RHCE: Success!

I have received the results of the RHCE exam and I have passed well! Hopefully I can begin updating my blog more frequently.

RHCE: I took the exam on 12/02/2005

After taking the exam yesterday, I should find out the results next week. I'll let you know how I did.



Note: As is common knowledge, no discussion of the exam or contents can occur after taking the exam by participants. Please refer to the website at http://redhat.com/training for any questions you may have. There is a detailed exam prep page that will outline all of the requirements.

RHCE: Run-time RAID Configuration

Here is a link to an excellent article on creating RAID arrays using the mdadm tool.

Here is an excerpt:

Creating an Array

Create (mdadm --create) mode is used to create a new array. In this example I use mdadm to create a RAID-0 at /dev/md0 made up of /dev/sdb1 and /dev/sdc1:

# mdadm --create --verbose /dev/md0 --level=0

--raid-devices=2 /dev/sdb1 /dev/sdc1

mdadm: chunk size defaults to 64K

mdadm: array /dev/md0 started.

The --level option specifies which type of RAID to create in the same way that raidtools uses the raid-level configuration line. Valid choices are 0,1,4 and 5 for RAID-0, RAID-1, RAID-4, RAID-5 respectively. Linear (--level=linear) is also a valid choice for linear mode. The --raid-devices option works the same as the nr-raid-disks option when using /etc/raidtab and raidtools.

In general, mdadm commands take the format:

mdadm [mode]  [options] 

Each of mdadm's options also has a short form that is less descriptive but shorter to type. For example, the following command uses the short form of each option but is identical to the example I showed above.

# mdadm -Cv /dev/md0 -l0 -n2 -c128 /dev/sdb1 /dev/sdc1

RHCE: Installing RPMs from an NFS share

Using an NFS share to install packages is a very convenient means of ensuring that all of your systems are running similar packages and always having those packages available. I will not cover configuring an NFS share and will assume that the reader is already familiar with that function or has the capacity to figure it out.

1. Verify that the NFS share is available and mount on the local filesystem, if not already mounted.

mount -t nfs /local/install/point /nfs/server

2. If using the command line, simple use the RPM command to install the application:

rpm -Uvh /path/to/share/application.rpm

3. If using the package manager, use the following command from the command line:

system-config-packages --tree=/path/to/nfs/share &

You will now be able to select the applications that you would like to add or remove.

RHCE: Logical Volume Manager

Red Hat Enterprise Linux 4.0 uses a logical volume manager to facilitate efficient management of disks and partitions. With the Logical Volume Manager, partitions can be created that span multiple physical volumes and partitions. In this sense a physical volume is a hard disk. With this ability, an administrator can easily expand a partition or create an efficient partition scheme. RHEL 4.0 uses LVM2 by default.

When using LVM, it may be difficult to remember all of the commands that are possible and necessary to create a Logical Volume. An easy way to get a list of all of the related commands is to enter the lvm console by typing 'lvm' on the command line. Once in the LVM console, type 'help' and all of the available commands will be listed with a short description.

CAUTION: using the logical volume manager can and probably will destroy data. Verify that you have created backups of all of your data before trying the samples below.

Using the Logical Volume Manager

1. Partition the physical hard disks that will be used as part of the Logical Volume(s)

Use 'fdisk' as appropriate. Remember to set the system type as 'Linux LVM', which is type '8e'.

2. Create physical volume(s)

From within the lvm console, use pvcreate on each partition that will participate in the logical volume group.

pvcreate 'physical partition'

Sample:

lvm> pvcreate /dev/hdd1
Incorrect metadata area header checksum
Physical volume "/dev/hdd1" successfully created

3. Create a volume group

Using the vgcreate command, create a volume group which consists of the physical volumes created previously.

vgcreate 'volume group name' 'physical volume' ['physical volume'] ...

Sample:

lvm> vgcreate test1 /dev/hdd1 /dev/hdd2
Incorrect metadata area header checksum
Volume group "test1" successfully created

Verification of the volume group creation can be done with the vgdisplay command:

lvm> vgdisplay
--- Volume group ---
VG Name test1
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 1
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 0
Open LV 0
Max PV 0
Cur PV 2
Act PV 2
VG Size 93.15 GB
PE Size 4.00 MB
Total PE 23846
Alloc PE / Size 0 / 0
Free PE / Size 23846 / 93.15 GB
VG UUID znEYOy-n4oJ-zmXq-QARI-cRvD-YmY5-Gq6qpd

4. Create a logical volume in an existing Logical Volume Group

Using the lvcreate command, create a logical volume:

lvcreate [-L 'size'] [-n 'logical volume name'] 'logical volume group'

Sample:

lvcreate -L 200M -n vol1 test1
Incorrect metadata area header checksum
Logical volume "vol1" created

Verify that the logical volume is as desired with the lvdisplay command:

lvm> lvdisplay
Incorrect metadata area header checksum
--- Logical volume ---
LV Name /dev/test1/vol1
VG Name test1
LV UUID HPqCiY-58NT-X1ae-5vk3-1hLw-f2no-AYe52O
LV Write Access read/write
LV Status available
# open 0
LV Size 200.00 MB
Current LE 50
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:0

5. Format the logical volume with the filesystem desired (ext3 shown)

[root@primary ~]# mke2fs -j /dev/test1/vol1
mke2fs 1.35 (28-Feb-2004)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
51200 inodes, 204800 blocks
10240 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
25 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729

Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.

6. In good Red Hat form, create a label for the filesystem with the e2label command

[root@primary ~]# e2label /dev/test1/vol1 test1

7. Create an entry in the /etc/fstab file for this logical volume so that it will be mounted on subsequent boots. Use a meaningful mount point:

LABEL=test1 /test1 ext3 defaults 0 0


These steps have covered how to create a logical volume and use it. You can also expand an existing logical volume and perform other maintenance tasks. The only other task covered here will be expanding an existing logical volume.

Expand a logical volume

1. Add desired disk space to your volume group, if necessary

a. use fdisk to create a new partition of type '8e'
b. use pvcreate to initialize the new partition as a physical volume

[root@primary ~]# pvcreate /dev/hdd3
Physical volume "/dev/hdd3" successfully created

c. use vgextend to add the physical volume to the volume group

[root@primary ~]# vgextend test1 /dev/hdd3
Incorrect metadata area header checksum
Incorrect metadata area header checksum
Volume group "test1" successfully extended

CAUTION: The next step will remove all data from the partitions in question. Verify that you have backups.

d. use lvextend to expand the logical volume to the desired size

[root@primary ~]# lvextend -L 300M /dev/test1/vol1
Incorrect metadata area header checksum
Extending logical volume vol1 to 300.00 MB
Logical volume vol1 successfully resized

e. re-format your logical volume, relabel it, and remount it

umount 'logical volume'
mke2fs -j 'logical volume'
e2label 'path to volume' 'label'
mount 'path to volume in /etc/fstab'


Trouble Shooting

1. 'physical partition' not identified as an existing physical volume

lvm> vgcreate 'volume group' 'physical partition' 'physical partition'
Incorrect metadata area header checksum
Incorrect metadata area header checksum
No physical volume label read from 'physical partition'
not identified as an existing physical volume
Unable to add physical volume 'physical partition' to volume group 'volume group'.

To correct this problem, use lvm to create a physical volume on each partition with the pvcreate command:

lvm> pvcreate 'physical partition'
Incorrect metadata area header checksum
Physical volume "physical partition" successfully created

Create the volume group with the vgcreate command.

RHCE: Networking and Network Configuration

One of the greatest things about Linux is the ability to easily network systems. Linux excels when using wired or wireless networking. There are several basic requirements that must be met for your Linux machine to communicate with other machines or devices on a network.

The first requirement is that your machine must have a means of communicating with other machines through hardware. This requirement is typically met through a network interface card (NIC) at the host level and a switch or router at the local area network (LAN) level. These devices are connected through ethernet cables or another suitable medium (which may also include wireless devices). This requirement is also referred to as the Physical Layer in the OSI Reference Model.

The next requirement is that each network interface must be configured properly. Each interface must be configured with an IP address, netmask, and gateway. These simple parameters allow the interface to communicate with other interfaces on the network. Each interface may be configured through the GUI tools which are provided by Red Hat, by editing configuration files with a text editor, or they can be manually configured from the command line. I will review the command line and text file configurations only. This requirement covers layers 2 and 3 of the OSI Reference Model.

Another requirement that must be met if communication with the network outside of the immediate network is desired is proper configuration of the /etc/resolv.conf file with the IP address of a valid DNS server:

     nameserver xxx.xxx.xxx.xxx
     nameserver xxx.xxx.xxx.xxx

The /etc/resolv.conf file, when configured properly, will allow the machine to obtain IP addresses for hosts which are known only by host name. It is critical that you do not allow any spaces before the nameserver directive in this file or it will not function. This file is configured automatically when using DHCP and manually when using a static IP.

There is a configuration file for each interface in the following directory:

     /etc/sysconfig/network-scripts

These files serve as parameter files for the network startup script which is:

     /etc/rc.d/rc5.d/S10network

When the network service is started, either manually or on system boot, the network startup script reads the configuration file to determine whether or not the interface should be configured to start and how to configure the interface. If the interface is configured to obtain an IP address via DHCP then it will broadcast for a DHCP server and set the IP address, netmask, default gateway, /etc/resolv.conf file, and possibly the hostname for the machine, depending on how the system is configured. If the interface is configured to use a static IP address then most of the above settings will be configured through the configuration file in:

     /etc/sysconfig/network-scripts

The hostname and /etc/resolv.conf file must be configured manually. An example of this file properly configured with a static IP address is as follows:

     [root@primary network-scripts]# cat ifcfg-eth0
     DEVICE=eth0
     BOOTPROTO=static
     BROADCAST=192.168.1.255
     HWADDR=00:E0:81:22:CC:8B
     IPADDR=192.168.1.10
     NETMASK=255.255.255.0
     NETWORK=192.168.1.0
     ONBOOT=yes
     TYPE=Ethernet

Most of the file is self-explanatory and fulfills the requirements listed above with regard to the interface configuration. If the interface is configured to use DHCP, the file will resemble the following:

     [root@primary ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
     DEVICE=eth0
     BOOTPROTO=dhcp

This simple file will cause the interface to obtain an IP address, netmask, and gateway on startup and configure the /etc/resolv.conf file with the nameserver used by the DHCP server. This is a very common configuration and makes network management very robust.

The last part of this article illustrate how to configure an interface manually on the command line. I will merely list the steps required to configure the same interface that is listed in the configuration file above with the same parameters:

     ifconfig eth0 192.168.1.10
     route add default gw 192.168.1.1
     ifconfig eth0 up

You can now verify your settings with:

     ifconfig devicename
     netstat -r

To manually obtain an IP address via DHCP, use the dhclient utility. If no interface is specified then the utility will attempt to obtain a DHCP address for each non-multicast address on the system. An example of using this utility is as follows:

     dhclient eth0

This command will configure the eth0 interface with an IP address, netmask, default gateway, and setup /etc/resolv.conf with the proper nameserver directives.

Through this article I explained what is required to network a Red Hat Enterprise Linux system. I also explained how to configure an interface so that the machine it is on will be able to communicate with other machines and devices on a network. The configuration can be done manually on the command line, through editting text files, and with the GUI tools provided by Red Hat with the operating system. The ability to configure Linux to interact with other systems is an essential skill, as a computer without the ability to network is useless.

RHEL: RAID Performance

I recently purchased 3 new 200GB Maxtor hard drives. I haven't bought a hard drive in a couple of years and the biggest one I owned before this was 80GB, with a second place runner up of 20GB. I'm doing pretty good with the new drives. They are 7200 rpm, IDE, 16MB cache type drives. I just hooked them up in my SMP athlon system and configured a few raid paritions in RAID 0 to test the performance:

root@primary ~]# hdparm -tT /dev/md1

/dev/md1:
Timing cached reads:   956 MB in  2.00 seconds = 477.36 MB/sec
Timing buffered disk reads:  264 MB in  3.01 seconds =  87.72 MB/sec
[root@primary ~]# hdparm -tT /dev/md3

/dev/md3:
Timing cached reads:   948 MB in  2.00 seconds = 473.60 MB/sec
Timing buffered disk reads:  270 MB in  3.01 seconds =  89.68 MB/sec

It's not often that you can get this kind of performance out of an IDE drive, so I'm pretty happy with my purchases. I did test them with Knoppix in a non-RAID configuration and was able to get 62 MB/sec, so this is nearly 30 MB/sec better!

RHCE: Exam Prep

All right, it's time to continue my studies for the RHCE exam. I've registered for the exam and I'll be taking it on Friday, December 2nd. I hope to be able to prepare fully by then with the book that I purchased and by practicing a lot. I just ordered some new hard disks so that I'll be able to play around with more configurations and have enough space on my main machine.

Tonight I'll be reviewing the RHCE exam prep guide.

Perl: Great scripting language...

I have always been a bash or ruby scripter and very rarely used Perl. Lately I have been using Perl quite a bit and have found that it is a joy to use! There is a lot of power behind Perl and it is very widely used in the industry. I realize that Google uses Python, but Amazon.com uses Perl. When performing job skill searches on the job boards of late, I have found quite a few that ask for Perl skills.

I am taking a short break from my studies for the RHCE because I received an un-solicited request for an interview from a large company in Seattle. I will keep you all updated.

NFS: Windows client?

In my recent studies for the RHCE I have covered the NFS file sharing system. I have used this system in the past, but not extensively. I have been told that it is faster than SMB by a great degree between Linux and Unix boxes so I am going to run some tests on it and see how it works. I am currently downloading Services for Unix from Microsoft so that I can test the Windows client that they provide for NFS. I'll post results.

RHCE: The Road to Certification

Aggregation of my posts on the RHCE:

Starting out!
RHCE Exam Prep Guide
RHCE Networking and Configuration

RHCE: The Road to Certification

Over the next couple of months I'm going to be studying for the RHCE exam. I have purchased the book, "RHCE 4th edition", by Michael Jang as a study guide since I heard it was the best one out there. I'm not terribly impressed with it so far, as I have found quite a few technical errors. I hope to be able to start posting about my learning experiences and relate that to how well I perform on the exam. One of the reasons that I am doing this is so that I can start doing some private consulting around my area and I'd like to have some certifications to back up my experience and knowledge. Stay tuned!

NX: Remote X-Server Session

I recently discovered an excellent client application for connecting to X remotely. NX is a client/server application developed by NoMachinewith some clever caching techniques which provide near real-time response for X-sessions. The NX server works with an SSH server to provide secure authentication and SSL encrypted traffic, if desired. A GPL'd server has been written and is available here, while a free client is available from Nomachine.com. The NX client will also connect to Microsoft applications which use the RDP protocol and VNC sessions. An excellent series of articles has been written on NX at Linuxjournal.com which provides some details as to the actual technical operations.

For anyone who has used VNC for remote GUI control of their systems, NX is far superior!

Speakeasy

I recently received an email from Speakeasy with an offer for broadband service in my area. I was impressed with the email as they gave me an option to test my current speed with one of their servers in Seattle. I have attached a link to this speed test in the left nav bar for all to use. I really like the way that Speakeasy does things and I do plan on switching to their service sometime in the next year. One of the good flexible options that Speakeasy has is that you can become a mini WISP if you purchase their service and they will take care of the billing and email problems with your customers. The bad part is that you have to take care of the tech support and security portions.

Responsible Disclosure: Ciscogate

For those who have not yet heard (shouldn't be anyone), Mike Flynn presented a flaw in Cisco routers at Black Hat 2005 that could bring the Internet to it's knees. There are conflicting sides to the story, but the gist is that Cisco was trying to down-play the seriousness of the flaw and keep the researcher from disclosing the vulnerability. Responsible disclosure means that after a reasonable amount of time trying to work with the vendor, the researcher must disclose the vulnerability to the security community so that the flaw may be fixed or defended against. There are rumors that the Chinese have already been exploiting this flaw, which makes it imperative that the security community know about it.

Open Standards: HTML and web technologies

As an avid supporter of open standards in all things digital, I was pleased to see this article on Slashdot wherein Paul Thurrott talks about boycotting Internet Explorer 7.0 until Microsoft comes out with a standards-compliant browser. I think that IE is a huge disappointment and a very lazy offering by MS. Any self-respecting tech company will strive to better the field that they work in and IE has made the field of web browsing and development worse for the wear. Please use Firefox.

Other reasons to not use Internet Explorer:

1. Privacy
2. Security
3. Diversity
4. Competition is better for innovation (not patents -- contrary to popular belief)

Linux Computing: Thin Clients

Thin clients may be the way of the future for computing in large corporations and governments. I do hope that thing clients never take over my PC computing at home though, I always want to be able to control my computing experience. This thin client is the best one that I have seen recently. I have done some work with the Linux Terminal Server Project which provides an excellent solution for using one server to host many thin clients that eases the burden of system administration. I really like the idea from a systems administrator perspective.

Black Hat USA 2005

I just got back from Las Vegas, NV where I attended Black Hat USA 2005. This IT security conference is incredible! All of the briefings are new material only, which give you a fresh perspective on security issues in the IT field. The presenters were people from The Schmoo Group, Dan Kaminsky, the Choicepoint CISO, and many others! I saw some excellent briefings and learned quite a bit. This conference is a "must attend" for any serious security professional.

Network Monitoring: Storage of capture data

I recently played around with trying to store some pcap capture data in a MySQL database so that I could analyze it and look for trends. I had the capture set to create 20MB full content files so that I could manipulate them easily:

tcpdump -s 1515 -C 20 -w content.lpc

I next created a Ruby script that would open the pcap file and write the data that I wanted to store to a CSV file that I would then bulk load into the MySQL database. This part worked very well and very quickly. I found that when I inserted the data into an InnoDB table, while only storing the source IP, destination IP and port, and the time of the packet, that 20 capture files would take up 1GB of space. Not only that, but it turned out to be over 1.3 million packets. This amount of data is really testing my SQL skills, as I try to create intelligent queries that will allow me to aggregate the data on specific parameters.

Anyone have any better solutions?

Securing the mother-in-law's computer.

This week I had the opportunity to take a look at my mother-in-law's computer, after having gone over it pretty thoroughly 6 months ago to make sure some basic security measures were in place, to make sure she was safe on-line. I was talking to her about how she accessed the internet and browsed web pages, as well as using her digital camera to create photo pages. She told me that when she accessed the Internet, she has to disable 'that ZoneAlarm' program so that it wouldn't take as long...and sometimes it stopped web pages from loading altogether! This really suprised me, as I thought that I had explained the situation better than that. Her firewall was being disabled at the time she needed it most.

My mother-in-law is running Microsoft Windows 98 and has been using it for nearly 7 years. She knows how to get around and sees no reason to upgrade to Windows XP or Linux. As security people, I believe that we need to advise people to use systems that are as secure as possible...especially since Microsoft does not, and cannot, maintain the security of it's Operating Systems. The real answer here is to use an Operating System that is more secure so that the users do not have to understand so much about how the technology works to be secure on-line.