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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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  • How do I convert a Linux disk image into a sparse file?

    - by endolith
    I have a bunch of disk images, made with ddrescue, on an EXT partition, and I want to reduce their size without losing data, while still being mountable. How can I fill the empty space in the image's filesystem with zeros, and then convert the file into a sparse file so this empty space is not actually stored on disk? For example: > du -s --si --apparent-size Jimage.image 120G Jimage.image > du -s --si Jimage.image 121G Jimage.image This actually only has 50G of real data on it, though, so the second measurement should be much smaller. This supposedly will fill empty space with zeros: cat /dev/zero > zero.file rm zero.file But if sparse files are handled transparently, it might actually create a sparse file without writing anything to the virtual disk, ironically preventing me from turning the virtual disk image into a sparse file itself. :) Does it? Note: For some reason, sudo dd if=/dev/zero of=./zero.file works when cat does not on a mounted disk image.

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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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  • 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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  • 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 set up a linux user that can only access a repository via ssh?

    - by GJ
    I have a mercurial repository on a secure server, to which I want to grant secure access to an external user. I added for him a user account and publickey ssh authentication so that now he could push/pull changesets via ssh. My question is: how can I make this new user account completely disabled from doing anything or accessing any data on the server other than accessing the repository? E.g. he shouldn't even have the possibility to enter an interactive shell session. Thanks

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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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  • Linux: Force fsck of a read-only mounted filesystem?

    - by Timothy Miller
    I'm developing for a headless embedded appliance, running CentOS 6.2. The user can connect a keyboard, but not a monitor, and a serial console would require opening the case, something we don't want the user to have to do. This all pretty much obviates the possibility of using a recovery USB drive to boot from, unless all it does is blindly reimage the harddrive. I would like to provide some recovery facilities, and I have written a tool that comes up on /dev/tty1 in place of getty to provide these functions. One such function is fsck. I have found out how to remount the root and other file systems read-only. Now that they are read-only, it should be safe to fsck them and then reboot. Unfortunately, fsck complains to me that the filesystems are mounted and refuses to do anything. How can I force fsck to run on a read-only mounted partition? Based on my research, this is going to have to be something obscure. "-f" just means to force repair of a clean (but unmounted) partition. I need to repair a clean or unclean mounted partition. From what I read, this is something "only experts" should do, but no one has bothered to explain how the experts do it. I'm hoping someone can reveal this to me. BTW, I've noticed that e2fsck 1.42.4 on Gentoo will let you fsck a mounted partition, even mounted read-write, but it seems only to do so if fsck is run from a terminal, so it can ask the user if they're sure they want to do something so dangerous. I'm not sure if the CentOS version does the same thing, but it appears that fsck CAN repair a mounted partition, but it flatly refuses to when not run from a terminal. One last-resort option is for me to compile my own hacked fsck. But I'm afraid I'll mess it up in some unexpected way. Thanks! Note: Originally posted here.

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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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  • 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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  • How to get an ARM CPU clock speed in Linux?

    - by MiKy
    I have an ARM-based embedded machine based on S3C2416 board. According to the specifications I have available there should be a 533 MHz ARM9 (ARM926EJ-S according to /proc/cpuinfo), however the software running on it "feels" slow, compared to the same software on my Android phone with a 528MHz ARM CPU. /proc/cpuinfo tells me that BogoMIPS is 266.24. I know that I should not trust BogoMIPS regarding performance ("Bogo" = bogus), however I would like to get a measurement on the actual CPU speed. On x86, I could use the rdtsc instruction to get the time stamp counter, wait a second (sleep(1)), read the counter again to get an approximation on the CPU speed, and according to my experience, this value was close enough to the real CPU speed. How can I find the actual CPU speed of given ARM processor? Update I found this simple Pi calculator, which I compiled both for my Android phone and the ARM board. The results are as follows: S3C2416 # cat /proc/cpuinfo Processor : ARM926EJ-S rev 5 (v5l) BogoMIPS : 266.24 Features : swp half fastmult edsp java ... #./pi_arm 10000 Calculation of PI using FFT and AGM, ver. LG1.1.2-MP1.5.2a.memsave ... 8.50 sec. (real time) Android # cat /proc/cpuinfo Processor : ARMv6-compatible processor rev 2 (v6l) BogoMIPS : 527.56 Features : swp half thumb fastmult edsp java # ./pi_android 10000 Calculation of PI using FFT and AGM, ver. LG1.1.2-MP1.5.2a.memsave ... 5.95 sec. (real time) So it seems that the ARM926EJ-S is slower than my Android phone, but not twice slower as I would expect by the BogoMIPS figures. I am still unsure about the clock speed of the ARM9 CPU.

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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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  • wireless internet in linux is very very slow... but in windows.... everythnings fine

    - by Cody Acer
    yesterday when i was connecting to our neighbors wifi connection which is the signal strength is below 50%, i cant browse anything... even ping to gateway. 100% packet loss, and sometimes.. i can connect awesomely i can open my facebook account for 15 minutes but after 15min.. connection is extremely slow. but not windows i can surf even the signal str is very poor weird ey??.. root@Emely:~# lspci -knn 00:00.0 Host bridge [0600]: Intel Corporation Atom Processor D4xx/D5xx/N4xx/N5xx DMI Bridge [8086:a010] Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: agpgart-intel 00:02.0 VGA compatible controller [0300]: Intel Corporation Atom Processor D4xx/D5xx/N4xx/N5xx Integrated Graphics Controller [8086:a011] Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: i915 Kernel modules: i915 00:02.1 Display controller [0380]: Intel Corporation Atom Processor D4xx/D5xx/N4xx/N5xx Integrated Graphics Controller [8086:a012] Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] 00:1b.0 Audio device [0403]: Intel Corporation NM10/ICH7 Family High Definition Audio Controller [8086:27d8] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: snd_hda_intel Kernel modules: snd-hda-intel 00:1c.0 PCI bridge [0604]: Intel Corporation NM10/ICH7 Family PCI Express Port 1 [8086:27d0] (rev 02) Kernel driver in use: pcieport Kernel modules: shpchp 00:1c.1 PCI bridge [0604]: Intel Corporation NM10/ICH7 Family PCI Express Port 2 [8086:27d2] (rev 02) Kernel driver in use: pcieport Kernel modules: shpchp 00:1c.2 PCI bridge [0604]: Intel Corporation NM10/ICH7 Family PCI Express Port 3 [8086:27d4] (rev 02) Kernel driver in use: pcieport Kernel modules: shpchp 00:1c.3 PCI bridge [0604]: Intel Corporation NM10/ICH7 Family PCI Express Port 4 [8086:27d6] (rev 02) Kernel driver in use: pcieport Kernel modules: shpchp 00:1d.0 USB controller [0c03]: Intel Corporation NM10/ICH7 Family USB UHCI Controller #1 [8086:27c8] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: uhci_hcd 00:1d.1 USB controller [0c03]: Intel Corporation NM10/ICH7 Family USB UHCI Controller #2 [8086:27c9] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: uhci_hcd 00:1d.2 USB controller [0c03]: Intel Corporation NM10/ICH7 Family USB UHCI Controller #3 [8086:27ca] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: uhci_hcd 00:1d.3 USB controller [0c03]: Intel Corporation NM10/ICH7 Family USB UHCI Controller #4 [8086:27cb] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: uhci_hcd 00:1d.7 USB controller [0c03]: Intel Corporation NM10/ICH7 Family USB2 EHCI Controller [8086:27cc] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: ehci-pci 00:1e.0 PCI bridge [0604]: Intel Corporation 82801 Mobile PCI Bridge [8086:2448] (rev e2) 00:1f.0 ISA bridge [0601]: Intel Corporation NM10 Family LPC Controller [8086:27bc] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: lpc_ich Kernel modules: lpc_ich 00:1f.2 SATA controller [0106]: Intel Corporation NM10/ICH7 Family SATA Controller [AHCI mode] [8086:27c1] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: ahci Kernel modules: ahci 00:1f.3 SMBus [0c05]: Intel Corporation NM10/ICH7 Family SMBus Controller [8086:27da] (rev 02) Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel modules: i2c-i801 05:00.0 Network controller [0280]: Broadcom Corporation BCM4313 802.11bgn Wireless Network Adapter [14e4:4727] (rev 01) Subsystem: Wistron NeWeb Corp. Device [185f:051a] Kernel driver in use: bcma-pci-bridge Kernel modules: bcma 09:00.0 Ethernet controller [0200]: Marvell Technology Group Ltd. 88E8040 PCI-E Fast Ethernet Controller [11ab:4354] Subsystem: Samsung Electronics Co Ltd Notebook N150P [144d:c072] Kernel driver in use: sky2 Kernel modules: sky2 root@Emely:~# ip addr show 1: lo: mtu 65536 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: eth0: mtu 1500 qdisc pfifo_fast state DOWN qlen 1000 link/ether e8:11:32:2e:a6:fd brd ff:ff:ff:ff:ff:ff 3: wlan0: mtu 1500 qdisc mq state UP qlen 1000 link/ether 00:1b:b1:a9:ac:e0 brd ff:ff:ff:ff:ff:ff inet 192.168.1.108/24 brd 192.168.1.255 scope global wlan0 inet6 fe80::21b:b1ff:fea9:ace0/64 scope link valid_lft forever preferred_lft forever root@Emely:~# ip link show 1: lo: mtu 65536 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth0: mtu 1500 qdisc pfifo_fast state DOWN qlen 1000 link/ether e8:11:32:2e:a6:fd brd ff:ff:ff:ff:ff:ff 3: wlan0: mtu 1500 qdisc mq state UP qlen 1000 link/ether 00:1b:b1:a9:ac:e0 brd ff:ff:ff:ff:ff:ff root@Emely:~# rfkill list all 0: samsung-wlan: Wireless LAN Soft blocked: no Hard blocked: no 1: samsung-bluetooth: Bluetooth Soft blocked: no Hard blocked: no 2: hci0: Bluetooth Soft blocked: no Hard blocked: no 3: phy0: Wireless LAN Soft blocked: no Hard blocked: no is this a wireless driver issue?

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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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  • Smartcards for storing gpg/ssh keys (Linux) - what do I need?

    - by Ninefingers
    Hi All, I'm interested in storing my SSH keys and gpg keys on a smartcard for added security. However, I'm a bit uncertain on a few points, which are as follows: How many keys can I get on a card? I assume both SSH and GPG can store keys on the card. Is there a limit to key size? I see a lot of cards saying they support 2048-bit keys, what about larger sizes? Hardware: can anyone recommend a card/reader combination that works well? I've done a fair amount of research and it seems PC/SC readers can be a bit iffy - is this your experience? Have I missed anything I should be asking? Are there any other hurdles? I'm aware fsf europe give away cards with membership - I'm not sure I want to join, but... are these cards any good?

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  • Removing grub and getting a dual boot of Linux Mint and Win 8.1 working after failed attempt

    - by ThroatOfWinter57
    I gave the details of my problem at reddit: http://www.reddit.com/r/linuxquestions/comments/27qrun/more_specific_questions_about_failed_win_81mint/ tl;dr: I deleted the /, /home, and swap partitions I made for mint after realizing my installation couldn't be booted into and gave the space back to my windows partition. Running boot-repair on my mint live session messed stuff up. Now I can't even boot to my live session usb because grub is left over. Windows 8.1 does work though.

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