Archive for the ‘Linux’ Category

Watch “Monitorama 2016: All of Your Networking Monitoring is (probably) wrong” talk

Just came across this talk being mentioned in the comments on Hacker news and, boy, it’s absolutely amazing! Watch this hilarious talk here – Monitorama 2016: All of Your Networking Monitoring is (probably) wrong Btw, the talk is presented, presumably, by the same guy who wrote Monitoring and Tuning the Linux Networking Stack: Receiving Data […]

Posted on February 8, 2017 at 11:55 am by sergeyt · Permalink · Leave a comment
In: Linux

TIL gethostbyname*() and gethostbyaddr*() functions are obsolete

It wasn’t obvious to me until I tried to run netcat utility (aka nc) on Ubuntu 10.04 (lucid) release to check Zookeeper’s status: echo “stat” | nc zookeer_server_name 2181 zookeer_server_name: forward host lookup failed: No address associated with name It wouldn’t have been a problem had Zookeeper server used IPv4 address but it was configured […]

Posted on January 28, 2017 at 11:54 am by sergeyt · Permalink · 2 Comments
In: Linux, TIL

jbd2 is munching your disks? Use ftrace to find why.

Have you ever been wondering why jbd2 (or jbd if your are still using ext3) is sitting at the top of iotop and consuming the most of IO bandwidth? Well, it’s certainly not because it’s doing that just to drive you nuts but there is a reason. And the reason is most probably there is […]

Posted on January 27, 2017 at 11:51 am by sergeyt · Permalink · Leave a comment
In: Linux, MongoDB

Have stalled snmpd in recvfrom()? Check Recv-Q

Not so while ago I had an issue with a monitoring system that paged about SNMP checks failing on a number of servers. Quick checking here and there (logs, strace, tcpdump, etc.) revealed that snmpd had stalled in recvfrom() without sending a single packet out in response to the constant queries from our monitoring system. […]

Posted on May 14, 2016 at 9:17 pm by sergeyt · Permalink · Leave a comment
In: Linux

Do initrd dance before turning Linux physical server into VM

If one day you decide to convert your physical server to a VM, which could be easily achieved if all its disks are presented from SAN, then don’t forget to rebuild initrd beforehand. Otherwise you would see something similar to this: No device found Scanning and configuring dmraid supported devices Scanning logical volumes Reading all […]

Posted on April 17, 2016 at 8:19 pm by sergeyt · Permalink · Leave a comment
In: Linux

Workaround for Tomcat7 on Linux, JDBC and javax.naming.NamingException

A few days ago I was dabbling with JDBC and Tomcat7 and the configuration that seemingly had no issues resulted in the following error in the log file: org.apache.catalina.core.NamingContextListener addResource WARNING: Failed to register in JMX: javax.naming.NamingException: Could not create resource factory instance [Root exception is java.lang.ClassNotFoundException: org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory] Thankfully, Google pointed me to this post […]

Posted on February 19, 2016 at 2:53 pm by sergeyt · Permalink · 2 Comments
In: Linux

Interview fizzle as a chance to get better

Not a long ago I had one of those humiliating moments when a simple question makes you numb a or even worse – you begin to mumble an absolute rubbish. That what exactly what has happened to me recently and being an afterthought person (which, of course, doesn’t give me any advantage) I decided to […]

Posted on December 2, 2015 at 2:19 pm by sergeyt · Permalink · Leave a comment
In: Life, Linux

Configuring FCoE in Linux (RHEL) and HP FlexFabric

Actually it’s easy. Very easy indeed, like going 1, 2, 3. Collect information about MAC addresses to distinguish pure Ethernet NICs and CNA that will pass FCoE traffic. The latter have both MAC and WWN addresses. Power on a server and update /etc/udev/rules.d/70-persistent-net.rules if required. Activate new dev rules: Install fcoe-utils and lldpad packages: Rename […]

Posted on April 23, 2015 at 12:31 pm by sergeyt · Permalink · 4 Comments
In: Linux

OpenSSL TLS 1.1 and wrong version number

If you, like myself, have been living under a rock you’d be also surprised to know that OpenSSL didn’t support TLSv1.1 and TLSv1.2 until version 1.0.1 . Found out that accidently by trying to disable TLSv1 in Nginx which was running on a RHEL5 box with OpenSSL 0.9.8e. Below is how TLS handshake looked when […]

Posted on February 20, 2015 at 11:15 am by sergeyt · Permalink · Leave a comment
In: Linux

Linux pptp stumbling blocks that I was hit by

While configuring a pptp on a Linux box I bumped into the several smalish issues which I’d like to blog about. Make sure that your network engineers have enabled traffic inspection on all intermediate firewalls between tunnel’s endpoints. Otherwise LCP won’t be able to finish its configuration negotiation phase even if the control channel on […]

Posted on February 18, 2015 at 9:13 pm by sergeyt · Permalink · Leave a comment
In: Linux