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  • Using Linux LVM, can I change the number of stripes and "rebalance" the logical volume?

    - by mss
    I created a RAID10 by adding two RAID1 md devices as physical volumes to a volume group. Unfortunately it looks like I forgot to specify the number of stripes when I created the logical volumes (it was late): PV VG Fmt Attr PSize PFree /dev/md312 volume lvm2 a- 927.01G 291.01G /dev/md334 volume lvm2 a- 927.01G 927.01G I know that I can move all the data of a logical volume from one physical volume to another with pvmove. It also looks like lvextend supports an -i switch to change the number of stripes. Is there any way to combine these two, ie. change the number of stripes and "rebalance" the data over the stripes based on the allocation policy? According to this mail by Ross Walker from March 2010 it isn't possible but maybe this has changed since then.

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  • Apache-Mina FTPServer Issue — unable to login into apache ftp server while using database user manager

    - by piyush
    I am unable to login into apache ftp server while using database user manager: while entering username and password,I am getting following error in log file: [ INFO] 2013-02-07 20:51:07,779 [] [0:0:0:0:0:0:0:1] RECEIVED: USER piyush [ INFO] 2013-02-07 20:51:07,781 [piyush] [0:0:0:0:0:0:0:1] SENT: 331 User name okay, need password for piyush. [ INFO] 2013-02-07 20:51:07,784 [piyush] [0:0:0:0:0:0:0:1] RECEIVED: PASS ***** [ WARN] 2013-02-07 20:51:07,785 [piyush] [0:0:0:0:0:0:0:1] User failed to log in [ WARN] 2013-02-07 20:51:08,285 [piyush] [0:0:0:0:0:0:0:1] Login failure - piyush [ INFO] 2013-02-07 20:51:08,286 [piyush] [0:0:0:0:0:0:0:1] SENT: 530 Authentication failed. [ INFO] 2013-02-07 20:51:08,286 [piyush] [0:0:0:0:0:0:0:1] RECEIVED: QUIT [ INFO] 2013-02-07 20:51:08,290 [piyush] [0:0:0:0:0:0:0:1] SENT: 221 Goodbye. [ INFO] 2013-02-07 20:51:08,291 [piyush] [0:0:0:0:0:0:0:1] CLOSED here is my xml file ftpd-typical.xml: <?xml version="1.0" encoding="UTF-8"?> <!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --> <server xmlns="http://mina.apache.org/ftpserver/spring/v1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:beans="http://www.springframework.org/schema/beans" xsi:schemaLocation=" http://mina.apache.org/ftpserver/spring/v1 http://mina.apache.org/ftpserver/ftpserver-1.0.xsd " id="Prometheus"> <listeners> <nio-listener name="default" port="2121" /> </listeners> <db-user-manager encrypt-passwords="salted"> <data-source> <beans:bean class="org.apache.commons.dbcp.BasicDataSource" > <beans:property name="driverClassName" value="com.mysql.jdbc.Driver" /> <beans:property name="url" value="jdbc:mysql://localhost/apache_test" /> <beans:property name="username" value="amy" /> <beans:property name="password" value="piyush" /> </beans:bean> </data-source> <insert-user>INSERT INTO FTP_USER (userid, userpassword, homedirectory, enableflag, writepermission, idletime, uploadrate, downloadrate) VALUES ('{userid}', '{userpassword}', '{homedirectory}', {enableflag}, {writepermission}, {idletime}, {uploadrate}, {downloadrate}) </insert-user> <update-user>UPDATE FTP_USER SET userpassword='{userpassword}',homedirectory='{homedirectory}',enableflag={enableflag},writepermission={writepermission},idletime={idletime},uploadrate={uploadrate},downloadrate={downloadrate} WHERE userid='{userid}' </update-user> <delete-user>DELETE FROM FTP_USER WHERE userid = '{userid}' </delete-user> <select-user>SELECT userid, userpassword, homedirectory, enableflag, writepermission, idletime, uploadrate, downloadrate, maxloginnumber, maxloginperip FROM FTP_USER WHERE userid = '{userid}' </select-user> <select-all-users>SELECT userid FROM FTP_USER ORDER BY userid </select-all-users> <is-admin>SELECT userid FROM FTP_USER WHERE userid='{userid}' AND userid='admin' </is-admin> <authenticate>SELECT userpassword from FTP_USER WHERE userid='{userid}'</authenticate> </db-user-manager> </server>

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  • Sysprep without audit mode?

    - by askvictor
    In preparing a (windows 7) machine for cloning, does one need to run it in audit mode before installing/customising? I have a customised machine I would like to sysprep and clone, without having to re-create in audit mode. And from where does one run sysprep? Is the command included in the windows distro, or do I need to run it from the AIK, or from a PE environment?

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  • Copy File Contiguously to Disk from OSX/Unix/Linux to FAT32 FS?

    - by alharaka
    So the Sysinternals guys have that cool contig.exe utility that allows me ensure a file is contiguous. I need to copy overs ISO files to a FAT32 USB flash key. Grub4DOS requires the files be continuous, but I do not have Windows access at the moment. Is there a way to copy a file so it is contiguous on the target drive, or a tool like the aforementioned that will make an existing file contiguous. Again, I need it on FAT32, and there lies the rub.

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  • Why is vCenter 5.1u1 exiting hosts from maintenance mode?

    - by Shane Madden
    This vCenter server was just upgraded to 5.1 update 1. I'm going through hosts and bringing firmware up to date, then upgrading them from various versions of 5.0 to 5.1u1. vCenter 5.1u1 seems to have an interesting new behavior: it's removing hosts from maintenance mode when they reconnect after being disconnected -- but very inconsistently, I've seen it maybe 4 or 5 times on ~25-30 host reboots. I've only seen it happen on 5.0 hosts that have not yet been upgraded to 5.1. In the image, I placed the host in maint mode and rebooted it into the HP SPP DVD's automatic update mode. After its usual ~40 minute update process, the host came back online.. and 7 seconds before even logging that the host had reconnected, vCenter had sent the host a task to exit maintenance mode. In my understanding, the only time vCenter should drop a host out of maintenance mode is when vCenter put it into maintenance mode itself (such as a VUM upgrade task). Why would this vCenter be unilaterally exiting a host from user-initiated maintenance mode? Edit, additional info: I ran the firmware upgrades on 5 more hosts, all at the same time. Two of them exited maint mode after reconnecting, three did not. The common factor of those exiting maint mode seems to be how long they were offline; the two that took a few tries to boot to the virtual media are the two that got knocked out of maint mode. esx31 (image above): 45 minutes unresponsive esx19 (exited maint): 87 minutes unresponsive esx24 (stayed in maint): 32 minutes unresponsive esx29 (stayed in maint): 39 minutes unresponsive esx32 (stayed in maint): 30 minutes unresponsive esx34 (exited maint): 70 minutes unresponsive Edit: The disconnect time idea seems to have been a red herring, as it's not happening consistently. Additionally, in the vpxd.log the exit maint mode task initiation seems to always immediately follow this vim.EnvironmentBrowser.queryProvisioningPolicy SOAP call. Here's the lines, slightly trimmed for clarity: 15:27:49.535 [info 'vpxdvpxdVmomi'] [ClientAdapterBase::InvokeOnSoap] Invoke done (esx31, vim.EnvironmentBrowser.queryProvisioningPolicy) 15:27:49.560 [info 'commonvpxLro'] [VpxLRO] -- BEGIN task -- esx31 -- HostSystem.exitMaintenanceMode -- Note that on the nodes that don't get the exit task, the vim.EnvironmentBrowser.queryProvisioningPolicy event still occurs. I'm not seeing any other differences in events before or after this in the reconnect process, aside from the extra events caused by exiting maintenance mode. Given the log's mention of provisioning policies, looking for autodeploy-related maintenance mode issues turns up complaints about similar behavior (though I'm not using autodeploy at all).

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  • Making Apache 2.2 on SuSE Linux Case In-Sensitive. Which is a better approach?

    - by pingu
    Problem: http://<server>/home/APPLE.html http://<server>/hoME/APPLE.html http://<server>/HOME/aPPLE.html http://<server>/hoME/aPPLE.html All the above should pick this http://<server>/home/apple.html I implemented 2 solutions and both are working fine. Not sure which one is better(performance). Please Suggest..Also Directive - CheckCaseOnly on never worked Option 1: a)Enable:mod_speling In /etc/sysconfig/apache2 - APACHE_MODULES="rewrite speling apparmor......" b) Add directive - CheckSpelling on (Either in .htaccess or add in httpd.conf) In httpd.conf <Directory srv/www/htdcos/home> Order allow,deny CheckSpelling on Allow from all </Directory> or In .htaccess inside /srv/www/htdcos/home(your content folder) CheckSpelling on Option 2: a) Enable: mod_rewrite b) Write the rule vhost(you can not write RewriteMap in directory. check apache docs ) <VirtualHost _default_:80> <IfModule mod_rewrite.c> Options +FollowSymLinks RewriteEngine on RewriteMap lc int:tolower RewriteCond %{REQUEST_URI} [A-Z] RewriteRule (.*) ${lc:$1} [R=301,L] </IfModule> </VirtualHost> <VirtualHost _default_:80> <IfModule mod_rewrite.c> Options +FollowSymLinks RewriteEngine on RewriteMap lc int:tolower RewriteCond %{REQUEST_URI} [A-Z] RewriteRule (.*) ${lc:$1} [R=301,L] </IfModule> </VirtualHost> This changes the entire request uri into lowercase. I want this to happen for specific folder, but RewriteMap doesn't work in .htaccess. I am novice in regex and Rewrite. I need a RewriteCond which checks only /css//. can any body help

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  • Is Linux Virtual Server old, or is it standing still?

    - by Vimvq1987
    Based on this question: http://serverfault.com/questions/124905/widely-used-load-balancing-solutions, LVS may be the right solution for my problem. But when I went to its homepage http://www.linuxvirtualserver.org/, I found that LVS has been updated since Nov, 2008. The world's moving fast, and I don't know if LVS was obsolete or not. Is LVS standing still, or there're some better solutions to replace it? Thank you so much.

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  • Understanding what needs to be in place for a server to send outgoing email from a linux box

    - by Matt
    I am attempting to configure an openSuse 11.1 box to send outgoing email for a domain that the same server is hosting. I don't understand enough about smtp servers and the like to know what needs to be in place and working. The system already had Postfix installed, and I confirmed it was running via a > sudo /etc/init.d/postfix status I examined the Postfix config file in /etc/main.cf and configured a couple of items regarding the domain/host name and such, but left it largely default. I attempted to send an email from the command line with the following command: > echo "test 123" | mail -s "test subject" [email protected] Where differentdomain.com was not the same domain as the one best hosted on the server. However, the email never reaches the target account. Any suggestions? EDIT: In the postfix log, (/var/log/mail.info, there's nothing in .err) I see that postfix is trying to connect to what appears to be a different smtp server on our network, with a connection refused: connect to ourdomain.com.inbound15.mxlogic.net[our ip address]:25: Connection refused However, I can't figure out why it is 1) trying to connect to that server and 2) not just sending the messages itself... I mean, isn't postfix an smtp server? I did a grep -ri on ourdomain from /etc and see no configuration files anywhere telling it to do this. Why is it?

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  • Strategy for using snapshots to back up Ubuntu Linux server?

    - by MountainX
    I need some backup advice for my home file server. Here are the mount points, volume groups, logical volumes and used/total space of all the volumes on my Ubuntu 8.10 home file server. / vgA/lvRoot [7.5G/50G] /tmp vgB/lvTmp [195M/30G] /var vgB/lvVar [780M/30G] swap vgB/lvSwap [16.00 GB] /media1 vgC/lvMedia1 [400G/975G] /media2 vgC/lvMedia2 [75G/295G] /boot partition (no volume group) [95M/200M] /video partition (no volume group) [450G/950G] /backups vgD/lvBackupTarget [800G/925G] /home vgE/lvHome [85G/200G] I have just added a 2.0 TB external USB drive that I would like to use to backup everything. (It will be a close fit to get it all on one 2.0 TB drive. I actually have a 2nd external USB drive if needed.) I'd like to backup "/", var, /media1, media2 and /home. I'll deal with /boot and /video separately since they are not logical volumes. For all the logical volumes I'm anticipating taking snapshots and then copying those snapshots to the 2.0 TB external USB drive. I have never done a task like that before. If I do that, I could use the tutorial I found here: http://www.howtoforge.com/linux_lvm_snapshots My questions are: What is the best overall strategy? Is it LVM snapshots, as I'm assuming? How should I prepare, subdivide and mount the 2.0 TB external USB drive? 2.a. Should I create one or more regular partitions or should I create a physical volume with one or more logical volumes? 2.b. Would it be advisable to extactly mirror the source pv/lv layout on the external drive, and if so, is this a good strategy? What's the best way to get the snapshots onto the external drive? dd? Even though this is a strategy question, feedback with actual commands is appreciated. I need step-by-step cookbook-style help because I don't do much server admin work. (Background: This is a home file server that I have rarely had to touch in about 2 years. It has done its job without much intervention. The really old PC that I used to back everything up recently failed, so I'm replacing that with the external USB drive(s) and I'd like to upgrade my backup strategy at the same time. Previously, I just copied stuff from /backups over to the other computer and that would not have made things very easy in a real restore situation. The /backups mount point contains backup copies of "most" of the important data on a file by file basis, but it does not contain copies of /boot, etc. BTW, the actual internal HDD that holds /backups is separate from the other storage devices.) EDIT: I'll propose a strategy... The idea came from a comment here: LVM mirroring VS RAID1 "LVM mirrors are for replication of a logical volume to a different physical volume. It's essentially meant to "move the data to a different disk". The mirror is then broken..." That would fit my requirements well. Here is an ideal situation: establish the LV mirror on the external drive break the link with the mirror create a (persistent) snapshot on the mirror after a week, resync the mirror with the original source and update the mirror break the link and create another snapshot on the mirror. Obviously, the mirror will be like a weekly full backup. And the snapshots on the mirror will represent earlier points in time. If this would work and if it would be time efficient, it would give a nice full & differential type backup on the external drive based on LVM. I have not heard of a strategy like this before. Will it work? Could it be scripted? Thoughts? EDIT 2: Creating Portable DiskSafes With LoopbackFS And LVM Snapshots This article seems intriguing: http://www.howtoforge.com/creating-portable-disksafes-with-loopbackfs-and-lvm-snapshots Unfortunately, I don't understand exactly how to map those ideas to the strategy I'm proposing above. I'm going to ask this last bit as a separate question. I will leave my original question in place because I still desire feedback on the overall best strategy. At this moment I'm assuming it is LVM mirroring in the style of "Creating Portable DiskSafes with LVM Snapshots" but that might be wrong.

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  • How to copy file preserving directory path in Linux?

    - by gasan
    I have Eclipse projects and ".project" file in them, the directory structure looks like 'myProject/.project'. I want to copy these '.project' files to another directory, but I want the enclosing directory name to be preserved. Let's say I have 'a/myProject/.project', I want to copy 'myProject/.project' to 'b', so it be 'b/myProject/.project', but 'b/myProject' doesn't exist. When I try in a: cp -r ./myProject/.project ../b it copies only '.project' file itself, without 'myProject' directory. Please advise.

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  • what firefall linux distro applicance could track internet usage per device in my home?

    - by GregH
    Hello, Anyone know of a community edition/open source/free firewall/gateway software product that I could install onto an old PC to act as my firewall/gateway/proxy etc, BUT for which it has the power to track internet usage per device in my home. So: a) Mandatory - Track internet usage for devices on my home network on a per device basis (e.g. various PCs/Xbox etc) b) Mandatory - Report/graph would would give a breakdown of internet usage, per device (e.g. IP address), per day. c) Desirable - as in b) above but per hour d) Desirable - realtime graph (e.g. 5 minute measurement intervals or something) that shows current internet usage per device e) Mandatory - Handles all internal<=internet requests for all protocols (e.g. HTTP, HTTPS, xbox etc) f) Mandatory - No explicit settings in clients required - i.e. Transparent Monitoring concept (for both HTTP and non-HTTP traffic like xbox, skype etc) g) Mandatory - easy "appliance" like installation onto a dedicated low spec PC thanks in advance

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  • database replication for new user signup

    - by Jeff Storey
    I have a database that stores the users of my application. When a new user signs up, a record is inserted into the database for that user. I have a replicated version (slave) of this database (using mysql for now). What I'm concerned about is this scenario: step 1: user signs up and user record is inserted into the database step 2: user then tries to login, and the login process queries the database for the user. however, this query hits the slave database, but the user record has not yet been replicated in the slave and it returns an error that the user does not exist. This is a pretty trivial example, but I can see how it can apply to a lot of cases. Is there a strategy for configuring replicated databases to help prevent this situation?

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  • How to create an alias for linux server name?

    - by Radek
    The openSUSE server name is 'darkhelmet'. I want to create an alias 'dh' for it. So I can also type 'ssh dh' and 'http://dh' would work too. What file/files and where do I have to edit to make this happen? Extract from /etc/hosts from darkhelmet 127.0.0.1 localhost # special IPv6 addresses ::1 localhost ipv6-localhost ipv6-loopback fe00::0 ipv6-localnet ff00::0 ipv6-mcastprefix ff02::1 ipv6-allnodes ff02::2 ipv6-allrouters ff02::3 ipv6-allhosts 127.0.0.2 darkhelmet.edumate darkhelmet 10.0.0.22 db2workgroup db2workgroup [root][skroob] nslookup darkhelmet Server: 10.0.0.10 Address: 10.0.0.10#53 Name: darkhelmet.edumate Address: 10.0.0.22

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  • How to install ADFS 3.0 in standalone mode?

    - by user18044
    I've installed Windows 2012 R2 and enabled the ADFS (3.0?) feature. After installation, it asks to configure ADFS, but this step requires a user account that is a domain administrator, as it wants to create certificate containers and SPN records. In ADFS 2.0, you could install in standalone mode which required only local admin rights, storing everything in the Windows Internal Database. If this still possible with the latest version? If so, how do I configure ADFS in standalone mode?

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  • How to execute with /bin/false shell

    - by Amar
    I am trying to setup per-user fastcgi scripts that will run each on a different port and with a different user. Here is example of my script: #!/bin/bash BIND=127.0.0.1:9001 USER=user PHP_FCGI_CHILDREN=2 PHP_FCGI_MAX_REQUESTS=10000 etc... However, if I add user with /bin/false (which I want, since this is about to be something like shared hosting and I don't want users to have shell access), the script is run under 1001, 1002 'user' which, as my Google searches showed, might be a security hole. My question is: Is it possible to allow user(s) to execute shell scripts but disable them so they cannot log in via SSH?

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  • How do you add a certificate for WLAN in Linux, at the command-line?

    - by Neil
    I'm using Maemo on a Nokia n810 Internet tablet, and when given a list of installed certificates to choose from when connecting to a PEAP wireless network, it's always blank. I've already installed a couple of certificates through the gui on the device, and only the certificate authorities show up. I've confirmed that Maemo's connection software that handles certificates is buggy, in such a way that certificates are never added, or properly added certificates cannot be found. Is there a way to add WLAN certificates at the command-line, and connect to a wireless network at the command-line as well? I used to use iwconfig to connect, but I never used it with PEAP. Note: I have nothing in /etc/ssl/certs

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  • Secure method of changing a user's password via Python script/non-interactively

    - by Matthew Rankin
    I've created a Python script using Fabric to configure a freshly built Slicehost Ubuntu slice. In case you're not familiar with Fabric, it uses Paramiko, a Python SSH2 client, to provide remote access "for application deployment or systems administration tasks." One of the first things I have the Fabric script do is to create a new admin user and set their password. Unlike Pexpect, Fabric cannot handle interactive commands on the remote system, so I need to set the user's password non-interactively. At present, I'm using the chpasswd command to change the password. This transmits the password as clear text over SSH to the remote system. Questions Is my current method of setting the password a security concern? Currently, the drawback I see is that Fabric shows the password as clear text on my local system as follows: [xxx.xx.xx.xxx] run: echo "johnsmith:supersecretpassw0rd" | chpasswd. Since I only run the Fabric script from my laptop, I don't think this is a security issue, but I'm interested in others' input. Is there a better method for setting the user's password non-interactively? Another option, would be to use Pexpect from within the Fabric script to set the password. Current Code # Fabric imports and host configuration excluded for brevity root_password = getpass.getpass("Root's password given by SliceManager: ") admin_username = prompt("Enter a username for the admin user to create: ") admin_password = getpass.getpass("Enter a password for the admin user: ") env.user = 'root' env.password = root_password # Create the admin group and add it to the sudoers file admin_group = 'admin' run('addgroup {group}'.format(group=admin_group)) run('echo "%{group} ALL=(ALL) ALL" >> /etc/sudoers'.format( group=admin_group) ) # Create the new admin user (default group=username); add to admin group run('adduser {username} --disabled-password --gecos ""'.format( username=admin_username) ) run('adduser {username} {group}'.format( username=admin_username, group=admin_group) ) # Set the password for the new admin user run('echo "{username}:{password}" | chpasswd'.format( username=admin_username, password=admin_password) ) Local System Terminal I/O $ fab config_rebuilt_slice Root's password given by SliceManager: Enter a username for the admin user to create: johnsmith Enter a password for the admin user: [xxx.xx.xx.xxx] run: addgroup admin [xxx.xx.xx.xxx] out: Adding group `admin' (GID 1000) ... [xxx.xx.xx.xxx] out: Done. [xxx.xx.xx.xxx] run: echo "%admin ALL=(ALL) ALL" >> /etc/sudoers [xxx.xx.xx.xxx] run: adduser johnsmith --disabled-password --gecos "" [xxx.xx.xx.xxx] out: Adding user `johnsmith' ... [xxx.xx.xx.xxx] out: Adding new group `johnsmith' (1001) ... [xxx.xx.xx.xxx] out: Adding new user `johnsmith' (1000) with group `johnsmith' ... [xxx.xx.xx.xxx] out: Creating home directory `/home/johnsmith' ... [xxx.xx.xx.xxx] out: Copying files from `/etc/skel' ... [xxx.xx.xx.xxx] run: adduser johnsmith admin [xxx.xx.xx.xxx] out: Adding user `johnsmith' to group `admin' ... [xxx.xx.xx.xxx] out: Adding user johnsmith to group admin [xxx.xx.xx.xxx] out: Done. [xxx.xx.xx.xxx] run: echo "johnsmith:supersecretpassw0rd" | chpasswd [xxx.xx.xx.xxx] run: passwd --lock root [xxx.xx.xx.xxx] out: passwd: password expiry information changed. Done. Disconnecting from [email protected]... done.

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  • Ideas for SVN/SQL/PHP/Linux Dev Enviroment Supporting Multiple Isolated Environments?

    - by jpganz18
    I am trying to create a "dev" for my users. In that environment they would access to their own account of PHPMyAdmin, SQL, Subversion and FTP which is not a big problem, but I would like to emulate like if each one would be in their own server. I mean so that they could change the PHP configuration (for example) and would be done only in its own environment. Any idea how to do this? Do I have to make something "special" at the installations of my server or something like that?

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  • rhel/centos vs. ubuntu (possibly other debian-based systems) linux in handling duplicate ips in the same subnet

    - by johnshen64
    This has bothered me for quite a while but I never found out why or how to change the behavior. ip duplicates could be caused by typos or dhcp errors etc., but they do occur from time to time. in rpm-based systems such as centos, the old server with the duplicate ip wins, and the new server will get an error in bringing up the nic (ip address already used). this is somewhat harmless because we can just fix the system that is coming up. ubuntu only the other hand happily grabs the used ip for itself and leave the old server/device without a valid ip. this is the more dangerous behavior because it causes outages. what i want is to change the ubuntu behavior to that of the centos/rhel so would appreciate any help.

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  • What is the easiest/simplest way to change the HD on a Linux server?

    - by ArmlessJohn
    Hello. I have a machine running Ubuntu Server that has been presenting some HD-related problems. Instead of reinstalling and reconfiguring everything (and to save time) we'd like to copy everything from the current hard drive to a new one and start using it. We only have a single hard drive with a main partition and a swap partition. What tools or methods would you recommend for replacing a hard drive with minimum difficulty and chance of problems? Thank you.

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  • Linux not buffering block I/O when the device is not "in use" (i.e. mounted)

    - by Radek Hladík
    I am installing new server and I've found an interesting issue. The server is running Fedora 19 (3.11.7-200.fc19.x86_64 kernel) and is supposed to host a few KVM/Qemu virtual servers (mail server, file server, etc..). The HW is Intel(R) Xeon(R) CPU 5160 @ 3.00GHz with 16GB RAM. One of the most important features will be Samba server and we have decided to make it as virtual machine with almost direct access to the disks. So the real HDD is cached on SSD (via bcache) then raided with md and the final device is exported into the virtual machine via virtio. The virtual machine is again Fedora 19 with the same kernel. One important topic to find out is whether the virtualization layer will not introduce high overload into disk I/Os. So far I've been able to get up to 180MB/s in VM and up to 220MB/s on real HW (on the SSD disk). I am still not sure why the overhead is so big but it is more than the network can handle so I do not care so much. The interesting thing is that I've found that the disk reads are not buffered in the VM unless I create and mount FS on the disk or I use the disks somehow. Simply put: Lets do dd to read disk for the first time (the /dev/vdd is an old Raptor disk 70MB/s is its real speed): [root@localhost ~]# dd if=/dev/vdd of=/dev/null bs=256k count=10000 ; cat /proc/meminfo | grep Buffers 2621440000 bytes (2.6 GB) copied, 36.8038 s, 71.2 MB/s Buffers: 14444 kB Rereading the data shows that they are cached somewhere but not in buffers of the VM. Also the speed increased to "only" 500MB/s. The VM has 4GB of RAM (more that the test file) [root@localhost ~]# dd if=/dev/vdd of=/dev/null bs=256k count=10000 ; cat /proc/meminfo | grep Buffers 2621440000 bytes (2.6 GB) copied, 5.16016 s, 508 MB/s Buffers: 14444 kB [root@localhost ~]# dd if=/dev/vdd of=/dev/null bs=256k count=10000 ; cat /proc/meminfo | grep Buffers 2621440000 bytes (2.6 GB) copied, 5.05727 s, 518 MB/s Buffers: 14444 kB Now lets mount the FS on /dev/vdd and try the dd again: [root@localhost ~]# mount /dev/vdd /mnt/tmp [root@localhost ~]# dd if=/dev/vdd of=/dev/null bs=256k count=10000 ; cat /proc/meminfo | grep Buffers 2621440000 bytes (2.6 GB) copied, 4.68578 s, 559 MB/s Buffers: 2574592 kB [root@localhost ~]# dd if=/dev/vdd of=/dev/null bs=256k count=10000 ; cat /proc/meminfo | grep Buffers 2621440000 bytes (2.6 GB) copied, 1.50504 s, 1.7 GB/s Buffers: 2574592 kB While the first read was the same, all 2.6GB got buffered and the next read was at 1.7GB/s. And when I unmount the device: [root@localhost ~]# umount /mnt/tmp [root@localhost ~]# cat /proc/meminfo | grep Buffers Buffers: 14452 kB [root@localhost ~]# dd if=/dev/vdd of=/dev/null bs=256k count=10000 ; cat /proc/meminfo | grep Buffers 2621440000 bytes (2.6 GB) copied, 5.10499 s, 514 MB/s Buffers: 14468 kB The bcache was disabled while testing and the results are same on faster (newer) HDDs and on SSD (except for the initial read speed of course). To sum it up. When I read from the device via dd first time, it gets read from the disk. Next time I reread it gets cached in the host but not in the guest (thats actually the same issue, more on that later). When I mount the filesystem but try to read the device directly it gets cached in VM (via buffers). As soon as I stop "using" it, buffers are discarded and the device is not cached anymore in the VM. When I looked into buffers value on the host I realized that the situation is the same. The block I/O gets buffered only when the disk is in use, in this case it means "exported to a VM". On host, after all the measurement done: 3165552 buffers On the host, after the VM shutdown: 119176 buffers I know it is not important as the disks will be mounted all the time but I am curious and I would like to know why it is working like this.

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