kumar's questions

I am trying to setup passwordless ssh to my localhost (itself).

I have host machine PM1 and then I lauch a VM(vm1) using qemu-kvm and logged into VM. Then, I am trying to setup passworless ssh within vm1, so that ssh root@vm1 (from vm1 itself) should log me in without password.

vm1# ssh-copy-id root@vm1

Then

vm1# ssh root@vm1

Now, I can login without password. no issues.

Then I started looking into authorized_keys. /root/.ssh/authorized_keys

Here I find a new entry like:

ssh-rsa <some key> <hostmachine username>@<hostmachine hostname>

how come hostmachine username and hostmachine hostname comes into picture here?? Should n't it be vm machine username @ vm machine hostname?

This looks bit weird.

[root@GFVM4 ~]# hostname
GFVM4
[root@GFVM4 ~]# 
[root@GFVM4 ~]# 
[root@GFVM4 ~]# getent hosts gfvm4
192.168.122.151 GFVM4
[root@GFVM4 ~]# getent hosts GFVM4
fe80::5054:ff:feac:787 GFVM4
[root@GFVM4 ~]# 
[root@GFVM4 ~]# 
[root@GFVM4 ~]# 
[root@GFVM4 ~]# ifconfig ens5
ens5: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.122.151  netmask 255.255.255.0  broadcast 192.168.122.255
        inet6 fe80::5054:ff:feac:787  prefixlen 64  scopeid 0x20<link>
        ether 52:54:00:ac:07:87  txqueuelen 1000  (Ethernet)
        RX packets 452  bytes 33008 (32.2 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 204  bytes 26112 (25.5 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[root@GFVM4 ~]# 

Is the above expected behaviour?

As you can see I have setup all caps HOSTNAME GFVM4.

if I use the same name(ALL CAPS) it returns ipv6 address. If I use small lettered hostname, it returns ipv4 address.

Is this correct behaviour?

Running Fedora21 as a qemu based VM.

Thanks

mkdir test_dir test_dir1 test_dir2 test_dir3
touch file1 file2 file3
cp -v file* test_dir*/

This copies only to test_dir3 and not in test_dir, test_dir1, test_dir2. Why?

For that matter it copies only to latest directory say test_dir4 and not into any other direcotry (it is omitting them).

I have created a VM with the below command in qemu with KVM enabled.

qemu-kvm -m 1024 -enable-kvm -hda /var/lib/libvirt/images/fedora.img

I would like to know the exact devices that are emulated for this VM, including storage and network (I can see a network interface enabled inside VM using ifconfig).

I just installed centos 6.3 freshly and noticed the following:

[root@localhost user1]# cat /etc/redhat-release CentOS release 6.3 (Final)

[root@localhost user1]#

[root@localhost user1]# cat /proc/sys/net/core/rmem_max 131071

[root@localhost user1]# cat /proc/sys/net/core/rmem_default 229376

[root@localhost user1]# cat /proc/sys/net/core/wmem_max 131071

[root@localhost user1]# cat /proc/sys/net/core/wmem_default 229376

As you can see rmem_max is "Lesser " than rmem_default and wmem_max is "Lesser" than wmem_default.

As per my knowledge wmem_max and rmem_max should be more than default values ?

EDIT:

# cat /etc/redhat-release CentOS release 6.3 (Final)

# uname -a Linux localhost.localdomain 2.6.32-279.el6.x86_64 #1 SMP Fri Jun 22 12:19:21 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

<< link : https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/7-Beta/html/Performance_Tuning_Guide/s-network-dont-adjust-defaults.html

Bear in mind that the value of rmem_default should be no greater than rmem_max (/proc/sys/net/core/rmem_max); if need be, increase the value of rmem_max.

I know that tail -f /var/log/messages will be keep updating on screen as the contents of file gets updated. But when I tried the same thing with a debug file system's file it is not working , any idea?

I tried ftrace and tried this: tail -f trace it is not working ?

Note, I can see the contents actually getting by using watch -n1 cat trace.

I would like to redirect the command executed along with the output to a file.

for example: #ls >ls_out.txt

ls_out.txt should be something like :

ls

file1 fil2

Thanks!

how (linux kernel) network modules gets loaded without modprobe.conf I have fedora distribution installed and can see e1000e module loaded automatically in the system.

Is there a configuration which specifies to load this module automatically ??

I have referred modprobe.conf, BUT no such entry exists. for that matter, I have grep'd entire /etc/ directory to check any entry to load this module, but no avail.

Please let me know 1. whether any configuration file mention about loaded specific modules automatically during bootup time ? 2. If there is not config file, how the modules are picked up by the system?

Thanks!

I am preparing to verify KVM with paravirtualization support(mainly for networking).

Does mentioning driver name as vhost is enough to make it run in paravirtualization mode ? I have all options relevant to paravirtualization enabled as part of kernel configuration.

Do I need to insmod any other module apart from kvm.ko and kvm_intel.ko ?

Also, do I need to mention any kernel parameters as part of loading these modules(kvm.ko kvm-intel.ko) ?

qemu-system-x86_64 version 1.4.2

Thanks.

Referring this link : http://www.linux-kvm.org/page/Virtio It seems no special drivers is needed at host side. <

I am trying to restrict bandwidth inside my containers. I have tried using the following commands , But I think it is not getting effective.

cd /sys/fs/cgroup/net_cls/
echo 0x1001 > A/net_cls.classid   # 10:1
echo 0x1002 > B/net_cls.classid   # 10:2
tc qdisc add dev eth0 root \
           handle 10: htb
tc class add dev eth0 parent 10: \
           classid 10:1 htb rate 40mbit
tc class add dev eth0 parent 10: \
           classid 10:2 htb rate 30mbit
tc filter add dev eth0 parent 10: \
           protocol ip prio 10 \
           handle 1: cgroup

Here A and B are containers created with this command.

lxc-execute -n A -f configfile /bin/bash
lxc-execute -n B -f configfile /bin/bash

Whereas configfile contains only this entry:

lxc.utsname = test_lxc

AFter starting the container , I have started vsftpd inside container A and try to access the files using the ftp client from another machine. Then I killed vsftpd in container A and started vsftpd in container B and try to access the files using ftp client from another machine.

I cannot observe any difference in performance, for that matter it is nowhere nearer to 40mbit/30mbit.

Please correct me whether anything wrong here.

When I create a partition using parted(mkpart) giving unit as Bytes, it is creating "size given - 16896" byte sized partition. Is there any specific reason to less 16896 bytes from the partition size(in bytes) given?

Here, after creating a partition I get the partition size like:

#parted /dev/sda unit B print.

Note: These partitions are used in RAID formation. Also, observed this happens only if it is the first partition created in disk.

While joining a domain from a linux machine , I give this command: net rpc join member -U Administrator. Now, the above command prompts for (Administrator) password.

Now, I wish to store the password somewhere(smb.conf OR krb5.conf) so that it does not prompts for password. Is it possible?

Note:Necessary changes to join a domain are carried out in /etc/samba/smb.conf

PS: Please do not consider any security issue with this.

Thanks!

Is it possible to create "workgroup" in a linux machine and join the same linux machine into that workgroup?

my understanding: smb.conf in /etc/samba/ have an entry name workgroup which can be filled with Actual work group name , say XYZ. This is for connecting with the existing workgroup XYZ?

But, I wish to create a new workgroup and same created machine(linux) to join the workgroup.? Then I should be able to add any computer to this workgroup? Please let me know the configuration details for the same.

Thanks!

Consider creating a linear mode RAID with single disk(more disks may be added later).

#echo y | mdadm --create /dev/md0 --level=linear --raid-disk=1 /dev/sda1 --force

Now consider another partition is available , is it possible to "grow" from linear mode to RAID1(mirroring) mode? I can do something like this before for raid1 to raid5 , but for linear to RAID1 I have observed this error.

// change the level
echo raid1 >  /sys/block/md0/md/level
"linear does not support online personality change"

I am aware about taking backup of existing contents of linear mode contents and then creating RAID1 with two partitions(one from span and another one newly added ) But, I am interested in doing it in place.

I have created a raid array say RAID5 or RAID10 with four drives. I wish to force resync of the same array, Please let me know the mdadm command for the same.

Also, in case of RAID1 (mirroring) what is being done as part of resync. Is it basically replication of same chunk of data in two drives? Linux is the OS used.

Thanks.

I have few questions related to raid5. consider creating a raid5 device, say md0 with three disks.

After creation, you start writing into the disk. Here whenever a file size of say 1gb is written , how much of actual data size is written into the three disks.?

I understand xor calculation is made while carrying out the write( for recovery alone). If xor calculation is not done properly(say bug in xor calculation algorithm), will the write still succeed.?

During read, how the xor calculated value is used? OR in other words XOR calculated value is really used during read?

For 1gb of data, every piece is data is distributed across three devices , say first_piece into first device, second_piece into second device and then third xor calulated piece(of first and second piece) into the third device.? Is my Understanding correct?

Consider Linux as the OS used. Thanks!

Can you create a partition in a usb disk using fdisk command in a single line.

fdisk command is interactive in nature, But I want to automate partition creation in a single line using fdisk command.

Is there really any meaning attached for assigning a IP address to a bridge interface. Note : the bridge is created using brctl and then an IP address is assigned to br0 created.

Is there any advantange/usage by assigning a IP address to the bridge interface

I wish to append & sign to the end of particular command (say tkdiff) whenenver I execute the command.

Please let me know what kind of alias / any other solution should I create in bashrc.

Thanks in advance.

Note: I may have few arguments to the command which i execute. & should come at the end so that I can execute in b/g and I can use the shell for any other purpose.

I have some lines like [ 17.440000] eth0: XYZCOMPANY ABC4353 802.11 Wireless Controller

[ 17.540000] eth1: XYZCOMPANY ABC4353 802.11 Wireless Controller

[ 17.640000] eth2: XYZCOMPANY ABC4353 802.11 Wireless Controller

I need to get eth0, eth1, eth2 into a variable in shell script. As you can notice all the other lines like XYZCOMPANY ABC4353 remains constant.but interface name is keep changing. I need to get those interface names into a variable.

Thanks!