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• Switched to new router and now experiencing lag?

  - by Mr_CryptoPrime

  I switched from a dynex-802.11b/g to a Netgear-802.11b/g/n just yesterday. My router is down stairs because my phoneline upstairs is retarded....but my PS3 is still upstairs (SOCOM: Confrontation is game I am experiencing issues). I have done everything I can to make sure the connection is solid and have checked the status and it has been as high as 80% and usually lingers at about 60%. I thought about upgrading my bandwidth from 1.5mbs to 7mbs, but I am guessing something is wrong if it worked fine before? Now the game seems more laggy and my voice chat is choppy. Others seem to receive my voice data fine because I can hear my own feedback clearly from other players (if you are in close proximity to another player and speak and there volume is loud enough sometimes you can hear yourself). I wonder if I port forward or setup DMZ then it will be fixed, but I am not sure and don't know quite how to do it. Has anyone else ever experienced this when switching routers? What did you do to fix it? Thanks!

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• VLC Crash when playing MKV files in Windows 7

  - by Phelios

  I'm not sure if the mkv file is corrupted, but when it is opened with VLC player, VLC loads up and displays nothing. Can't even close VLC after that. And also, VLC is running with 50% of the CPU. I have to use End Process to kill it. How do I know if the file is corrupted? How do I solve this? info from mediainfo Format : Matroska File size : 69.4 MiB Duration : 21mn 48s Overall bit rate : 445 Kbps Encoded date : UTC 2009-11-20 18:33:49 Writing application : mkvmerge v2.9.7 ('Tenderness') built on Jul 1 2009 18:43:35 Writing library : libebml v0.7.7 + libmatroska v0.8.1 Video ID : 1 Format : AVC Format/Info : Advanced Video Codec Format profile : [email protected] Format settings, CABAC : Yes Format settings, ReFrames : 2 frames Format settings, GOP : N=1 Codec ID : V_MPEG4/ISO/AVC Duration : 21mn 48s Width : 640 pixels Height : 352 pixels Display aspect ratio : 16:9 Frame rate : 23.976 fps Color space : YUV Chroma subsampling : 4:2:0 Bit depth : 8 bits Scan type : Progressive Audio ID : 2 Format : AAC Format/Info : Advanced Audio Codec Format profile : HE-AAC / LC Codec ID : A_AAC Duration : 21mn 48s Channel(s) : 2 channels Channel positions : Front: L R Sampling rate : 48.0 KHz / 24.0 KHz Compression mode : Lossy

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• Find which files an apache process is writing to?

  - by Haluk

  We have this apache process which becomes io-bound time to time. Using atop, we can see it is a write operation. Using lsof -p <PID> we can see a list of files open by the httpd process. First we thought "log" files must be the problem. So we turned them off just to test. However write operations still continues. We will continue testing a few other things. For instance we use php session variables a lot. Maybe php session files are getting all the writing. But is there a way to quickly identify files which get written to by the httpd process? This way we can focus our efforts on those files. UPDATE: We used the strace command as suggested. Here are two lines from the output. write(23, "\27\0\0\0\3SET CHARACTER SET utf8", 27) = 27 write(23, "\17\0\0\0\3SET NAMES utf8", 19) = 19 We do not have a mysql process on this server. So is strace also showing what is being written to an ethernet port? UPDATE2: During high io load, the process which consumes most of the write resources gives the following output to strace -e trace=write -p <PID>: --- SIGCHLD (Child exited) @ 0 (0) --- write(9, "!", 1) = 1 write(19, "OPTIONS * HTTP/1.0\r\nUser-Agent: Apache (internal dummy connection)\r\n\r\n", 70) = 70 However I cannot figure out where these are being written to.

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• What are the typical methods used to scale up/out email storage servers?

  - by nareshov

  Hi, What I've tried: I have two email storage architectures. Old and new. Old: courier-imapds on several (18+) 1TB-storage servers. If one of them show signs of running out of disk space, we migrate a few email accounts to another server. the servers don't have replicas. no backups either. New: dovecot2 on a single huge server with 16TB (SATA) storage and a few SSDs we store fresh mails on the SSDs and run a doveadm purge to move mails older than a day to the SATA disks there is an identical server which has a max-15min-old rsync backup from the primary server higher-ups/management wanted to pack in as much storage as possible per server in order to minimise the cost of SSDs per server the rsync'ing is done because GlusterFS wasn't replicating well under that high small/random-IO. scaling out was expected to be done with provisioning another pair of such huge servers on facing disk-crunch issues like in the old architecture, manual moving of email accounts would be done. Concerns/doubts: I'm not convinced with the synchronously-replicated filesystem idea works well for heavy random/small-IO. GlusterFS isn't working for us yet, I'm not sure if there's another filesystem out there for this use case. The idea was to keep identical pairs and use DNS round-robin for email delivery and IMAP/POP3 access. And if one the servers went down for whatever reasons (planned/unplanned), we'd move the IP to the other server in the pair. In filesystems like Lustre, I get the advantage of a single namespace whereby I do not have to worry about manually migrating accounts around and updating MAILHOME paths and other metadata/data. Questions: What are the typical methods used to scale up/out with the traditional software (courier-imapd / dovecot)? Do traditional software that store on a locally mounted filesystem pose a roadblock to scale out with minimal "problems"? Does one have to re-write (parts of) these to work with an object-storage of some sort - such as OpenStack object storage?

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• MySQL Memory Limit Windows Server 2003

  - by Matt

  I am running MySQL 5.0.51a on Windows Server 2003 Standard Edition on an HP DL580 G4 with 3GB installed. One of my database tables has grown to 5.3 GB with an index file of 2.5 GB, which I believe is causing MySQL to be slow due to having to constantly load and unload the index file when updates are made to the table. The server itself seems to be performing OK because MySQL is only using about 500MB of memory (there are other apps running on the system, but MySQL uses the most memory). The table is fairly active with new records getting adding all during day but no deletes, ever. The MySQL server has up to 600 connections allowed, but only small number (10 or 20) would actually be writing to this table. I increased the memory limits in MySQL but since the max connections is so high I don't think I can give each connection 1GB without risking a problem. Is there some tuning that would let just certain connections get a lot of memory? So I have started to look for alternatives to avert the crisis I know is coming soon. Some of the options I have: Upgrade to Server 2003 Enterprise to install 64GB of memory. Question: would 32 bit MySQL be able to access more than 2GB? Would that be 2GB per thread? That would still be smaller than the index table size so it might not solve the problem completely, but it would be better than now. Upgrade to Server 200x 64 bit and MySQL 64 bit. Switch to a *nix 64 bit server. If anybody has suggestions for things to do in the meantime, opinions on which way to go, or other things that I have overlooked I would appreciate the help. Thanks

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• How can I prevent a DDOS attack on Amazon EC2?

  - by cwd

  One of the servers I use is hosted on the Amazon EC2 cloud. Every few months we appear to have a DDOS attack on this sever. This slows the server down incredibly. After around 30 minutes, and sometimes a reboot later, everything is back to normal. Amazon has security groups and firewall, but what else should I have in place on an EC2 server to mitigate or prevent an attack? From similar questions I've learned: Limit the rate of requests/minute (or seconds) from a particular IP address via something like IP tables (or maybe UFW?) Have enough resources to survive such an attack - or - Possibly build the web application so it is elastic / has an elastic load balancer and can quickly scale up to meet such a high demand) If using mySql, set up mySql connections so that they run sequentially so that slow queries won't bog down the system What else am I missing? I would love information about specific tools and configuration options (again, using Linux here), and/or anything that is specific to Amazon EC2. ps: Notes about monitoring for DDOS would also be welcomed - perhaps with nagios? ;)

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• How to set an executable white list?

  - by izabera

  Under Linux, is it possible to set a white-list of executables for a certain group of users? I need them to be unable to use, for example, make, gcc and executables on removable disks. How can this be done? Edit, let me explain better. I'm dealing with a high school IT system, young geeks that (during the lessons) want to play, surf the net, damage those computer however they can. The major step to achieve this goal was to remove the system they're familiar with and install Ubuntu in all the computers. This actually works quite well, but recent events proved that this is not enough. I want to allow them to execute certain safe programs, like Open Office, and to deny any other program, whether it is preinstalled software, something they carry in usb drives, a downloaded program or a script they program on site. It's possible to remove the 'x' permission on any file on the pc, but of course it would be impractical. Furthermore, they would be able to run anything they download. I thought the best solution would be to make a white-list of safe programs and to deny anything else, but I don't really know how to do it. Any idea is helpful.

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• I need to build a mini computer lab with 6 PCs

  - by chiurox

  Hello everyone, This weekend I need to build a mini computer lab with 5-6 PCs. The purpose is for a small computer class that will be taking place. They're mostly going to be doing office and daily kind of stuff, so nothing high performance. However, I hope it will last at least for 2 more years. I already have some parts for 2 PCs, one is a P4 3.0 and another is Celeron 2.4GHz, both socket 478. For the other 4 PCs, I'm wondering if I should buy individual parts and put it all together or get workstations like those Dell Optiplex with P4s. To put things into perspective, I am not currently in the US. I'm in South America and prices here are ridiculously. Another really important thing is that I need to share an internet connection between a total of 8 PCs at this place. Right now I only have a crappy wireless router, should I get another one? Or go with switch hub? I'm not experienced in this matter. Thanks guys!

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• Linux iptables / conntrack performance issue

  - by tim

  I have a test-setup in the lab with 4 machines: 2 old P4 machines (t1, t2) 1 Xeon 5420 DP 2.5 GHz 8 GB RAM (t3) Intel e1000 1 Xeon 5420 DP 2.5 GHz 8 GB RAM (t4) Intel e1000 to test linux firewall performance since we got bitten by a number of syn-flood attacks in the last months. All machines run Ubuntu 12.04 64bit. t1, t2, t3 are interconnected through an 1GB/s switch, t4 is connected to t3 via an extra interface. So t3 simulates the firewall, t4 is the target, t1,t2 play the attackers generating a packetstorm thorugh (192.168.4.199 is t4): hping3 -I eth1 --rand-source --syn --flood 192.168.4.199 -p 80 t4 drops all incoming packets to avoid confusion with gateways, performance issues of t4 etc. I watch the packet stats in iptraf. I have configured the firewall (t3) as follows: stock 3.2.0-31-generic #50-Ubuntu SMP kernel rhash_entries=33554432 as kernel parameter sysctl as follows: net.ipv4.ip_forward = 1 net.ipv4.route.gc_elasticity = 2 net.ipv4.route.gc_timeout = 1 net.ipv4.route.gc_interval = 5 net.ipv4.route.gc_min_interval_ms = 500 net.ipv4.route.gc_thresh = 2000000 net.ipv4.route.max_size = 20000000 (I have tweaked a lot to keep t3 running when t1+t2 are sending as many packets as possible). The result of this efforts are somewhat odd: t1+t2 manage to send each about 200k packets/s. t4 in the best case sees aroung 200k in total so half of the packets are lost. t3 is nearly unusable on console though packets are flowing through it (high numbers of soft-irqs) the route cache garbage collector is no way near to being predictable and in the default setting overwhelmed by very few packets/s (<50k packets/s) activating stateful iptables rules makes the packet rate arriving on t4 drop to around 100k packets/s, efectively losing more than 75% of the packets And this - here is my main concern - with two old P4 machines sending as many packets as they can - which means nearly everyone on the net should be capable of this. So here goes my question: Did I overlook some importand point in the config or in my test setup? Are there any alternatives for building firewall system especially on smp systems?

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• New to server admin, Diagnosing Memory and CPU issues on DV

  - by G Thompson

  Sorry for my ignorance and lack of knowledge. I'm a PHP/Front-end developer just now venturing into very minor server management/diagnostics. I have a Media Temple DV account. I have 2 sites that run a PHP script through a subscription service to an API. Basically API hits site with said script. Script runs, gathers data from api, saves data to SQL database. I noticed that these sites seemed to causing memory overages on my server (not sure why). So I temporarily disabled them. The memory overage alerts stopped but my CPU still sits really high, like at 115% and above. I'm trying to diagnos this with tutorials and resources but just can't seem to find a solution. I'll attach screenshots(screenshots are without the PHP scripts I assume are responsible for the memory issues) I'm assuming are important to the diagnosis, but if anyone can point me in the right direction to start A. figuring out if and why the PHP script may be causing memory overages and B. Why my CPU is always over 100%. Thanks guys! Links to screen shots... can't post with low points. http://i.stack.imgur.com/A64k4.png http://i.stack.imgur.com/qm1rV.png

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• 3dmark score abnormal

  - by Sean

  I just bought a new laptop. It is core i7 3610QM.(Ivy bridge, 4 core plus hyperthreading), 8G ram, nvidia GT 610M 2GB. The OS is Win7 64bit. I ran 3dmark 11, but the score is frustrating. For 1280*720, the score is P730. It is too low right? I searched online, the score should at least above 1000. Am I right? I never use this software before. I know nvidia has optimus, so I made the laptop in high performance state and white-listed the 3dmark program. But there is no help. I am guessing 3dmark is using i7's graphic module. It cannot transform to nvidia. In the running detail of 3dmark, the graphic card cannot be identified(The row remain blank). Can anybody tell me is this the normal case? If not, can I use some other software to test if my nvidia card is working fine? If this nvidia card cannot work, I will return the new laptop asap. Thanks.

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• Why does my ftp(e)s server fails like half of the time

  - by user1092608

  I have this discussion at work regarding our ftp server running via vsftpd. Initially, we have opted to serve ftpes instead of sftp because this seemed the most flexible and straightforward solution for our server to have secure file transmission. Afterwards, our ftp server seems to be a source of issues for our end users. Half of the time, users complain about not working ftp connections. I must say, i tested our FTP trough different infrastructures (=in the field, at random times at random places) and indeed, sometimes behind some configurations (=no idea how they are configured, because the 'field' testing), i recieve errors. Some of the are: Error: Failed to retrieve directory listing (filezilla) Furthermore, behind my basic home configuration, everything seems to be running fine. I (think I) did all the basic configuration checks (passive mode?, firewall for all ports?, ...) and can't seem to find the source. Being a bunch of techies at our small office, yet knowing nothing about infrastructure, some start suggesting that ftps protocol could be the source of issues. ("No, i only knew sftp so far" "Ftps is not widespread"). I, however, strongly doubt this hypothesis, since reading around on the www, asking questions on serverfault, everyone seems to deny this. So, as I would like to avoid reconfiguring, since this involves messing around in our SSH service, our virtual user setup and ftp service, i would need some advice on 1) what could be potentially the general cause? 2) do you have some general tips? 3) would you mind having a look at my configuration file? ----- General Settings ----- write_enable=YES dirmessage_enable=YES nopriv_user=ftpsecure ftpd_banner="Welcome to XXXX FTP!" hide_ids=YES hide_file=.* max_per_ip=10 max_clients=10 local_enable=YES local_umask=022 chroot_local_user=YES secure_chroot_dir=/usr/share/empty userlist_enable=NO userlist_deny=YES userlist_file=/etc/vsftp_deny_users guest_enable=YES guest_username=ftpvirtual virtual_use_local_privs=YES user_sub_token=$USER local_root=/srv/ftp/ftpvirtual/$USER anonymous_enable=NO syslog_enable=NO xferlog_enable=YES xferlog_file=/var/log/vsftpd_xfer.log connect_from_port_20=YES pam_service_name=vsftpd listen=YES listen_port=21 pasv_enable=YES pasv_min_port=30000 pasv_max_port=30030 pasv_address=foo ssl_enable=YES rsa_cert_file=/etc/vsftpd.pem rsa_private_key_file=/etc/vsftpd.pem force_local_data_ssl=YES force_local_logins_ssl=YES ssl_tlsv1=YES ssl_sslv2=YES ssl_sslv3=YES ssl_ciphers=HIGH anon_mkdir_write_enable=NO anon_root=/srv/ftp anon_upload_enable=NO idle_session_timeout=900 log_ftp_protocol=NO dsa_cert_file=/etc/vsftpd.pem Thanks

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• Sound doesn't work anymore after replacing RAM

  - by thejh

  Hello, today, I replaced one old RAM module with two newer, bigger ones, but now, the sound doesn't seem to work anymore. Already ran alsaconf and it didn't help. Output of lspci for the audio device: 00:07.0 Audio device: nVidia Corporation MCP67 High Definition Audio (rev a1) Subsystem: Giga-byte Technology Device a002 Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx- Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx- Latency: 0 (500ns min, 1250ns max) Interrupt: pin A routed to IRQ 21 Region 0: Memory at f5100000 (32-bit, non-prefetchable) [size=16K] Capabilities: [44] Power Management version 2 Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot+,D3cold+) Status: D0 PME-Enable- DSel=0 DScale=0 PME- Capabilities: [50] Message Signalled Interrupts: Mask+ 64bit+ Queue=0/0 Enable- Address: 0000000000000000 Data: 0000 Masking: 00000000 Pending: 00000000 Capabilities: [6c] HyperTransport: MSI Mapping Enable+ Fixed+ Kernel driver in use: HDA Intel Kernel modules: snd-hda-intel The audio device is onboard and has six configurable outputs, two or so are also capable of being an input (if I remember it correctly), but I don't know how to control it under linux. Does somebody know how/whether replacing the RAM could be related to my problem and/or how to fix it?

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• Relinking a deleted file

  - by mbac32768

  Sometimes people delete files they shouldn't, a long-running process still has the file open, and recovering the data by catting /proc/<pid>/fd/N just isn't awesome enough. Awesome enough would be if you could "undo" the delete by running some magic option to ln that would let you re-link to the inode number (recovered through lsof). I can't find any Linux tools to do this, least with cursory Googling. What do you got, serverfault? EDIT1: The reason catting the file from /proc/<pid>/fd/N isn't awesome enough is because the process which still has the file open is still writing to it. A delete removes the reference to the inode from the filesystem namespace. What I want is a way of re-creating the reference. EDIT2: 'debugfs ln' works but the risk is too high since it frobs raw filesystem data. The recovered file is also crazy inconsistent. The link count is zero and I can't add links to it. I'm worse off this way since I can just use /proc/<pid>/fd/N to access the data without corrupting my fs.

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• connections in FIN_WAIT and CLOSE_WAIT state

  - by Raj

  I would like to elaborate the setup so You guys can understand the question and answer more accurately. I have HAProxy as load-balancer, 4 webservers (apache 2.2.3) and one database server (MySQL 5). I am monitoring these servers by nagios. I have disabled the keepalive on apache as we have only 8GB of memory. Now what happens whenever I receive alerts for high memory and cpu utilization, I have observed that the connections from apache to database server hang in established mode (keepalive with timeout value of 7200) and at other side means connections between haproxy and apache shows status as FIN_WAIT on haproxy server and CLOSE_WAIT at apache side. I also see the huge memory swapping and apache taking the most of the memory. I did strace on apache process and did not find any information. strace gets attached to apache process but did not produce any output. The processlist on Mysql server show s those processes in sleep mode. The application on webserver is Magento a php application. if you need further information please let me know. Thanks.

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• Good Hosting Providers With Zend Framework Support [closed]

  - by manyxcxi

  I currently use ixwebhosting for my hosting services. They're cheap and work (most of the time). The databases are horribly slow, the servers are horribly slow, and their support (though usually prompt) is tough to deal with. That being said, they're cheap, I've got like 20 domains hosted in my account, none of them are high volume, and they work JUST good enough- until today. This isn't meant to be a condemnation of ixwh though. Their prices are very low for what they do offer and most things work just fine, most of the time. I need to be able to host web apps written with Zend Framework in a fairly easy fashion. The server performance can't be worse than what I've already had (a pretty low hurdle to clear), and I don't want to spend $30/mo. These are not money making websites- they're projects. My requirements are PHP 5.3, ZF support, MySQL databases, multiple domains- not much. Who should I look at, and who should I look out for?

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• SQL Server Replication Backup

  - by user18039

  Hi We have a new system that runs on SQL Server 2008 r2 64-bit. There is a primary on-line transactional processing (OLTP) database that accepts a high volume of updates from several thousand Point of Sale systems at stores around the country. In order to protect this vital function, I have decided to introduce a dedicated reporting database server - from which multiple users will run some pretty complex reports. I realise that there were a number of choices but I decided to use Transaction Replication as the mechanism for copying the data from the OLTP database to the new reporting database - one way replication. The solution has worked well in test. I'm now being asked what changes need to be made to the backup policy to cover the architectural changes. I have read pages such as MSDN:Strategies for Backing Up and Restoring Snapshot and Transactional Replication but I think these are overkill for my solution. In fact, my current thinking is that we simply need to continue making backups of the OLTP data and logs. If the Reporting db or any of the system replication (eg distribution) databases fail then it's no big deal - we can clear all down then re-create the replication. I realise that taking a complete snapshot of the OLTP would be time consuming (approx 5 hours) but I'd be more relaxed about this that trying to restore backups of the various data and log files in the correct sequence. My view is that the complex strategies set out in the MSDN article would only be the way to go for a more complex replication solution than I have, eg if there were multiple subscribers with 2-way replication. Would you agree? I'd be grateful for any advice. Many thanks, Rob.,

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• vSphere education - What are the downsides of configuring virtual machines with *too* much RAM?

  - by ewwhite

  VMware memory management seems to be a tricky balancing act. With cluster RAM, Resource Pools, VMware's management techniques (TPS, ballooning, host swapping), in-guest RAM utilization, swapping, reservations, shares and limits, there are a lot of variables. I'm in a situation where clients are using dedicated vSphere cluster resources. However, they are configuring the virtual machines as though they were on physical hardware. In turn, this means a standard VM build may have 4 vCPUs and 16GB or more of RAM. I come from the school of starting small (1 vCPU, minimal RAM), checking real-world use and adjusting up as necessary. Some examples from a "problem" cluster. Resource pool summary - Looks almost 4:1 overcommitted. Note the high amount of ballooned RAM. Resource allocation - The Worst Case Allocation column shows that these VMs would have access to less than 50% of their configured RAM under constrained conditions. The real-time memory utilization graph of the top VM in the listing above. 4 vCPU and 64GB RAM allocated. It averages under 9GB use. Summary of the same VM What are the downsides of overcommitting and overconfiguring resources (specifically RAM) in vSphere environments? Assuming that the VMs can run in less RAM, is it fair to say that there's overhead to configuring virtual machines with more RAM than they need? What is the counter-argument to: "if a VM has 16GB of RAM allocated, but only uses 4GB, what's the problem??"? E.g. do customers need to be educated? What specific metric should be used to meter RAM usage. Tracking the peaks of "Active" versus time?

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• Problem with Amiga 1200 accelerator board

  - by cc0

  I just recently walked past a dump, where in the corner of my eye I spotted something that looked like a huge keyboard. I went to take a closer look, and found out that it was an Amiga 1200 with a 030 accellerator board and scala dongle. Jackpot! So anyway; I dried it, cleaned it, it works, but the floppy was not powering on and same with the harddrive. I am using an old Amiga 1200 PSU that was making some strange high pitch noise when I tried to boot the amiga with the harddrive installed in it. I removed the harddrive and it booted fine with the PSU not emitting any detectable noise. However, when I have the 030 installed it sometimes reboots and shows a red "Software Error" screen. I tried removing the memory on the board, same effect. Sometimes it does not boot at all, just gives a black screen. Someone suggested the card had problems with 3.1 roms, but this amiga has only 3.0 roms installed. Does anyone have any apparent theories as to why it seems unstable? I don't have any other Amiga parts to cross-swap with to test a lot of things, so I'd really appreciate some sound input here so I'd know what to look for in order to try fix it. And merry Christmas everyone :]

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• Setting up a global MySQL Cluster in the cloud

  - by GregB

  I'm giving the question an overhaul to more specifically identify where I need help. I use two tools to manage a bunch of cloud server: Puppet and Rundeck. Both of these can be configured to use a mysql backend. I'd like to setup an instance of each application in both the U.S., and the U.K., treating the U.K. servers as hot stand-bys in case of failure in the U.S. I want to use a MySql cluster so that the data is automatically replicated from the U.S. to the U.K. Because these are hot standbys, high performance is not a goal. Redundancy and data integrity are most important. My question revolves around the setup of the mysql cluster. I want to run three servers, each one running a data node, a sql node, and a management node. Is this a valid configuration for mysql server? If so, could someone point me in the right direction for creating such a setup? I've downloaded the offical tarball, and the official debian, and the documentation for them contradicts many of the online tutorials. I'm installing on Ubuntu 10.04.

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• Scaling a node.js application, nginx as a base server, but varnish or redis for caching?

  - by AntelopeSalad

  I'm not close to being well versed in using nginx or varnish but this is my setup at the moment. I have a node.js server running which is serving either json, html templates, or socket.io events. Then I have nginx running in front of node which is serving all static content (css, js, etc.). At this point I would like to cache both static content and dynamic content to memory. It's to my understanding that varnish can cache static content quite well and it wouldn't require touching my application code. I also think it's capable of caching dynamic content too but there cannot be any cookie headers? I do use redis at the moment for holding session data and planned to use it for other things in the future like keeping track of non-crucial but fun stats. I just have no idea how I should handle caching everything on the site. I think it comes down to these options but there might be more: Throw varnish in front of nginx and let varnish cache static pages, no app code changes. Redis would cache dynamic db calls which would require modifying my app code. Ignore using varnish completely and let redis handle caching everything, then use one of the nginx-redis modules. I'm not sure if this would require a lot of app code changes (for the static files). I'm not having any luck finding benchmarks that compare nginx+varnish vs nginx+redis and I'm too inexperienced to bench it myself (high chances of my configs being awful). I'm basically looking for the solution that would be the most efficient in terms of req/sec and scalable in the future (throw new hardware at the problem + maybe adjust some values in a config = new servers up and running semi-painlessly).

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• How do I know if I managed to completely remove an undetected trojan?

  - by ubuntuisbetter

  I catched a trojan that uses explorer.exe to reproduce itself in case of deletion of its autostart entry or main exe file in Programs/x. It had already tried to contact a suspicious server over explorer.exe, blocked that via my firewall. I: Removed the autostart entries from the registry Looked through my services if there was anything suspicious Deleted the trojan from Programs/ Went through System Volume Information to find a 2 month old explorer.exe and replaced the possibly infected one. There are no suspicious processes running now anymore (no duplicate explorer.exe) and nothing wants to connect this trojan owners sever either. I checked my system with several anti-malware programs too. What the trojan did: Started a second explorer.exe Always when I deleted the main trojan exe file it was reproduced (by the second explorer.exe) Always when I deleted the autostart entry it was reproduced by the explorer.exe too. When I terminated the suspicious explorer.exe, which used only half as much memory as the less suspicious one from Windows, a strange thing that I know from the computers in my Informatics class happened: A window popped up in the top left of my explorer-less desktop, titled "Personal settings for ... are ..." that obviously copied some files. Then both explorer.exes started again and the trojan was everywhere again. What did the trojan actually do to get explorer to rescue it? Is my PC clean of this newish trojan now? What are the other locations I should check for the trojan? The trjoan doesn't seem very high-level, could it have changed other system files or is the autostart entry vital for it? Thanks in advance, Your trojan paranoid friend (Getting linux in a week)

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• pgpool2+streaming replication failover on only 2 servers?

  - by aneez

  I am trying to configure pgpool2 and postgresql 9.1 to handle failover. I currently have streaming replication running, and are using pgpool2 for read-only load balancing. I have 2 servers in my setup, both running postgresql - 1 master and 1 slave. The master is also running pgpool2. My question is how do I configure this setup to handle failover? Specifically in the case that the master crashes, and the slave has to take over and run pgpool2 as well. Most documentation and examples I have been able to find assumes that pgpool2 is running on a separate server and thus "never" crashes. I may or may not be attacking the problem using the wrong tools. In my production setup I have a total of 3 identical servers all in independent locations. The main goal of the setup is to achieve a high uptime. Thus failover should be automatic, and bringing a failed node back up should cause only minimal downtime. I want all 3 nodes to be as close to identical as possible, and be able to run with just 1 or 2 nodes available. And if possible I want to use load balancing to improve performance. If anyone can help me gain some insight into how to do this using my current setup or suggest a different/better setup. Thank you!

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• What is the typical maximum number of database connections for Oracle running on Windows server ?

  - by Sake

  We are maintaining a database server that serve a large number of clients. Each client typically running serveral client-applications. The total number of connections to the database server (Oracle 9i) is reaching 800 connections on peak load. The windows 2003 server is starting to run out of memory. We are now planning to move to 64bit Windows in order to gain higher memory capability. As a developer I suggest moving to multi-tier architecture with conneciton pooling, which I believe is a natural solution to this problem. However, in order to support my idea, I want the information on: what exactly is the typical number of connections allowed for Oracle database ? What is the problem when the number connections is too high ? Too much memory comsumption ? or too many sockets opened ? or too many context switching between threads ? To be a little bit specific, how could Oracle Forms application scale to thousand of users without facing this problem ? Shall Oracle RAC applied to this case ? I'm sure the answer to this question should depend on quite a number of factors, like the exact spec of the hardware being used. I'm expecting a rough estimation or some experience from the real world.

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• Identifying Exchange 2010 regular process that is walking the mailbox database

  - by toongeneral

  I have an Exchange 2010 server running on a SAN-backed platform. The platform does block-level backups based on a snapshot/incremental basis, that only capture changed data. I was surprised to see a regular period of time where the data changes were happening at a high, sustained rate. Due to the way this system works, that can lead to 1.2TB of stored data per month. The regularity implied a scheduled task, but it is not a fixed interval. It is approximately every 26-32hrs. The disks were performing read operations of ~5MB/s and write operations of ~4.5MB/s, for a period of 3-4hrs. The total written data was ~55-60GB. Reading on TechNet, I am wondering if the following is causing this: http://blogs.technet.com/b/exchange/archive/2011/12/14/database-maintenance-in-exchange-2010.aspx#checksumming The somewhat restrictive thing is that the process only happens at most once every 24 hours. I was able to investigate while it was running, finding the following: the process is store.exe it is working on the mailbox database files while running, it is generating .log files (in the mailbox database folder) consistent with database changes the mailbox database is ~60GB in size, which fits with the total data changes on each iteration I have currently switched to a fixed maintenance window, as a test. It's not clear whether this is the cause, as the symptoms fit, but are not conclusive. Does anyone have any suggestions for additional troubleshooting?

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