Simon Krenger

Some years ago, I wrote some examples for the WMI client on Linux. I still get a lot of queries from people trying to use the WMI client to access Windows hosts and I am often happy to help if there are any problems.

One of the latest problems occurred when trying to access a Windows host over IPv6:

$ wmic -U 'user%password' //FD00:180::0:0:0:0:0 "Select Caption From Win32_OperatingSystem" [..] UNKNOWN - The WMI query had problems. The error text from wmic is: [librpc/rpc/dcerpc_util.c:343:dcerpc_parse_binding()] Unknown dcerpc transport 'FD00' [librpc/rpc/dcerpc_connect.c:337:dcerpc_pipe_connect_ncacn_ip_tcp_recv()] failed NT status (c0000017) in dcerpc_pipe_connect_ncacn_ip_tcp_recv [librpc/rpc/dcerpc_connect.c:828:dcerpc_pipe_connect_b_recv()] failed NT status (c0000017) in dcerpc_pipe_connect_b_recv [wmi/wmic.c:196:main()] ERROR: Login to remote object. NTSTATUS: NT_STATUS_NO_MEMORY - Memory allocation error

This was quite a funny problem, because the same query seemed to work when accessing the host over IPv4. So we quickly suspected that the WMI client does not support IPv6. By looking at the underlying Samba code (e.g. dcerpc_util.c and binding.c), I guessed that this seems to be a parsing issue of some kind.

So today I tried to install the Oracle Preinstall RPM on a freshly installed Oracle Linux 7 machine. However, when I executed yum search rdbms the preinstall package was nowhere to be seen!

It turns out that we need to enable the Oracle Linux 7 “addons” repository in order to find the package. Swiss blogger Martin Berger put me on the right track.

To enable the repository, open the file /etc/yum.repos.d/public-yum-ol7.repo and find the following repository entry:

So lately I have been working a lot more with Linux networking. Consider an iptables configuration like this:

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [7752:8249066]
[..]
-A RH-Firewall-1-FORWARD -p icmp -m icmp --icmp-type any -j ACCEPT 
-A RH-Firewall-1-FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A RH-Firewall-1-FORWARD -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT 
[..]
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited 
COMMIT
# Completed on Fri Nov 21 15:44:47 2014

Ever noticed the brackets right next to the chain? What are those? What do the numbers mean?

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [7752:8249066]

The answer is pretty easy and pretty obvious in hindsight. These numbers report

• packet counter for the chain
• byte counter for the chain

So in our example above, the OUTPUT chain matched 7752 packets and 8249066 bytes.

Since Google shut down its Reader service, I am a regular user of the Tiny Tiny RSS reader. Having my own RSS reader installation gives me more power regarding my privacy and the services I am using. Consider me a happy user.

However, there are some issued regarding full UTF8 support when using MySQL. When a feed uses UTF8 emoijs, tt-rss will throw up and report an error. Unfortunately, this only manifests itself with log entries like this:

So often when issuing a emctl (Enterprise Manager Command Line Utility) command, one needs to specify a target type. This is often the case when the command affects a certain target (for example emctl reload agent dynamicproperties ...).

The most often used target types are the following:

• oracle_database (Oracle Instance)
• oracle_emd (Agent)
• host (Host Machine)

However, there are a lot of other target types available. We can get all available target types for Oracle Enterprise Manager Cloud Control 12c if we query the SYSMAN.EM_TARGET_TYPES table in the Enterprise manager repository:

So recently I stumbled across a programming quiz to which I later returned because it somehow fascinated me.

Problem

Finding the first available number (or the smallest missing number) in a list is a common problem in Computer Science (for example for Defragmenting or generating keys) and describes the search for the smallest natural number, which is not part of a set X of natural numbers. X is a set of distinct natural numbers (and being a set, is not ordered).

We are now looking for a function with linear worst-case time complexity O(n).

Example

We define X as a set of distinct natural numbers:

X = {23,9,12,0,11,1,13,7,21,14,5,4,17,19,3,6,2}

So in this set, we find that the number 8 is the first available number (smallest missing number). So running the algorithm over the above set should return 8.

When you install the InstantClient binaries, you often want to use your existing TNSNAMES.ORA file containing all your databases. So how do you specify the location of your TNSNAMES.ORA file?

The Oracle website has the answer:

For Nagios, many, many Oracle plugins are available for checking database availability and performance. But if you just want to check if the instance is up and running (and not add more complexity), you can use the simple script provided here.

In an earlier post, I showed how to install SQL*Plus on Debian and based on that tutorial, I wrote a little shell script to query a database (I called it check_oracle_dual.sh):

Last week, someone at work approached me, stating that he was unable to log into the web interface of a VMware Server machine. I was shocked to learn that we still had a VMware Server up and running. Then, I tried to log into the web interface myself and received an SSL error as well.

It turns out the machine was standing under someones desk and still had one single VM running. In order to migrate the machine to our ESXi infrastructure and fix the problem, I examined the logs on the server and found this:

In a script I was working on, the tar command always reported the following error when I tried to extract an archive:

Cannot change ownership to uid 1000 , gid 1000: Permission denied

But I was executing the script as root! The reason for this error to occur turned out to be relatively simple. Hint: It has to do with CIFS.