I recently had to restore databases from a rough mysqldump backup in a piecemeal fashion. One necessity is to SET the environment correctly, lest some weird encoding issues happen when restoring the data, leading to failures.

A sed one-liner can help for this.

sed -n "/^-- Server version/,/^-- Current Database/p;/^-- Current Database.*${DBNAME}\`/,/^-- Current Database/{p}" mysqldump.sql > ${DBNAME}.sql

This extracts SQL from the initial header, to the first database, which contains all the sessions SETs. It then captures statements any time the target database is the current one. Note that this doesn’t restore the GRANTs.

Befor blindly piping the output SQL into mysql, one would be well advised to review the contents of the file, to ensure only the desired modifications are included.

We’ve been having some fun with Click and Python decorators at work.

We had a situation where we wanted to

  1. transform any Exception to a click.ClickException, so they would be rendered nicely, and
  2. catch one particular exception, and retry the function that raised it with a different parameter value as a fallback.

We got the first behaviour quickly into a decorator. We then realised that the second could also be done nicely with a decorator, too.

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GitHub now allows to expand/collapse all files in a PR diff at once (pressing Alt while clicking one of the toggles). Unfortunately, there is no similar feature to mark all files as viewed. This is handy after having reviewed meaningful changes to file, and automatically modified/generated files can be ignored.

So here goes a one-liner for the JS console.

Array.from(document.getElementsByClassName('js-reviewed-toggle')).forEach(c => c.getElementsByTagName('input')[0].checked || c.click())
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Every now and then, some spurious peaks show up on munin graphs. The peaks are order of magnitude higher than the expected range of the data. This particularly happens with DERIVE plugins, that are notably used for network interfaces.

One way to fix this, as suggested by Steve Schnepp (and in the faq), is to set the maximum straight into the RRD database, and then let it reprocess the data to honour this maximum.

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When using syspatch on OpenBSD, the upgrade sometimes fails with

Relinking to create unique kernel... failed!
!!! "/usr/libexec/reorder_kernel" must be run manually to install the new kernel

This generally happens after a system upgrade, or an otherwise manual change of kernel. This fix is to update the kernel hash, before re-running reorder_kernel.

# sha256 /bsd > /var/db/kernel.SHA256
# /usr/libexec/reorder_kernel 

I use Munin to monitor a few machines, and bubble up alerts when issues show up. It’s pretty good, easy to set up, and has a large number of contributed plugins to monitor pretty much everything. If still out of luck, it’s easy enough to write your own.

To ease the task of viewing the data, each machine runs munin-node, but only a couple of masters do the data collection with munin-update. This works reasonably well, except that machines monitored by more than one server need to work extra time to provide the same data to both.

Fortunately, Munin 2.0 introduced a proxy mode, allowing to decouple running the plugins to collect fresh data (with munin-asyncd) from giving that data to collection servers (via munin-async).

Setting this up is relatively easy, and the benefits show quickly, in the form of a reduced collection time, and fewer gaps in the data.

Reduced update time for the master, and no more gaps in the data.

Surprisingly it also showed as a substantially reduced load on low-power machines. But beware of the --fork parameter to munin-asyncd.

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I finally mastered the shell (beit bash or zsh, but really, this is readline)’s history with command replacement. It took me 19 years and my entire family fortune to gather enough wits to read that part of the manual with enough attention and will as to learn to use it.

Essentially, you can recall previous commands from the history with !number. You can then change some content of the previous command programmatically before running it by adding :s/PATTERN/REPLACEMENT/ or :gs/PATTERN/REPLACEMENT/ (the first one will replace the first occurrence, the second one will replace them all).

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