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  • sudoers - simple explanation requested

    - by Redsandro
    Everytime I want to be able to run something that requires me to be a sudoer too many times, I need to google for the formatting of /etc/sudoers to remind me again what exactly is the proper way to write it. Now I see different writing styles in my sudoers file, which is the consequence of different google results over the months. I've also noticed that the second example (below) seems to work in XFCE, but not in Cinnamon (Gnome 3). This could be totally unrelated, but nontheless I'd like to know once and for all, what is the correct grammar of the sudoer line, and what is the difference between the given examples? redsandro ALL=NOPASSWD:/path/to/command redsandro ALL=(ALL) NOPASSWD:/path/to/command redsandro ALL=(ALL:ALL) NOPASSWD:/path/to/command Also, what are all the ALL's for? One user, one command, yet I need to use the ALL keyword up to three times? Am I doing this wrong? Of course, omitting NOPASSWD: makes you enter your password before you are permitted to run the command, but one point of confusion is the usage of = and :, for the final command that is the subject of the line can be prepended by either =, :, , or ), confusing grammar for similar semantics.

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  • Validation and Verification explanation (Boehm) - I cannot understand its point

    - by user970696
    Hopefully my last thread about V&V as I found the B.Boehm is text which I just do not understand well (likely my technical English is not that good). http://csse.usc.edu/csse/TECHRPTS/1979/usccse79-501/usccse79-501.pdf Basically he says that verification is about checking that products derived from requirements baseline must correspond to it and that deviation leads only to changes in these derived products (design, code). But he says it begins with design and ends with acceptance tests (you can check the V model inside). The thing is, I have accepted ISO12207 in terms of all testing is validation, yet it does not make any sense here. In order to be sure the product complies with requirements (acceptance test) I need to test it. Also it says that validation problems means that requirements are bad and needs to be changed - which does not happen with testing that testers do, who just checks correspondence with requirements.

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  • Very original V&V explanation (Bohm) - I cannot understand its point

    - by user970696
    Hopefully my last thread about V&V as I found the B.Boehm is text which I just do not understand well (likely my technical English is not that good). http://csse.usc.edu/csse/TECHRPTS/1979/usccse79-501/usccse79-501.pdf Basically he says that verification is about checking that products derived from requirments baseline must correspond to it and that deviation leads only to changes in these derived products (design, code). But he says it begins with design and ends with acceptance tests (you can check the V model inside). The thing is, I have accepted ISO12207 in terms of all testing is validation, yet it does not make any sense here. In order to be sure the product complies with requirements (acceptance test) I need to test it. Also it says that validation problems means that requirements are bad and needs to be changed - which does not happen with testing that testers do, who just checks correspondence with requirements.

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  • Vector transform equation explanation

    - by cyberdemon
    I'm trying to understand the maths of moving points in a 3d space by making a game written in C#. I'm looking at this wolfire blog series which explains some basic 3d maths. I've read the first two parts but am stuck on the 3rd. I know it's all really rudimentary stuff but I find Googling for help with equations really hard. The one I'm struggling with is: 0*(0.66,0.75) + 2*(-0.75, 0.66) = (-1.5, 1.3) How can anything multiplied by 0 not be 0? So my question is how does this look in code: x(a,b) + y(c,d) I know it's basic stuff but I just can't see it.

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  • explanation of RAM specs, and what do I need for a Gaming rig

    - by ewok
    I am looking into upgrading my custom built PC's RAM. I use the machine mostly for gaming, but I don't really know a ton about RAM, so I wanted to ask a few questions. The research I've done tells me there is a negligible increase in speed for anything above 1600 MHz. is this true or is it worth the extra money to go higher? Other than drawing more power from the PSU, is there any real difference in performance with different voltages (1.5V vs 1.65V)? most of the kits I've found in the 2x4 1600 range have a CAS latency of 9 and timing of 9-9-9-24. For a significant increase in price (usually about 1.5x), I can get either 8 or 7 and lower timing. Is it worth the cost? What I am looking for here is someone to give a good explanation of what the different specs represent, and how that relates to the performance of the machine. Specifically, I'm looking for what specs I need to focus on for a good gaming rig. I am NOT looking for a "buy this, it's the best RAM" without an explanation of why. The information will be much more valuable as it will allow me to make my own informed decision. As they say, give a man a fish, he'll eat for a day. teach a man to fish, and he'll eat for the rest of his life.

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  • MVC (model-view-controller) - can it be explained in simple terms?

    - by DVK
    I need to explain to a not-very-technical manager the MVC (model-view-controller) concept and ran into trouble. The problem is that the explanation needs to be on a "your grandma will get it" level - e.g. even the fairly straightforward explanation offered on MVC Wiki page didn't work, at least with my commentary. Does anyone have a reference to a good MVC explanation in simple terms? It would ideally be done with non-techie metaphor examples (e.g. similar to "Decorator pattern is like glasses") - one reason I failed was that all MVC examples I could come up with were development related. I once saw a list of pattern explanations but to the best of my memory MVC was not on it. Thanks!

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  • Looking for a good explanation of the table generation macro idiom

    - by detly
    I want to make this clear up front : I know how this trick works, what I want is a link to a clear explanation to share with others. One of the answers to a C macro question talks about the "X macro" or "not yet defined macro" idiom. This involves defining something like: #define MAGIC_LIST \ X(name_1, default_1) \ X(name_2, default_2) \ ... Then to create, say, an array of values with named indices you do: typedef enum { #define X(name, val) name, MAGIC_LIST #undef X } NamedDefaults; You can repeat the procedure with a different #define for X() to create an array of values, and maybe debugging strings, etc. I'd like a link to a clear explanation of how this works, pitched at someone who is passably familiar with C. I have no idea what everyone usually calls this pattern, though, so my attempts to search the web for it have failed thus far. (If there is such an explanation on SO, that'd be fine...)

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  • Explanation of nodev and nosuid in fstab

    - by Ivan Kovacevic
    I see those two options constantly suggested on the web when someone describes how to mount a tmpfs or ramfs. Often also with noexec but I'm specifically interested in nodev and nosuid. I basically hate just blindly repeating what somebody suggested, without real understanding. And since I only see copy/paste instructions on the net regarding this, I ask here. This is from documentation: nodev - Don't interpret block special devices on the filesystem. nosuid - Block the operation of suid, and sgid bits. But I would like a practical explanation what could happen if I leave those two out. Let's say that I have configured tmpfs or ramfs(without these two mentioned options set) that is accessible(read+write) by a specific (non-root)user on the system. What can that user do to harm the system? Excluding the case of consuming all available system memory in case of ramfs

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  • Dependency Injection -Colloquial explanation

    - by nettguy
    Recently I was asked to express the DI in colloquial explanation. I answered : 1) I am going to a hotel.I ordered food.The hotel management asks me to clean the plates and clean the tables.So here i am a client,I am responsible for managing the service (Instantiating,executing,disposing).But DI decouples such tasks so the service consumer no need not worry about controlling the life cycle of the service. 2) He also asked is there any microsoft API follows DI ?.I answered (This was my guess) In WCF you can create a Proxy using ChannelFactory that controls the life time of your factory. for item (1) he said only 10% is correct for item(2) he said that is factory pattern not dependency injection. Actually what went wrong in my explanation (apart from my bad English) ? What is the real answers for those? I am waiting for your valuable suggestions.

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  • Need for explanation: NetBIOS over TCP/IP on VMware network adapter disturbs access to network share

    - by gyrolf
    Some time ago nearly all workstations in our team (Windows XP SP2) exhibited intermittend but frequent delays when accessing shares on the network. Typically the first access to a share which hadn't been accessed for some time resulted in a nearly frozen workstation for up to 30 seconds. Then everything started working fine again. Using TCPView from Sysinternals I saw that during this delays there was a connection to the netbios-ssn port on the file server which was in state SYN_SENT. First try: Disable NetBIOS over TCP/IP for the intranet network adapter. Problem solved, but I didn't like to manipulate our centrally managed network configuration for the intranet. Second try: Disable NetBIOS over TCP/IP only for the VMWare network adapter (VMNet1 used for host only communications). Problem solved again! My questions: Why does NetBIOS over TCP/IP on one network adapter disturb NetBIOS over TCP/IP on another network adapter? Is this problem specific to VMWare network adapters? Has anybody else seen this phenomen? Additional information: VMWare Workstation version 6.0.3 At the time I started seriously analysing the problem it was no more possible to find out what had been changed to our systems at the time the problems started.

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  • Explanation for kernel error - Eeeek! page_mapcount went negative

    - by Aditya Advani
    Internet says this is a genuine Kernel Bug but does anyone know what triggers it?? Server running CentOS x86_64 with kernel 2.6.27.24 Here is my crash output: [root@u15345757 httpdocs]# Message from syslogd@ at Thu Aug 6 01:42:22 2009 ... u15345757 kernel: [1145736.506380] Eeek! page_mapcount(page) went negative! (-1) Message from syslogd@ at Thu Aug 6 01:42:22 2009 ... u15345757 kernel: [1145736.517515] page pfn = d0a3 Message from syslogd@ at Thu Aug 6 01:42:22 2009 ... u15345757 kernel: [1145736.523814] page->flags = 10000000000083c Message from syslogd@ at Thu Aug 6 01:42:22 2009 ... u15345757 kernel: [1145736.532489] page->count = 2 Message from syslogd@ at Thu Aug 6 01:42:22 2009 ... u15345757 kernel: [1145736.538741] page->mapping = ffff88001f01a110 Message from syslogd@ at Thu Aug 6 01:42:22 2009 ... u15345757 kernel: [1145736.547924] vma->vm_ops = 0x0 Message from syslogd@ at Thu Aug 6 01:42:22 2009 ... u15345757 kernel: [1145736.554543] [ cut here ] Message from syslogd@ at Thu Aug 6 01:42:23 2009 ... u15345757 kernel: [1145736.564528] invalid opcode: 0000 [1] SMP Message from syslogd@ at Thu Aug 6 01:42:23 2009 ... u15345757 kernel: [1145736.564528] Code: 80 e8 22 51 fd ff 48 8b 85 90 00 00 00 48 85 c0 74 19 48 8b 40 20 48 85 c0 74 10 48 8b 70 58 48 c7 c7 10 7f 7d 80 e8 fd 50 fd ff <0f> 0b eb fe 8b 77 18 41 58 5b 5d 83 e6 01 f7 de 83 c6 04 e9 df Broadcast message from root (pts/3) (Thu Aug 6 01:49:29 2009): The system is going down for reboot NOW!

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  • Everything on hard drive suddenly vanished without explanation, but the drive seems otherwise functional

    - by user160705
    Windows 7 Ultimate x64 Custom-built desktop I have a new desktop that I built a few months ago that has a four-year-old WD hard drive and a two-year-old drive. I had set it up so that the newer drive had Windows and most of my files on it while the older drive had my music library, some movies and games, and a backup of all of my documents. About a month ago, I installed some new case fans and, in the process, I temporarily unplugged my hard drive (while the computer was off of course - I took all the necessary precautions) for wire management. I plugged it back in, and didn't really think anything of it. At around that time, however, I noticed that my older hard drive wasn't showing up in Windows Explorer anymore but I didn't really have time to check into it (I had just started college) and I'm finally getting a chance to now. That drive doesn't show up in Windows Explorer at all but it does show up in Disk Management. That screen shows the following: http://puu.sh/17mMN Any idea what happened? Is there any way to recover my files? Thanks in advance for your help! EDIT: The music and games and stuff used to be on "Disc 1", the 465.71 GB of what is now showing as unallocated space.

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  • High load without explanation

    - by Sebastian
    I have a very high load on my machine and don't know what is responsible or how to find out. On the machine runs a jboss appserver and mysql. Here is a top from the user at peak time: top - 16:23:01 up 101 days, 6:50, 1 user, load average: 23.42, 21.53, 24.73 Tasks: 9 total, 1 running, 8 sleeping, 0 stopped, 0 zombie Cpu(s): 17.2%us, 1.6%sy, 0.0%ni, 80.4%id, 0.1%wa, 0.1%hi, 0.7%si, 0.0%st Mem: 16440784k total, 16263720k used, 177064k free, 151916k buffers Swap: 16780872k total, 30428k used, 16750444k free, 8963648k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 27344 b 40 0 16.0g 6.5g 14m S 169 41.7 1184:09 java 6047 b 40 0 11484 1232 1228 S 0 0.0 0:00.01 mysqld_safe 6192 b 40 0 604m 182m 4696 S 0 1.1 93:30.40 mysqld 7948 b 40 0 84036 1968 1176 S 0 0.0 0:00.07 sshd 7949 b 40 0 14004 2900 1608 S 0 0.0 0:00.03 bash 7975 b 40 0 8604 1044 840 S 0 0.0 0:00.44 top The CPU usage of the java process is normal. The peaks only show up when i deployed a certain web application. Could the resulting network traffic boost the load in such way that i don't see it in top?

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  • Explanation of command to uppercase the first letter of a filename

    - by hazielquake
    I'm trying to learn to rename files with the command line, and after browsing around a lot of pages I finally found a command that uppercases the first letter of a file, but the problem is that I want to understand the meaning of each command. The command is: for i in *; do new=`echo "$i" | sed -e 's/^./\U&/'`; mv "$i" "$new";done I understand the 'for' kinda... but not the 'echo' or '`' and especially the sed command. if someone has a little patience to explain the meaning of each thing that'd be awesome! Thanks!

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  • Need for explanation: NetBIOS over TCP/IP on VMware network adapter disturbs access to network share

    - by gyrolf
    (Moved here from StackOverflow) Some time ago nearly all workstations in our team (Windows XP SP2) exhibited intermittend but frequent delays when accessing shares on the network. Typically the first access to a share which hadn't been accessed for some time resulted in a nearly frozen workstation for up to 30 seconds. Then everything started working fine again. Using TCPView from Sysinternals I saw that during this delays there was a connection to the netbios-ssn port on the file server which was in state SYN_SENT. First try: Disable NetBIOS over TCP/IP for the intranet network adapter. Problem solved, but I didn't like to manipulate our centrally managed network configuration for the intranet. Second try: Disable NetBIOS over TCP/IP only for the VMWare network adapter (VMNet1 used for host only communications). Problem solved again! My questions: Why does NetBIOS over TCP/IP on one network adapter disturb NetBIOS over TCP/IP on another network adapter? Is this problem specific to VMWare network adapters? Has anybody else seen this phenomen? Additional information: VMWare Workstation version 6.0.3 At the time I started seriously analysing the problem it was no more possible to find out what had been changed to our systems at the time the problems started.

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  • How do you explain what the BIOS is to non-Super User?

    - by David Johnstone
    In a particularly nerdy Facebook status update I mentioned that I had flashed my BIOS. One of my friends asked what the BIOS is. My question is: How do you explain what the BIOS is and does to a layperson? (Hint: "The BIOS is the basic input/output system" is not going to be accepted as the answer.) (Of course, the real question is "does she like me?", but I'm not sure there's a site for this :-p )

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  • Explanation of the init.d/scripts Fedora

    - by Shahmir Javaid
    Below is a copy of vsftpd, i need some explanations of some of the scripts mentioned below in this script: #!/bin/bash # ### BEGIN INIT INFO # Provides: vsftpd # Required-Start: $local_fs $network $named $remote_fs $syslog # Required-Stop: $local_fs $network $named $remote_fs $syslog # Short-Description: Very Secure Ftp Daemon # Description: vsftpd is a Very Secure FTP daemon. It was written completely from # scratch ### END INIT INFO # vsftpd This shell script takes care of starting and stopping # standalone vsftpd. # # chkconfig: - 60 50 # description: Vsftpd is a ftp daemon, which is the program \ # that answers incoming ftp service requests. # processname: vsftpd # config: /etc/vsftpd/vsftpd.conf # Source function library. . /etc/rc.d/init.d/functions # Source networking configuration. . /etc/sysconfig/network RETVAL=0 prog="vsftpd" start() { # Start daemons. # Check that networking is up. [ ${NETWORKING} = "no" ] && exit 1 [ -x /usr/sbin/vsftpd ] || exit 1 if [ -d /etc/vsftpd ] ; then CONFS=`ls /etc/vsftpd/*.conf 2>/dev/null` [ -z "$CONFS" ] && exit 6 for i in $CONFS; do site=`basename $i .conf` echo -n $"Starting $prog for $site: " daemon /usr/sbin/vsftpd $i RETVAL=$? echo if [ $RETVAL -eq 0 ]; then touch /var/lock/subsys/$prog break else if [ -f /var/lock/subsys/$prog ]; then RETVAL=0 break fi fi done else RETVAL=1 fi return $RETVAL } stop() { # Stop daemons. echo -n $"Shutting down $prog: " killproc $prog RETVAL=$? echo [ $RETVAL -eq 0 ] && rm -f /var/lock/subsys/$prog return $RETVAL } # See how we were called. case "$1" in start) start ;; stop) stop ;; restart|reload) stop start RETVAL=$? ;; condrestart|try-restart|force-reload) if [ -f /var/lock/subsys/$prog ]; then stop start RETVAL=$? fi ;; status) status $prog RETVAL=$? ;; *) echo $"Usage: $0 {start|stop|restart|try-restart|force-reload|status}" exit 1 esac exit $RETVAL Question I What the hell is the difference between the && and || signs in the below commands, and is it just an easy way to do a simple if check or is it completely different to a if[..something..]; then ..something.. fi: # Check that networking is up. [ ${NETWORKING} = "no" ] && exit 1 [ -x /usr/sbin/vsftpd ] || exit 1 Question II i get what -eq and -gt is (equal to, greater than) but is there a simple website that explains what -x, -d and -f are? Any help would be apreciated Running Fedora 12 on my OS. Script copied from /etc/init.d/vsftpd Question III It says required starts are $local_fs $network $named $remote_fs $syslog but i cant see any where it checks for those.

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  • Explanation of various domain name records?

    - by Kumar
    At the time of hosting, normally we just change name servers in the domain control panel. It's fine if both mail and web servers are the same. When they're different, we need to change the DNS records. When I try to point my blog to my domain name, I came to know about the various types of DNS records - A Records, AAA Records, MX Records, CNAME Records, NS Records, TXT Records, SRV Records, SOA Records, etc. I searched on Google, but would like to know more about these deeply. I found this link on the Internet - http://www.directnic.com/help/faq/?question_id=103 and got some idea about the different DNS records. But I have some more questions. How do the domain name records work? Is there any difference between NS record and other records in the way they work? Where should the NS record point to when using A record, CNAME record and MX record?

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  • Requesting better explanation for expires headers

    - by syn4k
    I have successfully implemented expires headers however, for several days I have been stumped by one thing. This article: http://www.tipsandtricks-hq.com/how-to-add-far-future-expires-headers-to-your-wordpress-site-1533 states Keep in mind that when you use expires header the files are cached in the browser until it expires so do not use this on files that changes frequently. Other sites indicate the same in my reading. But this doesn't seem to be true. I have updated an image, using the same name, several times. Each time I update and refresh my browser, the new image (with the same name) displays. I understand from this article that the old image should display unless I use a new name. Do you happen to know where the misunderstanding is? I have verified that the image in question has expires headers set on it: Request Headers: Host domain.com User-Agent Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.28) Gecko/20120306 Firefox/3.6.28 FirePHP/0.5 Accept image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language en-us,en;q=0.5 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 115 Connection keep-alive Referer http://domain.com/index.php Cookie __utma=1.61479883.1332439113.1332783348.1332796726.4; __utmz=1.1332439113.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none);PHPSESSID=lv2hun9klt2nhrdkdbqt8abug7; __utmb=1.33.10.1332796726; __utmc=1; ck_authorized=true x-insight activate If-Modified-Since Mon, 26 Mar 2012 21:55:33 GMT Cache-Control max-age=0 Response Headers: Date Mon, 26 Mar 2012 22:06:50 GMT Server Apache/2.2.3 (CentOS) Connection close Expires Wed, 25 Apr 2012 22:06:50 GMT Cache-Control max-age=2592000

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  • Requesting better explanation for etag/expiration of favicon.ico

    - by syn4k
    Following this article: Configuring favicon with expires header in htaccess Using YSlow, I keep getting: (no expires) http://devwww.someplace.com/favicon.ico Also, YSlow indicates: Grade C on Configure entity tags (ETags) for the same file. My relevant config (.htaccess): # Configure ETags FileETag MTime Size <IfModule mod_expires.c> # Enable Expires Headers for this directory and sub directories that don't override it ExpiresActive on # Set default expiration for all files ExpiresDefault "access plus 24 hours" # Add Proper MIME-Type for Favicon AddType image/x-icon .ico # Set specific expriation by file type ExpiresByType image/x-icon "access plus 1 month" ExpiresByType image/ico "access plus 1 month" ExpiresByType image/icon "access plus 1 month" </IfModule> As you can see, I am setting both, etags and expiration however, both seem to be ignored. Yes, mod_expires is being loaded by my Apache configuration.

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  • Screencasting with explanation boxes

    - by Bakhtiyor
    I wanted to make a video demonstration of one software. I wanted to use text description instead of using voice description, a simple example of what I've explained could be this short screencasting, where author uses short text messages instead of explaining it with his own voice. Could you recommend any free software for doing such a screencasting please? Would be better if it works in Ubuntu or if it is a web application. UPDATE I have found out Wink which could add explanations boxes as I said. Now the problem is that it doesn't support Linux 64bit, has only 32bit. Any other app like Wink for 64bit Linux?

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  • unable to copy file to folder, permission denied without explanation

    - by ValekHalfHeart
    Recently Norton Internet security deleted ml.exe (an assembler I use to program in masm32) off of my computer, thinking that one of the programs I had written with it was a virus (it was most certainly not). Fortunately, I had a copy of ml.exe backed up in an external hard drive, and tried to copy it over to my computer. The old ml.exe was located in C:\masm32\bin, so I tried to copy the new one to that location. After disabling Norton (which had opened the folder and preventing me from accessing it), I am still unable to copy the new file to C:\masm32\bin. When I tried, Windows announced that I would need Administrator permission to copy the file. Since I'm an admin, I figured this wouldn't be a problem although it was unexpected, as I have never had to provide administrator permission to access this folder before. However, instead of prompting me to enter my password, Windows simply refuses to copy the file: I repeat, I was not asked to provide a password. It simply says that I do not have permission. Does anyone know what's happening and how to fix it? Is Norton still causing problems, or it something else?

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  • SharePoint 2010 MySites - Simple explanation needed!

    - by Chris W
    I've been playing around with the 2010 beta for a couple of weeks, experimenting with topology options etc. I think I've got myself totally confused as to how it works hence if there's any SP experts out there that can explain things in simple terms for me I'd appreciate it! I want to setup a farm with 3 servers providing the content & MySites. I presume that the way to do this is to load balance or DNS round robin traffic between the 3 servers. The bit where I'm confused is that My Site Settings page asks for a specific My Site Host hence all my site traffic will be pushed to a single server even though we have 3 in the farm. If this hosts fails I presume MySites will be unavailable. Is this right? How do I configure it so that access to MySites is load balanced across the 3 servers in the farm?

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  • Explanation of command to uppercase the first letter of a file

    - by hazielquake
    Hi I'm trying to learn to rename files with the command line, and after browsing around a lot of pages I finally found a command that uppercases the first letter of a file, but the problem is that I want to understand the meaning of each command. The command is: for i in *; do new=echo "$i" | sed -e 's/^./\U&/'; mv "$i" "$new";done I understand the 'for' kinda... but not the 'echo' or '`' and especially the sed command. if someone has a little patience to explain the meaning of each thing that'd be awesome! Thanks!

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