In these days I’m planning a lot of Redhat systems patching.
It’s important to see when i have a system with RAID hardware or not , it’s critical for planning a best rollback strategy.
But how can i get info about raid hardware without using the BIOS?
Looking on the web i found this awesome link. It’s helping me A LOT!!
I suggest to save it or print 🙂
Today i finished to work on a RHCSA practice test. It covers just some topic of the whole course!
Follow the details:
Q: What is this lab for?
A: This is useful for who thinks is ready to get the RHCSA exam
Q: What is the goal?
A: The goals are:
1) configure web server with any index ( it’s your choice )
2) configure ftp server WITHOUT anonymous login
3) configure luks encrypted fs on ‘secret’ volumegroup and /secret mount point.
4) configure additional swap ( even 50 mb is enough )
5) server must have network services available through the network ( ssh , ftp , http , etc.etc. )
Every goal must be PERSISTENT AT REBOOT
Q: Where i can get the software packages?
A: Configure a local repository with the cd/dvd image of centos.
Q: Where i can get help for this lab?
A: For the best exam simulation , DON’T LOOK ON INTERNET. I also add this: DON’T READ THE KICKSTART COMMANDS!!!! Otherwise you are not able to troubleshooting issues. I tought about it for a realistic simulation so if you read the commands u are not helping yourself.
Q: What I need for this lab?
A: I used a vmware workstation guest , CentOS 6 x86_64, with 20gb disk and 1540 memory
This is the kickstart file, have fun!!!
Today i did and passed RHCSA exam with score of 300!!!
I’m very very happy and finally i can come back to write on my blog 😀
I’m working about prepare a kickstart profile where people can test their knowledge before take RHCSA exam
This week i was in Milan for a Redhat course.
I took the RH-436 ( cluster and storage management ) course and i learned A LOT OF NEW THINGS ! Finally I got some reply about my olders questions about redhat 6 cluster.
The most interesting thing was gluster , i hope to work on it soon .
Now i have to make a gluster presentation on my company because it’s very useful .
I’m not RHCE and i was not able to do the exam but i’m working on it ( RHCSA exam FIRST ).
Soon i will patch a lot of systems ( RHEL 5 – RHEL 6 ) and i’m planning every rollback strategy.
Studying and looking for the web I found that people usually use RPM rollback but this is NOT RECOMMENDED!!
People on RHEL 5 add RPM macro , on RHEL 6 use yum history but both struments can be used for small rollbacks, not for minor release rollbacks!
I read this from Redhat:
Note: Downgrading a system to minor version (ex: RHEL-6.1 to RHEL-6.0) is not recommended as this might leave the system in broken state where libgcc and other libraries won’t rollback as expected. Use the history option for small update rollbacks.
Same is for RHEL 5.
So what can I think about rollback?
1) LVM snapshot ( usually estimated as ~ 20% lvol source space, only on RHEL 6 )
2) Files copy from / and /boot partitions with dd. This is useful with soft/hard links and it’s bit a bit copy. I just need a filesystem from SAN or NFS. If snapshot will not work I just need to boot the system in rescue mode , configure the network , mount the filesystems and use dd for rollback!
3) Disk from RAID HARDWARE
4) Dedicated software backup ( Networker Legato for example )
Yesterday i was doing some test on my SLES 11 for SAP.
I was trying to mount an ext4 filesystem on /mnt.
During the mount i saw the message:
mount: warning: /mnt seems to be mounted read-only
I was surprised to see that message , so i tought about some problem with lvm or iSCSi ( i maked a volume group on a disk via iSCSi ).
Looking the system messages i saw this:
Mar 19 15:59:19 suse1 kernel: [ 1147.951164] EXT4-fs (dm-2): ext4 is supported in read-only mode only
Now it was clear! I understand too why SLESS 11 had the root filesystem on ext3 🙂
In these days i’m playing a lot with mdadm and grub on Linux. I need to learn how make a root disks mirror starting from /dev/sd* booting devices.
During the tasks i did, I encoutered a problem with grub. I had:
– hd0 (sda)
– hd1 (sdb)
/dev/md1 -> /dev/sdb1 ( /boot )
/dev/md3 -> /dev/sdb3 ( / )
/dev/md2 -> /dev/sdb2 ( swap )
I edited /boot/grub/grub.conf as follow:
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
# all kernel and initrd paths are relative to /boot/, eg.
# root (hd0,0)
# kernel /vmlinuz-version ro root=/dev/sda3
# initrd /initrd-[generic-]version.img
#boot=/dev/sda
default=0
fallback=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS MD (2.6.32-279.el6.x86_64)
root (hd1,0)
kernel /vmlinuz-2.6.32-279.el6.x86_64 ro root=/dev/md3 rd_NO_LUKS LANG=en_US.UTF-8 KEYBOARDTYPE=pc KEYTABLE=it rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_NO_LVM rd_NO_DM rhgb quiet
initrd /initramfs-2.6.32-279.el6.x86_64.img
title CentOS (2.6.32-279.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-279.el6.x86_64 ro root=UUID=7c1ba3b1-756c-4124-9079-d11a32ceea78 rd_NO_LUKS LANG=en_US.UTF-8 KEYBOARDTYPE=pc KEYTABLE=it rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_NO_LVM rd_NO_DM rhgb quiet
initrd /initramfs-2.6.32-279.el6.x86_64.img
After i tried to run:
[root@localhost grub]# grub
Probing devices to guess BIOS drives. This may take a long time.
GNU GRUB version 0.97 (640K lower / 3072K upper memory)
[ Minimal BASH-like line editing is supported. For the first word, TAB
lists possible command completions. Anywhere else TAB lists the possible
completions of a device/filename.]
grub> root (hd0,0)
root (hd0,0)
Filesystem type is ext2fs, partition type 0x83
grub> setup (hd0)
setup (hd0)
Checking if “/boot/grub/stage1” exists… no
Checking if “/grub/stage1” exists… yes
Checking if “/grub/stage2” exists… yes
Checking if “/grub/e2fs_stage1_5” exists… yes
Running “embed /grub/e2fs_stage1_5 (hd0)”… 27 sectors are embedded.
succeeded
Running “install /grub/stage1 (hd0) (hd0)1+27 p (hd0,0)/grub/stage2 /grub/grub.conf”… succeeded
Done.
grub> root (hd1,0)
root (hd1,0)
Filesystem type unknown, partition type 0xfd
grub> setup (hd1)
setup (hd1)
Error 1: Cannot mount selected partition
grub>
Looking on the web i found that the problem is with md devices metadata.
I maked them with:
mdadm –create /dev/md1 –level=1 –raid-disks=2 –metadata=default missing /dev/sdb1
default metadata is 1.2 , and it’s incompatible with GRUB!
So for boot disks the solution is make them with:
mdadm –create /dev/md1 –level=1 –raid-disks=2 –metadata=0.90 missing /dev/sdb1
Today I installed CentOS6 on my notebook for KVM purposes.
After the installation I tried to test Windows boot and i got this error:
BOOTMGR is missing
Press CTRL + ALT + DEL to restart
I immediately tought “damn i’m using my work-notebook this is bad”.
From Linux I saw /etc/grub entries and for Windows I saw:
root (hd0,7)
Watching fdisk -l output i saw the first partition with little size and I tried to map it as follow:
root (hd0,1)
After this I was able to boot Windows 🙂
I’m doing a lot of tests , experiments on my CentOS.
Yesterday i was experimenti a LVM mirror recovery and i found two devices mounted on same mount point: /mnt
I tought “damn due to my experiments i erased the system again…”
Later i was curious about to try it again. IT WORKED , how is that possible?
I can do this even now:
[root@centos6 ~]# cat /etc/issue
CentOS release 6.3 (Final)
Kernel \r on an \m
[root@centos6 ~]# lvs
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
ale rootvg -wi-a— 1.00g
ale2 rootvg -wi-a— 104.00m
mau rootvg -wi-a— 1.00g
rootvol rootvg -wi-ao– 13.46g
swap2vol rootvg -wi-a— 2.00g
swapvol rootvg -wi-ao– 2.05g
test rootvg -wi-ao– 200.00m
mirrvol testvg mwi-a-m- 2.00g mirrvol_mlog 100.00
[root@centos6 ~]# vgs
VG #PV #LV #SN Attr VSize VFree
rootvg 1 7 0 wz–n- 24.51g 4.70g
testvg 2 1 0 wz–n- 9.98g 5.98g
[root@centos6 ~]# mount /dev/mapper/rootvg-test /mnt
[root@centos6 ~]# mount /dev/mapper/testvg-mirrvol /mnt
[root@centos6 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rootvg-rootvol
14G 4.4G 8.2G 35% /
tmpfs 498M 188K 498M 1% /dev/shm
/dev/sda1 485M 33M 427M 8% /boot
/dev/mapper/rootvg-test
2.0G 67M 1.9G 4% /mnt
/dev/mapper/testvg-mirrvol
2.0G 67M 1.9G 4% /mnt
I need to understand. NOW !!
RHEL6 introduces new features about LVM. One of these is the snapshots.
I wanted to test it for rollback purpose. I will think about it for a patching task 😉
For this test I maked a screenshot of root logical volume , I deleted /etc directory and restored it from the sreenshot. All worked !
[root@localhost ~]# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/rootvg-rootvol 23G 3.1G 18G 15% / tmpfs 498M 0 498M 0% /dev/shm /dev/sda1 485M 33M 427M 8% /boot
[root@localhost ~]# vgs
VG #PV #LV #SN Attr VSize VFree
rootvg 1 2 0 wz–n- 24.51g 0
I saw no free space on rootvg so i added a new disk
Disk /dev/sdb: 652 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0
Device Boot Start End #cyls #blocks Id System
/dev/sdb1 0+ 651 652- 5237158+ 8e Linux LVM
/dev/sdb2 0 – 0 0 0 Empty
/dev/sdb3 0 – 0 0 0 Empty
/dev/sdb4 0 – 0 0 0 Empty
s attribute said to me that rootsnap is a snapshot !
First test I did:
THE SPACE ON THE SNAPSHOT MUST BE CHECKED !!!
[root@localhost ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/rootvg-rootvol
23G 4.2G 17G 20% /
tmpfs 498M 0 498M 0% /dev/shm
/dev/sda1 485M 33M 427M 8% /boot
After i erased /etc directory!
I did a reboot and as expected the system was not able to boot up.
So , I used rescue mode from CD and I ran on the shell:
At next boot the system came up without any problem/warning!
[root@localhost ~]# cd /root
[root@localhost ~]# ls
anaconda-ks.cfg install.log install.log.syslog
( The 1 gb file does not exist anymore )
[root@localhost ~]# lvs
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
rootvol rootvg -wi-ao– 22.46g
swapvol rootvg -wi-ao– 2.05g
Alessio dini's Blog 