Suppose, not entirely hypothetically, that you want to print outsome information about every fcntl() lock call that fails, system-wide. These days this is relatively easy to dowith bpftrace , especiallysince there are system call entry and exit tracepoints .However, you might reasonably wonder how the fcntl(2) system callactually returns errno , the error code, and how this manifestsat the level of the sys_exit_fcntl syscalls tracepoint. As itturns out, there's some tribal knowledge

In my entry on how web server should refuse requests for randomURLs , I mentioned that wehave an open source security and vulnerability scanner. Among thereactions I saw to that entry was people who felt that such scannersare basically a bad idea, and in thinking about the issue I'vedecided that I can see two views of such scanners.

Some people have a heavily controlled and locked down environment.They know every machine on the network and every service that'ssupposed to be running on every machine,

When I wrote about how blocking JavaScript by default is not aneasy path , I mentioned this:

I also have a bunch of magic things in my personal desktop environmentthat make it relatively easy to start with a link or URL from onebrowser [the one with JavaScript off] and open it in the other [the onewith JavaScript on].

Recently poebbel (in a comment) askedhow this works. While I've mentioned the various pieces in variousarticles, I've never put the picture together

Now that I've tried out NFS v4 on Ubuntu 22.04 ,I have some additional notes on NFS v4 locks and /proc/locks, to go with my earlier notes on NFS (v3) locks . It turns outthat there are some changes from NFS v3 to NFS v4, at least on your NFSserver.

Here is what an exclusive POSIX lock looks like on an Ubuntu 22.04NFS v4 server:

4: POSIX  ADVISORY  WRITE 7

Over on the Fediverse, I had a hot take :

My hot take on inheritance in programming languagesis that it's a good thing to separate polymorphism , codereuse, and relationships between types. Also, the really importantthing is polymorphism.

(We can see that polymorphism is the most important from how large Ccodebases keep re-inventing systems to create it.)

This was in fact too much of a hot take, because I left out somethingthat's sufficiently important that it keeps being reinvented.

In a comment on my entry on how web servers shouldn't give HTTP 200results for random URLs , Jonathan reported something that I find fascinating:

This reminds me of a personal bugbear with the RHEL httpd package,which is the inverse situation: OOTB it’s configured to serve a“hello” page on / via an error handler, so you get an error codefor a success.

I personally find this fascinating and can't really vote againstit (in contrast to Jonathan ). To

A while back I wrote about how I'd now used nftables on a newmachine and it was okay . This came aboutbecause Ubuntu 22.04's default setup is that the 'iptables' commandis actually a frontend for nftables , andwhen I noticed that I decided that I might as well write nftablesrules directly for this. Today I had cause to remember this , and also toreflect on our other uses of nftables on Ubuntu 22.04. These otheruses came about

I've been saying grumpy things about NFS v4 for a fairly long timenow, and in response for a while people have been telling me thatthese days NFS v4 can look basically just like NFS v3. You can haveyour traditional Unix permissions model (the NFS without Kerberosone ) and you don't have to reorganizeyour exports and so on. Recently I decided to give it a try on somescratch virtual machines running our standard Ubuntu 22.04 LTSsetup, and to

There are a variety of situations where you (in the sense of programsand systems) want to know if a web server supports something or isunder someone's control. One traditional way is to require thepublication of specific URLs on the web server, often URLs withpartially random names. The simplest way to implement this is tosimply require the URL to exist and be accessible, which is to saythat fetching it returns a HTTP 200 response. However, in lightof web server implementations which will