Derwynd's Weblog

Linux disk cache

Linux has a supposedly good memory management feature that will use up any “extra” RAM you have to cache stuff.
Accessed file’s content gets cached in RAM for fast access eventhough we might not need it later in RAM.

$ free -m
total used free shared buffers cached
Mem: 1504 1490 14 0 24 809
-/+ buffers/cache: 656 848
Swap: 0 0 0

In Linux, you can clear the cache of the memory by using

$ sync; echo 3 > /proc/sys/vm/drop_caches; echo 0 > /proc/sys/vm/drop_caches
or
$ sync; sysctl -w vm.drop_caches=3; sysctl -w vm.drop_caches=0

$ free -m
total used free shared buffers cached
Mem: 1504 650 854 0 1 67
-/+ buffers/cache: 581 923
Swap: 0 0 0

sync should be run because this is a non-destructive operation, and dirty objects are not freeable. So you run sync in order to make sure all cached objects are freed.

Doing echo 3 is clearing pagecache, dentries and inodes but you could choose echo 1 to free pagecache only or echo 2 to free dentries and inodes.

July 22, 2010 Posted by derwynd | Uncategorized | Leave a comment

redhat/centos build kernel rpm

Preparing System

$ yum install gcc make bison ncurses-devel rpm-build

Downloading the kernel source linux-2.6.30.10.tar.gz from http://kernel.org

$ nohup wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.30.10.tar.gz &

After you have done it, extract to /usr/src

$ tar zxvf linux-2.6.30.10.tar.gz -C /usr/src

enter to /usr/src
create a symlink to source code called linux, do this:

$ cd /usr/src
$ ln -sf linux-2.6.30.10 linux
drwxr-xr-x 3 root root 4096 Jul 16 14:09 kernels
lrwxrwxrwx 1 root root 12 Jul 16 16:18 linux -> linux-2.6.31
drwxr-xr-x 23 root root 4096 Sep 10 2009 linux-2.6.31
drwxr-xr-x 7 root root 4096 Jul 16 14:11 redhat

Copying the stock config into the dir
$ cd /usr/src/linux
$ cp /boot/config-`uname -r` .config

Compiling the kernel
$ cd /usr/src/linux
$ make clean
$ make menuconfig

If you want to add a custom tag that will identify the new kernel (if you want or skip this) , to accomplish this, do that:
I did not enter anything here and skipped this step

* On initial screen, go to General setup —>
* Select Local version – append to kernel release

┌─────────────── Local version – append to kernel release ────────────────┐
│ Please enter a string value. Use the key to move from the input |
│ field to the buttons below it. │
│ ┌─────────────────────────────────────────────────────────────────────┐
│ │ │
│ └─────────────────────────────────────────────────────────────────────┘

With this done, the resulting kernel.rpm will have the tag identifying it.
It is time to customize the kernel configuration to fit with your hardware.

After this quit menuconfig and start the compilation.

While you get out the configuration, you will be asked to save the changes. Answer Yes.

Run make rpm

$ make rpm

The compilation will start, good time to grab a coffee cause this is going to be long
WROTE:…….
/usr/src/redhat/SRPMS/kernel-2.6.30.10-1.src.rpm
/usr/src/redhat/RPMS/x86_64/kernel-2.6.30.10-1.x86_64.rpm

Take a backup of /boot dir for safety

$ tar czvf boot.tgz /boot/ /etc/grub.conf

Installing the new kernel rpm
$ rpm -ivh rpm -ivh /usr/src/redhat/RPMS/x86_64/kernel-2.6.30.10-1.x86_64.rpm
Preparing… ########################################### [100%]
1:kernel ########################################### [100%]

Confirming that alls ok
$ ls /boot
config-2.6.18-128.el5 grub message System.map-2.6.18-128.el5 vmlinux-2.6.30.10.bz2 vmlinuz-2.6.30.10
config-2.6.30.10 initrd-2.6.18-128.el5.img lost+found symvers-2.6.18-128.el5.gz System.map-2.6.30.10 vmlinuz-2.6.18-128.el5

Hmmm no initrd-2.6.30.10.img

To create the dependencies for the modules:

$ depmod 2.6.30.10

Create a new initrd with mkinitrd

$ mkinitrd -v /boot/initrd-2.6.30.10.img 2.6.30.10
Creating initramfs
Looking for deps of module ehci-hcd
Looking for deps of module ohci-hcd
Looking for deps of module uhci-hcd
Looking for deps of module ext3: jbd
Looking for deps of module jbd
Found root device hda2 for LABEL=/
Looking for driver for device hda2
Looking for deps of module ide:m-disk
Looking for driver for device hda3
Looking for deps of module ide:m-disk
Looking for deps of module ips: scsi_mod
Looking for deps of module scsi_mod
Looking for deps of module sd_mod: scsi_mod
Looking for deps of module ata_piix: scsi_mod libata
Looking for deps of module libata: scsi_mod
Looking for deps of module ide-disk
Looking for deps of module dm-mem-cache
No module dm-mem-cache found for kernel 2.6.30.10, aborting.

Opps errors …… Need to fix this
$ echo “DMRAID=no” > /etc/sysconfig/mkinitrd/noraid
$ chmod 755 /etc/sysconfig/mkinitrd/noraid
$ mkinitrd -v /boot/initrd-2.6.30.10.img 2.6.30.10

Creating initramfs
Looking for deps of module ehci-hcd
Looking for deps of module ohci-hcd
Looking for deps of module uhci-hcd
Looking for deps of module ext3: jbd
Looking for deps of module jbd
Found root device hda2 for LABEL=/
Looking for driver for device hda2
Looking for deps of module ide:m-disk
Looking for driver for device hda3
Looking for deps of module ide:m-disk
Looking for deps of module ips: scsi_mod
Looking for deps of module scsi_mod
Looking for deps of module sd_mod: scsi_mod
Looking for deps of module ata_piix: scsi_mod libata
Looking for deps of module libata: scsi_mod
Looking for deps of module ide-disk
Using modules: /lib/modules/2.6.30.10/kernel/drivers/usb/host/ehci-hcd.ko /lib/modules/2.6.30.10/kernel/drivers/usb/host/ohci-hcd.ko /lib/modules/2.6.30.10/kernel/drivers/usb/host/uhci-hcd.ko /lib/modules/2.6.30.10/kernel/fs/jbd/jbd.ko /lib/modules/2.6.30.10/kernel/fs/ext3/ext3.ko /lib/modules/2.6.30.10/kernel/drivers/scsi/scsi_mod.ko /lib/modules/2.6.30.10/kernel/drivers/scsi/sd_mod.ko /lib/modules/2.6.30.10/kernel/drivers/scsi/ips.ko /lib/modules/2.6.30.10/kernel/drivers/ata/libata.ko /lib/modules/2.6.30.10/kernel/drivers/ata/ata_piix.ko
/sbin/nash -> /tmp/initrd.w19233/bin/nash
/sbin/insmod.static -> /tmp/initrd.w19233/bin/insmod
copy from `/lib/modules/2.6.30.10/kernel/drivers/usb/host/ehci-hcd.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/ehci-hcd.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/drivers/usb/host/ohci-hcd.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/ohci-hcd.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/drivers/usb/host/uhci-hcd.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/uhci-hcd.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/fs/jbd/jbd.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/jbd.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/fs/ext3/ext3.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/ext3.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/drivers/scsi/scsi_mod.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/scsi_mod.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/drivers/scsi/sd_mod.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/sd_mod.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/drivers/scsi/ips.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/ips.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/drivers/ata/libata.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/libata.ko’ [elf64-x86-64]
copy from `/lib/modules/2.6.30.10/kernel/drivers/ata/ata_piix.ko’ [elf64-x86-64] to `/tmp/initrd.w19233/lib/ata_piix.ko’ [elf64-x86-64]
Adding module ehci-hcd
Adding module ohci-hcd
Adding module uhci-hcd
Adding module jbd
Adding module ext3
Adding module scsi_mod
Adding module sd_mod
Adding module ips
Adding module libata
Adding module ata_piix

Checking …….

$ ls /boot/initrd-2.6.30.10.img
initrd-2.6.30.10.img

Editing grub

Final phase, it remains only edit the grub.conf to use the new kernel.

Add the lines in and change default to boot with new kernel

title CentOS (2.6.30.10)
root (hd0,0)
kernel /vmlinuz-2.6.30.10 ro root=LABEL=/ rhgb quiet noacpi irqpoll acpi=off
initrd /initrd-2.6.30.10.img

Reboot. and check
$ reboot

After reboot
$ uname -a
Linux localhost.localdomain 2.6.30.10 #1 SMP Sat Jul 17 13:25:46 IST 2010 x86_64 x86_64 x86_64 GNU/Linux

July 17, 2010 Posted by derwynd | Uncategorized | Leave a comment

KVM on centos5

Disable Selinux

Make sure that SELinux is disabled. Open /etc/selinux/config…

$ vi /etc/selinux/config

… set SELINUX to disabled:

$ reboot

or

Run

$ setenforce 0
[edit] Installing KVM

check if your CPU supports hardware virtualization

$ egrep ‘(vmx|svm)’ –color=always /proc/cpuinfo

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm

install KVM and virtinst

$ yum install zlib-devel alsa-lib-devel SDL-devel gnutls-devel dev86 texi2html glibc-devel kvm qemu\
libvirt python-virtinst virt-manager libvirt libvirt-python python-virtinst qemu

$ yum install kvm qemu libvirt python-virtinst
$ yum install virt-manager libvirt libvirt-python python-virtinst

In case rpmforge repo is recquired for qemu

$ rpm -Uhv http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/RPMS//rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm

[edit] Service Starting

Then start the libvirt daemon:

$ /etc/init.d/libvirtd start

To check if KVM has successfully been installed, run

$ virsh -c qemu:///system list

Id Name State
———————————-

Next we need to set up a network bridge on our server so that our virtual machines can be accessed from other hosts as if they were physical systems in the network.

$ yum install bridge-utils

… and configure a bridge. Delete the system startup links for NetworkManager and create system startup links for network:

$ chkconfig –del NetworkManager
$ chkconfig –levels 235 network on

[edit] Networking

Then create the file /etc/sysconfig/network-scripts/ifcfg-br0 (please use the BOOTPROTO, DNS1 (plus any other DNS settings, if any), GATEWAY, IPADDR, NETMASK and SEARCH values from the /etc/sysconfig/network-scripts/ifcfg-eth0 file):

$ vi /etc/sysconfig/network-scripts/ifcfg-br0

DEVICE=br0
TYPE=Bridge
BOOTPROTO=static
DNS1=192.168.2.234
GATEWAY=192.168.2.234
IPADDR=192.168.40.112
NETMASK=255.255.0.0
ONBOOT=yes

Modify /etc/sysconfig/network-scripts/ifcfg-eth0 by keeping these lines and hashing everything else

DEVICE=eth0
HWADDR=00:1E:C9:B5:0D:51
ONBOOT=yes
BRIDGE=br0

Then reboot the system:

$ reboot

[edit] Starting Hosts

Use graphical installation and run “Creating guests with virt-manager”

$ virt-manager &

Open the File -> Open Connection. The dialog box below appears. . Select a hypervisor and click the Connect button

OR

$ virt-install –accelerate –hvm –connect qemu:///system –network bridge:br0 –name rhel5support –ram=512 –file=/xen/rhel5support.img –file-size=6 –vnc –cdrom=/dev/cdrom

Using virt-install with KVM to create a Red Hat Enterprise Linux 5 guest using cdrom –hvm (full virt)

$ virt-install –name fedora11 –ram 512 –file=/var/lib/libvirt/images/fedora11.img –file-size=3 –vnc –cdrom=/var/lib/libvirt/images/fedora11.iso

Using virt-install to create a fedora 11 guest

[edit] Info

the xml files are loacted at

$ cd /etc/libvirt/qemu/

Starting the virt machines

$ virsh create kvm2.xml

List domains

$ virsh -c qemu:///system list
Id Name State
———————————-
1 kvm2 running
2 kvm1 running

Connect to kvm

$ virsh console kvm1

[edit] Managing Virtual Machines from the command line with `virsh`

Virtual machines can be managed on the command line with the virsh utility. The virsh utility is built around the libvirt management API and has a number of advantages over the traditional Xen xm tool:

virsh has a stable set of commands whose syntax & semantics will be preserved across updates to Xen.
virsh can be used as an unprivileged user for read-only operations (eg listing domains, getting info, etc)
virsh will (in future) be able to manage QEMU, VMWare, etc machines in additional to Xen, since libvirt is hypervisor agnostic.

To start a new virtual machine from an XML vm definition:

$ virsh create

To list the virtual machines currently running, use:

$ virsh list

To gracefully power off a guest use:

$ virsh shutdown

To save a snapshot of the machine to a file of your choosing:

$ virsh save

To restore a previously saved snapshot:

$ virsh restore

To export the XML config associated with a virtual machine:

$ virsh dumpxml <virtual machine (name | id | uuid)

For a complete list of commands available for use with virsh run:

$ virsh help

Or consult the manual page virsh(1)

July 14, 2010 Posted by derwynd | Uncategorized | Leave a comment