Posts Tagged ‘linux’

It’s docker, it’s a container, it’s… a process?

Thursday, November 29th, 2018

In a previous post I discussed Docker from a high level. In this post, we’ll take a closer look at how processes run in a container and how it differs from the common view of the architecture that is used to explain Docker. Remember this?

Common Docker Architecture Overview

The problem with this image, however, is that while it helps conceptualize what we’re talking about, it doesn’t reflect reality. If you listed the processes outside of the container, one might think you’d see the docker daemon running and a bunch of additional processes that represent the containers themselves:

[root@dockerhost ~]# ps -ef
root         1     0  0 Oct15 ?        00:02:40 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
root         2     0  0 Oct15 ?        00:00:03 [kthreadd]
root         3     2  0 Oct15 ?        00:03:44 [ksoftirqd/0]
root      4000     1  0 Oct15 ?        00:03:44 dockerd
root      4353  4000  0 Oct15 ?        00:03:44 myawesomecontainer1
root      4354  4000  0 Oct15 ?        00:03:44 myawesomecontainer2
root      4355  4000  0 Oct15 ?        00:03:44 myawesomecontainer3

And while this might be what you’d expect based on the image above, it does not represent reality. What you’ll actually see is the docker daemon running with a number of additional helper daemons to handle things like networking, and the processes that are running “inside” of the containers like this:

[root@dockerhost ~]# ps -ef
root         1     0  0 Oct15 ?        00:02:40 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
root         2     0  0 Oct15 ?        00:00:03 [kthreadd]
root         3     2  0 Oct15 ?        00:03:44 [ksoftirqd/0]
root      1514     1  0 Oct15 ?        04:28:40 /usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt nat
root      1673  1514  0 Oct15 ?        01:27:08 /usr/bin/docker-containerd-current -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeout
root      4035  1673  0 Oct31 ?        00:00:07 /usr/bin/docker-containerd-shim-current d548c5b83fa61d8e3bd86ad42a7ffea9b7c86e3f9d8095c1577d3e1270bb9420 /var/run/docker/libcontainerd/
root      4054  4035  0 Oct31 ?        00:01:24 apache2 -DFOREGROUND
33        6281  4054  0 Nov13 ?        00:00:07 apache2 -DFOREGROUND
33        8526  4054  0 Nov16 ?        00:00:03 apache2 -DFOREGROUND
33       24333  4054  0 04:13 ?        00:00:00 apache2 -DFOREGROUND
root     28489  1514  0 Oct31 ?        00:00:01 /usr/libexec/docker/docker-proxy-current -proto tcp -host-ip -host-port 443 -container-ip -container-port 443
root     28502  1514  0 Oct31 ?        00:00:01 /usr/libexec/docker/docker-proxy-current -proto tcp -host-ip -host-port 80 -container-ip -container-port 80
33       19216  4054  0 Nov13 ?        00:00:08 apache2 -DFOREGROUND

Without diving too deep into this, the docker processes you see above serve a few processes. There’s the main dockerd process which is responsible for management of docker containers on this host. The containerd processes handle all of the lower level management tasks for the containers themselves. And finally, the docker-proxy processes are responsible for the networking layer between the docker daemon and the host.

You’ll also see a number of apache2 processes mixed in here as well. Those are the processes running within the container, and they look just like regular processes running on a linux system. The key difference is that a number of kernel features are being used to isolate these processes so they are isolated away from the rest of the system. On the docker host you can see them, but when viewing the world from the context of a container, you cannot.

What is this black magic, you ask? Well, it’s primarily two kernel features called Namespaces and cgroups. Let’s take a look at how these work.

Namespaces are essentially internal mapping mechanisms that allow processes to have their own collections of partitioned resources. So, for instance, a process can have a pid namespace allowing that process to start a number of additional processed that can only see each other and not anything outside of the main process that owns the pid namespace. So let’s take a look at our earlier process list example. Inside of a given container you may see this:

[root@dockercontainer ~]# ps -ef
root         1     0  0 Nov27 ?        00:00:12 apache2 -DFOREGROUND
www-data    18     1  0 Nov27 ?        00:00:56 apache2 -DFOREGROUND
www-data    20     1  0 Nov27 ?        00:00:24 apache2 -DFOREGROUND
www-data    21     1  0 Nov27 ?        00:00:22 apache2 -DFOREGROUND
root       559     0  0 14:30 ?        00:00:00 ps -ef

While outside of the container, you’ll see this:

[root@dockerhost ~]# ps -ef
root         1     0  0 Oct15 ?        00:02:40 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
root         2     0  0 Oct15 ?        00:00:03 [kthreadd]
root         3     2  0 Oct15 ?        00:03:44 [ksoftirqd/0]
root      1514     1  0 Oct15 ?        04:28:40 /usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt nat
root      1673  1514  0 Oct15 ?        01:27:08 /usr/bin/docker-containerd-current -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeout
root      4035  1673  0 Oct31 ?        00:00:07 /usr/bin/docker-containerd-shim-current d548c5b83fa61d8e3bd86ad42a7ffea9b7c86e3f9d8095c1577d3e1270bb9420 /var/run/docker/libcontainerd/
root      4054  4035  0 Oct31 ?        00:01:24 apache2 -DFOREGROUND
33        6281  4054  0 Nov13 ?        00:00:07 apache2 -DFOREGROUND
33        8526  4054  0 Nov16 ?        00:00:03 apache2 -DFOREGROUND
33       24333  4054  0 04:13 ?        00:00:00 apache2 -DFOREGROUND
root     28489  1514  0 Oct31 ?        00:00:01 /usr/libexec/docker/docker-proxy-current -proto tcp -host-ip -host-port 443 -container-ip -container-port 443
root     28502  1514  0 Oct31 ?        00:00:01 /usr/libexec/docker/docker-proxy-current -proto tcp -host-ip -host-port 80 -container-ip -container-port 8033       19216  4054  0 Nov13 ?        00:00:08 apache2 -DFOREGROUND

There are two things to note here. First, within the container, you’re only seeing the processes that the container runs. No systems, no docker daemons, etc. Only the apache2 and ps processes. From outside of the container, however, you see all of the processes running on the system, including those within the container. And, the PIDs listed inside if the container are different from those outside of the container. In this example, PID 4054 outside of the container would appear to map to PID 1 inside of the container. This provides a layer of security such that running a process inside of a container can only interact with other processes running in the container. And if you kill process 1 inside of a container, the entire container comes to a screeching halt, much as if you kill process 1 on a linux host.

PID namespaces are only one of the namespaces that Docker makes use of. There are also NET, IPC, MNT, UTS, and User namespaces, though User namespaces are disabled by default. Briefly, these namespaces provide the following:

  • NET
    • Isolates a network stack for use within the container. Network stacks can, and typically are, shared between containers.
  • IPC
    • Provides isolated Inter-Process Communications within a container, allowing a container to use features such as shared memory while keeping the communication isolated within the container.
  • MNT
    • Allows mount points to be isolated, preventing new mount points from being added to the host system.
  • UTS
    • Allows different host and domains names to be presented to containers
  • User
    • Allows a mapping of users and groups with container to the host system, thereby preventing a root user within a container from running as did 1 outside of the container.

The second piece of black magic used is Control Groups or cgroups. Cgroups isolates resource usage for a process. Where Namespaces creates a localized view of resources for a process, cgroups creates a limited pool of resources for a process. For instance, you can assign specific CPU, Memory, and Disk I/O limits to a container. With a cgroup is assigned, the process cannot exceed the limits put on it, thereby preventing processes from “running away” and exhausting system resources. Instead, the process either deals with the lower resource limits, or crashes.

By themselves, these features can be a bit daunting to set up for each process or group of processes. Docker conveniently packages this up, making deployment as simple as a docker run command. Combined with the packaging of a Docker container (which I’ll cover in a future post), Docker becomes a great way to deploy software in a reproducible, secure manner.

Multiple Personalities With The Linux Kernel

Friday, June 29th, 2012

Virtualization is all the rage these days. Taking a single computer system and installing multiple “guest” operating systems on it. The benefits are a reduced footprint and better utilization of existing resources. There is a danger, however, in having many systems dependent on a single piece of hardware. The solution, of course, is to use multiple pieces of hardware and allow your “guests” to be moved between the individual hardware units, thus making the system more resilient to failure.

I’ve started playing a bit with virtualization, specifically, KVM virtualization. For my purposes, I’m using CentOS 6.x on a 64-bit capable system.

The hypervisor itself is a standard CentOS base install with the addition of kvm and various management packages. I installed the hypervisor on a RAID1 LVM, allowing me some room to grow if necessary, and reserving the remainder of the hard drive for virtual hosts. While you can use binary blobs for virtual disk, I prefer using a raided LVM which gives me the ability to grow the disk if necessary as well as minor bumps in speed.

Using yum, adding KVM to an existing installation is a pretty straightforward process :

yum install virt-manager libvirt libvirt-python python-virtinst

That should take care of any dependencies required to get KVM virtualization up and running.

Next up, we need to tackle networking. There are many, many different configurations, far too many to go through here. So, I’m going to keep it simple. For my purposes, I need a single connection to the outside network, all in the same VLAN, as well as a local NAT for some VMs that I need local access to, but that don’t need to be accessed via the Internet.

Setting this up is brilliantly simple. First, copy the /etc/sysconfig/network-scripts/ifcfg-eth0 file to /etc/sysconfig/network-scripts/ifcfg-br0. Next, edit the ifcfg-eth0 file. You’ll need to remove a bunch of lines and add a BRIDGE line as follows :





Next, edit the ifcfg-br0 file. All you really need to do here is change the DEVICE= line to reflect br0. I also recommend disabling NM_CONTROLLED … NetworkManager shouldn’t be installed anyway since you used a base install, but better safe than sorry. In the end, the ifcfg-br0 file should look something like this :









Restart networking and you’ll be all set. The NAT portion of this is handled by KVM itself, so there’s nothing to do there. And networking should be all ready to go.

Without guests, however, all you have is a basic Linux system with a few extra packages taking up space. The real magic starts when you create and install your first VM. My recommendation is to start with creating a template system you can clone later rather than hand-installing every single VM. To install the template, first decide on the base disk size. I’m using 15 GB volumes which is more than enough for the base install and leaves room for most basic server configurations. If you need more space, you can attach additional disks later.

I’m not going to go into how I set up LVM, there are plenty of tutorials out there. For the purposes of this article, I have a volume group names vg_libvirt where I plan to store all of the virtual machines. So first we create the disk necessary for the template :

lvcreate -L15G -n template_base vg_libvirt

Next we install the OS. virt-install is essentially a wrapper script that sets all the necessary values within KVM to get you going. After the settings are configured and the VM is started, girt-installer will automatically attach you to the VM console. The full command I used to install is as follows :

virt-install –accelerate –hvm –connect qemu:///system –network bridge:bra –name template –ram 512 –disk=/dev/mapper/vg_libvirt-template_base –vcpus=1 –check-cpu –nographics –extra-args=”console=ttyS0 text” –location=/tmp/CentOS-6.2-x86_64-bin-DVD1.iso

Since this is effectively a text install, you do run into a bit of a problem. Namely, you can’t configure the drives the way you want. There is a way around this, though it takes a bit of work. Of course, since you’re creating a template, the little bit of work now is easily made up for later. So, here’s how I handled the drive configuration.

First, run through a basic install using the above install method. Once you’re up and running, log into the new VM and head to the root home directory. In that directory you’ll find a kickstart file called anaconda-ks.cfg. Make a local copy of that file and shut down the VM.

The kickstart file gives you the basic parameters that CentOS used to configure the system. You can edit this file and use it yourself to automatically install and configure systems. For our purposes, we’re interested in editing the drive configuration and then using the kickstart file to create the template. So, edit the file and set the parameters as you see fit. An example is as follows :

# Kickstart file automatically generated by anaconda.




lang en_US.UTF-8

keyboard us

network –onboot no –device eth0 –noipv4 –noipv6

rootpw –iscrypted somerandomstringthatiwontrevealtoyoubutnicetry

firewall –service=ssh

authconfig –enableshadow –passalgo=sha512

selinux –enforcing

timezone –utc America/New_York

bootloader –location=mbr –driveorder=vda –append=” console=ttyS0 crashkernel=auto”

# The following is the partition information you requested

# Note that any partitions you deleted are not expressed

# here so unless you clear all partitions first, this is

# not guaranteed to work

clearpart –all –drives=vda

part /boot –fstype=ext4 –size=500

part swap –size=2048

part pv.253002 –grow –size=1

volgroup VolGroup –pesize=4096 pv.253002

logvol / –fstype=ext4 –name=lv_root –vgname=VolGroup –size=4096

logvol /tmp –fstype=ext4 –name=lv_tmp –vgname=VolGroup –size=2048

logvol /var –fstype=ext4 –name=lv_var –vgname=VolGroup –size=4096

logvol /home –fstype=ext4 –name=lv_home –vgname=VolGroup –size=2048

#repo –name=”CentOS” –baseurl=cdrom:sr0 –cost=100

%packages –nobase



Once you have this, you can re-run the girt-install command from above with a slight tweak to make the install use the kickstart file you created (I named it kick1.ks) :

virt-install –accelerate –hvm –connect qemu:///system –network bridge:bra –name template –ram 512 –disk=/dev/mapper/vg_libvirt-template_base –vcpus=1 –check-cpu –nographics –initrd-inject=/path/to/kick1.ks –extra-args=”ks=file:/kick1.ks console=ttyS0 text” –location=/tmp/CentOS-6.2-x86_64-bin-DVD1.iso

This will nuke the existing VM and replace it with one configured with the drive partitions as set in the kickstart file. And now you almost have a template.

You could use this new VM as a clone, but if you’ve set an IP on it, you’ll run into duplicate IP problems. SSH keys on the machine will be cloned, making all of your systems contain the same keys. And other machine-specific settings will be cloned as well. This can be worked around, though.

I recommend that you first configure this new template with the basic settings you want on all of your VMs. For instance, if you’re using Spacewalk for server management, you can install all of the necessary spacewalk binaries. You can configure a standard iptables template for the system. Maybe you have some standard security software you use such as OSSEC. And, of course, create the standard users on the system so you don’t have to create them each time you clone the VM. Once everything is installed and running how you want it, perform the following actions to make the template :

touch /.unconfigured

rm -rf /etc/ssh/ssh_host_*


The VM will power down and you’ll have your template. Cloning this to a new VM is quick and simple. First, create the new logical volume as we did before. Next, clone the VM to the new drive :

virt-clone -o template -n new_vm -f /dev/mapper/vg_libvirt-new_vm_base

Simple enough, right? Run this command and when it completed, you can start the VM and connect to the console. You’ll be greeted with the standard first boot process and then dropped at a login prompt. Congratulations, you now have a VM. Set the IP, configure whatever services you need, and you’re off to the races.

If you need to modify the RAM, number of CPUs, etc., then use the virsh command on the hypervisor. You’ll need to shut down the VM and restart it in order for these changes to take effect.

And that’s really all there is to it. The VMs themselves can be treated as self-contained systems with no special care necessary … One note, however. If you reboot the hypervisor, the VMs are paused before rebooting and resumed after reboot. This leads to an interesting problem in that the uptime on a VM can easily exceed that of the hypervisor. Be aware of this and don’t depend on a VMs uptime to be accurate.

Hey KVM, you’ve got your bridge in my netfilter…

Monday, April 18th, 2011

It’s always interesting to see how new technologies alter the way we do things.  Recently, I worked on firewalling for a KVM-based virtualization platform.  From the outset it seems pretty straightforward.  Set up iptables on the host and guest and move on.  But it’s not that simple, and my google-fu initially failed me when searching for an answer.

The primary issue was that when iptables was enabled on the host, the guests became unavailable.  If you enable logging, you can see the traffic being blocked by the host, thus never making it to the guest.  So how do we do this?  Well, if we start with a generic iptables setup, we have something that looks like this:

# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
:RH-Firewall-1-INPUT – [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp –icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 22 -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT –reject-with icmp-host-prohibited

Adding logging to identify what’s going on is pretty straightforward.  Add two logging lines, one for the INPUT chain and one for the FORWARD chain.  Make sure these are added as the first rules in the chain, otherwise you’ll jump to the RH-Firewall-1-INPUT chain and never make it to the log.

-A INPUT -j LOG –log-prefix “Firewall INPUT: ”
-A FORWARD -j LOG –log-prefix “Firewall FORWARD: ”


Now, with this in place you can try sending traffic to the domU.  If you tail /var/log/messages, you’ll see the blocking done by netfilter.  It should look something like this:

Apr 18 12:00:00 example kernel: Firewall FORWARD: IN=br123 OUT=br123 PHYSIN=vnet0 PHYSOUT=eth1.123 SRC= DST= LEN=56 TOS=0x00 PREC=0x00 TTL=64 ID=18137 DF PROTO=UDP SPT=56712 DPT=53 LEN=36

There are a few things of note here.  First, this occurs on the FORWARD chain only.  The INPUT chain is bypassed completely.  Second, the system recognizes that this is a bridged connection.  This makes things a bit easier to fix.

My attempt at resolving this was to put in a rule that allowed traffic to pass for the bridged interface.  I added the following:

-A FORWARD -i br123 -o br123 -j ACCEPT

This worked as expected and allowed the traffic through the FORWARD chain, making it to the domU unmolested.  However, this method means I have to add a rule for every bridge interface I create.  While explicitly adding rules for each interface should make this more secure, it means I may need to change iptables while the system is in production and running, not something I want to do.

A bit more googling led me to this post about KVM and iptables.  In short it provides two additional methods for handling this situation.  The first is a more generalized rule for bridged interfaces:

-A FORWARD -m physdev –physdev-is-bridged -j ACCEPT

Essentially, this rule tells netfilter to accept any traffic for bridged interfaces.  This removes the need to add a new rule for each bridged interface you create making management a bit simpler.  The second method is to completely remove bridged interfaces from netfilter.  Set the following sysctl variables:

net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0

I’m a little worried about this method as it completely bypasses iptables on dom0.  However, it appears that this is actually a more secure manner of handling bridged interfaces.  According to this bugzilla report and this post, allowing bridged traffic to pass through netfilter on dom0 can result in a possible security vulnerability.  I believe this is somewhat similar to cryptographic hash collision.  Attackers can take advantage of netfilter entries with similar IP/port combinations and possibly modify traffic or access systems.  By using the sysctl method above, the traffic completely bypasses netfilter on dom0 and these attacks are no longer possible.

More testing is required, but I believe the latter method of using sysctl is the way to go.  In addition to the security considerations, bypassing netfilter has a positive impact on throughput.  It seems like a win-win from all angles.

Centralized Firewall Logging

Tuesday, September 15th, 2009

I currently maintain a number of Linux-based servers. The number of servers is growing, and management becomes a bit wieldy after a while. One move I’ve made is to start using Spacewalk for general package and configuration management. This has turned out to be a huge benefit and I highly recommend it for anyone in the same position as I am. Sure, Spacewalk has its bugs, but it’s getting better with every release. Kudos to Redhat for bringing such a great platform to the public.

Another area of problematic management is the firewall. I firmly believe in defense in depth and I have several layers of protection on these various servers. One of those layers is the iptables configuration on the server itself. Technically, iptables is the program used to configure the filtering ruleset for a Linux kernel with the ip_tables packet filter installed. For the purposes of this article, iptables encompasses both the filter itself as well as the tools used to configure it.

Managing the ruleset on a bunch of disparate servers can be a daunting task. There are often a set of “standard” rules you want to deploy across all of the servers, as well as specialized rules based on what role the server plays. The standard rules are typically for management subnets, common services, and special filtering rules to drop malformed packets, source routes, and more. There didn’t seem to be an easy way to deploy such a ruleset, so I ended up rolling my own script to handle the configuration. I’ll leave that for a future blog entry, though.

In addition to centralized configuration, I wanted a way to monitor the firewall from a central location. There are several reasons for this. One of the major reasons is convenience. Having to wade through tons of logwatch reports, or manually access each server to check the local firewall rules is difficult and quickly reaches a point of unmanageability. What I needed was a way to centrally monitor the logs, adding and removing filters as necessary. Unfortunately, there doesn’t seem to be much out there. I stumbled across the iptablelog project, but it appears to be abandoned.

Good did come of this project, however, as it lead me to look into ulogd. The ulog daemon is a userspace logger for iptables. The iptables firewall can be configured to send security violations, accounting, and flow information to the ULOG target. Data sent to the ULOG target is picked up by ulogd and sent wherever ulogd is configured to send it. Typically, this is a text file or a sql database.

Getting started with ulogd was a bit of a problem for me, though. To start, since I’m using a centralized management system, I need to ensure that any new software I install uses the proper package format. So, my first step was to find an RPM version of ulogd. I can roll my own, of course, but why re-invent the wheel? Fortunately, Fedora has shipped with ulogd since about FC6. Unfortunately for me, however, I was unable to get the SRPM for the version that ships with Fedora 11 to install. I keep getting a cpio error. No problem, though, I just backed up a bit and downloaded a previous release. It appears that nothing much has changed as ulogd 1.24 has been released for some time.

Recompiling the ulog SRPM for my CentOS 5.3 system failed, however, complaining about linker problems. Additionally, there were errors when the configure script was run. So before I could get ulogd installed and running, I had to get it to compile. It took me a while to figure it out as I’m not a linker expert, but I came up with the following patch, which I added to the RPM spec file.

— ./configure 2006-01-25 06:15:22.000000000 -0500
+++ ./configure 2009-09-10 22:37:24.000000000 -0400
@@ -1728,11 +1728,11 @@

MYSQLINCLUDES=`$d/mysql_config –include`
– MYSQLLIBS=`$d/mysql_config –libs`
+ MYSQLLIBS=`$d/mysql_config –libs | sed s/-rdynamic//`


# no change to DATABASE_LIB_DIR, since –libs already includes -L

DATABASE_DRIVERS=”${DATABASE_DRIVERS} ../mysql/mysql_driver.o ”
@@ -1747,7 +1747,8 @@
echo $ac_n “checking for mysql_real_escape_string support””… $ac_c” 1>&6
echo “configure:1749: checking for mysql_real_escape_string support” >&5

– MYSQL_FUNCTION_TEST=`strings ${MYSQLLIBS}/ | grep mysql_real_escape_string`
+ LIBMYSQLCLIENT=`locate | grep$`
+ MYSQL_FUNCTION_TEST=`strings $LIBMYSQLCLIENT | grep mysql_real_escape_string`

if test “x$MYSQL_FUNCTION_TEST” = x

In short, this snippet modifies the linker flags to add /usr/lib as a directory and removed the -rdynamic flag which mysql_config seems to errantly present. Additionally, it modifies how the script identifies whether the mysql_real_escape_string function is present in the version of MySQL installed. Both of these changes resolved my compile problem.

After getting the software to compile, I was able to install it and get it running. Happily enough, the SRPM I started with included patches to add an init script as well as a logrotate script. This makes life a bit easier when getting things running. So now I had a running userspace logger as well as a standardized firewall. Some simple changes to the firewall script added ULOG support. You can download the SRPM here.

At this point I have data being sent to both the local logs as well as a central MySQL database. Unfortunately, I don’t have any decent tools for manipulating the data in the database. I’m using iptablelog as a starting point and I’ll expand from there. To make matters more difficult, ulogd version 2 seems to make extensive changes to the database structure, which I’ll need to keep in mind when building my tools.

I will, however, be releasing them to the public when I have something worth looking at. Having iptablelog as a starting point should make things easier, but it’s still going to take some time. And, of course, time is something I have precious little of to begin with. Hopefully, though, I’ll have something worth releasing before the end of this year. Here’s hoping!


The Case of the Missing RAID

Saturday, June 27th, 2009

I have a few servers with hardware RAID directly on the motherboard. They’re not the best boards in the world, but they process my data and serve up the information I want. Recently, I noticed that one of the servers was running on the /dev/sdb* devices, which was extremely odd. Digging some more, it seemed that /dev/sda* existed and seemed to be ok, but wasn’t being used.

After some searching, I was able to determine that the server, when built, actually booted up on /dev/mapper/via_* devices, which were actually the hardware RAID. At some point these devices disappeared. To make matters worse, it seems that kernel updates weren’t being applied correctly. My guess is that either the grub update was failing, or it updated a boot loader somewhere that wasn’t actually being used to boot. As a result, an older kernel was loading, with no way to get to the newer kernel.

I spent some time tonight digging around with Google, posting messages on the CentOS forums, and digging around on the system itself. With guidance from a user via the forums, I discovered that my system should be using dmraid, which is a program that discovers and runs RAID devices such as the one I have. Digging around a bit more with dmraid and I found this :

[user@dev ~]$ sudo /sbin/dmraid -ay -v
INFO: via: version 2; format handler specified for version 0+1 only
INFO: via: version 2; format handler specified for version 0+1 only
RAID set “via_bfjibfadia” was not activated
[user@dev ~]$

Apparently my RAID is running version 2 and dmraid only supports versions 0 and 1. Since this was initially working, I’m at a loss as to why my RAID is suddenly not supported. I suppose I can rebuild the machine, again, and check, but the machine is about 60+ miles from me and I’d rather not have to migrate data anyway.

So how does one go about fixing such a problem? Is my RAID truly not supported? Why did it work when I built the system? What changed? If you know what I’m doing wrong, I’d love to hear from you… This one has me stumped. But fear not, when I have an answer, I’ll post a full writeup!


Introducing, The Touchbook

Wednesday, March 4th, 2009

Engadget posted a story about a new Netbook from a company called Always Innovating. A press release about the product can be found here. In short, it’s a netbook, and a tablet PC, but without the typical “fold it over on top of the keyboard” scenario. The screen literally detaches from the keyboard and becomes an autonomous unit.

Inside this little beast is an ARM OMAP3 processor with 8 Gig of storage on a micro SD chip. They don’t specify which OMAP3 processor is included, so both speed and die size is unknown. It touts an 8.9″ screen, typical of the current netbook generation. For network access it has 802.11b/g/n Wifi. Bluetooth is also included, so the possibility of tethering exists as well.
Both the tablet and keyboard have built-in batteries. Battery life is expected to be 10 to 15 hours when both the tablet and keyboard are used in-concert. The tablet is expected to last between 3 and 5 hours on battery when it is disconnected from the keyboard. Battery life in the keyboard is, of course, irrelevant.

Always Innovating demonstrated the Touchbook at DEMO 2009, a technical conference that wrapped up yesterday. The demonstration video is included below:

Overall, this looks to be a fairly decent device. I’m a bit concerned about the ARM processor, and I wonder what sort of OS support it will have. The TouchBook OS will be installed by default, though from reading the FAQs, it appears that it will run anything from Android, to Ubuntu, to Windows CE.

I’m also curious as to what the device will be using for memory. Is memory shared on the SD card? Or will there be actual RAM in the device? All questions I hope to have answers for in the near future. Looks good, though, and I’m excited at the prospect of possibly getting one. Definitely something I could put to good use!


Headless Linux Testing Clients

Friday, June 13th, 2008

As part of my day to day job, I’ve been working on a headless Linux client that can be transported from site to site to automate some network testing.  I can’t really go into detail on what’s being tested, or why, but I did want to write up a (hopefully) useful entry about headless client and some of the changes I made to the basic CentOS install to get everything to work.

First up was the issue of headless operation.  We’re using Cappuccino SlimPRO SP-625 units with the triple Gigabit Ethernet option.  They’re not bad little machines, though I do have a gripe with the back cover on them.  It doesn’t properly cover all of the ports on the back, leaving rather large holes where dust and dirt can get in.  What’s worse is that the power plug is not surrounded and held in place by the case, so I can foresee the board cracking at some point from the stress of the power cord…  But, for a sub-$800 machine, it’s not all that bad.

Anyway, on to the fun.  These machines will be transported to various locations where testing is to be performed.  On-site, there will be no keyboard, no mouse, and no monitor for them.  However, sometimes things go wrong and subtle adjustments may need to be made.  This means we need a way to get into the machine, locally, just in case there’s a problem with the network connection.  Luckily, there’s a pretty simple means of accessing a headless Linux machine without the need to lug around an extra monitor, keyboard, and mouse.  If you’ve ever worked on a switch or router, you’ll know where I’m going with this.

Most technician have access to a laptop, especially if they have to configure routers or switches.  Why not access a Linux box the same way?  Using the agetty command, you can.  A getty is a program that manages terminals within Unix.  Those terminals can be physical, like the local keyboard, or virtual, like a telnet or ssh session.  The agetty program is an alternative getty program that has some non-standard features such as baud rate detection, adaptive tty, and more.  In short, it’s perfect for direct serial, or even dial-in connections.

Setting this all up is a snap, too.  By default, CentOS (and most Linux distros) set up six gettys for virtual terminals.  These virtual terminals use yet another getty, mingetty, which is a minimalized getty program with only enough features for virtual terminals.  In order to provide serial access, we need to add a few lines to enable agettys on the serial ports.

But wait, what serial ports do we have?  Well, assuming they are enabled in the BIOS, we can see them using the dmesg and setserial commands.  The dmesg command prints out the current kernel message buffer to the screen.  This is usually the output from the boot sequence, but if your system has been up a while, it may contain more recent messages.  We can use dmesg to determine the serial interfaces like this :

[friz@test ~]$ dmesg | grep serial
serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
serial8250: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A

As you can see from the output above, we have both a ttyS0 and a ttyS1 port available on this particular machine.  Now, we use setserial to make sure the system recognizes the ports:

[friz@test ~]$ sudo setserial -g /dev/ttyS[0-1]
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: 16550A, Port: 0x02f8, IRQ: 3

The output is similar to dmesg, but setserial actually polls the port to get the necessary information, thereby ensuring that it’s active.  Also note, you will likely need to run this command as root to make it work.

Now that we know what serial ports we have, we just need to add them to the inittab and reload the init daemon.  Adding these to the inittab is pretty simple.  Your inittab will look something like this:

# inittab       This file describes how the INIT process should set up
#               the system in a certain run-level.
# Author:       Miquel van Smoorenburg, <>
#               Modified for RHS Linux by Marc Ewing and Donnie Barnes

# Default runlevel. The runlevels used by RHS are:
#   0 – halt (Do NOT set initdefault to this)
#   1 – Single user mode
#   2 – Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 – Full multiuser mode
#   4 – unused
#   5 – X11
#   6 – reboot (Do NOT set initdefault to this)

# System initialization.

l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

ca::ctrlaltdel:/sbin/shutdown -t3 -r now

# When our UPS tells us power has failed, assume we have a few minutes
# of power left.  Schedule a shutdown for 2 minutes from now.
# This does, of course, assume you have powerd installed and your
# UPS connected and working correctly.
pf::powerfail:/sbin/shutdown -f -h +2 “Power Failure; System Shutting Down”

# If power was restored before the shutdown kicked in, cancel it.
pr:12345:powerokwait:/sbin/shutdown -c “Power Restored; Shutdown Cancelled”

# Run gettys in standard runlevels
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6

# Run xdm in runlevel 5
x:5:respawn:/etc/X11/prefdm -nodaemon

Just add the following after the original gettys lines:

# Run agettys in standard runlevels
s0:2345:respawn:/sbin/agetty -L -f /etc/issue.serial 9600 ttyS0 vt100
s1:2345:respawn:/sbin/agetty -L -f /etc/issue.serial 9600 ttyS1 vt100

Let me explain quickly what the above means.  Each line is broken into multiple fields, separated by a colon.  At the very beginning of the line is an identifier, s0 and s1 in our case.  Next comes a list of the runlevels for which this program should be spawned.  Finally, the command to run is last.

The agetty command takes a number of arguments:

    • The -L switch disables carrier detect for the getty.
    • The next switch, -f, tells agetty to display the contents of a file before the login prompt, /etc/issue.serial in our case.
    • Next is the baud rate to use.  9600 bps is a good default value to use.  You can specify speeds up to 152,200 bps, but they may not work with all terminal programs.
    • Next up is the serial port, ttyS0 and ttyS1 in our example.
    • Finally, the terminal emulation to use.  VT100 is probably the most common, but you can use others.

Now that you’ve added the necessary lines, reload the init daemon via this command:

[friz@test ~]$ sudo /sbin/init q

At this point, you should be able to connect a serial cable to your Linux machine and access it via a program such as minicom, PuTTY, or hyperterminal.  And that’s all there is to it.

You can also redirect the kernel to output all console messages to the serial port as well.  This is accomplished by adding a switch to the kernel line in your /etc/grub.conf file like this:

# 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/hdc3
#          initrd /initrd-version.img
title CentOS (2.6.18-53.1.21.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-53.1.21.el5 ro root=LABEL=/ console=ttyS0,9600
initrd /initrd-2.6.18-53.1.21.el5.img

The necessary change is highlighted above.  The console switch tells the kernel that you want to re-direct the console output.  The first option is the serial port to re-direct to, and the second is the baud rate to use.

And now you have a headless Linux system!  These come in handy when you need a Linux machine for remote access, but you don’t want to deal with having a mouse, keyboard, and monitor handy to access the machine locally.

Instant Kernel-ification

Monday, April 28th, 2008


Server downtime is the scourge of all administrators, sometimes to the extent of bypassing necessary security upgrades, all in the name of keeping machines online.  Thanks to an MIT graduate student, Jeffery Brian Arnold, keeping a machine online, and up to date with security patches, may be easier than ever.

Ksplice, as the project is called, is a small executable that allows an administrator the ability to patch security holes in the Linux kernel, without rebooting the system.  According to the Ksplice website :

“Ksplice allows system administrators to apply security patches to the Linux kernel without having to reboot. Ksplice takes as input a source code change in unified diff format and the kernel source code to be patched, and it applies the patch to the corresponding running kernel. The running kernel does not need to have been prepared in advance in any way.”

Of course, Ksplice is not a perfect silver bullet, some patches cannot be applied using Ksplice.  Specifically, any patch that require “semantic changes to data structures” cannot be applied to the running kernel.  A semantic change is a change “that would require existing instances of kernel data structures to be transformed.”

But that doesn’t mean that Ksplice isn’t useful.  Jeffery looked at 32 months of kernel security patches and found that 84% of them could be applied using Ksplice.  That’s sure to increase the uptime.

I have to wonder, though, what is so important that you need that much uptime.  Sure, it’s nice to have the system run all the time, but if you have something that is absolutely mission critical, that must run 24×7, regardless, won’t you have a backup or two?  Besides which, you generally want to test patches before applying them to such sensitive systems.

There are, of course, other uses for this technology.  As noted on the Ksplice website, you can also use Ksplice to “add debugging code to the kernel or to make any other code changes that do not modify data structure semantics.”  Jeffery has posted a paper detailing how the technology works.

Pretty neat technology.  I wonder if this will lead to zero downtime kernel updates direct from Linux vendors.  As it is now, you’ll need to locate and manually apply kernel patches using this tool.


Backups? Where?

Friday, July 6th, 2007

It’s been a bit hectic, sorry for the long time between posting.


So, backups.  Backups are important, we all know that.  So how many people actually follow their own advice and back their data up?  Yeah, it’s a sad situation for desktops.  The server world is a little different, though, with literally tens, possibly hundreds of different backup utilities available.


My preferred backup tool of choice is the Advanced Maryland Automatic Network Disk Archiver, or AMANDA for short.  AMANDA has been around since before 1997 and has evolved into a pretty decent backup system.  Initially intended for single tape-based backups, options have been added recently to allow for tape spanning and disk-based backups as well.

Getting started with AMANDA can be a bit of a chore.  The hardest part, at least for me, was getting the tape backup machine running.  Once that was out of the way, the rest of it was pretty easy.  The config can be a little overwhelming if you don’t understand the options, but there are a lot of guides on the Internet to explain it.  In fact, the “tutorial” I originally used is located here.

Once it’s up and running, you’ll receive a daily email from Amanda letting you know how the previous nights backup went.  All of the various AMANDA utilities are command-line based.  There is no official GUI at all.  Of course, this causes a lot of people to shy away from the system.  But overall, once you get the hang of it, it’s pretty easy to use.

Recovery from backup is a pretty simple process.  On the machine you’re recovering, run the amrecover program.  You then use regular filesystem commands to locate the files you want to restore and add them to the restore list.  When you’ve added all the files, issue the extract command and it will restore all of the files you’ve chosen.  It’s works quite well, I’ve had to use it once or twice…  Lemme tell ya, the first time I had to restore from backups I was sweatin bullets..  After the first one worked flawlessly, subsequent restores were completed with a much lower stress level.  It’s great to know that there are backups available in the case of an emergency.

AMANDA is a great tool for backing up servers, but what about clients?  There is a Windows client as well that runs using Cygwin, a free open-source Linux-like environment for Windows.  Instructions for setting something like this up are located in the AMANDA documentation.  I haven’t tried this, but it doesn’t look too hard.  Other client backup options include remote NFS and SAMBA shares.

Overall, AMANDA is a great backup tool that has saved me a few times.  I definitely recommend checking it out.

Linux Software Raid

Friday, January 26th, 2007

I had to replace a bad hard drive in a Linux box recently and I thought perhaps I’d detail the procedure I used.  This particular box uses software raid, so there are a few extra steps to getting the drive up and running.

Normally when a hard drive fails, you lose any data on it.  This is, of course, why we back things up.  In my case, I have two drives in a raid level 1 configuration.  There are a number of raid levels that dictate various states of redundancy (or lack thereof in the instance of level 0).  The raid levels are as follows (Copied from Wikipedia):

  • RAID 0: Striped Set
  • RAID 1: Mirrored Set
  • RAID 3/4: Striped with Dedicated Parity
  • RAID 5: Striped Set with Distributed Parity
  • RAID 6: Striped Set with Dual Distributed Parity

There are additional raid levels for nested raid as well as some non-standard raid levels.  For more information on those, see the Wikipedia article referenced above.


The hard drive in my case failed in kind of a weird way.  Only one of the partitions on the drive was malfunctioning.  Upon booting the server, however, the bios complained about the drive being bad.  So, better safe than sorry, I replaced the drive.

Raid level 1 is a mirrored raid.  As with most raid levels, the hard drives being raided should be identical.  It is possible to use different models and sizes in the same raid, but there are drawbacks such as a reduction in speed, possible increased failure rates, wasted space, etc.  Replacing a drive in a mirrored raid is pretty straightforward.  After identifying the problem drive, I physically removed the faulty drive and replaced it with a new one.

The secondary drive was the failed drive, so this replacement was pretty easy.  In the case of a primary drive failure, it’s easiest to move the secondary drive into the primary slot before replacing the failed drive.

Once the new drive has been installed, boot the system up and it should load up your favorite Linux distro.  The system should boot normally with a few errors regarding the degraded raid state.

After the system has booted, login to the system and use fdisk to partition the new drive.  Make sure you set the drive IDs back to Linux raid.  When finished, the partition table will look something like this :

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1   *           1          26      208813+  fd  Linux raid autodetect
/dev/hdb2              27        3850    30716280   fd  Linux raid autodetect
/dev/hdb3            3851        5125    10241437+  fd  Linux raid autodetect
/dev/hdb4            5126       19457   115121790    f  W95 Ext'd (LBA)
/dev/hdb5            5126        6400    10241406   fd  Linux raid autodetect
/dev/hdb6            6401        7037     5116671   fd  Linux raid autodetect
/dev/hdb7            7038        7164     1020096   82  Linux swap
/dev/hdb8            7165       19457    98743491   fd  Linux raid autodetect

Once the partitions have been set up, you need to format the drive with a filesystem.  This is a pretty painless process depending on your filesystem of choice.  I happen to be using ext3 as my filesystem, so I use the mke2fs program to format the drive.  To format an ext3 partition use the following command (This command, as well as the commands that follow, need to be run as root, so be sure to use sudo.) :

mke2fs -j /dev/hdb1

Once all of the drives have been formatted you can move on to creating the swap partition.  This is done using the mkswap program as follows :

mkswap /dev/hdb7

Once the swap drive has been formatted, activate it so the system can use it.  The swapon command achieves this goal :

swapon -a /dev/hdb7

And finally you can add the drives to the raid using mdadm.  mdadm is a single command with a plethora of uses.  It builds, monitors, and alters raid arrays.  To add a drive to the array use the following :

mdadm -a /dev/md1 /dev/hdb1

And that’s all there is to it.  If you’d like to watch the array rebuild itself, about as much fun as watching paint dry, you can do the following :

watch cat /proc/mdstat

And that’s all there is to it.  Software raid has come a long way and it’s quite stable these days.  I’ve been happily running it on my Linux machines for several years now.  It works well when hardware raid is not available or as a cheaper solution.  I’m quite happy with the performance and reliability of software raid and I definitely recommend it.