "ordinary" authentication (e.g. pam, apache,...) now we would like to dump our department's user-db, and instead use authenticate against the user-db of our upstream-organisation. these user-accounts are managed in a novell-edirectory, which i can already use to authenticate using pam (e.g. for ssh-logins; on another host). our upstream organisation provides smb/cifs based access (via some novell service) to some directories, which i can access from my linux client via smbclient. what i currently don't manage to do is to use the upstream-ldap (the eDirectory) to authenticate our institution's samba: i configured my samba-server to auth against the upstream ldap server: passdb backend = ldapsam:ldaps://ldap.example.com but when i try to authenticate a user, i get: $ smbclient -U USER \\\\SMBSERVER\\test Enter USER's password: Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.6.6] tree connect failed: NT_STATUS_ACCESS_DENIED the logfiles show: [2012/10/02 09:53:47.692987, 0] passdb/secrets.c:350(fetch_ldap_pw) fetch_ldap_pw: neither ldap secret retrieved! [2012/10/02 09:53:47.693131, 0] lib/smbldap.c:1180(smbldap_connect_system) ldap_connect_system: Failed to retrieve password from secrets.tdb i see two problems i'm having: i don't have any administrator password for the upstream ldap (and most likely, they won't give me one). i only want to authenticate my users, write-access is not needed at all. can i go away with that? the upstream ldap does not have any samba-related attributes in the db. i was under the impression, that for samba to authenticate, those attributes are required, as smb/cifs uses some trivial hashing which is not compatible with the usual posixAccount hashes. is there a way for my department's samba server to authenticate against such an ldap server?

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  • Is there a local yubnub.org replacement?

    - by Justin Keogh
    I use yubnub very often... every google search I do by just (in firefox) "ctrl-t" - (now in the url bar) "y g searchterms" [Enter] "y" in this case is a search keyword I added by right clicking in the yubnub.org command box it's really fast, and I just do it automatically now... but the problem is now I am stuck with whatever the yubnub command that I am so used to using does. I cant change it... for example, what if I dont want to use google... but I still want to use the "g" command to search? or say I want to use google's https search... ect... I suppose this would be kinda trivial to implement locally... but I would hate to re-invent the code if it's allready done and in use... ideas? Also a local yubnub.org replacement would save me the DNS lookup and traffic to yubnub.org. I dont expect to be able to import all commands from yubnub.org but that would be cool if possible.

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  • Can't install Hyper-V in Windows 8 Pro. Causes boot loop, pain & suffering

    - by Nick
    Hardware: Intel i7 2600K (not overclocked, SLAT compatible, virt. features enabled in bios) Asus Maximus IV Extreme-Z (Z68) 16Gb RAM 256Gb SSD Other non-trivial working parts Adding Hyper-V is causing a boot loop resulting in an attempt at automatic repair by Windows 8 after the second or third loop: I'm trying to get the Windows Phone 8 SDK installed and I've narrowed down my troubles to the Hyper-V feature in Win8. This is required to run the WP8 emulator and there are no install options to omit this feature. My first attempt completely borked the OS as I did not have a recent restore point or system image, so I did a completely clean install and made plenty of backups/restore points. I skipped the SDK install and went straight for the windows feature add-on for Hyper-V. This confirmed that Hyper-V is the issue as the same behavior resulted. I cannot find any hint in the Event Logs. Cancelling automatic recovery causes the same behavior to repeat. I don't have any other VM products installed. My only recourse is to use a restore point, try something else, install it again, and see what happens. No luck so far. I'm on my 10th attempt here. Any help would be much appreciated.

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  • Is there a way to do a sector level copy/clone from one hard drive to another?

    - by irrational John
    Without going into distracting details, I'm attempting to duplicate the contents of the 500GB drive in my MacBook to another 500GB drive. But this is turning out to be an unexpected hassle because the drive contains both the OS X partition and an NTFS partition with Win 7 via Apple's Boot Camp. With the exception of Clonezilla, the tools I have looked at so far all have some limitation. The Mac tools don't want to deal with the NTFS partition. The Windows tools are totally clueless about either the HFS+ partition and/or the hybrid MBR/GPT Boot Camp partitioning. Clonezilla looked like it would do what I want but apparently I can't figure out how to use it. After doing what I thought was a sector to sector copy I found that only the NTFS partition had been migrated. The others were apparently empty. (And frankly, I'm not positive Clonezilla migrated the partition table correctly either). Note: It takes over 2 hours using SATA to read/write all sectors with these drives. So I'm not up for using trial & error to narrow in on the right combination of Clonezilla options to use. I'm beginning to think that maybe the answer is to boot Linux (probably Ubuntu) and then use some ancient BSD command. Trouble is I don't know what command (or parameters to use) in order to do a sector level copy from one drive to another. As far as I know the drives have the same number of sectors so this should be trivial. Sigh.

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  • Free blog sites where the blogs can (if the template does) validate as XHTML Strict 1.0?

    - by Deleted
    I'm looking for a site where I may register a free blog and have the blog validate as XHTML Strict 1.0. On the surface this may seem like a trivial problem only related to the theme/template in use, but that's unfortunately not the case. One example of a provider which can't fullfill this requirement is Blogger. Altough the pages of the blogs there presents themselfs as XHTML 1.0 Strict it is impossible to actually comply with the requirements inheritied by that markup type in the blog (as the XHTML which is generated by Blogger makes the page as a whole invalid). I've sent a mail to Tumblr to see if it was possible with them, but so far my reply consists of them having forwarded my mail with a "suggestion" to the development department. I don't know if we had a communication error or if I'm actually going to receive a proper answer later. Time will tell. I haven't had time to investigate Tumblr myself, so they may very well be the solution to this problem. To sum things up, I'm looking for any provider: Of a free blog. The blog must have the capability to validate as XHTML Strict 1.0. With capability I mean that the system shouldn't get in the way of creating/using a theme which complies as XHTML Strict 1.0. Preferably is large or at least likely to stay around for a couple of years to come. But I'm willing to take my chances if none of the established providers are up to the task. Thank you for reading! I hope you know of any provider which would be suitable, preferably with proof by linking to a blog there which validates. I'm not looking for suggestions to look into, as there are far to many to investigate and far too little time. If you know of something for sure, I'd be very happy to know about it.

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  • What needs to be considered when setting up for Linux Development? [closed]

    - by user123586
    I want to set up a box for Linux development. I have a working linux install with the usual toolchain and an IDE. I'm looking for advice on how to approach structuring accounts and folders for development. As the Perl folks say "There's always more than one way to do it." Left to my own devices, I'll come up with several unproductive ways of doing it before figuring out what an experienced Linux programmer would think obvious. I'm not looking for instructions to follow for a specific set of tools or a specific software package. Instead, I'm looking for insight into what decisions need to be made and how to make them, with understanding of the advantages and disadvantages of each individual choice. These are some of the questions that come up: Where to put sources Where to put built object files and libraries where to install what to set in environment variables what compiler flags matter and how do you manage them across several types of builds what configuration entries to make in an IDE how to manage libraries to support multiple environments how to handle different build versions such as debug vs release, or cross platform builds If you are an experienced Linux developer, the answers to these questions may seem trivial and obvious. I'd like to learn to make decisions about these questions that result in as little manual configuration as possible, given some existing sources, a particular IDE, or no IDE at all, a paticular set of development libraries etc. At this point you're probably thinking: Can you be more specific? Sure. But remember that I'm trying to learn how to think about this stuff, not just follow a recipie for a specific set of results. Example: Setup a project that uses CMake for some of its components, autogen.sh followed by configure for others and just configure for a few more: debug builds without an IDE debug builds in NetBeans debug builds in Eclipse debug build in Visual Studio all of the above with release builds for Linux, Mac and Windows. So... **What are your thoughts on an approach that works for all four? Do you have any advice on what to read?**

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  • Wifi antenna extension with F-connector/RG-6(RG-59) cable?

    - by rjz2000
    In an older house, the wire mesh in walls surrounding the furnace behave like a Faraday cage and block wifi signals. It is also difficult to lay new cable, however there is television cable to multiple locations due to there once having been a roof-installed, television antenna. It would be relatively trivial to install the wifi router at the center distribution point, then have the antenna broadcasting/receiving the signal plugged in at each of the old television outlets. I assume that it would not be too difficult to find an adapter for SMA <- F-type connectors. The cable is actually RG-59 rather than RG-6, but I assume that it still has relatively good RF isolation along its length, which is no more than a couple hundred feet in any direction. Does anyone know a problem with the idea? Will a router get confused if there is /too little/ interference between the two antenna? Is that length of cable (~100ft) too long for the signal a router broadcasts? I have seen that it is also possible to use old ~$30/each FiOS cable modems available on eBay to extend a network over television cable. However, that seems like a less elegant solution, and might interfere with upnp and dlna services I'd like to have work on a single network. Thanks if anyone has answers or suggestions before I try this project!

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  • Searching SharePoint site with Windows Explorer

    - by alexsome
    Every week, I manually backup recent versions of the files on my group's SharePoint site. I open the library in Windows Explorer, search for all files modified in the past week, then copy and paste them to a network location. We need this process because our SharePoint site has a quota that we would easily meet if we had unlimited versions, so we keep a history of older versions on the network. Recently I got an upgrade to my work computer and I am unable to search the site using Windows Explorer. When I run the search for files modified in the last week no results are returned. If I run a search with no criteria on the file library, all the files are found but the "modified on" field is blank. So the search results only have the file and type fields. The new computer has Windows XP, just like the old one did. I hope this makes sense. Does anyone have any clue what the problem could be? I'd be happy to provide more info if necessary. It's bugging me to no end and I'm not even sure where to begin looking - it's either a trivial issue or a very obscure one. Thanks a lot.

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  • Reverse NAT Setup for Hyper-V on Win 2008 R2

    - by sukru
    I'm trying to setup a Linux server behind a Windows Hyper-V host that will help supply some of the services (SSH, HTTPS, etc). However getting RRAS configured for reverse NAT (port forwarding) turned out to be a non trivial task. As a staring point, I tried forwarding port 22 (SSH) to the virtual machine. The virtual machine is on a public interface (i.e.: it also has a visible IP on the same network as the host). On RRAS management console I tried to add a rule, by adding "Local Area Connection" to NAT pool (Public Interface - Enable Nat), and an incoming rule for port 22 - :22. I also tried with the same port enabled on Windows Firewall (and not). The NAT management page tells there are "1 mappings" and "30+ Outbound packets transleted". However all other counters (Inbound packets translated, and respective rejected ones) are always zero. (I'm trying to access the server from an external machine). I can directly access the service if I give the VM's public IP, but not the host's one. Is there a way to enable this on RRAS?

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  • Install KVM based Windows 2008 remotely over SSH on a headless, no graphics Ubuntu 10.04 server?

    - by taazaa
    Hi, I have a Dell server at a remote data center with Ubuntu 10.04 as the host. It is a minimal install with the necessary virtulization packages. There is no X and the machine is headless. I have the win2008 DVD in the machine and want to remotely install it. I tried: virt-install --connect qemu:///system -n vmwin2k8 -r 1024 --disk path=server2k8.qcow2,size=50 --cdrom /dev/sr0 --vnc --noautoconsole --os-type windows --os-variant win2k8 The qcow2 image get created However I don't understand how to connect to see the install via VNC. This is my first time doing it so it may be trivial or may not be possible. Remotely I have a Win 7 machine with Putty and RealVNC viewer. Where is the graphic output of VNC going? Do I have to have VNC server running on the host or some other machine and then connect to it from my VNC client? Please let me know or point me to the right direction. I have been searching the web for several days to figure out how this is suppose to work. Thanks!

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  • How to securely control access to a backend key server?

    - by andy
    I need to securely encrypt data in my database so that if the database is dumped, hackers are unable to decrypt the data. I'm planning on creating a simple key server on a different machine, and allowing the DB server access to it (restricted by IP address on the key server to permit the DB server). The key server would contain the key required to encrypt/decrypt data. However, if a hacker were able to get a shell on the DB server, they could request the key from the key server and therefore decrypt the data in the database. How could I prevent this (assuming all firewalls are in place, DB is not connected directly to the internet, etc)? i.e. is there some method I could use that could secure a request from the DB server to the key server so that even if a hacker had a shell on the DB server they'd be unable to make those same requests? Signed requests from the DB server could make issuing these requests less trivial - I suppose that'd help increase the amount of time it'd take to compromise the key server, something a hacker probably wouldn't have much of. As far as I can see, if someone can get a shell on the DB server everything's lost anyway. This could be mitigated by using one key per data item in the DB so at least there's not a single "master" key, but multiple keys that the hacker would need to access. What would be a secure method of ensuring requests from the DB server to the key server were authentic and could be trusted?

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  • value types in the vm

    - by john.rose
    value types in the vm p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} p.p2 {margin: 0.0px 0.0px 14.0px 0.0px; font: 14.0px Times} p.p3 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times} p.p4 {margin: 0.0px 0.0px 15.0px 0.0px; font: 14.0px Times} p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier} p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier; min-height: 17.0px} p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p8 {margin: 0.0px 0.0px 0.0px 36.0px; text-indent: -36.0px; font: 14.0px Times; min-height: 18.0px} p.p9 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p10 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; color: #000000} li.li1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} li.li7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} span.s1 {font: 14.0px Courier} span.s2 {color: #000000} span.s3 {font: 14.0px Courier; color: #000000} ol.ol1 {list-style-type: decimal} Or, enduring values for a changing world. Introduction A value type is a data type which, generally speaking, is designed for being passed by value in and out of methods, and stored by value in data structures. The only value types which the Java language directly supports are the eight primitive types. Java indirectly and approximately supports value types, if they are implemented in terms of classes. For example, both Integer and String may be viewed as value types, especially if their usage is restricted to avoid operations appropriate to Object. In this note, we propose a definition of value types in terms of a design pattern for Java classes, accompanied by a set of usage restrictions. We also sketch the relation of such value types to tuple types (which are a JVM-level notion), and point out JVM optimizations that can apply to value types. This note is a thought experiment to extend the JVM’s performance model in support of value types. The demonstration has two phases.  Initially the extension can simply use design patterns, within the current bytecode architecture, and in today’s Java language. But if the performance model is to be realized in practice, it will probably require new JVM bytecode features, changes to the Java language, or both.  We will look at a few possibilities for these new features. An Axiom of Value In the context of the JVM, a value type is a data type equipped with construction, assignment, and equality operations, and a set of typed components, such that, whenever two variables of the value type produce equal corresponding values for their components, the values of the two variables cannot be distinguished by any JVM operation. Here are some corollaries: A value type is immutable, since otherwise a copy could be constructed and the original could be modified in one of its components, allowing the copies to be distinguished. Changing the component of a value type requires construction of a new value. The equals and hashCode operations are strictly component-wise. If a value type is represented by a JVM reference, that reference cannot be successfully synchronized on, and cannot be usefully compared for reference equality. A value type can be viewed in terms of what it doesn’t do. We can say that a value type omits all value-unsafe operations, which could violate the constraints on value types.  These operations, which are ordinarily allowed for Java object types, are pointer equality comparison (the acmp instruction), synchronization (the monitor instructions), all the wait and notify methods of class Object, and non-trivial finalize methods. The clone method is also value-unsafe, although for value types it could be treated as the identity function. Finally, and most importantly, any side effect on an object (however visible) also counts as an value-unsafe operation. A value type may have methods, but such methods must not change the components of the value. It is reasonable and useful to define methods like toString, equals, and hashCode on value types, and also methods which are specifically valuable to users of the value type. Representations of Value Value types have two natural representations in the JVM, unboxed and boxed. An unboxed value consists of the components, as simple variables. For example, the complex number x=(1+2i), in rectangular coordinate form, may be represented in unboxed form by the following pair of variables: /*Complex x = Complex.valueOf(1.0, 2.0):*/ double x_re = 1.0, x_im = 2.0; These variables might be locals, parameters, or fields. Their association as components of a single value is not defined to the JVM. Here is a sample computation which computes the norm of the difference between two complex numbers: double distance(/*Complex x:*/ double x_re, double x_im,         /*Complex y:*/ double y_re, double y_im) {     /*Complex z = x.minus(y):*/     double z_re = x_re - y_re, z_im = x_im - y_im;     /*return z.abs():*/     return Math.sqrt(z_re*z_re + z_im*z_im); } A boxed representation groups component values under a single object reference. The reference is to a ‘wrapper class’ that carries the component values in its fields. (A primitive type can naturally be equated with a trivial value type with just one component of that type. In that view, the wrapper class Integer can serve as a boxed representation of value type int.) The unboxed representation of complex numbers is practical for many uses, but it fails to cover several major use cases: return values, array elements, and generic APIs. The two components of a complex number cannot be directly returned from a Java function, since Java does not support multiple return values. The same story applies to array elements: Java has no ’array of structs’ feature. (Double-length arrays are a possible workaround for complex numbers, but not for value types with heterogeneous components.) By generic APIs I mean both those which use generic types, like Arrays.asList and those which have special case support for primitive types, like String.valueOf and PrintStream.println. Those APIs do not support unboxed values, and offer some problems to boxed values. Any ’real’ JVM type should have a story for returns, arrays, and API interoperability. The basic problem here is that value types fall between primitive types and object types. Value types are clearly more complex than primitive types, and object types are slightly too complicated. Objects are a little bit dangerous to use as value carriers, since object references can be compared for pointer equality, and can be synchronized on. Also, as many Java programmers have observed, there is often a performance cost to using wrapper objects, even on modern JVMs. Even so, wrapper classes are a good starting point for talking about value types. If there were a set of structural rules and restrictions which would prevent value-unsafe operations on value types, wrapper classes would provide a good notation for defining value types. This note attempts to define such rules and restrictions. Let’s Start Coding Now it is time to look at some real code. Here is a definition, written in Java, of a complex number value type. @ValueSafe public final class Complex implements java.io.Serializable {     // immutable component structure:     public final double re, im;     private Complex(double re, double im) {         this.re = re; this.im = im;     }     // interoperability methods:     public String toString() { return "Complex("+re+","+im+")"; }     public List<Double> asList() { return Arrays.asList(re, im); }     public boolean equals(Complex c) {         return re == c.re && im == c.im;     }     public boolean equals(@ValueSafe Object x) {         return x instanceof Complex && equals((Complex) x);     }     public int hashCode() {         return 31*Double.valueOf(re).hashCode()                 + Double.valueOf(im).hashCode();     }     // factory methods:     public static Complex valueOf(double re, double im) {         return new Complex(re, im);     }     public Complex changeRe(double re2) { return valueOf(re2, im); }     public Complex changeIm(double im2) { return valueOf(re, im2); }     public static Complex cast(@ValueSafe Object x) {         return x == null ? ZERO : (Complex) x;     }     // utility methods and constants:     public Complex plus(Complex c)  { return new Complex(re+c.re, im+c.im); }     public Complex minus(Complex c) { return new Complex(re-c.re, im-c.im); }     public double abs() { return Math.sqrt(re*re + im*im); }     public static final Complex PI = valueOf(Math.PI, 0.0);     public static final Complex ZERO = valueOf(0.0, 0.0); } This is not a minimal definition, because it includes some utility methods and other optional parts.  The essential elements are as follows: The class is marked as a value type with an annotation. The class is final, because it does not make sense to create subclasses of value types. The fields of the class are all non-private and final.  (I.e., the type is immutable and structurally transparent.) From the supertype Object, all public non-final methods are overridden. The constructor is private. Beyond these bare essentials, we can observe the following features in this example, which are likely to be typical of all value types: One or more factory methods are responsible for value creation, including a component-wise valueOf method. There are utility methods for complex arithmetic and instance creation, such as plus and changeIm. There are static utility constants, such as PI. The type is serializable, using the default mechanisms. There are methods for converting to and from dynamically typed references, such as asList and cast. The Rules In order to use value types properly, the programmer must avoid value-unsafe operations.  A helpful Java compiler should issue errors (or at least warnings) for code which provably applies value-unsafe operations, and should issue warnings for code which might be correct but does not provably avoid value-unsafe operations.  No such compilers exist today, but to simplify our account here, we will pretend that they do exist. A value-safe type is any class, interface, or type parameter marked with the @ValueSafe annotation, or any subtype of a value-safe type.  If a value-safe class is marked final, it is in fact a value type.  All other value-safe classes must be abstract.  The non-static fields of a value class must be non-public and final, and all its constructors must be private. Under the above rules, a standard interface could be helpful to define value types like Complex.  Here is an example: @ValueSafe public interface ValueType extends java.io.Serializable {     // All methods listed here must get redefined.     // Definitions must be value-safe, which means     // they may depend on component values only.     List<? extends Object> asList();     int hashCode();     boolean equals(@ValueSafe Object c);     String toString(); } //@ValueSafe inherited from supertype: public final class Complex implements ValueType { … The main advantage of such a conventional interface is that (unlike an annotation) it is reified in the runtime type system.  It could appear as an element type or parameter bound, for facilities which are designed to work on value types only.  More broadly, it might assist the JVM to perform dynamic enforcement of the rules for value types. Besides types, the annotation @ValueSafe can mark fields, parameters, local variables, and methods.  (This is redundant when the type is also value-safe, but may be useful when the type is Object or another supertype of a value type.)  Working forward from these annotations, an expression E is defined as value-safe if it satisfies one or more of the following: The type of E is a value-safe type. E names a field, parameter, or local variable whose declaration is marked @ValueSafe. E is a call to a method whose declaration is marked @ValueSafe. E is an assignment to a value-safe variable, field reference, or array reference. E is a cast to a value-safe type from a value-safe expression. E is a conditional expression E0 ? E1 : E2, and both E1 and E2 are value-safe. Assignments to value-safe expressions and initializations of value-safe names must take their values from value-safe expressions. A value-safe expression may not be the subject of a value-unsafe operation.  In particular, it cannot be synchronized on, nor can it be compared with the “==” operator, not even with a null or with another value-safe type. In a program where all of these rules are followed, no value-type value will be subject to a value-unsafe operation.  Thus, the prime axiom of value types will be satisfied, that no two value type will be distinguishable as long as their component values are equal. More Code To illustrate these rules, here are some usage examples for Complex: Complex pi = Complex.valueOf(Math.PI, 0); Complex zero = pi.changeRe(0);  //zero = pi; zero.re = 0; ValueType vtype = pi; @SuppressWarnings("value-unsafe")   Object obj = pi; @ValueSafe Object obj2 = pi; obj2 = new Object();  // ok List<Complex> clist = new ArrayList<Complex>(); clist.add(pi);  // (ok assuming List.add param is @ValueSafe) List<ValueType> vlist = new ArrayList<ValueType>(); vlist.add(pi);  // (ok) List<Object> olist = new ArrayList<Object>(); olist.add(pi);  // warning: "value-unsafe" boolean z = pi.equals(zero); boolean z1 = (pi == zero);  // error: reference comparison on value type boolean z2 = (pi == null);  // error: reference comparison on value type boolean z3 = (pi == obj2);  // error: reference comparison on value type synchronized (pi) { }  // error: synch of value, unpredictable result synchronized (obj2) { }  // unpredictable result Complex qq = pi; qq = null;  // possible NPE; warning: “null-unsafe" qq = (Complex) obj;  // warning: “null-unsafe" qq = Complex.cast(obj);  // OK @SuppressWarnings("null-unsafe")   Complex empty = null;  // possible NPE qq = empty;  // possible NPE (null pollution) The Payoffs It follows from this that either the JVM or the java compiler can replace boxed value-type values with unboxed ones, without affecting normal computations.  Fields and variables of value types can be split into their unboxed components.  Non-static methods on value types can be transformed into static methods which take the components as value parameters. Some common questions arise around this point in any discussion of value types. Why burden the programmer with all these extra rules?  Why not detect programs automagically and perform unboxing transparently?  The answer is that it is easy to break the rules accidently unless they are agreed to by the programmer and enforced.  Automatic unboxing optimizations are tantalizing but (so far) unreachable ideal.  In the current state of the art, it is possible exhibit benchmarks in which automatic unboxing provides the desired effects, but it is not possible to provide a JVM with a performance model that assures the programmer when unboxing will occur.  This is why I’m writing this note, to enlist help from, and provide assurances to, the programmer.  Basically, I’m shooting for a good set of user-supplied “pragmas” to frame the desired optimization. Again, the important thing is that the unboxing must be done reliably, or else programmers will have no reason to work with the extra complexity of the value-safety rules.  There must be a reasonably stable performance model, wherein using a value type has approximately the same performance characteristics as writing the unboxed components as separate Java variables. There are some rough corners to the present scheme.  Since Java fields and array elements are initialized to null, value-type computations which incorporate uninitialized variables can produce null pointer exceptions.  One workaround for this is to require such variables to be null-tested, and the result replaced with a suitable all-zero value of the value type.  That is what the “cast” method does above. Generically typed APIs like List<T> will continue to manipulate boxed values always, at least until we figure out how to do reification of generic type instances.  Use of such APIs will elicit warnings until their type parameters (and/or relevant members) are annotated or typed as value-safe.  Retrofitting List<T> is likely to expose flaws in the present scheme, which we will need to engineer around.  Here are a couple of first approaches: public interface java.util.List<@ValueSafe T> extends Collection<T> { … public interface java.util.List<T extends Object|ValueType> extends Collection<T> { … (The second approach would require disjunctive types, in which value-safety is “contagious” from the constituent types.) With more transformations, the return value types of methods can also be unboxed.  This may require significant bytecode-level transformations, and would work best in the presence of a bytecode representation for multiple value groups, which I have proposed elsewhere under the title “Tuples in the VM”. But for starters, the JVM can apply this transformation under the covers, to internally compiled methods.  This would give a way to express multiple return values and structured return values, which is a significant pain-point for Java programmers, especially those who work with low-level structure types favored by modern vector and graphics processors.  The lack of multiple return values has a strong distorting effect on many Java APIs. Even if the JVM fails to unbox a value, there is still potential benefit to the value type.  Clustered computing systems something have copy operations (serialization or something similar) which apply implicitly to command operands.  When copying JVM objects, it is extremely helpful to know when an object’s identity is important or not.  If an object reference is a copied operand, the system may have to create a proxy handle which points back to the original object, so that side effects are visible.  Proxies must be managed carefully, and this can be expensive.  On the other hand, value types are exactly those types which a JVM can “copy and forget” with no downside. Array types are crucial to bulk data interfaces.  (As data sizes and rates increase, bulk data becomes more important than scalar data, so arrays are definitely accompanying us into the future of computing.)  Value types are very helpful for adding structure to bulk data, so a successful value type mechanism will make it easier for us to express richer forms of bulk data. Unboxing arrays (i.e., arrays containing unboxed values) will provide better cache and memory density, and more direct data movement within clustered or heterogeneous computing systems.  They require the deepest transformations, relative to today’s JVM.  There is an impedance mismatch between value-type arrays and Java’s covariant array typing, so compromises will need to be struck with existing Java semantics.  It is probably worth the effort, since arrays of unboxed value types are inherently more memory-efficient than standard Java arrays, which rely on dependent pointer chains. It may be sufficient to extend the “value-safe” concept to array declarations, and allow low-level transformations to change value-safe array declarations from the standard boxed form into an unboxed tuple-based form.  Such value-safe arrays would not be convertible to Object[] arrays.  Certain connection points, such as Arrays.copyOf and System.arraycopy might need additional input/output combinations, to allow smooth conversion between arrays with boxed and unboxed elements. Alternatively, the correct solution may have to wait until we have enough reification of generic types, and enough operator overloading, to enable an overhaul of Java arrays. Implicit Method Definitions The example of class Complex above may be unattractively complex.  I believe most or all of the elements of the example class are required by the logic of value types. If this is true, a programmer who writes a value type will have to write lots of error-prone boilerplate code.  On the other hand, I think nearly all of the code (except for the domain-specific parts like plus and minus) can be implicitly generated. Java has a rule for implicitly defining a class’s constructor, if no it defines no constructors explicitly.  Likewise, there are rules for providing default access modifiers for interface members.  Because of the highly regular structure of value types, it might be reasonable to perform similar implicit transformations on value types.  Here’s an example of a “highly implicit” definition of a complex number type: public class Complex implements ValueType {  // implicitly final     public double re, im;  // implicitly public final     //implicit methods are defined elementwise from te fields:     //  toString, asList, equals(2), hashCode, valueOf, cast     //optionally, explicit methods (plus, abs, etc.) would go here } In other words, with the right defaults, a simple value type definition can be a one-liner.  The observant reader will have noticed the similarities (and suitable differences) between the explicit methods above and the corresponding methods for List<T>. Another way to abbreviate such a class would be to make an annotation the primary trigger of the functionality, and to add the interface(s) implicitly: public @ValueType class Complex { … // implicitly final, implements ValueType (But to me it seems better to communicate the “magic” via an interface, even if it is rooted in an annotation.) Implicitly Defined Value Types So far we have been working with nominal value types, which is to say that the sequence of typed components is associated with a name and additional methods that convey the intention of the programmer.  A simple ordered pair of floating point numbers can be variously interpreted as (to name a few possibilities) a rectangular or polar complex number or Cartesian point.  The name and the methods convey the intended meaning. But what if we need a truly simple ordered pair of floating point numbers, without any further conceptual baggage?  Perhaps we are writing a method (like “divideAndRemainder”) which naturally returns a pair of numbers instead of a single number.  Wrapping the pair of numbers in a nominal type (like “QuotientAndRemainder”) makes as little sense as wrapping a single return value in a nominal type (like “Quotient”).  What we need here are structural value types commonly known as tuples. For the present discussion, let us assign a conventional, JVM-friendly name to tuples, roughly as follows: public class java.lang.tuple.$DD extends java.lang.tuple.Tuple {      double $1, $2; } Here the component names are fixed and all the required methods are defined implicitly.  The supertype is an abstract class which has suitable shared declarations.  The name itself mentions a JVM-style method parameter descriptor, which may be “cracked” to determine the number and types of the component fields. The odd thing about such a tuple type (and structural types in general) is it must be instantiated lazily, in response to linkage requests from one or more classes that need it.  The JVM and/or its class loaders must be prepared to spin a tuple type on demand, given a simple name reference, $xyz, where the xyz is cracked into a series of component types.  (Specifics of naming and name mangling need some tasteful engineering.) Tuples also seem to demand, even more than nominal types, some support from the language.  (This is probably because notations for non-nominal types work best as combinations of punctuation and type names, rather than named constructors like Function3 or Tuple2.)  At a minimum, languages with tuples usually (I think) have some sort of simple bracket notation for creating tuples, and a corresponding pattern-matching syntax (or “destructuring bind”) for taking tuples apart, at least when they are parameter lists.  Designing such a syntax is no simple thing, because it ought to play well with nominal value types, and also with pre-existing Java features, such as method parameter lists, implicit conversions, generic types, and reflection.  That is a task for another day. Other Use Cases Besides complex numbers and simple tuples there are many use cases for value types.  Many tuple-like types have natural value-type representations. These include rational numbers, point locations and pixel colors, and various kinds of dates and addresses. Other types have a variable-length ‘tail’ of internal values. The most common example of this is String, which is (mathematically) a sequence of UTF-16 character values. Similarly, bit vectors, multiple-precision numbers, and polynomials are composed of sequences of values. Such types include, in their representation, a reference to a variable-sized data structure (often an array) which (somehow) represents the sequence of values. The value type may also include ’header’ information. Variable-sized values often have a length distribution which favors short lengths. In that case, the design of the value type can make the first few values in the sequence be direct ’header’ fields of the value type. In the common case where the header is enough to represent the whole value, the tail can be a shared null value, or even just a null reference. Note that the tail need not be an immutable object, as long as the header type encapsulates it well enough. This is the case with String, where the tail is a mutable (but never mutated) character array. Field types and their order must be a globally visible part of the API.  The structure of the value type must be transparent enough to have a globally consistent unboxed representation, so that all callers and callees agree about the type and order of components  that appear as parameters, return types, and array elements.  This is a trade-off between efficiency and encapsulation, which is forced on us when we remove an indirection enjoyed by boxed representations.  A JVM-only transformation would not care about such visibility, but a bytecode transformation would need to take care that (say) the components of complex numbers would not get swapped after a redefinition of Complex and a partial recompile.  Perhaps constant pool references to value types need to declare the field order as assumed by each API user. This brings up the delicate status of private fields in a value type.  It must always be possible to load, store, and copy value types as coordinated groups, and the JVM performs those movements by moving individual scalar values between locals and stack.  If a component field is not public, what is to prevent hostile code from plucking it out of the tuple using a rogue aload or astore instruction?  Nothing but the verifier, so we may need to give it more smarts, so that it treats value types as inseparable groups of stack slots or locals (something like long or double). My initial thought was to make the fields always public, which would make the security problem moot.  But public is not always the right answer; consider the case of String, where the underlying mutable character array must be encapsulated to prevent security holes.  I believe we can win back both sides of the tradeoff, by training the verifier never to split up the components in an unboxed value.  Just as the verifier encapsulates the two halves of a 64-bit primitive, it can encapsulate the the header and body of an unboxed String, so that no code other than that of class String itself can take apart the values. Similar to String, we could build an efficient multi-precision decimal type along these lines: public final class DecimalValue extends ValueType {     protected final long header;     protected private final BigInteger digits;     public DecimalValue valueOf(int value, int scale) {         assert(scale >= 0);         return new DecimalValue(((long)value << 32) + scale, null);     }     public DecimalValue valueOf(long value, int scale) {         if (value == (int) value)             return valueOf((int)value, scale);         return new DecimalValue(-scale, new BigInteger(value));     } } Values of this type would be passed between methods as two machine words. Small values (those with a significand which fits into 32 bits) would be represented without any heap data at all, unless the DecimalValue itself were boxed. (Note the tension between encapsulation and unboxing in this case.  It would be better if the header and digits fields were private, but depending on where the unboxing information must “leak”, it is probably safer to make a public revelation of the internal structure.) Note that, although an array of Complex can be faked with a double-length array of double, there is no easy way to fake an array of unboxed DecimalValues.  (Either an array of boxed values or a transposed pair of homogeneous arrays would be reasonable fallbacks, in a current JVM.)  Getting the full benefit of unboxing and arrays will require some new JVM magic. Although the JVM emphasizes portability, system dependent code will benefit from using machine-level types larger than 64 bits.  For example, the back end of a linear algebra package might benefit from value types like Float4 which map to stock vector types.  This is probably only worthwhile if the unboxing arrays can be packed with such values. More Daydreams A more finely-divided design for dynamic enforcement of value safety could feature separate marker interfaces for each invariant.  An empty marker interface Unsynchronizable could cause suitable exceptions for monitor instructions on objects in marked classes.  More radically, a Interchangeable marker interface could cause JVM primitives that are sensitive to object identity to raise exceptions; the strangest result would be that the acmp instruction would have to be specified as raising an exception. @ValueSafe public interface ValueType extends java.io.Serializable,         Unsynchronizable, Interchangeable { … public class Complex implements ValueType {     // inherits Serializable, Unsynchronizable, Interchangeable, @ValueSafe     … It seems possible that Integer and the other wrapper types could be retro-fitted as value-safe types.  This is a major change, since wrapper objects would be unsynchronizable and their references interchangeable.  It is likely that code which violates value-safety for wrapper types exists but is uncommon.  It is less plausible to retro-fit String, since the prominent operation String.intern is often used with value-unsafe code. We should also reconsider the distinction between boxed and unboxed values in code.  The design presented above obscures that distinction.  As another thought experiment, we could imagine making a first class distinction in the type system between boxed and unboxed representations.  Since only primitive types are named with a lower-case initial letter, we could define that the capitalized version of a value type name always refers to the boxed representation, while the initial lower-case variant always refers to boxed.  For example: complex pi = complex.valueOf(Math.PI, 0); Complex boxPi = pi;  // convert to boxed myList.add(boxPi); complex z = myList.get(0);  // unbox Such a convention could perhaps absorb the current difference between int and Integer, double and Double. It might also allow the programmer to express a helpful distinction among array types. As said above, array types are crucial to bulk data interfaces, but are limited in the JVM.  Extending arrays beyond the present limitations is worth thinking about; for example, the Maxine JVM implementation has a hybrid object/array type.  Something like this which can also accommodate value type components seems worthwhile.  On the other hand, does it make sense for value types to contain short arrays?  And why should random-access arrays be the end of our design process, when bulk data is often sequentially accessed, and it might make sense to have heterogeneous streams of data as the natural “jumbo” data structure.  These considerations must wait for another day and another note. More Work It seems to me that a good sequence for introducing such value types would be as follows: Add the value-safety restrictions to an experimental version of javac. Code some sample applications with value types, including Complex and DecimalValue. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. A staggered roll-out like this would decouple language changes from bytecode changes, which is always a convenient thing. A similar investigation should be applied (concurrently) to array types.  In this case, it seems to me that the starting point is in the JVM: Add an experimental unboxing array data structure to a production JVM, perhaps along the lines of Maxine hybrids.  No bytecode or language support is required at first; everything can be done with encapsulated unsafe operations and/or method handles. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. That’s enough musing me for now.  Back to work!

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  • SharpDX: best practice for multiple RenderForms?

    - by Rob Jellinghaus
    I have an XNA app, but I really need to add multiple render windows, which XNA doesn't do. I'm looking at SharpDX (both for multi-window support and for DX11 / Metro / many other reasons). I decided to hack up the SharpDX DX11 MultiCubeTexture sample to see if I could make it work. My changes are pretty trivial. The original sample had: [STAThread] private static void Main() { var form = new RenderForm("SharpDX - MiniCubeTexture Direct3D11 Sample"); ... I changed this to: struct RenderFormWithActions { internal readonly RenderForm Form; // should just be Action but it's not in System namespace?! internal readonly Action RenderAction; internal readonly Action DisposeAction; internal RenderFormWithActions(RenderForm form, Action renderAction, Action disposeAction) { Form = form; RenderAction = renderAction; DisposeAction = disposeAction; } } [STAThread] private static void Main() { // hackity hack new Thread(new ThreadStart(() = { RenderFormWithActions form1 = CreateRenderForm(); RenderLoop.Run(form1.Form, () = form1.RenderAction(0)); form1.DisposeAction(0); })).Start(); new Thread(new ThreadStart(() = { RenderFormWithActions form2 = CreateRenderForm(); RenderLoop.Run(form2.Form, () = form2.RenderAction(0)); form2.DisposeAction(0); })).Start(); } private static RenderFormWithActions CreateRenderForm() { var form = new RenderForm("SharpDX - MiniCubeTexture Direct3D11 Sample"); ... Basically, I split out all the Main() code into a separate method which creates a RenderForm and two delegates (a render delegate, and a dispose delegate), and bundles them all together into a struct. I call this method twice, each time from a separate, new thread. Then I just have one RenderLoop on each new thread. I was thinking this wouldn't work because of the [STAThread] declaration -- I thought I would need to create the RenderForm on the main (STA) thread, and run only a single RenderLoop on that thread. Fortunately, it seems I was wrong. This works quite well -- if you drag one of the forms around, it stops rendering while being dragged, but starts again when you drop it; and the other form keeps chugging away. My questions are pretty basic: Is this a reasonable approach, or is there some lurking threading issue that might make trouble? My code simply duplicates all the setup code -- it makes a duplicate SwapChain, Device, Texture2D, vertex buffer, everything. I don't have a problem with this level of duplication -- my app is not intensive enough to suffer resource issues -- but nonetheless, is there a better practice? Is there any good reference for which DirectX structures can safely be shared, and which can't? It appears that RenderLoop.Run calls the render delegate in a tight loop. Is there any standard way to limit the frame rate of RenderLoop.Run, if you don't want a 400FPS app eating 100% of your CPU? Should I just Thread.Sleep(30) in the render delegate? (I asked on the sharpdx.org forums as well, but Alexandre is on vacation for two weeks, and my sister wants me to do a performance with my app at her wedding in three and a half weeks, so I'm mighty incented here! http://robjsoftware.org for details of what I'm building....)

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  • PowerShell Control over Nikon D3000 Camera

    My wife got me a Nikon D3000 camera for Christmas last year, and Im loving it but still trying to wrap my head around some of its features.  For instance, when you plug it into a computer via USB, it doesnt show up as a drive like most cameras Ive used to, but rather it shows up as Computer\D3000.  After a bit of research, Ive learned that this is because it implements the MTP/PTP protocol, and thus doesnt actually let Windows mount the cameras storage as a drive letter.  Nikon describes the use of the MTP and PTP protocols in their cameras here. What Im really trying to do is gain access to the cameras file system via PowerShell.  Ive been using a very handy PowerShell script to pull pictures off of my cameras and organize them into folders by date.  Id love to be able to do the same thing with my Nikon D3000, but so far I havent been able to figure out how to get access to the files in PowerShell.  If you know, Id appreciate any links/tips you can provide.  All I could find is a shareware product called PTPdrive, which Im not prepared to shell out money for (yet).  (and yes you can do much the same thing with Windows 7s Import Pictures and Videos wizard, which is pretty good too) However, in my searching, I did find some really cool stuff you can do with PowerShell and one of these cameras, like actually taking pictures via PowerShell commands.  Credit for this goes to James ONeill and Mark Wilson.  Heres what I was able to do: Taking Pictures via PowerShell with D3000 First, connect your camera, turn it on, and launch PowerShell.  Execute the following commands to see what commands your device supports.  $dialog = New-Object -ComObject "WIA.CommonDialog" $device = $dialog.ShowSelectDevice() $device.Commands You should see something like this: Now, to take a picture, simply point your camera at something and then execute this command: $device.ExecuteCommand("{AF933CAC-ACAD-11D2-A093-00C04F72DC3C}") .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Imagine my surprise when this actually took a picture (with auto-focus): Imagine what you could do with a camera completely under the control of your computer  Time-lapse photography would be pretty simple, for instance, with a very simple loop that takes a picture and then sleeps for a minute (or whatever time period).  Hooked up to a laptop for portability (and an A/C power supply), this would be pretty trivial to implement.  I may have to give it a shot and report back. Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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