Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Hello Friends,

In this post, I would explain to you how to resolve one of the most intreseting issue on linux servers "Kernel Panic". I think the linux lovers much awaited such issue while they are working on Unix troubleshooting part.

As everyone knows Kernel are most importent part of any operating system and if it is crashed that's means your system crashed.

Normally kernel panic occur when you upgrade the server or upgrade the packages on the server. Here, you can find one of the Kernel panic issue as describe below.

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Pid: 1, comm: swapper Not tainted 2.6.32-502.el6.x86_64 #1

Call Trace:

 [<ffffffff815292bc>] ? panic+0xa7/0x16f

 [<ffffffff81c2b432>] ? mount_block_root+0x216/0x2cb

 [<ffffffff81002930>] ? bstat+0x2b0/0x980

 [<ffffffff81c2b53d>] ? mount_root+0x56/0x5a

 [<ffffffff81c2b6b1>] ? prepare_namespace+0x170/0x1a9

 [<ffffffff81c2a92a>] ? kernel_init+0x2e1/0x2f7

 [<ffffffff8100c20a>] ? child_rip+0xa/0x20

 [<ffffffff81c2a649>] ? kernel_init+0x0/0x2f7

 [<ffffffff8100c200>] ? child_rip+0x0/0x20

Solution : Normally this issue occur while you upgrade your server using yum and after reboot server is not boot due to kernel panic problem. This problem occur while kernel version has not been changed properly.

You can boot your linux server in grup mode and check the kernel and initrd paramtere. Match both the parameter if they are using same kernel version. During upgrade the initrd version normally not changed so you can manually change the correct kernel version entry in this file.

Once you modified the initrd files boot the server and make a same changes in grub.conf file too, otherwise once you take a reboot or shutdown the machine same kerenl panic error will occur.

[root@localhost]# vi /etc/grub.conf

#boot=/dev/sda

default=0

timeout=5

splashimage=(hd0,0)/grub/splash.xpm.gz

hiddenmenu

title CentOS 6 (2.6.32-504.el6.x86_64)

        root (hd0,0)

        kernel /vmlinuz-2.6.32-504.el6.x86_64 ro root=/dev/mapper/vstorage-root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=vstorage/root  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet

        initrd /initramfs-2.6.32-504.el6.x86_64.img

In above example, the default value 0 identifies the first title option to be used as default, the corresponding kernel version in title option line as 2.6.32-504.el6.x86_64 and the initramfs image file as initramfs-2.6.32-504.el6.x86_64.img. 

Before changing thing please take a backup of grub.conf file. now you can rename the kernel version in the initrd line and matched the same version at both the line and reboot the server, after reboot your linux machine will boot normally.

Hope your kernel panic issue will be resolved after reading this post. Please let me know if you are still facing this issue, I would try to help you.

How To Fix “Device eth0 does not seem to be present, delaying initialization” Error

This Ethernet card error is normally occur on Linux operating system like CentOS, Red Hat Linux etc. When you try to up the Ethernet card it is showing you the above topic error.

So in this post, we will provide you the step by step solutions and troubleshoot all the issue related this error.

In the initial step, you will check which Ethernet card is down , for this you can run the "ifconfig -a" command. Using this command you can check how many internet card is present on the server and on which Ethernet card used IP address.

Let's suppose you are using eth0 on your machine, and if this Ethernet card not taking any ip address and now show on your device that means it is down right now, so please try to start Eth0 device as given below command.

[root@localhost]# ifup eth0

Device eth0 does not seem to be present, delaying initialization

If your internet card show such issue that means you have an issue with MAC address. So in this post I would explain you how to resolve such issue.

1. In this step, please check the MAC Addresses are set correctly or not. For checking this you need to go the network card directory "/etc/sysconfig/network-scripts"

[root@localhost]# cd /etc/sysconfig/network-scripts

[root@localhost]# cat ifcfg-eth0

HWADDR=”00:15:5D:00:91:91”

In the configuration file, you can see the current hardware address of eth0 card, I have show you only HWADDR entry of my eth0 file. In this directory you can see if other Ethernet card is present or not. In my Linux machine i have two Ethernet card , please find the below second Ethernet card MAC address.

[root@localhost]# cat ifcfg-eth1

HWADDR=”00:15:5D:00:91:90”

2. Now we will see which link is present on the system currently and which is not active, for this you can use the below command to check the status.

[root@localhost]# ip -o link

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN \    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000\    link/ether 00:15:5D:00:91:90 brd ff:ff:ff:ff:ff:ff

3: eth2: mtu 1500 qdisc   pfifo_fast state UP qlen 1000\ link/ether 00:15:5D:00:91:91 brd ff:ff:ff:ff:ff:ff

Here, no eth1 but there is an eth2 present on the system, so might be problem is that the eth0 is renamed to eth2 but we will confirm with below command.

[root@localhost]# dmesg | grep eth0

udev: renamed network interface eth0 to eth2

udev: renamed network interface rename3 to eth0

From this command it shows that udev rename the network interface, so in the next step we will remove the wrong entry and configure the Ethernet card 

3. Now please open the network rules file to confirm the mac address. Please open this file "/etc/udev/rules.d/70-persistent-net.rules" 

[root@localhost]# cat /etc/udev/rules.d/70-persistent-net.rules

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:90", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:91", ATTR{type}=="1", KERNEL=="eth*", NAME="eth2"

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:91", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

Looks like there are multiple entries for the same MAC address. Removed the incorrect entry and restart the interface using below command.

[root@localhost]# ifup eth0

Now you eth0 card is up and if you are running "ifconfig -a" command you can see the eth0 card with mac address. 

Hope you are get the solution of the above issue, also please let me know if you have any other issue.

How to Configure Proxy Settings in Linux

In this post, I will explain , how we set or configure the proxy setting in Linux server. Usually when you work on the cooperate server you work behind the proxy. So if you are trying to download any packages or software on the Linux operating system machine, you need to configure the proxy on your browser or on system profile.

1. If you want to set http_proxy shell variable on Linux terminal or bash shell, then please use the below command or method to set the proxy settings on terminal.

# export http_proxy=http://Proxy_IP:Proxyport

or

# export http_proxy=http://Proxy_Domain:ProxyPort

You can use above command to set the proxy on bash shell or on terminal. You can use Proxy IP as well as Proxy DNS name to configure the proxy on shell. In my case I have use proxy IP on my server.

#export http_proxy=http://192.168.1.70:8080

If you want to use https proxy then please run the below command to set the proxy settings on bash or any other shell.

#export https_proxy=https://Proxy_IP:ProxyPort

or

#export https_proxy=https://Proxy_Domain:ProxyPort

You can use this proxy on open shell only if you close the terminal or shell then you need to set proxy variable again.

If your proxy use authentication then you need to give proxy user name and password while you are running the above command.

#export http_proxy=http://Proxy_User:Proxy_Password@Proxy_IP:Port

2. If you want to setup proxy variable for all users then you need to set proxy environment as a global variable. To do this you need to set proxy variable on /etc/profile file.

# vi /etc/profile

export http_proxy=http://Proxy_IP:Proxyport

or

export http_proxy=http://Proxy_User:Proxy_Password@Proxy_IP:Port

3. If you want to set the proxy access to a specific user then you need to set the variable on their bash profile.

# vi /home/vibhor/.bash_profile

Append the following line:

export http_proxy=http://Proxy_User:Proxy_Password@Proxy_IP:Port

or 

export http_proxy=http://Proxy_IP:Proxyport

You can use the https proxy or ftp proxy also only required to change the name of the varibale. 

HP-UX Logical Volume Manager (LVM) Commands with an Example

In this post, You can get an idea about HP-UX logical volume manager commands with an example. As you know LVM is basically used for disk management in operating system that allow to manager the physical disks and logical volume.

Please find the below HP-UX LVM commands with an example.

1. Create a new volume group, logical volume and file system:

You can used the below command in HP-UX operating system to create a new volume group, logical volume and file system.

hpx:/>pvcreate /dev/rdsk/c2t1d0

For creating a new volume group first we need to create physical volume as describe in above command.

hpx:/>mkdir /dev/vg01

hpx:/>mknod /dev/vg01/group c 64 0x010000

In above step we will create a directory where we need to create a volume group.

hpx:/>vgcreate /dev/vg01 /dev/dsk/c2t1d0

After successfully creation of volume group we will create a new logical voulme as describe in below command.

hpx:/>lvcreate -L 2048 /dev/vg01

hpx:/>newfs -F vxfs -o largefiles /dev/vg01/vgvol1

Using above command we create a new file system now in next step we will create a directory where we need to mount the newly created file system.

hpx:/>mkdir /backup

hpx:/>mount /dev/vg01/vgvol1 /backup

Once you mount the logical voulme with file system you can run the file system checking command to verify that mounting is succesfully or not.

2. Create a stripped filesystem:

In this, we will create a stripped file system with the help of volume group and logical voulme.

hpx:/>lvcreate -i 2 -I 32 -L 48 -n vgvol1 /dev/vg01

-i number of stripes

-I stripe size of 32KB

-L size of the volume

3. HP-UX display boot information:

You can use the below command to display boot information.

hpx:/>lvlnboot -v /dev/vg00

Boot Definitions for Volume Group /dev/vg00:

Physical Volumes belonging in Root Volume Group:

        /dev/dsk/c2t0d0 (0/1/1/0.0.0) -- Boot Disk

        /dev/dsk/c2t1d0 (0/1/1/0.1.0) -- Boot Disk

Boot: lvol1     on:     /dev/dsk/c2t0d0

                        /dev/dsk/c2t1d0

Root: lvol3     on:     /dev/dsk/c2t0d0

                        /dev/dsk/c2t1d0

Swap: lvol2     on:     /dev/dsk/c2t0d0

                        /dev/dsk/c2t1d0

Dump: lvol2     on:     /dev/dsk/c2t0d0, 0

When you run the above command you can find the above output , if you see the boot information you can find you have two disk which is available for boot.

4. HP-UX display all disks system information:

hpx:/> ioscan -funC disk

Class     I  H/W Path        Driver   S/W State   H/W Type     Description

==============================================================

disk      0  0/0/2/0.0.0.0   sdisk    CLAIMED     DEVICE       TEAC    DV-28E-N

                            /dev/dsk/c0t0d0   /dev/rdsk/c0t0d0

disk      1  0/1/1/0.0.0     sdisk    CLAIMED     DEVICE       HP 146 GMAX3147NC

                            /dev/dsk/c2t0d0   /dev/rdsk/c2t0d0

disk      2  0/1/1/0.1.0     sdisk    CLAIMED     DEVICE       HP 146 GMAX3147NC

                            /dev/dsk/c2t1d0   /dev/rdsk/c2t1d0

In the above output you can found the all the disk which is available in the system.

5. HP-UX display dump devices:

hpx:/> lvlnboot -v

Normally it is showing the boot information in which you can check the dump devices name.

Solaris Processes Monitoring - prstat

In this post, I will explain you which commands is used for display the Solaris zone process information.

Using "prstat" command we can display the solaris zone process information. This command generate the reports information about the processes and zones.

The prstat statistics utility shows a summary of the processes that are using system resources currently. The prstat utility summarizes this information for an every 5 seconds by default and reports the statistics for that period.

Display the zones process informtion:

[sun]# prstat -Z

 PID USERNAME  SIZE   RSS STATE   PRI NICE      TIME  CPU PROCESS/NLWP

 18638 20159    2118M 1502M cpu43    10    0   0:00:44 2.4% oracle/7

 20927 24076    8784K 8136K cpu127    0    2   0:00:17 1.8% prstat/1

   897 24865     916M  512M sleep    59    0  27:52:32 0.7% java/95

 17511 26055     599M  285M sleep    59    0  35:08:33 0.6% java/115

 12540 26055     951M  341M sleep    59    0  31:00:01 0.5% java/101

 ZONEID    NPROC  SWAP   RSS MEMORY      TIME  CPU ZONE

     8     3427   73G   27G    21%  44:01:48 2.8% sunz01

     0      100  465M  132M   0.1% 507:26:46 2.6% global

     6     4056   86G   32G    25%  35:23:30 2.3% sunz02    

Total: 13382 processes, 36594 lwps, load averages: 9.11, 9.27, 9.47

Using above command "prstat -Z" we can monitor the server process utilization in every 5 second. This command is show you the global zone & their local zone process utilization only.

If you want to only specific zone process utilization then you can use the below command.

[sun]# prstat -z sun01

This command output show you only process utilization of specific zone only.

Note:

-Z Reports information about processes and zones.

-z Reports information about a particular zone.

You can use the below syntax to monitor the Global zone as well as only specific zone.

Sun Solaris zonecfg commands

In the last post, I had explained the usage of zoneadm command for Solaris servers, now in this post we will get the information about the "zonecfg" command. 

This is very useful command which is mostly used during configuration of new zone or installed zone as well as for removal of any zone configuration files.

1. Command for creating a Solaris zone:

Please find the below commands to creating a zone on Sun Solaris server. The command must be run on Global zone with root user.

[sun]#zonecfg -z <zone>

Example: [sun]#zonecfg -z sunz01

Once you run the above command, you can enter in the configuration file, where you can add or edit the configuration for the zone.

2. Command for deleting a Solaris zone:

Please find the below command to deleting a Solaris zone from Global zone.

[sun]#zonecfg -z <zone> delete -F

Example: [sun]#zonecfg -z sunz01 delete -F

using above command you can delete or remove the configuration file of solaris local zone.

Note: You need to shutdown and uninstall the local zone before deleting the configuration files of Sun Solaris local zone.

3. Command for display zone current configuration:

Please find the below command to display the current configuration of local Solaris zones.

[sun]#zonecfg -z <zone> info

Example: [sun]#zonecfg -z sunz01 info

This command output show you the zonename, zonepath, autoboot etc attributes information of the solaris zone.

4. Command for zone creation file:

Please find the below command to create a solaris zone creation file.

[sun]#zonecfg -z <zone> export

Example: [sun]#zonecfg -z sunz0 export

Once the creation file has been export you can use this file to another zone creation as well as for restoration of this local zone if any problem occur on this zone.

How to use zoneadm command in Solaris Servers

When you are working on the Solaris operating system then you must aware about this command "zoneadm" which is basic command in Solaris operating system. In this post I would like to explain you how to use the zoneadm command in Solaris servers.

"zoneadm" command are used for verification, installation, boot or viewing of the local zones which are created on the Solaris Server. Please find the below syntax with an example.

1. Verify a Solaris zone:

To verify the local solaris zone you need to run the below command with syntax.

[sun]#zoneadm -z <zone> verify

Example: [sun]#zoneadm -z sunz01 verify

In this example once you run the above command, if your zone is installed properly without any error then this is not showing you any output, that's means it is verified. After running the command if it is showing a message then you need to check the configuration of this zone.

2. Installing a Solaris zone:

To install the local Solaris zone you need to run the below command with syntax.

[sun]#zoneadm -z <zone> install

Example: [sun]#zoneadm -z sunz01 install

In this example when you run the above command then your local zone has been started for installation. It is installed the local zone using the Solaris repostiory or flar images which you are kept at server location.

3. Ready a Solaris zone:

To move the local zone in ready or maintainance state you need to run the below command.

[sun]#zoneadm -z <zone> ready

Example: [sun]#zoneadm -z sunz01 ready

In this example, when we run the above command then your local zone moved in to ready or maintianance state.

4. Boot a Solaris zone:

To boot the solaris zone on global system, you need to run the below command with syantx.

[sun]#zoneadm -z <zone> boot

Example: [sun]#zoneadm -z sunz01 boot

After running the above command your local solaris zone has been boot successfully if it is not showing any error during boot time. If you see any message during the boot time then please check where is the issue.

5. Reboot a Solaris zone:

To reboot or restart the solaris zone on Solaris server, you need to perform the below command on global zone.

[sun]#zoneadm -z <zone> reboot

Example: [sun]#zoneadm -z sunz01 reboot

Using this command the local zone "sunz01" has been restart again successfully. You need to run this command from global zone only.

6. Shutdown/Halt a Solaris zone:

If you want to shutdown or halt your local zone without login it, then you need to run the below command from global zone.

[sun]#zoneadm -z <zone> halt

Example: [sun]#zoneadm -z sunz01 halt

After running this command local solaris zone state change from running to installed state that's means your server is shutdown now.

7. Uninstall a Solaris zone:

If you want to uninstall any solaris zone then you need to run the below command for uninstall the zone.

[sun]#zoneadm -z <zone> uninstall -F

Example: [sun]#zoneadm -z sunz01 uninstall -F

"-F" syntax is used to uninstall the zone forcefully. 

8. Viewing a Solaris zone:

if you want to local zone current status and any other display information you need to run the below command. 

[sun]#zoneadm list -icv

 ID NAME       STATUS      PATH               BRAND   IP

   0 global         running        /                        solaris      shared

   1 sunz01        running       /zones/sunz01   solaris      excl

   2 sunz02        running       /zones/sunz02   solaris      excl

Using above command you can check the current status of all installed zones on Solaris server. It is show you the zone path and zone information. All the above command you need to run from Global zone with root privileges.