Skip to content

Entries tagged "notes".

Smartctl - a note to myself

2nd September 2010
A note to my future self as I never seem to remember these smartctl commands (partly and fortunately because I don't need them often):
1. Quick check
/usr/sbin/smartctl -q errorsonly -H -l selftest -l error /dev/sdX
2. Run some tests if the command above reported any errors:
smartctl -t short /dev/sdX && smartctl -l selftest /dev/sdX
Tags: linux, notes, smartctl. | No comments

Linux Raid - replacing a physical device

2nd September 2010
Right now I'm dealing with a broken linux raid 1 in which both physical drives are reporting lots of bad blocks.
I have chosen the drive that exhibited the least problems and I'm having it cloned with dd_rescue on to a new one from a SysRescCD Live CD
dd_rescue /dev/old-b0rk3d-drive /dev/new-clone-drive
It's a good idea to run the above in a screen, especially if you're doing this via the internet.
Once the cloning is completed I simply put the new drive in the original server and expect it to boot - with a degraded but working raid.
In the next step I add a new empty drive, with a similar size (500 GB in my case) and clone the partition table with sfdisk:
sfdisk -d /dev/existing-drive | sfdisk /dev/new-empty-drive
Use `fdisk -l` before and after the partition cloning to be sure you're doing the right thing.
Once we have an identical partition table on both drives we can start adding partitions from the new drive to our linux raid. Assuming the cloned drive is sda and the new drive is sdb, our md setup should loook like this:
root@sysresccd /root % cat /proc/mdstat 
Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md3 : active raid1 sda6[1]
      297780736 blocks [2/1] [U_]
      
md1 : active raid1 sda3[1]
      4192896 blocks [2/1] [U_]
      
md2 : active raid1 sda2[1]
      153597376 blocks [2/1] [U_]
      
md0 : active raid1 sda1[1]
      30716160 blocks [2/1] [U_]
And now let's add partitions to our raid layout:
mdadm /dev/md0 --add /dev/sdb1
mdadm /dev/md1 --add /dev/sdb3
mdadm /dev/md2 --add /dev/sdb2
mdadm /dev/md3 --add /dev/sdb6
And that's that, now we can see the raid resync'ing:
cat /proc/mdstat


We're not finished yet!
As this drive (and therefore its clone as well) was secondary (sdb) on the original system I expect problems with grub.
By default, when installing on to a linux raid Centos/Anaconda only installs grub on the first drive (sda in this case) and therefore my drive being sdb will lack this in its MBR.
If this is the case, we won't be able to boot at all from the cloned hdd, so we need to boot again from the Live CD, mount the linux raid from it and then chroot in to the OS and do the grub magic from there.
Assuming everything works nicely form the Live CD and the md devices are properly mounted under /mnt we can start:
export SHELL=/bin/bash
chroot /mnt/clone
#grub
grub> find /boot/grub/stage1
 (hd0,0)
 (hd1,0)
grub> root (hd0,0)
 Filesystem type is ext2fs, partition type 0xfd

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd0)"...  15 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/boot/grub/stage2 /boot/grub/grub.conf"... succeeded
Done.

grub> root (hd1,0)
 Filesystem type is ext2fs, partition type 0xfd

grub> setup (hd1)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd1)"...  15 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2 /boot/grub/grub.conf"... succeeded
Done.

grub>quit
And we're done now: reboot.
! - Please pay extra attention when doing this kind of operations, it's very easy to format the wrong HDD etc. :-)
Tags: centos, linux, notes, raid. | No comments

Change the default source address in Linux

1st October 2010
Quick note to my future self on how to change the default source address in Linux (usually the 1st IP that resides on the primary NIC):
ip ro replace default via GATEWAY src IP
Where GATEWAY is the default gateway of the system and IP is the new source IP address (this has to be an existing assigned IP).
Tags: ip, linux, notes, routing. | No comments

Newer kernel for Centos

10th October 2010
Want to try the latest kernel on a Centos server? Although that is highly unadvisable, in the desperate and cataclismic event that you really need it, do not forget to enable CONFIG_SYSFS_DEPRECATED_V2, otherwise you'll end up in a kernel panic.
Thanks Toracat for the tip!
Tags: centos, kernel, linux, notes. | No comments

OpenVPN problems on Windows 7

7th November 2010
Tonight I had a problem with a OpenVPN client running on Windows 7.
It was connecting and authenticating properly, but the pushed routes from the OpenVPN server were not respected. Apparently this is specific to Windows (7?) and it's fixed by adding the following to the client config file:
script-security 2 system
I found this solution here.
Tags: notes, openvpn, vpn, windows7. | No comments

25 sick linux commands

6th December 2010
Something that just got into my bookmarks folder:
http://blog.urfix.com/25-sick-linux-commands/
Tags: cli, linux, notes. | No comments

Elastix on Xen howto

14th January 2011
Elastix is an open source Unified Communications Server software that brings together IP PBX, email, IM, 
faxing and collaboration functionality.
It has a Web interface and includes capabilities such as a Call Center software with predictive dialing.

The Elastix functionality is based on open source projects including Asterisk, HylaFAX, Openfire and Postfix.
Those packages offer the PBX, fax, instant messaging and email functions, respectively.

As presented above (fragment from the wikipedia page), Elastix can be quite useful if you want to run your own PBX.
As it is based on Centos I initially tried to install it the Centos way, but I encountered lots of problems so I ended up using a Linux KVM vm (I'm in love!), tweak that a bit, tar it up and transfer it to a xen dom0.
I have already lost too much time trying to get it installed so I will not comment on this anymore.
I will assume that you will use my Elastix (v2.0.3) xen image and that you also have a working LVM based (Centos) xen dom0. As most things linux there are multiple ways of doing this, this is my way. Let's begin:

- 1 - Let's create 2 LVM volumes for the elastix vps:
lvcreate -L10G -nelastix-root vg0; lvcreate -L1G -nelastix-swap vg0

- 2 - Download and extract the image:
wget http://dl.nux.ro/xen/domU/elastix_32/elastix.tar.bz2; tar xjf elastix.tar.bz2

- 3 - Format the volumes and copy the contents of the tar archive on to the root one:
mkfs.ext3 /dev/vg0/elastix-root
mkswap /dev/vg0/elastix-swap
mkdir /mnt/elastix
mount /dev/vg0/elastix-root /mnt/elastix
cp -a elastix/* /mnt/elastix/
umount /mnt/elastix/

- 4 - Create a xen cfg file for this domU: vi /etc/xen/auto/elastix.cfg
bootloader = "/usr/bin/pygrub"
name = "elastix"
memory = "512"
disk = [ 'phy:/dev/vg0/elastix-root,sda1,w', 'phy:/dev/vg0/elastix-swap,sda2,w' ]
vif = ['vifname=elastix,bridge=xenbr0']
on_poweroff = 'destroy'
on_reboot = 'restart'
on_crash = 'restart'

- 5 - After saving that file start the virtual machine:
xm create -c /etc/xen/auto/elastix.cfg

- 6 - Log in the vm, change the password using the "passwd" command and set up the networking (run "setup" if you don't know which system config files to edit). When asked for a password please input "parola2011" (without the quotes). Please change the root password ASAP!!
- 7 - Visit http://IP_of_VM/ and log in as admin with password parola2011 (change the admin password ASAP!).

Enjoy!

PS: You may want to change some system settings like the keyboard layout (set to uk) and timezone (set to Europe/Bucharest).
Tags: centos, elastix, howto, linux, notes, virt, xen. | No comments

When was a linux OS installed?

25th January 2011
By mistake I found out how one can discover when his linux OS was installed, well..in most of the cases. Previously I had no idea how to do this and not even this may be the best idea (if you know other ways to do this, let me know):
dumpe2fs -h /your/root/partition|grep created

The command will show when the filesystem was created initially, but if we ask for the / or /boot fs information, then this should be the install date.
E.g.:
sudo dumpe2fs -h /dev/sda2|grep created
dumpe2fs 1.41.12 (17-May-2010)
Filesystem created:       Thu Dec  9 21:34:06 2010

Voila!
Tags: dumpe2fs, linux, notes. | No comments