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• Capabilities of business and SOHO routers

  - by Q8Y

  I'm currently studying for the CCNA certifications (especially for Cisco routers and configuration). I know that business routers provide more features than SOHO routers, the processing speed and RAM can be enough. Assume I need to connect a number of users through a network (accessing internet, share files, printers, ...). I have a high speed connection to the internet and I already applied QoS. How can I find out how many users such a single (SOHO) router could handle? In my case I'd attach to it multiple switches until I have the number of ports needed. Would everything work well and smoothly with 50 users? What about 300? At which point would I need a business router instead? If I implemented VLAN here, would it make any difference in the performance? When do I really need to use more than one router? (Both SOHO and business) I'm thinking that I may need them only if I want to increase the performance (instead of replacing the existing one) and if I have multiple locations, so in this situation I need to have multiple routers, right? Put differently: Is there is a need to have another router if my business all in one place?

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• Is there a better way to do bonded vlan tagged interfaces with XEN

  - by AJ01

  We have a number of XEN servers all running CentOS or RHEL. The VM's that they run are all required to be on their own VLAN for no other reason than the customer expects them to be. Long story short however, I can't change this right now. We are also required to have bonding enabled on the interfaces. So to accommodat this we enslave eth1 and eth2 to bond0. We then create a seperate interface called bond0.VLANID where VLANID corresponds to the correct vlan; eg ifcfg-bond0.204 DEVICE=bond0.204 BOOTPROTO=static ONBOOT=yes VLAN=yes BRIDGE=xenvlan204 Bridge to XEN As you will see, we eventually have to bridge this out to XEN, and we do this by adding another interface called xenvlan204 (in this instance) which contains; ifcfg-xenvlan204 DEVICE=xenvlan204 BOOTPROTO=none ONBOOT=yes TYPE=bridge XEN Vm Config Finally in our XEN config for each VM, we add vif = [ "bridge=xenvlan204" ] This then allows the vm host to access that particular vlan The Problem We've noticed a few problems with this setup. One being that we currently create the interfaces manually. Which means if we add more vlan enabled interfaces and bridges we usually have to restart xend which is something I'm not so hot about. Also lower level staff have their heads melted by the number of interfaces and the risk of a mistake occurring is high. Secondly, it can take sometime for a host to come up if it has a number of vlan taged interfaces. Thirdly, its just not scaling well on the management aspects The Question Is there a better more flexible way to do this (in particular with Xen that ships with centos 5.3, 5.4 and 5.5 as we have to support all three) that leverages either scripting or other solutions to allow an arbitrary amount of interfaces to be created when a vm is instanced. Your advise and expertise is more that welcomed.

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• Google Chrome is running my system out of memory

  - by jasondavis

  I am running Windows 7 x64 with 12GB of RAM I often have multiple windows and a ton of tabs open. I use the extension Session Buddy to restore all my windows and tabs once the memory gets too high. So my 12gb of ram will get up to around 93% used because of Chrome, now I can close chrome down and restore the same amount of windows and tabs and it will only use about 25% of memory, it then over time increases back up to the 90% zone after several hours. It seems that when I close tabs, instead of freeing that memory up, it doesn't so that is why the huge increase of memory usage as new tabs are opened and closed it just adds up, this sounds like a huge bug in chrome. Just for an example I just re-booted my system, I only have 1 window with 4 tabs open and in the task manager, it shows 29 chrome.exe processes I then killed all chrome processes and opened a chrome window with just 1 tab, it made 27 chrome.exe processes. Is this an issue that others have? More importantly, is there a fix? UPDATE I just read that each plugin and extension creates a chrome.exe process, I then couunted 24 extensions so that helps explain a portion of the large processes. Still not sure about memory not being freed up though!

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• Find slow network nodes between two data centers

  - by 2called-chaos

  I've got a problem with syncing big amount of data between two data centers. Both machines have got a gigabit connection and are not fully occupied but the fastest that I am able to get is something between 6 and 10 Mbit = not acceptable! Yesterday I made some traceroute which indicates huge load on a LEVEL3 router but the problem exists for weeks now and the high response time is gone (20ms instead of 300ms). How can I trace this to find the actual slow node? Thought about a traceroute with bigger packages but will this work? In addition this problem might not be related to one of our servers as there are much higher transmission rates to other servers or clients. Actually office = server is faster than server <= server! Any idea is appreciated ;) Update We actually use rsync over ssh to copy the files. As encryption tends to have more bottlenecks I tried a HTTP request but unfortunately it is just as slow. We have a SLA with one of the data centers. They said they already tried to change the routing because they say this is related to a cheap network where the traffic gets routed through. It is true that it will route through a "cheapnet" but only the other way around. Our direction goes through LEVEL3 and the other way goes through lambdanet (which they said is not a good network). If I got it right (I'm a network intermediate) they simulated a longer path to force routing through LEVEL3 and they announce LEVEL3 in the AS path. I basically want to know if they're right or they're just trying to abdicate their responsibility. The thing is that the problem exists in both directions (while different routes), so I think it is in the responsibility of our hoster. And honestly, I don't believe that there is a DC2DC connection which only can handle 600kb/s - 1,5 MB/s for weeks! The question is how to detect WHERE this bottleneck is

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• Apache using 100% CPU, once again

  - by CBenni

  Recently, apache2 started using 100% of CPU power: top gives me From other, similar threads, I took the tip to use mod_status. Aside from HUGE amounts of NULL requests, it gives: CPU Usage: u2.16 s1.32 cu0 cs0 - .0835% CPU load 1.2 requests/sec - 17.6 kB/second - 14.6 kB/request 8 requests currently being processed, 42 idle workers The access and error logs do not show anything surprising or intriguing at all. Note the .8% CPU usage. Another tip was to use strace: root@server:~# strace -p 1956 Process 1956 attached - interrupt to quit restart_syscall(<... resuming interrupted call ...> And remains like this for at least half an hour, without producing any additional output. Restarting apache fixed the problem for less than a second The server runs a few custom python scripts aswell as a django-powered website on apache2 (up-to-date), but even turning the scripts off (or not having them active in the first place) did not change anything. After I stopped apache and powered my server off, powered it on a few minutes afterwards and restarted all my services, the CPU usage remained low for several hours, just in order to pop up again randomly (?) The DigitalOcean CPU stats on my server are: You can see how the CPU usage was super high for almost half a day until I restarted the bot - just to remain stable for several hours and then pop up again. I am completely at a loss of words and don't know what I could do to find out what piece of my code is giving me these problems or if apache itself is the cause... Therefore I would greatly appreciate any hints to the questions: What else can I try to do? Which things might I not have checked? Is this definitely in my own code? How do you find what part of python code crashes an app via a infinite loop or similar?

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• SSL Handshake negotiation on Nginx terribly slow

  - by Paras Chopra

  I am using Nginx as a proxy to 4 apache instances. My problem is that SSL negotiation takes a lot of time (600 ms). See this as an example: http://www.webpagetest.org/result/101020_8JXS/1/details/ Here is my Nginx Conf: user www-data; worker_processes 4; events { worker_connections 2048; use epoll; } http { include /etc/nginx/mime.types; default_type application/octet-stream; access_log /var/log/nginx/access.log; sendfile on; keepalive_timeout 0; tcp_nodelay on; gzip on; gzip_proxied any; server_names_hash_bucket_size 128; } upstream abc { server 1.1.1.1 weight=1; server 1.1.1.2 weight=1; server 1.1.1.3 weight=1; } server { listen 443; server_name blah; keepalive_timeout 5; ssl on; ssl_certificate /blah.crt; ssl_certificate_key /blah.key; ssl_session_cache shared:SSL:10m; ssl_session_timeout 5m; ssl_protocols SSLv2 SSLv3 TLSv1; ssl_ciphers RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP; ssl_prefer_server_ciphers on; location / { proxy_pass http://abc; proxy_set_header X-Real-IP $remote_addr; proxy_set_header Host $host; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; } } The machine is a VPS on Linode with 1 G of RAM. Can anyone please tell why SSL Hand shake is taking ages?

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• Improve wireless performance

  - by djechelon

  Hello, I have a Trust Speedshare Turbo Pro router, which is running on channel 6. I found that the wireless signal (and network performance) dramatically drops from my PDA (I can barely attach to the network, even if I set the PDA's energy settings to maximum wireless performance) when I even exit my room, and I don't have shielded walls or something like that. I can't even stream a SD video from my desktop (connected via LAN) to my laptop using WiFi, while via LAN it works fine. I read that changing router's channel could improve performance due to interference reducing. I found that almost all wireless networks around here run on channels 6 and 11. I tried to go to my router's settings page to change channel, but I found that the combo box only allows me to select 6!! I'm not sure, but I may have been able in the past to change channel, though not to all of the available channels. A few minutes ago I tried a firmware upgrade, but it didn't solve my problem. My question is Is it possible that my router is someway locked to its channel? I bought it on my own, I didn't receive it from my ISP Apart from boosting the antenna power to the maximum (which, by the way, increases the EM radiation my and my family's bodies absorb 24/7 and is little more environment-unfriendly), do you have any tips on getting high quality transmission up to 5 metres from the antenna? Thank you

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• Intermittent Trouble Entering Hibernate on WinXP

  - by kquinn

  My personal desktop, running 32-bit Windows XP SP2 (with 4GB RAM, 2.75GB addressable, swap disabled, hiberfil.sys existing and contiguous on C:\; SP3 is not installed because SP2 has been working fine and I do not want to re-qualify with SP3 just for sheer perversity) typically gets hibernated at night. For a long time this worked great, but recently the machine has had trouble entering hibernation. Sometimes when I press my power button (configured to hibernate), the box will start the procedure for hibernating (i.e., go to the blue "Windows XP" background logo and display a message about entering hibernation), but before displaying the usual blue-on-black hibernation progress bar it will drop back to the desktop. No error messages appear, on screen or in the system log. The only record of unsuccessful hibernation attempts in the system log, which proudly proclaims that "The Windows Image Acquisition (WIA) service entered the running state." once per failed hibernation attempt. The problem is almost certainly resource related: if I then close one or more applications which are running, and repeat the exact same process, the machine will hibernate perfectly. There does not appear to be a reliable high-water mark for virtual or physical memory use, below which the machine is guaranteed to hibernate; it's different every time (though typically, below about 1.1–1.4 GB memory usage seems to be where hibernate succeeds most often). Memory may not even be the relevant resource; as far as I know, it could also be handles or sockets. This behavior is relatively recent: it has only started in the last few months; before then, I could hibernate reliably no matter what the current resource use of the system. This machine claims to have hotfix Q909095 installed, but since the symptoms of my problem match KB909095 rather well, I'm suspicious if this fix is actually working as intended. Any ideas on how to fix this or where to start debugging?

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• How to prevent eMule from jamming up the router?

  - by the searcher

  Usually, when eMule is started, after some time, I find that the router is jammed, so the internet connection on that computer stopped working, or it seemed to be waiting for some port to be freed up before it can connect to a website. This sometimes affect even other PCs or Macs using the same router. Is there a way to prevent eMule from hogging too much resource or ports? I see that there is under Options -> Connection "Max Sources/File" and a "Connection Limits - Maximum Connections". Right now I set them to really low numbers: the first to 120 and the second to 200, but what are good numbers to fill in there so that it can work well without jamming up the router or use up the network resource of the PC or Mac? Or could it be that the number of files that are "Waiting" is too high, and used up too much resource? (If so, can emule automatically limit the number to 10 or 20 to prevent using too much resource?) (This happened before on Linksys router, Netgear router, and the AT&T U-verse router.)

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• Why are certain folders in my XP network share really, really slow?

  - by bikefixxer

  I have a workgroup set up with Windows XP. My file "server" is running XP Pro and the clients are running XP home. I've turned simple file sharing off on the server because certain clients need access to certain folders and not to others, and I want to keep it that way. Therefore, I've used the granular sharing/security settings to enable certain clients access to certain folders. I'm using the net use command in a batch file on the clients to add the share when they logon so it's always available via a mapped drive or a shortcut. On some clients "My Documents" points to the mapped drive, but all of the local and application settings stay local. Everything works well except for accessing a certain folder on the network. It contains a lot of random batch files and self-executable programs I use for diagnostics and what not, and nearly every time I open the folder the computer hangs for 15-60 seconds. This happens on every machine, including the server (but not nearly as often as the clients). I've searched high and low and cannot figure it out and it's driving me crazy. Here are all the things I've tried to no avail: Disabled firewall (XP) and anti-virus (ESET NOD32) Deleted any desktop.ini file I can find in the share Disabled "automatically search for network folders and printers" Disabled "remember each folder's view settings" Set HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer NoRecentDocsNetHood = 1 Tried with mapped drives and with UNC shortcuts Ran CHKDSK Removed Read-Only attribute from all folders (well, tried to remove, it always came back on with a half check) Added the server's static IP to the hosts file on the clients I've tried monitoring the server's performance to see if anything makes sense. Occasionally the issue coincides with a spike in pages/sec (memory) but not always. Other than that, everything else seems normal. The anti-virus would seem to be the most likely cause to me considering the batch files and what not, but it still hangs when it is completely disabled. I'm at a loss and if anyone can help me with this I'd greatly appreciate it!

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• Ubuntu 10.10 forgets desktop theme.

  - by Marcelo Cantos

  I am running Ubuntu in VirtualBox (on a Windows 7 host). Several times now, the top-level menu bar, the task bar — and seemingly every system dialog — have forgotten the out-of-the-box "Ambiance" theme they conform to when I first installed the system. Window captions still preserve the theme, but pretty much nothing else does. I have searched high and low on Google for assistance with this problem. Everything I've found suggests either running some gconf reset or deleting .gconf* .gnome* and other similar directories. I have followed all this advice and nothing works. I still get a boring Windows-95-style gray 3D look and feel. On previous occasions, after much messing around I've given up and rebooted the VM instance, and been pleasantly suprised to see the original "Ambience" theme restored throughout the UI, but invariably it disappears again some time later, usually after a reboot, so I can never figure out what I did that broke it. Here's a sample from Ubuntu's site of what I want it to look like. And here's a screenshot of my system as it currently looks. Also note that my GNOME Terminals normally have a nice purple semi-translucent look, and as can be seen from the screenshot, they are now just a solid matt white. This last time (just this morning), trying numerous combinations all the usual tricks and rebooting several times hasn't fixed it, so here I am on SU wondering: How do I recover the out-of-the-box theme for my Gnome/Ubuntu desktop, noting that blowing away all config files — as suggested in many places online — fails to achieve this? EDIT: It might help to know that it seems to fail either after I resize the VM instance, forcing the Ubuntu desktop to resize itself, or after I play around with Compiz settings. I haven't been able to figure out which of these it is, and it could be neither. Given the amount of pain I have had to go through to get things back to normal (and given that I am at a loss as to how to do so), it has proven difficult to definitively isolate the cause.

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• Postfix : outgoing mail in TLS for a specific domain

  - by vercetty92

  I am trying to configure postfix to send mail in TLS (starttls in fact), but only for a specific destination. I tried with "smtp_tls_policy_maps". This is the only line in my main.cf file regarding TLS configuration, but it seems not working. Here is my main.cf file: queue_directory = /opt/csw/var/spool/postfix command_directory = /opt/csw/sbin daemon_directory = /opt/csw/libexec/postfix html_directory = /opt/csw/share/doc/postfix/html manpage_directory = /opt/csw/share/man sample_directory = /opt/csw/share/doc/postfix/samples readme_directory = /opt/csw/share/doc/postfix/README_FILES mail_spool_directory = /var/spool/mail sendmail_path = /opt/csw/sbin/sendmail newaliases_path = /opt/csw/bin/newaliases mailq_path = /opt/csw/bin/mailq mail_owner = postfix setgid_group = postdrop mydomain = ullink.net myorigin = $myhostname mydestination = $myhostname, localhost.$mydomain, localhost masquerade_domains = vercetty92.net alias_maps = dbm:/etc/opt/csw/postfix/aliases alias_database = dbm:/etc/opt/csw/postfix/aliases transport_maps = dbm:/etc/opt/csw/postfix/transport smtp_tls_policy_maps = dbm:/etc/opt/csw/postfix/tls_policy inet_interfaces = all unknown_local_recipient_reject_code = 550 relayhost = smtpd_banner = $myhostname ESMTP $mail_name debug_peer_level = 2 debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin xxgdb $daemon_directory/$process_name $process_id & sleep 5 And here is my "tls_policy" file: gmail.com encrypt protocols=SSLv3:TLSv1 ciphers=high I also tried gmail.com encrypt My wish is to use TLS only for the gmail domain. With this configuration, I don't see any TLS line in the source of the mail. But if I tell postfix to use TLS if possible for all destination with this line, it works: smtp_tls_security_level = may Beause I can see this line in the source of my mail: (version=TLSv1/SSLv3 cipher=OTHER); But I don't want to try to use TLS for the others domains...only for gmail... Do I miss something in my conf? (I also try whith "hash:/etc/opt/csw/postfix/tls_policy", and it's the same) Thanks a lot in advance

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• No sound out of headphone port on laptop

  - by Thanatos

  I cannot get sound out of the headphone port on a laptop. Headphones are plugged in, and sound comes out of the internal speakers. Windows behaves normally (sound switches to headphones when headphones are inserted). It did work in Linux at one point, but something changed, we're just not sure what. Rebooting doesn't fix. This appears to occur whether or not PulseAudio is running. Things I've tried: Rebooting. No effect. Booting into Windows. It works properly, so probably not a hardware issue. All of alsamixer. My only controls are this: "Master" Volume bar & mutable, unmuted. Controls volume. "PCM" Volume bar only. 100%. "S/PDIF" Mutable only, currently muted, has no effect. "S/PDIF" Default PCM", Mutable only, currently unmuted, has no effect. Killing PulseAudio. No effect. (It also won't stay dead! Something appears to be restarting it, and I can't tell what, but it is annoying as fuck.) alsactl init 0, no effect. sudo rm -f /var/lib/alsa/asound.state, no effect. General system info: Ubuntu 10.04 LTS Toshiba Satellite T135D-S1324 lspci says I have: 00:14.2 Audio device: ATI Technologies Inc SBx00 Azalia (Intel HDA) 01:05.1 Audio device: ATI Technologies Inc RS780 Azalia controller Some edits: Yes, the headphones are in all the way. This works in Windows: You plug headphones in, the internal speakers stop making noise, and noise comes out the head phones. Windows says I only have two sound cards: the HDMI port (which I don't care about) and the "sound card", which it claims is a "Conexant Pebble High Definition SmartAudio" In Windows, both the internal speakers and the headphone jack show up as one soundcard, which in my experience, is typical. (This is a laptop)

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• How do I permanently delete /var/log/lastlog?

  - by GregB

  My /var/log/lastlog file is huge. I know it's really only a few kilobytes, but tar isn't smart enough to know that, so when I image a virtual machine, my restore fails because it thinks I'm trying to load more data than I have capacity on my disk. I want to delete /var/log/lastlog and stop any and all logging to the file. I'm aware of the security implications. This logging needs to stop to preserve my backup strategy. I've made a change to /etc/pam.d/login which I was told would disable logging to /var/log/lastlog, but it does not appear to work as /var/log/lastlog keeps growing. # Prints the last login info upon succesful login # (Replaces the `LASTLOG_ENAB' option from login.defs) #session optional pam_lastlog.so Any ideas? EDIT For anyone interested, I use Centrify Express to authenticate my users via LDAP. Centrify Express is "free", but one of the drawbacks is that I can't manage user UIDs via LDAP, so they are given a dynamic UID when they login to a server. Centrify picks some crazy high UID values (so they don't conflict with local users on the server, presumably). /var/log/lastlog is indexed by UID, and grows to accommodate the largest UID on the system. This means that when a Centrify user logs in, they get a UID in the upper-end of the UID range, which causes lastlog to allocate an obscene amount of space, according to the file system. ~$ ll /var/log/lastlog -rw-rw-r-- 1 root root 291487675780 Apr 10 16:37 /var/log/lastlog ~$ du -h /var/log/lastlog 20K /var/log/lastlog More Into --- Sparse Files

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• Short, intermittent USB port timeouts

  - by jacobsee

  I have a data acquisition application controlled by a Windows PC. I am using an Intel Desktop Board DH67CL motherboard. This has 6 USB2 ports along with 2 of the new blue USB3 ports. The DAQ instrument connects via USB to the computer. Roughly once every day or two there is a short communication glitch with the USB that causes the instrument to disconnect briefly and then reconnect. This is logged so I know whenever it happens. Occasionally it will cause the data acquisition to stop. I've verified that the glitches will go away if I use the USB3 ports, or if I use a PCI add-on card with USB ports. So it seems that there is something going on with these built-in USB2 ports on this motherboard. I haven't yet had a chance to test with other motherboards. My question: what could be causing these glitches and how to get rid of them for this board, or is there a better motherboard to use? We have standardized on the DH67CL because it's inexpensive, has 3 PCI slots that we need, and is readily available. We don't need the power of higher-end server boards but reliability is important. Thanks. Update: This problem has been reproduced many times on different hardware, though we always use the same model of motherboard (DH67CL) and power supply (Antec EA-430D). I don't think the power requirements are very high but will check on that.

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• 3000 videos songs... some are loud in voice & some low.. I want to make them equal (equal in volume only)

  - by Mister.9

  I have thousands Video flv/avi files, which are all songs only. Some of them are high in volume and some are low. Every time the song ends I have to up or down the volume at once..to escape my ears ruined by headphones... and by woofers, save my life from my neighbor sleeping after hard-earning all the day long. :-( Any idea to make all files sound equal? Does such kind of application/software exist? Any converter that may convert all audio files into same volume? I know iTunes has sound-check option but can it convert? If I want to write CDs, does any burner have the feature like this, to burn in equal sound? If yes, suggest something for me... For, I am really really worried... It would be a great help..... Hoping your kind reply, Thanks in advance! (I am I am John.martin188@yahoo for having mails also in this regard)

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• VMWare Workstation 8 Disk I/O & Hard Faults

  - by Scott

  I have VMWare Workstation 8 installed on a host machine with the following specs: Intel i5 2500k CPU 16GB DDR3 1600 ram 1TB Western Digital Caviar Black HD I have two Windows 7 virtual machines configured (currently running one at a time but will be operating both at once when my 32GB RAM kit arrives in a couple days). Each one is configured with 8GB of RAM and no tweaks/performance customizations or anything done. All of the VMWare settings are the defaults. When I boot into these machines and run various programs (Visual Studio, Outlook, etc), I can hear the disk thrashing quite a bit and checking Resource Monitor, I can see that I'm getting anywhere between 300-800 hard faults per second. From the host machine, it shows they're coming from the VMWare image. If I go to the virtual machine, whatever app I'm currently loading is the image that's causing the hard faults. As I understand it, hard faults are (simply) when an address in memory has been swapped out to the page file and has to be read from the page file instead of from memory. I don't understand why this is happening though. With 8GB of ram on the guest machine and 6.5GB available, what could be causing this? I know Windows 7 supposedly improved on page file management over XP but it seems excessive for this kind of slowdown, disk thrashing and high hard fault count when I have that much free RAM. Is there anything I can to to improve the performance in my guest machines? On the host machine, I can open/run any applications at all and hard faults stays around 0 with low disk I/O.

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• Mysqld shutting down by itself

  - by AJ Naidas

  I'm running a Wordpress Blog that gets medium-high traffic. It is hosted in an Ubuntu Server 2GB Memory 2 Core Processor 40GB SSD Disk, 3TB Transfer. The problem is that MySQL shuts down by itself after an hour or two. I had to restart mysql each and every time this happens. I checked the logs and this is what I found: 140612 6:48:14 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead. 140612 6:48:14 [Note] Plugin 'FEDERATED' is disabled. 140612 6:48:14 InnoDB: The InnoDB memory heap is disabled 140612 6:48:14 InnoDB: Mutexes and rw_locks use GCC atomic builtins 140612 6:48:14 InnoDB: Compressed tables use zlib 1.2.3.4 140612 6:48:14 InnoDB: Initializing buffer pool, size = 1.4G InnoDB: mmap(1502412800 bytes) failed; errno 12 140612 6:48:14 InnoDB: Completed initialization of buffer pool 140612 6:48:14 InnoDB: Fatal error: cannot allocate memory for the buffer pool 140612 6:48:14 [ERROR] Plugin 'InnoDB' init function returned error. 140612 6:48:14 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 140612 6:48:14 [ERROR] Unknown/unsupported storage engine: InnoDB 140612 6:48:14 [ERROR] Aborting 140612 6:48:14 [Note] /usr/sbin/mysqld: Shutdown complete judging by this line: 140612 6:48:14 InnoDB: Fatal error: cannot allocate memory for the buffer pool I suspect that this is a memory problem, but I would like to hear from the experts here before I conclude. Is this a lack of memory problem? Do you think the value of max_connections in my.cnf (currently 100) is a potential cause and needs increasing? TIA.

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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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• What does opening a serial port do?

  - by reve_etrange

  What does opening the standard PC serial port do, in electrical terms (i.e. what voltages on which pins)? For example, the ancient VB6 program which controls an apparatus I am tasked with maintaining toggles .PortOpen to control some TTL. The connection only used 2 pins (bad solders fell apart), so which pins do I solder to? The only labels / documentation refer to pins 7 and 9, saying 0V and 5V parenthetically, but does .PortOpen really just put 5V between RI and RTS?. As a post script, this isn't the weirdest thing about the set up. The TTL I referred to above also connects to an instrument via a BNC to DB9 (!), with only 1 pin used. I guess there was an assumption about a common ground, since the BNC shielding isn't connected to the GND pin? The connection is to the instrument's 'foot pedal' pin, it was a way to remotely trigger the device. Update According to this page, the DTR and RTS pins can go high when the port is opened. If they were so configured, they will subsequently go low when the port is closed. If DTR and RTS are not enabled, opening the port should set both to low (and keep them low).

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• How to stop Firefox on an SSD from freezing when using the search box or submitting a form?

  - by sblair

  Firefox usually freezes for about a second whenever I search for something from the toolbar search box, when submitting a form, or when clearing the search box history. I suspect it has something to do with the auto-complete feature. Using Windows 7's Resource Monitor, the problem seems to be from the file: C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\formhistory.sqlite-journal I believe this is a temporary file which caches database writes. The following screenshot shows the very high response times from six different searches, and that the queue length on drive C shoots off the scale: My Firefox profile is on an Intel X25-M G2 SSD. The problem doesn't seem to occur if I create a new profile on a hard disk drive. However, I'd like to know why the problem exists on the SSD in the first place (because it's an annoying problem which contradicts the reason I bought an SSD, and it might happen with other applications too), and how to prevent it. It still occurs if Firefox is started in safe mode, and with the recent beta versions. Updates: VACUUMing the Firefox profile databases does not help with this problem. The SSD Optimizer in the Intel SSD Toolbox does not help either.

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• How to verify TRIM/discard on encrypted swap?

  - by svarni

  I am using an encrypted swap partition via ecryptfs-setup-swap on my Ubuntu 13.04 computer using a SSD. I have manually set up trim for my ext4 root partition (simply by adding the "discard" option in /etc/fstab). I also manually ran fstrim on the root partition prior to booting and using dstat I saw that for a few seconds several GB/s of data have been written to the disk. That was presumably the effect of the trim command. These high writerates are reproducable by deleting huge files and have not occured before setting up trim, so I take them as evidence for working trim/discard. Manually enabling trim on my root partition has stopped the wearout of my precious new disk from 365 used reserved blocks (out of 6176 total) within three months down to 0 additional used reserved blocks within three additional months (data from SMART attributes). Because I want to minimize the wearout of my SSD I now would like to know whether my swap partition (which is encrypted using ecryptfs-setup-swap) also makes use of the trim/discard option. I tried sudo swapon -d -v /dev/mapper/cryptswap1 but did not receive particular information ("-v") about whether trim/discard ("-d") was applied. If unsupported, i would expect a message. Then I tried sudo dd if=/dev/sda6 count=1 BS=1M | xxd | less directly after booting and when no swapspace was used but I saw not only zeroes. I assume, when looking at freshly trimmed regions, the disk would send zeroes instead of reading random sectors (and according to some forums, (unencrypted) swap space is trimmed once upon boot). Long story short: Are there any ideas on how to test if trim is effectively used for my encrypted swap? And if not, any ideas on how to - at least manually, for once - trim the whole swap space? I wouldn't want to tinker with the partition itself, because I dont know if it needs to be reinitialized as (encrypted) swap - I dont want to be left with an unbootable system :)

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• Log shipping on select tables.

  - by Scott Chamberlain

  I know I am most likely using incorrect terminology so please correct me if I use the wrong terms so I can search better. We have a very large database at a client's site and we would like to have up to date copies of some of the tables sent across the internet to our servers at our office. We would like to only copy a few of the tables because the bandwidth requirement to do log shipping of the entire database (our current solution) is too high. Also replication directly to our servers is out of the question as our servers are not accessible from the internet and management does not want to do replication (more on that later). One possible Idea we had is to do some form of replication on the tables we need to another database on the same server and do log shipping of that second smaller database but management is concerned that the clients have broken replication (it was between two servers on their internal network however) on us in the past and would like to stay away from it if possible. Any recommendations would be greatly appreciated. If using some form of replication is the only solution, I am not against replication, I just need compelling arguments to convince management to do it. This is to be set up on multiple sites that are running either Sql2005 or Sql2008 we will have both versions on our end to restore the data to so that is not a issue. Thank you.

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• Raspberry pi slows down my entire network

  - by gnusouth

  Whenever my Raspberry Pi is connected to the network (via ethernet) the entire network is slowed to a crawl. On my main computer, ping times for google.com go from ~10ms to ~200ms and it takes forever to load web pages. Connections are also slow on the Pi, with an apt-get update showing pathetic speeds in the order of 1KB/s. Turning off the Pi completely removes the drag from the network. I've tried static and dynamic IP addresses for the Pi, but both have the same problems. I'm currently using Raspbian (downloaded today), but also had this problem with Arch Linux. I've checked the connection's duplex with dmesg | grep -i duplex, which shows that the Pi's connection is running at 100Mbps, full-duplex, as expected. My modem/router is a Billion 7404VNPX (an Australian thing); relatively high-end, albeit a bit buggy at times (it will occassionally delete all its firewall settings). It assigns IPs in the range 192.168.1.1 to 192.168.1.20 and has 192.168.1.254 as its own IP. When I assign static IPs I tend to use the 192.168.1.200 area. Does anyone have any idea as to what could be causing this weird slowdown? Or any tests I could try? Thanks

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• What is the best private cloud storage setup

  - by vdrmrt

  I need to create a private cloud and I'm searching for the best setup. These are my 2 most important requirements 1. Disk and system redundant 2. Price / GB as low as possible The system is going to be used as backup setup which will receive data 24/7 over SFTP and rsync. High throughput is not that important. I'm planning to use glusterfs and consumer grade 4TB hard-drives. I have worked out 3 possible setups 3 servers with 11 4TB HDD Setup up a replica 3 glusterfs and setup each hard drive as a separate ext4 brick. Total capacity: 44TB HDD / TB ratio of 0.75 (33HDD / 44TB) 2 servers with 11 4TB HDD The 11 hard-drives are combined in a RAIDZ3 ZFS storage pool. With a replica 2 gluster setup. Total capacity: 32TB (+ zfs compression) HDD / TB ratio of 0.68 (22HDD / 32TB) 3 servers with 11 4TB consumer hard-drives Setup up a replica 3 glusterfs and setup each hard-drive as a separate zfs storage pool and export each pool as a brick. Total capacity: 32TB (+ zfs compression) HDD / TB ratio of 0.68 (22HDD / 32TB) (Cheapest) My remarks and concerns: If a hard drive fails which setup will recover the quickest? In my opinion setup 1 and 3 because there only the contents of 1 hard-drive needs to be copied over the network. Instead of setup 2 were the hard-drive needs te be reconstructed by reading the parity of all the other harddrives in the system. Will a zfs pool on 1 harddrive give me extra protection against for example bit rot? With setup 1 and 3 I can loose 2 systems and still be up and running with setup 2 I can only loose 1 system. When I use ZFS I can enable compression which will give me some extra storage.

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