.pQd

xiaomi robot vaccuum disassembly

by .pQd
i have 1st gen xiaomi mi robot vacuum cleaner. it’s been serving very well for the past 3 years. this video was very helpful with disassembly when i had to replace the main sucking motor fan: https://www.youtube.com/watch?v=wdDSBgJ1kRM i had to replace a fan and bought https://www.aliexpress.com/item/4000804127893.html instead of https://www.aliexpress.com/item/4000259186760.html ; not an exact fit but ... Read More

clickhouse

by .pQd
clickhouse is a column oriented OLAP database. i’ve started using it about half a year ago. i’m impressed. earlier i’ve read about it on percona’s blog but did not fully grasp how performant it was. i’ve tried it when i wrestling with MariaDB’s query planner on table with ~100M rows got me tired and each ... Read More

supermicro server getting stuck on “loading initial ramdisk”

by .pQd
i had a quite puzzling moment today when a server refused to boot up after routine maintenance. order of events: datacenter technician has taken server down and added Mellanox 25Gbit network card server booted up cleanly with Debian Buster and aged kernel 4.19.0-6 i’ve rebooted the server again and changed cpu performance settings in bios ... Read More

supermicro IPMI – mounting iso image via samba

by .pQd
reminder for my self in case i need to do it again, relevant for X11DDW-NT and likely – other their platforms: log-in to the IPMI web interface, go to virtual media > CD-ROM image, provide: share host – ip or hostname of samba server. for instance: 10.1.2.3 paht to image – backlash share name backslash ... Read More

letting dbeaver talk with manticoresearch

by .pQd
here’s what i did to get dbeaver 7.3.2 + oracle’s JDBC mysql-connector-java-8.0.17.jar work with manticoresearch 3.5.4: /etc/manticoresearch/manticore.conf, under searchd: in dbeaver – new connection using oracle’s JDBC driver as above, under data editor – set ResultFetchSize to 0 to prevent errors like this: when i initially tried to get it working with JDBC driver from ... Read More

black hole, somewhere in the internet, swallowing UDP packets

by .pQd
UDP packets sent from specific source port, with public source IP address do not reach specific destination port of the public destination IP address. changing any of the parameters [ usually source port ] – fixes the issue. i’ve observed this phenomenon multiple times for long-running OpenVPN and Wireguard VPNs encapsulating encrypted traffic in UDP ... Read More

UPC WiFree on Mikrotik and OpenWRT

by .pQd
UPC turns your cable modem into WiFi hot-spot available for others. outrageous! and i’ve been using it for quite a while – it generally works. below – how to connect OpenWRT or Mikrotik to such connection.

using dedicated server from hetzner

by .pQd
4 months ago i’ve started renting a dedicated server at https://www.hetzner.com/ and – so far – i’m quite happy with the service. i’ve picked cheapest suitable hardware from their auctions, after a month of trouble-free usage i’ve switched to quarterly billing. then server has crashed few times with “shutting down cpus with nmi” kernel messages. ... Read More

resizing btrfs on luks on mdadm raid10

by .pQd
one of my KVM VMs keeps data on BTRFS on top of encrypted LUKS drive. that drive is a block device passed from virtualization server to VM… a block device which is mdadm software RAID10. below – steps taken to resize it.

detecting duplicate network packets from linux command line

by .pQd
while going down the rabbit hole of bed network performance at work we’ve narrowed the problem cause to duplicate packets showing up on a specific segment of leased metro Ethernet service. tshark filter helped us to see when duplicates occurred on monitored link we’ve got pair of computers – A and B connected at both ... Read More

resizing btrfs on top of luks

by .pQd
recently we needed to expand storage space available on one of our servers. originally it was using RAID10 on 4 4TBSSD drives handled by Dell’s PERC h730p controller, we wanted to add 2 more 4TB drives and go from 8 to 12TB array. we’ve decided to be brave and use RAID10 -> RAID10 array expansion. ... Read More

backup via ssh-tunneled connection

by .pQd
in one context i need to pull backup from server C to server A. normally i’d use rsync with direct ssh connection as a transport method. in this particular case C is not directly reachable from A, so i need to use ssh tunneling to connect from A to C via jump-host B: public ssh ... Read More

fighting a false-positive flagging by multiple antivirus vendors

by .pQd
recently i woke up to this: “Hi, some of our employees are using your application. This morning they have received an upgrade notification (in yellow banner) to get the latest version of your app. Our anti-virus/malware has triggered on your module called “somefile.exe” detected at risk being a “Trojan.Gen.MBT “. below few resources that i’ve ... Read More

apache2 – reverse proxy with sticky sessions and fail-over

by .pQd
i needed to set up apache2 as a reverse proxy that will forward requests to few backends. yes – i know that there are better tools to do it – like haproxy or nginx – but in this case apache2 was preferred for the simplicity of the setup. requirements: sticky sessions – in normal conditions ... Read More

guacamole under Debian

by .pQd
Apache Guacamole is a clientless remote desktop gateway – with it you can access RDP-enabled Windows PC using ordinary web browser and HTTP[S]. below – notes taken while setting it up under Debian 10.

useful network-related tools

by .pQd
internet-wide scanners: https://censys.io/ https://www.shodan.io/ ssl: https://www.ssllabs.com/ smtp: https://www.mail-tester.com/ dns: http://dns.squish.net/

upgrading firmware on Intel’s SATA SSD drives behind Dell’s h730p RAID

by .pQd
fetch Intel_SSD_Data_Center_Tool from here. the zip archive contained, among other, .deb for 64 bit OS – that worked for me under debian stretch. to see drives run: to upgrade the firmware where 0 corresponds to the Index of drive returned by the first command the same likely works for other LSI/Avago cards – no matter ... Read More

iostat -x 1 reporting 100% utilization of nearly-idle NVMe drives

by .pQd
after an upgrade to debian buster i’ve noticed that both iostat -x 1 and munin’s diskstats_utilization report that NVMe drives are busy most of the time. some empirical tests showed that disks are actually idle, performance did not drop. upgrade to 5.2 kernel resolved the miss-reporting issue.