Author Archive
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 […]
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 […]
MongoDB – Defeating RangeDeleter
Not closing a cursor in MongoDB could hurt you big, so it’s generally not recommended to use no_cursor_timeout=True (pymongo3) or timeout=False (pymongo2). Especially when you run shared MongoDB installation: PyMongo does “close” cursors when they are garbage collected, but they aren’t closed immediately and closing a cursor in all current versions of MongoDB is asynchronous. […]
Another FreeBSD drop into the Digital Ocean
After several happy years with FreeBSD running in AWS I finally have switched to Digital Ocean. That happened a few days ago and was driven mainly by the lack of the console support which “aws ec2 get-console-output”, in my opinion, is certainly not. After the upgrade to FreeBSD 11 I found my instance unreachable and […]
Turned the page
After 5 exciting and tumultuous years in the enterprise IT as a Unix and SAN engineer it’s time to switch gears and taste something new. Of course, the alley I’m stepping into is not universally novel but for me personally it’s like an uncharted territory and something I could only dream about. The idea for […]
TIL Common Name (CN) is legacy and subjectAltName must always be used.
Seems I’ve been living under a rock for far too log. From RFC2818: Although the use of the Common Name is existing practice, it is deprecated and Certification Authorities are encouraged to use the dNSName instead. So in today’s world CN is only evaluated when subjectAltName is not present and if it’s set all host […]
Calculating percentile in Python
If you need to find the percentile in Python do that correctly. Which means is by following one of the following receipts: Finding the percentile of the values Use numpy library
Lecture on OpenZFS read and write code paths
If you are interested in ZFS this is the absolute must see video (which is actually a lecture) from Matt Ahrens (one of the two original ZFS creators): Matt Ahrens – Lecture on OpenZFS read and write code paths
Pair “Listen queue overflow” FreeBSD errors with pcb
Just yesterday, after an upgrade to MySQL 5.7.12, saw plenty of errors were being logged in the system: sonewconn: pcb 0xfffff8006311c870: Listen queue overflow: 151 already in queue awaiting acceptance (1 occurrences) sonewconn: pcb 0xfffff8006311c870: Listen queue overflow: 151 already in queue awaiting acceptance (1 occurrences) sonewconn: pcb 0xfffff8006311c870: Listen queue overflow: 151 already in […]
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. […]