UPC WiFree on Mikrotik and OpenWRT
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.
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using dedicated server from hetzner
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
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
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
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
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
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
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
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
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
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
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.
openvpn – “OpenSSL: error:1408518A:SSL routines:ssl3_ctx_ctrl:dh key too small” after upgrade to Debina Buster
another thing to adjust after upgrade to Buster. on openvpn endpoint that in it’s config – /etc/openvpn/whatever.conf – had: dh dh1024.pem the vpn service did not start. tail -f /var/log/syslog showed: apparently the new version of openssl no longer accepts 1024 Diffie Hellman group. solution: and change in /etc/openvpn/whatever.conf – from dh dh1024.pem to dh ... Read More
bind9 fails to start after an upgrade to Debian Buster
i’ve done a routine upgrade to Buster on some server and all went fine… except bind9 no longer started. every attempt to restart it ended up with long waiting and an error message: logs did not contain anything interesting – actually they showed that bind would start and then after ~ a minute was shut ... Read More
allowing custom file extensions to be uploaded to wordpress
WordPress restricts types of files you can upload. it not only checks the extension of what you’re adding to the media library but also its mime type. so you cannot fool it by uploading .exe renamed to .jpeg – if you try it, you’ll get an error saying: “Sorry, this file type is not permitted ... Read More
“error: internal error: unable to execute QEMU command ‘transaction’: Could not create file: Permission denied” when creating a snapshot under KVM
debian buster brings apparmor. apparmor brings problems – eg it’s too restrictive for libvirt KVM guests and does not allow KVM to create snapshot-related files in VM’s folders. so far i did not find a clean and generic way to address it so i had to disable apparmor for libvirt by adding security_driver = “none” ... Read More
let’s encrypt via proxy server under debian
i prefer to have strict DROP policy for the outgoing traffic from production servers. let’s encrypt API endpoint is behind Akamai’s CDN and IP address to which acme-v02.api.letsencrypt.org resolves changes frequently. i don’t like playing whack-a-mole every 3 months so i’ve: set up a squid-based proxy server that allows for filtering based on domain names: ... Read More
raspberry pi as a serial console terminal
i’ve bricked a cheap home router. i’ve installed a beta of dd-wrt firmware which did not work. raspberry pi gave me serial connection to it.
“Your IT department has turned off signup for Partner Center” when migrating to new Action Pack / Microsoft Partner Center
i got stuck on that one while trying to migrate action pack account to the new MS Partner Center. without the migration it would not let me renew. after 3 attempts i ended up talking with someone competent who found that this error might occur for users who have o365-hosted mails for domain used in ... Read More
kvm: disabled by bios
does your kvm VM feel sluggish? mine did feel pretty slow.. as it turned out virt-install quietly overrode ‘hvm’ preferences and created a fully emulated qemu vm when it failed to make use of hardware-assisted virtualization.