online tools to test your mail infrastructure
once in a while i’m involed in moving mail servers around, to and from the could. those tools are useful each time it’s done: also related – a deep dive into e-mail delivery in 2024.
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rsync with more efficient compression, hash algorithm
rsync 3.2.0 and newer supports more compression and hash algorithms. zstd compression is well suited for slower network connections [ tens mbit/s ], lz4 – for faster. xxh3 hash is worth using regardless of the network speed. syntax:
nrpe’s check_http – POSTing a file
i needed to monitor some service available via HTTP, this service is expecting to get a file posted – as if it was submitted via HTML form. so the file’s content is in the POST body, wrapped in Content-Type: multipart/form-data and stored between boundaries. Is it possible to simulate via check_http? yes!
Best Practical’s RT – recovering specific tickets from backups
I needed to recover a particular, old and already shredded, RT ticket from a backup to web interface. I’ve restored the database to a separate server and run those commands to get INSERT statements for two tickets i was interested in – 69187, 100112: To be on the safe side – always recover to a ... Read More
mysqldump headaches
over the years i’ve set up multiple backup workflows. one of them is described here. part of the cycles involves taking database backups. for MySQL i’m mostly using mysqldump. it comes with some headaches: it’s single-threaded by nature – both for backup, and restore [ unless you chop the dump file into pieces and try ... Read More
colorized side-by-side diff in console
this one does the trick for me:
WordPress’ Gutenberg editor failing to save anything
i’ve run into an odd situation – wordpress was working just fine yet the new / Gutenberg editor did not save anything. No errors, but also no content saved – the only thing that was left was ‘Auto Draft’ with an empty content. i’ve tracked it down to fact that .htaccess was not actually used ... Read More
public domain image searchers
https://wordpress.org/openverse/?referrer=creativecommons.org https://commons.wikimedia.org/w/index.php?search=image&title=Special:MediaSearch&go=Go&type=image https://www.flickr.com/search/?q=image https://pixabay.com/
bash – finding files which have one of parent folders with a very specific name, and contain specific sub string
and to compress all of the files into single tar archive:
play.pl mobile – 100GB for a month for 5pln
play.pl seems to have never ending promotion where you get 100GB of data traffic for a month when you buy a new starter and activate bonus package. here’s what i do to activate it [ every 30 days ]: buy play-as-you-go sim card e.g. in Zabka convenience store – Play odNowa for 5PLN, register the ... Read More
.net core under linux throws “The remote certificate is invalid because of errors in the certificate chain: NotTimeValid” when communicating with HTTPS server having letsencrypt cert
i’ve stumbled on an issue – simple .net core code using HttpWebRequest failed to communicate with any server that had lets encrypt cert. no matter if the server used new or old certificate chain – i was getting: at the same time curl or wget could communicate with the same site without issues. i’ve tried ... Read More
manual and service manual for LG F4J6TG0W washing and drying machine
maybe it’ll be useful for someone. instrukcja oraz instrukcja seriwsowa do pralko-suszarki LG F4J6TG0W service manual – LG-F4J6TG0W-LG_directdrive_8-145881-2.pdf, user instruction mfl69739861rev4pdf-en.pdf MFL70561437-EN
intellij freezing on startup + putty routinely failing to bind to ports used for ssh tunneling
for the past few weeks i was plagued by putty randomly failing to bind to ports used for ssh tunneling giving me in its log “forwarding failed: Network error: Permission denied” today my intellij failed to launch – it was freezing on the splash screen, C:\Users\xxxxxxxxxxxx\AppData\Local\JetBrains\IdeaIC2021.2\log\log.log had: that brought me to https://youtrack.jetbrains.com/issue/IDEA-238995 and workaroudn described ... Read More
crude way to restore postgresql database dump to table with a different name
i needed to restore specific table, backed up via pg_dump, to the same database / schema but under different name. that’s what i’ve done pv dump.zstd|pzstd -dc - |sed 's/name_of_original_table/name_of_renamed_table/g'|su - postgres -c 'psql dbname' this only works if all constrains / indices have in their name name of the original table.
booting KVM VM from an iso image
let’s say you have a vm, maybe with debian. and that vm stopped booting, maybe because of grub corruption. what do you do? add under devices – for pc-i440fx arch: and for pc-q35-3.1: then in the os section change boot from dev=’hd’ to dev=’cdrom’: then also – this article describes how to go back from ... Read More
20x performance difference between two VMs running the same version of Elastic opendistro
i’ve just spent way too much time trying to figure out why the same query run on one VM with elastic 0.1s while on another – 2s. both VMs were running on the same physical server, had the same amount of cores allocated. i’ve finally found it – there was a tiny difference in amount ... Read More
ClickHouse – dictionary with string keys
i wanted to create a clickhouse dictionary that used String as a key, not an int. docs mention here: “A composite key can consist of a single element. This makes it possible to use a string as the key, for instance”. I’ve been trying this and failed few times. creation worked but i could not ... Read More
“initramfs unpacking failed: write error” due to stupid typo in virsh-install
i’ve been trying to set up a new vm using: trying and trying, and each time i got the same boot failure: root cause? allocating 128MB instead of intended 128GB of RAM for the VM. hopefully this post helps some poor soul who runs into a similar issue.
clickhouse – getting n most significant digits of a number
i’m testing some wild idea of finding matches in quite a large dataset. part of the problem is that scaling of input is unknown, 123 might be correct match for 1.23 or for 12.3. here’s an expression that returns me n=4 most significant digits of each float from the input array:
suddenly in-kernel communication between lxc containers gets erratic
we’re using LXC containers to host multiple workloads on the same physical servers. e.g. few instances of database servers running side-by-side. once in a while we end up with strange situation where tcp connections between containers running on the same physical server get torn down abruptly. in our case – this manifested e.g. by those ... Read More